draft-ietf-teep-architecture-15.txt   draft-ietf-teep-architecture-16.txt 
TEEP M. Pei TEEP M. Pei
Internet-Draft Broadcom Internet-Draft Broadcom
Intended status: Informational H. Tschofenig Intended status: Informational H. Tschofenig
Expires: January 13, 2022 Arm Limited Expires: 1 September 2022 Arm Limited
D. Thaler D. Thaler
Microsoft Microsoft
D. Wheeler D. Wheeler
Amazon Amazon
July 12, 2021 28 February 2022
Trusted Execution Environment Provisioning (TEEP) Architecture Trusted Execution Environment Provisioning (TEEP) Architecture
draft-ietf-teep-architecture-15 draft-ietf-teep-architecture-16
Abstract Abstract
A Trusted Execution Environment (TEE) is an environment that enforces A Trusted Execution Environment (TEE) is an environment that enforces
that any code within that environment cannot be tampered with, and that any code within that environment cannot be tampered with, and
that any data used by such code cannot be read or tampered with by that any data used by such code cannot be read or tampered with by
any code outside that environment. This architecture document any code outside that environment. This architecture document
motivates the design and standardization of a protocol for managing motivates the design and standardization of a protocol for managing
the lifecycle of trusted applications running inside such a TEE. the lifecycle of trusted applications running inside such a TEE.
skipping to change at page 1, line 40 skipping to change at page 1, line 40
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 13, 2022. This Internet-Draft will expire on 1 September 2022.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 8 3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 8
3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 8 3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 8
3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 8 3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 9
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. System Components . . . . . . . . . . . . . . . . . . . . 8 4.1. System Components . . . . . . . . . . . . . . . . . . . . 9
4.2. Multiple TEEs in a Device . . . . . . . . . . . . . . . . 11 4.2. Multiple TEEs in a Device . . . . . . . . . . . . . . . . 11
4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 13 4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 13
4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 14 4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 15
4.4.1. Example: Application Delivery Mechanisms in Intel SGX 16 4.4.1. Example: Application Delivery Mechanisms in Intel
SGX . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4.2. Example: Application Delivery Mechanisms in Arm 4.4.2. Example: Application Delivery Mechanisms in Arm
TrustZone . . . . . . . . . . . . . . . . . . . . . . 17 TrustZone . . . . . . . . . . . . . . . . . . . . . . 17
4.5. Entity Relations . . . . . . . . . . . . . . . . . . . . 17 4.5. Entity Relations . . . . . . . . . . . . . . . . . . . . 17
5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 19 5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 19
5.1. Trust Anchors in a TEEP Agent . . . . . . . . . . . . . . 21 5.1. Trust Anchors in a TEEP Agent . . . . . . . . . . . . . . 21
5.2. Trust Anchors in a TEE . . . . . . . . . . . . . . . . . 21 5.2. Trust Anchors in a TEE . . . . . . . . . . . . . . . . . 21
5.3. Trust Anchors in a TAM . . . . . . . . . . . . . . . . . 21 5.3. Trust Anchors in a TAM . . . . . . . . . . . . . . . . . 21
5.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 21 5.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 22
5.5. Message Security . . . . . . . . . . . . . . . . . . . . 22 5.5. Message Security . . . . . . . . . . . . . . . . . . . . 22
6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 22 6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Role of the TEEP Broker . . . . . . . . . . . . . . . . . 23 6.1. Role of the TEEP Broker . . . . . . . . . . . . . . . . . 23
6.2. TEEP Broker Implementation Consideration . . . . . . . . 23 6.2. TEEP Broker Implementation Consideration . . . . . . . . 23
6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 24 6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 24
6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 25 6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 25
7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 25 7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 25
8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 27 8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 28
9. Security Considerations . . . . . . . . . . . . . . . . . . . 28 9. Security Considerations . . . . . . . . . . . . . . . . . . . 28
9.1. Broker Trust Model . . . . . . . . . . . . . . . . . . . 28 9.1. Broker Trust Model . . . . . . . . . . . . . . . . . . . 28
9.2. Data Protection . . . . . . . . . . . . . . . . . . . . . 28 9.2. Data Protection . . . . . . . . . . . . . . . . . . . . . 29
9.3. Compromised REE . . . . . . . . . . . . . . . . . . . . . 29 9.3. Compromised REE . . . . . . . . . . . . . . . . . . . . . 30
9.4. CA Compromise or Expiry of CA Certificate . . . . . . . . 30 9.4. CA Compromise or Expiry of CA Certificate . . . . . . . . 31
9.5. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 30 9.5. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 31
9.6. Malicious TA Removal . . . . . . . . . . . . . . . . . . 31 9.6. Malicious TA Removal . . . . . . . . . . . . . . . . . . 31
9.7. Certificate Expiry and Renewal . . . . . . . . . . . . . 31 9.7. Certificate Expiry and Renewal . . . . . . . . . . . . . 32
9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 32 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 33
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 9.9. REE Privacy . . . . . . . . . . . . . . . . . . . . . . . 33
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 32
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
13. Informative References . . . . . . . . . . . . . . . . . . . 32 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34
13. Informative References . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
Applications executing in a device are exposed to many different Applications executing in a device are exposed to many different
attacks intended to compromise the execution of the application or attacks intended to compromise the execution of the application or
reveal the data upon which those applications are operating. These reveal the data upon which those applications are operating. These
attacks increase with the number of other applications on the device, attacks increase with the number of other applications on the device,
with such other applications coming from potentially untrustworthy with such other applications coming from potentially untrustworthy
sources. The potential for attacks further increases with the sources. The potential for attacks further increases with the
complexity of features and applications on devices, and the complexity of features and applications on devices, and the
unintended interactions among those features and applications. The unintended interactions among those features and applications. The
danger of attacks on a system increases as the sensitivity of the danger of attacks on a system increases as the sensitivity of the
applications or data on the device increases. As an example, applications or data on the device increases. As an example,
exposure of emails from a mail client is likely to be of concern to exposure of emails from a mail client is likely to be of concern to
its owner, but a compromise of a banking application raises even its owner, but a compromise of a banking application raises even
greater concerns. greater concerns.
The Trusted Execution Environment (TEE) concept is designed to The Trusted Execution Environment (TEE) concept is designed to let
execute applications in a protected environment that enforces that applications execute in a protected environment that enforces that
any code within that environment cannot be tampered with, and that any code within that environment cannot be tampered with, and that
any data used by such code cannot be read or tampered with by any any data used by such code cannot be read or tampered with by any
code outside that environment, including by a commodity operating code outside that environment, including by a commodity operating
system (if present). In a system with multiple TEEs, this also means system (if present). In a system with multiple TEEs, this also means
that code in one TEE cannot be read or tampered with by code in the that code in one TEE cannot be read or tampered with by code in
other TEE. another TEE.
This separation reduces the possibility of a successful attack on This separation reduces the possibility of a successful attack on
application components and the data contained inside the TEE. application components and the data contained inside the TEE.
Typically, application components are chosen to execute inside a TEE Typically, application components are chosen to execute inside a TEE
because those application components perform security sensitive because those application components perform security sensitive
operations or operate on sensitive data. An application component operations or operate on sensitive data. An application component
running inside a TEE is referred to as a Trusted Application (TA), running inside a TEE is referred to as a Trusted Application (TA),
while an application running outside any TEE, i.e., in the Rich while an application running outside any TEE, i.e., in the Rich
Execution Environment (REE), is referred to as an Untrusted Execution Environment (REE), is referred to as an Untrusted
Application. In the example of a banking application, code that Application. In the example of a banking application, code that
relates to the authentication protocol could reside in a TA while the relates to the authentication protocol could reside in a TA while the
application logic including HTTP protocol parsing could be contained application logic including HTTP protocol parsing could be contained
in the Untrusted Application. In addition, processing of credit card in the Untrusted Application. In addition, processing of credit card
numbers or account balances could be done in a TA as it is sensitive numbers or account balances could be done in a TA as it is sensitive
data. The precise code split is ultimately a decision of the data. The precise code split is ultimately a decision of the
developer based on the assets he or she wants to protect according to developer based on the assets he or she wants to protect according to
the threat model. the threat model.
TEEs are typically used in cases where a software or data asset needs
to be protected from unauthorized entities that may include the owner
(or pwner) or possesser of a device. This situation arises for
example in gaming consoles where anti-cheat protection is a concern,
devices such as ATMs or IoT devices placed in locations where
attackers might have physical access, cell phones or other devices
used for mobile payments, and hosted cloud environments. Such
environments can be thought of as hybrid devices where one user or
administrator controls the REE and a different (remote) user or
administrator controls a TEE in the same physical device. It may
also be the case in some constrained devices that there is no REE
(only a TEE) and there may be no local "user" per se, only a remote
TEE administrator. For further discussion of such confidential
computing use cases and threat model, see [CC-Overview] and
[CC-Technical-Analysis].
TEEs use hardware enforcement combined with software protection to TEEs use hardware enforcement combined with software protection to
secure TAs and its data. TEEs typically offer a more limited set of secure TAs and its data. TEEs typically offer a more limited set of
services to TAs than is normally available to Untrusted Applications. services to TAs than is normally available to Untrusted Applications.
Not all TEEs are the same, however, and different vendors may have Not all TEEs are the same, however, and different vendors may have
different implementations of TEEs with different security properties, different implementations of TEEs with different security properties,
different features, and different control mechanisms to operate on different features, and different control mechanisms to operate on
TAs. Some vendors may themselves market multiple different TEEs with TAs. Some vendors may themselves market multiple different TEEs with
different properties attuned to different markets. A device vendor different properties attuned to different markets. A device vendor
may integrate one or more TEEs into their devices depending on market may integrate one or more TEEs into their devices depending on market
needs. needs.
To simplify the life of TA developers interacting with TAs in a TEE, To simplify the life of TA developers interacting with TAs in a TEE,
an interoperable protocol for managing TAs running in different TEEs an interoperable protocol for managing TAs running in different TEEs
of various devices is needed. This software update protocol needs to of various devices is needed. This software update protocol needs to
make sure that compatible trusted and untrusted components (if any) make sure that compatible trusted and untrusted components (if any)
of an application are installed on the correct device. In this TEE of an application are installed on the correct device. In this TEE
ecosystem, there often arises a need for an external trusted party to ecosystem, there often arises a need for an external trusted party to
verify the identity, claims, and rights of TA developers, devices, verify the identity, claims, and rights of TA developers, devices,
and their TEEs. This trusted third party is the Trusted Application and their TEEs. This external trusted party is the Trusted
Manager (TAM). Application Manager (TAM).
The Trusted Execution Environment Provisioning (TEEP) protocol The Trusted Execution Environment Provisioning (TEEP) protocol
addresses the following problems: addresses the following problems:
- An installer of an Untrusted Application that depends on a given * An installer of an Untrusted Application that depends on a given
TA wants to request installation of that TA in the device's TEE so TA wants to request installation of that TA in the device's TEE so
that the Untrusted Application can complete, but the TEE needs to that the Untrusted Application can complete, but the TEE needs to
verify whether such a TA is actually authorized to run in the TEE verify whether such a TA is actually authorized to run in the TEE
and consume potentially scarce TEE resources. and consume potentially scarce TEE resources.
- A TA developer providing a TA whose code itself is considered * A TA developer providing a TA whose code itself is considered
confidential wants to determine security-relevant information of a confidential wants to determine security-relevant information of a
device before allowing their TA to be provisioned to the TEE device before allowing their TA to be provisioned to the TEE
within the device. An example is the verification of the type of within the device. An example is the verification of the type of
TEE included in a device and that it is capable of providing the TEE included in a device and that it is capable of providing the
security protections required. security protections required.
- A TEE in a device wants to determine whether an entity that wants * A TEE in a device wants to determine whether an entity that wants
to manage a TA in the device is authorized to manage TAs in the to manage a TA in the device is authorized to manage TAs in the
TEE, and what TAs the entity is permitted to manage. TEE, and what TAs the entity is permitted to manage.
- A Device Administrator wants to determine if a TA exists (is * A Device Administrator wants to determine if a TA exists (is
installed) on a device (in the TEE), and if not, install the TA in installed) on a device (in the TEE), and if not, install the TA in
the TEE. the TEE.
- A Device Administrator wants to check whether a TA in a device's * A Device Administrator wants to check whether a TA in a device's
TEE is the most up-to-date version, and if not, update the TA in TEE is the most up-to-date version, and if not, update the TA in
the TEE. the TEE.
- A Device Administrator wants to remove a TA from a device's TEE if * A Device Administrator wants to remove a TA from a device's TEE if
the TA developer is no longer maintaining that TA, when the TA has the TA developer is no longer maintaining that TA, when the TA has
been revoked or is not used for other reasons anymore (e.g., due been revoked, or is not used for other reasons anymore (e.g., due
to an expired subscription). to an expired subscription).
For TEEs that simply verify and load signed TA's from an untrusted For TEEs that simply verify and load signed TA's from an untrusted
filesystem, classic application distribution protocols can be used filesystem, classic application distribution protocols can be used
without modification. The problems in the bullets above, on the without modification. The problems in the bullets above, on the
other hand, require a new protocol, i.e., the TEEP protocol, for TEEs other hand, require a new protocol, i.e., the TEEP protocol, for TEEs
that can install and enumerate TAs in a TEE-secured location and that can install and enumerate TAs in a TEE-secured location and
where another domain-specific protocol standard (e.g., [GSMA], where another domain-specific protocol standard (e.g., [GSMA],
[OTRP]) that meets the needs is not already in use. [OTRP]) that meets the needs is not already in use.
2. Terminology 2. Terminology
The following terms are used: The following terms are used:
- Device: A physical piece of hardware that hosts one or more TEEs, * Device: A physical piece of hardware that hosts one or more TEEs,
often along with an REE. often along with an REE.
- Device Administrator: An entity that is responsible for * Device Administrator: An entity that is responsible for
administration of a device, which could be the Device Owner. A administration of a device, which could be the Device Owner. A
Device Administrator has privileges on the device to install and Device Administrator has privileges on the device to install and
remove Untrusted Applications and TAs, approve or reject Trust remove Untrusted Applications and TAs, approve or reject Trust
Anchors, and approve or reject TA developers, among possibly other Anchors, and approve or reject TA developers, among possibly other
privileges on the device. A Device Administrator can manage the privileges on the device. A Device Administrator can manage the
list of allowed TAMs by modifying the list of Trust Anchors on the list of allowed TAMs by modifying the list of Trust Anchors on the
device. Although a Device Administrator may have privileges and device. Although a Device Administrator may have privileges and
device-specific controls to locally administer a device, the device-specific controls to locally administer a device, the
Device Administrator may choose to remotely administer a device Device Administrator may choose to remotely administer a device
through a TAM. through a TAM.
- Device Owner: A device is always owned by someone. In some cases, * Device Owner: A device is always owned by someone. In some cases,
it is common for the (primary) device user to also own the device, it is common for the (primary) device user to also own the device,
making the device user/owner also the Device Administrator. In making the device user/owner also the Device Administrator. In
enterprise environments it is more common for the enterprise to enterprise environments it is more common for the enterprise to
own the device, and any device user has no or limited own the device, and any device user has no or limited
administration rights. In this case, the enterprise appoints a administration rights. In this case, the enterprise appoints a
Device Administrator that is not the device owner. Device Administrator that is not the device owner.
- Device User: A human being that uses a device. Many devices have * Device User: A human being that uses a device. Many devices have
a single device user. Some devices have a primary device user a single device user. Some devices have a primary device user
with other human beings as secondary device users (e.g., parent with other human beings as secondary device users (e.g., a parent
allowing children to use their tablet or laptop). Other devices allowing children to use their tablet or laptop). Other devices
are not used by a human being and hence have no device user. are not used by a human being and hence have no device user.
Relates to Device Owner and Device Administrator. Relates to Device Owner and Device Administrator.
- Personalization Data: A set of configuration data that is specific * Personalization Data: A set of configuration data that is specific
to the device or user. The Personalization Data may depend on the to the device or user. The Personalization Data may depend on the
type of TEE, a particular TEE instance, the TA, and even the user type of TEE, a particular TEE instance, the TA, and even the user
of the device; an example of Personalization Data might be a of the device; an example of Personalization Data might be a
secret symmetric key used by a TA to communicate with some secret symmetric key used by a TA to communicate with some
service. service.
- Raw Public Key: The raw public key only consists of the * Raw Public Key: A raw public key consists of only the algorithm
SubjectPublicKeyInfo structure of a PKIX certificate [RFC5280] identifier (type) of the key and the cryptographic public key
that carries the parameters necessary to describe the public key. material, such as the SubjectPublicKeyInfo structure of a PKIX
Other serialization formats that do not rely on ASN.1 may also be certificate [RFC5280]. Other serialization formats that do not
used. rely on ASN.1 may also be used.
- Rich Execution Environment (REE): An environment that is provided * Rich Execution Environment (REE): An environment that is provided
and governed by a typical OS (e.g., Linux, Windows, Android, iOS), and governed by a typical OS (e.g., Linux, Windows, Android, iOS),
potentially in conjunction with other supporting operating systems potentially in conjunction with other supporting operating systems
and hypervisors; it is outside of any TEE. This environment and and hypervisors; it is outside of the TEE(s) managed by the TEEP
applications running on it are considered untrusted (or more protocol. This environment and applications running on it are
precisely, less trusted than a TEE). considered untrusted (or more precisely, less trusted than a TEE).
- Trust Anchor: As defined in [RFC6024] and * Trust Anchor: As defined in [RFC6024] and
[I-D.ietf-suit-manifest], "A trust anchor represents an [I-D.ietf-suit-architecture], "A trust anchor represents an
authoritative entity via a public key and associated data. The authoritative entity via a public key and associated data. The
public key is used to verify digital signatures, and the public key is used to verify digital signatures, and the
associated data is used to constrain the types of information for associated data is used to constrain the types of information for
which the trust anchor is authoritative." The Trust Anchor may be which the trust anchor is authoritative." The Trust Anchor may be
a certificate or it may be a raw public key along with additional a certificate or it may be a raw public key.
data if necessary such as its public key algorithm and parameters.
- Trust Anchor Store: As defined in [RFC6024], "A trust anchor store * Trust Anchor Store: As defined in [RFC6024], "A trust anchor store
is a set of one or more trust anchors stored in a device. A is a set of one or more trust anchors stored in a device... A
device may have more than one trust anchor store, each of which device may have more than one trust anchor store, each of which
may be used by one or more applications." As noted in may be used by one or more applications." As noted in
[I-D.ietf-suit-manifest], a Trust Anchor Store must resist [I-D.ietf-suit-architecture], a Trust Anchor Store must resist
modification against unauthorized insertion, deletion, and modification against unauthorized insertion, deletion, and
modification. modification.
- Trusted Application (TA): An application (or, in some * Trusted Application (TA): An application (or, in some
implementations, an application component) that runs in a TEE. implementations, an application component) that runs in a TEE.
- Trusted Application Manager (TAM): An entity that manages Trusted * Trusted Application Manager (TAM): An entity that manages Trusted
Applications and other Trusted Components running in TEEs of Applications and other Trusted Components running in TEEs of
various devices. various devices.
- Trusted Component: A set of code and/or data in a TEE managed as a * Trusted Component: A set of code and/or data in a TEE managed as a
unit by a Trusted Application Manager. Trusted Applications and unit by a Trusted Application Manager. Trusted Applications and
Personalization Data are thus managed by being included in Trusted Personalization Data are thus managed by being included in Trusted
Components. Trusted OS code or trusted firmware can also be Components. Trusted OS code or trusted firmware can also be
expressed as Trusted Components that a Trusted Component depends expressed as Trusted Components that a Trusted Component depends
on. on.
- Trusted Component Developer: An entity that develops one or more * Trusted Component Developer: An entity that develops one or more
Trusted Components. Trusted Components.
- Trusted Component Signer: An entity that signs a Trusted Component * Trusted Component Signer: An entity that signs a Trusted Component
with a key that a TEE will trust. The signer might or might not with a key that a TEE will trust. The signer might or might not
be the same entity as the Trusted Component Developer. For be the same entity as the Trusted Component Developer. For
example, a Trusted Component might be signed (or re-signed) by a example, a Trusted Component might be signed (or re-signed) by a
Device Administrator if the TEE will only trust the Device Device Administrator if the TEE will only trust the Device
Administrator. A Trusted Component might also be encrypted, if Administrator. A Trusted Component might also be encrypted, if
the code is considered confidential. the code is considered confidential.
- Trusted Execution Environment (TEE): An execution environment that * Trusted Execution Environment (TEE): An execution environment that
enforces that only authorized code can execute within the TEE, and enforces that only authorized code can execute within the TEE, and
data used by that code cannot be read or tampered with by code data used by that code cannot be read or tampered with by code
outside the TEE. A TEE also generally has a device unique outside the TEE. A TEE also generally has a device unique
credential that cannot be cloned. There are multiple technologies credential that cannot be cloned. There are multiple technologies
that can be used to implement a TEE, and the level of security that can be used to implement a TEE, and the level of security
achieved varies accordingly. In addition, TEEs typically use an achieved varies accordingly. In addition, TEEs typically use an
isolation mechanism between Trusted Applications to ensure that isolation mechanism between Trusted Applications to ensure that
one TA cannot read, modify or delete the data and code of another one TA cannot read, modify or delete the data and code of another
TA. TA.
- Untrusted Application: An application running in an REE. An * Untrusted Application: An application running in an REE. An
Untrusted Application might depend on one or more TAs. Untrusted Application might depend on one or more TAs.
3. Use Cases 3. Use Cases
3.1. Payment 3.1. Payment
A payment application in a mobile device requires high security and A payment application in a mobile device requires high security and
trust in the hosting device. Payments initiated from a mobile device trust in the hosting device. Payments initiated from a mobile device
can use a Trusted Application to provide strong identification and can use a Trusted Application to provide strong identification and
proof of transaction. proof of transaction.
skipping to change at page 8, line 18 skipping to change at page 8, line 40
3.2. Authentication 3.2. Authentication
For better security of authentication, a device may store its keys For better security of authentication, a device may store its keys
and cryptographic libraries inside a TEE limiting access to and cryptographic libraries inside a TEE limiting access to
cryptographic functions via a well-defined interface and thereby cryptographic functions via a well-defined interface and thereby
reducing access to keying material. reducing access to keying material.
3.3. Internet of Things 3.3. Internet of Things
The Internet of Things (IoT) has been posing threats to critical Weak security in Internet of Things (IoT) devices has been posing
infrastructure because of weak security in devices. It is desirable threats to critical infrastructure that relies upon such devices. It
that IoT devices can prevent malware from manipulating actuators is desirable that IoT devices can prevent malware from manipulating
(e.g., unlocking a door), or stealing or modifying sensitive data, actuators (e.g., unlocking a door), or stealing or modifying
such as authentication credentials in the device. A TEE can be the sensitive data, such as authentication credentials in the device. A
best way to implement such IoT security functions. TEE can be the best way to implement such IoT security functions.
3.4. Confidential Cloud Computing 3.4. Confidential Cloud Computing
A tenant can store sensitive data, such as customer details or credit A tenant can store sensitive data, such as customer details or credit
card numbers, in a TEE in a cloud computing server such that only the card numbers, in a TEE in a cloud computing server such that only the
tenant can access the data, preventing the cloud hosting provider tenant can access the data, preventing the cloud hosting provider
from accessing the data. A tenant can run TAs inside a server TEE from accessing the data. A tenant can run TAs inside a server TEE
for secure operation and enhanced data security. This provides for secure operation and enhanced data security. This provides
benefits not only to tenants with better data security but also to benefits not only to tenants with better data security but also to
cloud hosting providers for reduced liability and increased cloud cloud hosting providers for reduced liability and increased cloud
adoption. adoption.
4. Architecture 4. Architecture
4.1. System Components 4.1. System Components
Figure 1 shows the main components in a typical device with an REE. Figure 1 shows the main components in a typical device with an REE
Full descriptions of components not previously defined are provided and a TEE. Full descriptions of components not previously defined
below. Interactions of all components are further explained in the are provided below. Interactions of all components are further
following paragraphs. explained in the following paragraphs.
+-------------------------------------------+ +-------------------------------------------+
| Device | Trusted Component | Device | Trusted Component
| +--------+ | Signer | +--------+ | Signer
| +-------------+ | |-----------+ | | +-------------+ | |-----------+ |
| | TEE-1 | | TEEP |---------+ | | | | TEE-1 | | TEEP |---------+ | |
| | +--------+ | +----| Broker | | | | +--------+ | | | +--------+ | +----| Broker | | | | +--------+ |
| | | TEEP | | | | |<---+ | | +->| |<-+ | | | TEEP | | | | |<---+ | | +->| |<-+
| | | Agent |<----+ | | | | | +-| TAM-1 | | | | Agent |<----+ | | | | | +-| TAM-1 |
| | +--------+ | | |<-+ | | +->| | |<-+ | | +--------+ | | |<-+ | | +->| | |<-+
skipping to change at page 9, line 26 skipping to change at page 9, line 46
| +-->|TA1| |TA2| | +-------+ | | | +--------+ | | +-->|TA1| |TA2| | +-------+ | | | +--------+ |
| | | | | | |<---------| App-2 |--+ | | | | | | | | | |<---------| App-2 |--+ | | |
| | | +---+ +---+ | +-------+ | | | Device Administrator | | | +---+ +---+ | +-------+ | | | Device Administrator
| | +-------------+ | App-1 | | | | | | +-------------+ | App-1 | | | |
| | | | | | | | | | | | | |
| +--------------------| |---+ | | | +--------------------| |---+ | |
| | |--------+ | | | |--------+ |
| +-------+ | | +-------+ |
+-------------------------------------------+ +-------------------------------------------+
Figure 1: Notional Architecture of TEEP Figure 1: Notional Architecture of TEEP
- Trusted Component Signers and Device Administrators utilize the * Trusted Component Signers and Device Administrators utilize the
services of a TAM to manage TAs on devices. Trusted Component services of a TAM to manage TAs on devices. Trusted Component
Signers do not directly interact with devices. Device Signers do not directly interact with devices. Device
Administators may elect to use a TAM for remote administration of Administators may elect to use a TAM for remote administration of
TAs instead of managing each device directly. TAs instead of managing each device directly.
- Trusted Application Manager (TAM): A TAM is responsible for * Trusted Application Manager (TAM): A TAM is responsible for
performing lifecycle management activity on Trusted Components on performing lifecycle management activity on Trusted Components on
behalf of Trusted Component Signers and Device Administrators. behalf of Trusted Component Signers and Device Administrators.
This includes installation and deletion of Trusted Components, and This includes installation and deletion of Trusted Components, and
may include, for example, over-the-air updates to keep Trusted may include, for example, over-the-air updates to keep Trusted
Components up-to-date and clean up when one should be removed. Components up-to-date and clean up when Trusted Components should
TAMs may provide services that make it easier for Trusted be removed. TAMs may provide services that make it easier for
Component Signers or Device Administators to use the TAM's service Trusted Component Signers or Device Administators to use the TAM's
to manage multiple devices, although that is not required of a service to manage multiple devices, although that is not required
TAM. of a TAM.
The TAM performs its management of Trusted Components on the The TAM performs its management of Trusted Components on the
device through interactions with a device's TEEP Broker, which device through interactions with a device's TEEP Broker, which
relays messages between a TAM and a TEEP Agent running inside the relays messages between a TAM and a TEEP Agent running inside the
TEE. TEEP authentication is performed between a TAM and a TEEP TEE. TEEP authentication is performed between a TAM and a TEEP
Agent. Agent.
As shown in Figure 1, the TAM cannot directly contact a TEEP As shown in Figure 1, the TAM cannot directly contact a TEEP
Agent, but must wait for the TEEP Broker to contact the TAM Agent, but must wait for the TEEP Broker to contact the TAM
requesting a particular service. This architecture is intentional requesting a particular service. This architecture is intentional
in order to accommodate network and application firewalls that in order to accommodate network and application firewalls that
normally protect user and enterprise devices from arbitrary normally protect user and enterprise devices from arbitrary
connections from external network entities. connections from external network entities.
A TAM may be publicly available for use by many Trusted Component A TAM may be publicly available for use by many Trusted Component
Signers, or a TAM may be private, and accessible by only one or a Signers, or a TAM may be private, and accessible by only one or a
limited number of Trusted Component Signers. It is expected that limited number of Trusted Component Signers. It is expected that
many manufacturers and network carriers will run their own private many enterprises, manufacturers, and network carriers will run
TAM. their own private TAM.
A Trusted Component Signer or Device Administrator chooses a A Trusted Component Signer or Device Administrator chooses a
particular TAM based on whether the TAM is trusted by a device or particular TAM based on whether the TAM is trusted by a device or
set of devices. The TAM is trusted by a device if the TAM's set of devices. The TAM is trusted by a device if the TAM's
public key is, or chains up to, an authorized Trust Anchor in the public key is, or chains up to, an authorized Trust Anchor in the
device. A Trusted Component Signer or Device Administrator may device. A Trusted Component Signer or Device Administrator may
run their own TAM, but the devices they wish to manage must run their own TAM, but the devices they wish to manage must
include this TAM's public key or certificate, or a certificate it include this TAM's public key or certificate, or a certificate it
chains up to, in the Trust Anchor Store. chains up to, in the Trust Anchor Store.
A Trusted Component Signer or Device Administrator is free to A Trusted Component Signer or Device Administrator is free to
utilize multiple TAMs. This may be required for managing Trusted utilize multiple TAMs. This may be required for managing Trusted
Components on multiple different types of devices from different Components on multiple different types of devices from different
manufacturers, or mobile devices on different network carriers, manufacturers, or mobile devices on different network carriers,
since the Trust Anchor Store on these different devices may since the Trust Anchor Store on these different devices may
contain different TAMs. A Device Administrator may be able to add contain keys for different TAMs. A Device Administrator may be
their own TAM's public key or certificate to the Trust Anchor able to add their own TAM's public key or certificate, or a
Store on all their devices, overcoming this limitation. certificate it chains up to, to the Trust Anchor Store on all
their devices, overcoming this limitation.
Any entity is free to operate a TAM. For a TAM to be successful, Any entity is free to operate a TAM. For a TAM to be successful,
it must have its public key or certificate installed in a device's it must have its public key or certificate installed in a device's
Trust Anchor Store. A TAM may set up a relationship with device Trust Anchor Store. A TAM may set up a relationship with device
manufacturers or network carriers to have them install the TAM's manufacturers or network carriers to have them install the TAM's
keys in their device's Trust Anchor Store. Alternatively, a TAM keys in their device's Trust Anchor Store. Alternatively, a TAM
may publish its certificate and allow Device Administrators to may publish its certificate and allow Device Administrators to
install the TAM's certificate in their devices as an after-market- install the TAM's certificate in their devices as an after-market
action. action.
- TEEP Broker: A TEEP Broker is an application component running in * TEEP Broker: A TEEP Broker is an application component running in
a Rich Execution Environment (REE) that enables the message a Rich Execution Environment (REE) that enables the message
protocol exchange between a TAM and a TEE in a device. A TEEP protocol exchange between a TAM and a TEE in a device. A TEEP
Broker does not process messages on behalf of a TEE, but merely is Broker does not process messages on behalf of a TEE, but merely is
responsible for relaying messages from the TAM to the TEE, and for responsible for relaying messages from the TAM to the TEE, and for
returning the TEE's responses to the TAM. In devices with no REE returning the TEE's responses to the TAM. In devices with no REE
(e.g., a microcontroller where all code runs in an environment (e.g., a microcontroller where all code runs in an environment
that meets the definition of a Trusted Execution Environment in that meets the definition of a Trusted Execution Environment in
Section 2), the TEEP Broker would be absent and instead the TEEP Section 2), the TEEP Broker would be absent and instead the TEEP
protocol transport would be implemented inside the TEE itself. protocol transport would be implemented inside the TEE itself.
- TEEP Agent: The TEEP Agent is a processing module running inside a * TEEP Agent: The TEEP Agent is a processing module running inside a
TEE that receives TAM requests (typically relayed via a TEEP TEE that receives TAM requests (typically relayed via a TEEP
Broker that runs in an REE). A TEEP Agent in the TEE may parse Broker that runs in an REE). A TEEP Agent in the TEE may parse
requests or forward requests to other processing modules in a TEE, requests or forward requests to other processing modules in a TEE,
which is up to a TEE provider's implementation. A response which is up to a TEE provider's implementation. A response
message corresponding to a TAM request is sent back to the TAM, message corresponding to a TAM request is sent back to the TAM,
again typically relayed via a TEEP Broker. again typically relayed via a TEEP Broker.
- Certification Authority (CA): A CA is an entity that issues * Certification Authority (CA): A CA is an entity that issues
digital certificates (especially X.509 certificates) and vouches digital certificates (especially X.509 certificates) and vouches
for the binding between the data items in a certificate [RFC4949]. for the binding between the data items in a certificate [RFC4949].
Certificates are then used for authenticating a device, a TAM, or Certificates are then used for authenticating a device, a TAM, or
a Trusted Component Signer, as discussed in Section 5. The CAs do a Trusted Component Signer, as discussed in Section 5. The CAs do
not need to be the same; different CAs can be chosen by each TAM, not need to be the same; different CAs can be chosen by each TAM,
and different device CAs can be used by different device and different device CAs can be used by different device
manufacturers. manufacturers.
4.2. Multiple TEEs in a Device 4.2. Multiple TEEs in a Device
skipping to change at page 12, line 42 skipping to change at page 12, line 52
| | | | | | | | | | | | | | | |
| | +---+ | | | | | | | | +---+ | | | | | |
| | |TA3|<----+ | | +----------+ | | | | | |TA3|<----+ | | +----------+ | | |
| | | | | | | TEEP |<--+ | | | | | | | | | TEEP |<--+ | |
| | +---+ | +--| Broker | | | | | +---+ | +--| Broker | | |
| | | | 2 |----------------+ | | | | 2 |----------------+
| +-------------+ +----------+ | | +-------------+ +----------+ |
| | | |
+-------------------------------------------+ +-------------------------------------------+
Figure 2: Notional Architecture of TEEP with multiple TEEs Figure 2: Notional Architecture of TEEP with multiple TEEs
In the diagram above, TEEP Broker 1 controls interactions with the In the diagram above, TEEP Broker 1 controls interactions with the
TAs in TEE-1, and TEEP Broker 2 controls interactions with the TAs in TAs in TEE-1, and TEEP Broker 2 controls interactions with the TAs in
TEE-2. This presents some challenges for a TAM in completely TEE-2. This presents some challenges for a TAM in completely
managing the device, since a TAM may not interact with all the TEEP managing the device, since a TAM may not interact with all the TEEP
Brokers on a particular platform. In addition, since TEEs may be Brokers on a particular platform. In addition, since TEEs may be
physically separated, with wholly different resources, there may be physically separated, with wholly different resources, there may be
no need for TEEP Brokers to share information on installed Trusted no need for TEEP Brokers to share information on installed Trusted
Components or resource usage. Components or resource usage.
4.3. Multiple TAMs and Relationship to TAs 4.3. Multiple TAMs and Relationship to TAs
As shown in Figure 2, a TEEP Broker provides communication between As shown in Figure 2, a TEEP Broker provides communication between
one or more TEEP Agents and one or more TAMs. The selection of which one or more TEEP Agents and one or more TAMs. The selection of which
TAM to communicate with might be made with or without input from an TAM to interact with might be made with or without input from an
Untrusted Application, but is ultimately the decision of a TEEP Untrusted Application, but is ultimately the decision of a TEEP
Agent. Agent.
A TEEP Agent is assumed to be able to determine, for any given A TEEP Agent is assumed to be able to determine, for any given
Trusted Component, whether that Trusted Component is installed (or Trusted Component, whether that Trusted Component is installed (or
minimally, is running) in a TEE with which the TEEP Agent is minimally, is running) in a TEE with which the TEEP Agent is
associated. associated.
Each Trusted Component is digitally signed, protecting its integrity, Each Trusted Component is digitally signed, protecting its integrity,
and linking the Trusted Component back to the Trusted Component and linking the Trusted Component back to the Trusted Component
skipping to change at page 14, line 29 skipping to change at page 14, line 38
and beginning a TEEP exchange. If multiple TAM URIs are considered and beginning a TEEP exchange. If multiple TAM URIs are considered
trusted, only one needs to be contacted and they can be attempted in trusted, only one needs to be contacted and they can be attempted in
some order until one responds. some order until one responds.
Separate from the Untrusted Application's manifest, this framework Separate from the Untrusted Application's manifest, this framework
relies on the use of the manifest format in [I-D.ietf-suit-manifest] relies on the use of the manifest format in [I-D.ietf-suit-manifest]
for expressing how to install a Trusted Component, as well as any for expressing how to install a Trusted Component, as well as any
dependencies on other TEE components and versions. That is, dependencies on other TEE components and versions. That is,
dependencies from Trusted Components on other Trusted Components can dependencies from Trusted Components on other Trusted Components can
be expressed in a SUIT manifest, including dependencies on any other be expressed in a SUIT manifest, including dependencies on any other
TAs, or trusted OS code (if any), or trusted firmware. Installation TAs, trusted OS code (if any), or trusted firmware. Installation
steps can also be expressed in a SUIT manifest. steps can also be expressed in a SUIT manifest.
For example, TEEs compliant with GlobalPlatform may have a notion of For example, TEEs compliant with GlobalPlatform [GPTEE] may have a
a "security domain" (which is a grouping of one or more TAs installed notion of a "security domain" (which is a grouping of one or more TAs
on a device, that can share information within such a group) that installed on a device, that can share information within such a
must be created and into which one or more TAs can then be installed. group) that must be created and into which one or more TAs can then
It is thus up to the SUIT manifest to express a dependency on having be installed. It is thus up to the SUIT manifest to express a
such a security domain existing or being created first, as dependency on having such a security domain existing or being created
appropriate. first, as appropriate.
Updating a Trusted Component may cause compatibility issues with any Updating a Trusted Component may cause compatibility issues with any
Untrusted Applications or other components that depend on the updated Untrusted Applications or other components that depend on the updated
Trusted Component, just like updating the OS or a shared library Trusted Component, just like updating the OS or a shared library
could impact an Untrusted Application. Thus, an implementation needs could impact an Untrusted Application. Thus, an implementation needs
to take into account such issues. to take into account such issues.
4.4. Untrusted Apps, Trusted Apps, and Personalization Data 4.4. Untrusted Apps, Trusted Apps, and Personalization Data
In TEEP, there is an explicit relationship and dependence between an In TEEP, there is an explicit relationship and dependence between an
skipping to change at page 15, line 13 skipping to change at page 15, line 26
uses one or more TAs in a TEE appears no different from any other uses one or more TAs in a TEE appears no different from any other
Untrusted Application in the REE. However, the way the Untrusted Untrusted Application in the REE. However, the way the Untrusted
Application and its corresponding TAs are packaged, delivered, and Application and its corresponding TAs are packaged, delivered, and
installed on the device can vary. The variations depend on whether installed on the device can vary. The variations depend on whether
the Untrusted Application and TA are bundled together or are provided the Untrusted Application and TA are bundled together or are provided
separately, and this has implications to the management of the TAs in separately, and this has implications to the management of the TAs in
a TEE. In addition to the Untrusted Application and TA(s), the TA(s) a TEE. In addition to the Untrusted Application and TA(s), the TA(s)
and/or TEE may also require additional data to personalize the TA to and/or TEE may also require additional data to personalize the TA to
the device or a user. Implementations must support encryption of the device or a user. Implementations must support encryption of
such Personalization Data to preserve the confidentiality of such Personalization Data to preserve the confidentiality of
potentially sensitive data contained within it and support integrity potentially sensitive data contained within it, and must support
protection of the Personalization Data. Other than the requirement integrity protection of the Personalization Data. Other than the
to support confidentiality and integrity protection, the TEEP requirement to support confidentiality and integrity protection, the
architecture places no limitations or requirements on the TEEP architecture places no limitations or requirements on the
Personalization Data. Personalization Data.
There are three possible cases for bundling of an Untrusted There are multiple possible cases for bundling of an Untrusted
Application, TA(s), and Personalization Data: Application, TA(s), and Personalization Data. Such cases include
(possibly among others):
1. The Untrusted Application, TA(s), and Personalization Data are 1. The Untrusted Application, TA(s), and Personalization Data are
all bundled together in a single package by a Trusted Component all bundled together in a single package by a Trusted Component
Signer and either provided to the TEEP Broker through the TAM, or Signer and either provided to the TEEP Broker through the TAM, or
provided separately (with encrypted Personalization Data), with provided separately (with encrypted Personalization Data), with
key material needed to decrypt and install the Personalization key material needed to decrypt and install the Personalization
Data and TA provided by a TAM. Data and TA provided by a TAM.
2. The Untrusted Application and the TA(s) are bundled together in a 2. The Untrusted Application and the TA(s) are bundled together in a
single package, which a TAM or a publicly accessible app store single package, which a TAM or a publicly accessible app store
maintains, and the Personalization Data is separately provided by maintains, and the Personalization Data is separately provided by
the Trusted Component Signer's TAM. the Personalization Data provider's TAM.
3. All components are independent. The Untrusted Application is 3. All components are independent packages. The Untrusted
installed through some independent or device-specific mechanism, Application is installed through some independent or device-
and the TAM provides the TA and Personalization Data from the specific mechanism, and one or more TAMs provide (directly or
Trusted Component Signer. Delivery of the TA and Personalization indirectly by reference) the TA(s) and Personalization Data.
Data may be combined or separate.
4. The TA(s) and Personalization Data are bundled together into a
package provided by a TAM, while the Untrusted Application is
installed through some independent or device-specific mechanism
such as an app store.
5. Encrypted Personalization Data is bundled into a package
distributed with the Untrusted Application, while the TA(s) and
key material needed to decrypt and install the Personalization
Data are in a separate package provided by a TAM.
The TEEP protocol can treat each TA, any dependencies the TA has, and The TEEP protocol can treat each TA, any dependencies the TA has, and
Personalization Data as separate Trusted Components with separate Personalization Data as separate Trusted Components with separate
installation steps that are expressed in SUIT manifests, and a SUIT installation steps that are expressed in SUIT manifests, and a SUIT
manifest might contain or reference multiple binaries (see manifest might contain or reference multiple binaries (see
[I-D.ietf-suit-manifest] for more details). The TEEP Agent is [I-D.ietf-suit-manifest] for more details). The TEEP Agent is
responsible for handling any installation steps that need to be responsible for handling any installation steps that need to be
performed inside the TEE, such as decryption of private TA binaries performed inside the TEE, such as decryption of private TA binaries
or Personalization Data. or Personalization Data.
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4.4.1. Example: Application Delivery Mechanisms in Intel SGX 4.4.1. Example: Application Delivery Mechanisms in Intel SGX
In Intel Software Guard Extensions (SGX), the Untrusted Application In Intel Software Guard Extensions (SGX), the Untrusted Application
and TA are typically bundled into the same package (Case 2). The TA and TA are typically bundled into the same package (Case 2). The TA
exists in the package as a shared library (.so or .dll). The exists in the package as a shared library (.so or .dll). The
Untrusted Application loads the TA into an SGX enclave when the Untrusted Application loads the TA into an SGX enclave when the
Untrusted Application needs the TA. This organization makes it easy Untrusted Application needs the TA. This organization makes it easy
to maintain compatibility between the Untrusted Application and the to maintain compatibility between the Untrusted Application and the
TA, since they are updated together. It is entirely possible to TA, since they are updated together. It is entirely possible to
create an Untrusted Application that loads an external TA into an SGX create an Untrusted Application that loads an external TA into an SGX
enclave, and use that TA (Case 3). In this case, the Untrusted enclave, and use that TA (Cases 3-5). In this case, the Untrusted
Application would require a reference to an external file or download Application would require a reference to an external file or download
such a file dynamically, place the contents of the file into memory, such a file dynamically, place the contents of the file into memory,
and load that as a TA. Obviously, such file or downloaded content and load that as a TA. Obviously, such file or downloaded content
must be properly formatted and signed for it to be accepted by the must be properly formatted and signed for it to be accepted by the
SGX TEE. In SGX, for Case 2 and Case 3, the Personalization Data is SGX TEE.
normally loaded into the SGX enclave (the TA) after the TA has
started. Although Case 1 is possible with SGX, there are no In SGX, any Personalization Data is normally loaded into the SGX
enclave (the TA) after the TA has started. Although it is possible
with SGX to include the Untrusted Application in an encrypted package
along with Personalization Data (Cases 1 and 5), there are no
instances of this known to be in use at this time, since such a instances of this known to be in use at this time, since such a
construction would require a special installation program and SGX TA construction would require a special installation program and SGX TA
to receive the encrypted binary, decrypt it, separate it into the (which might or might not be the TEEP Agent itself based on the
three different elements, and then install all three. This implementation) to receive the encrypted package, decrypt it,
installation is complex because the Untrusted Application decrypted separate it into the different elements, and then install each one.
inside the TEE must be passed out of the TEE to an installer in the This installation is complex because the Untrusted Application
REE which would install the Untrusted Application; this assumes that decrypted inside the TEE must be passed out of the TEE to an
the Untrusted Application package includes the TA code also, since installer in the REE which would install the Untrusted Application.
otherwise there is a significant problem in getting the SGX enclave Finally, the Personalization Data would need to be sent out of the
code (the TA) from the TEE, through the installer, and into the TEE (encrypted in an SGX enclave-to-enclave manner) to the REE's
Untrusted Application in a trusted fashion. Finally, the installation app, which would pass this data to the installed
Personalization Data would need to be sent out of the TEE (encrypted Untrusted Application, which would in turn send this data to the SGX
in an SGX enclave-to-enclave manner) to the REE's installation app, enclave (TA). This complexity is due to the fact that each SGX
which would pass this data to the installed Untrusted Application, enclave is separate and does not have direct communication to other
which would in turn send this data to the SGX enclave (TA). This SGX enclaves.
complexity is due to the fact that each SGX enclave is separate and
does not have direct communication to other SGX enclaves.
As long as signed files (TAs and/or Personalization Data) are As long as signed files (TAs and/or Personalization Data) are
installed into an untrusted filesystem and trust is verified by the installed into an untrusted filesystem and trust is verified by the
TEE at load time, classic distribution mechanisms can be used. Some TEE at load time, classic distribution mechanisms can be used. Some
uses of SGX, however, allow a model where a TA can be dynamically uses of SGX, however, allow a model where a TA can be dynamically
installed into an SGX enclave that provides a runtime platform. The installed into an SGX enclave that provides a runtime platform. The
TEEP protocol can be used in such cases, where the runtime platform TEEP protocol can be used in such cases, where the runtime platform
could include a TEEP Agent. could include a TEEP Agent.
4.4.2. Example: Application Delivery Mechanisms in Arm TrustZone 4.4.2. Example: Application Delivery Mechanisms in Arm TrustZone
In Arm TrustZone [TrustZone] for A-class devices, the Untrusted In Arm TrustZone [TrustZone] for A-class devices, the Untrusted
Application and TA may or may not be bundled together. This differs Application and TA may or may not be bundled together. This differs
from SGX since in TrustZone the TA lifetime is not inherently tied to from SGX since in TrustZone the TA lifetime is not inherently tied to
a specific Untrused Application process lifetime as occurs in SGX. A a specific Untrused Application process lifetime as occurs in SGX. A
TA is loaded by a trusted OS running in the TEE such as a TA is loaded by a trusted OS running in the TEE such as a
GlobalPlatform compliant TEE, where the trusted OS is separate from GlobalPlatform [GPTEE] compliant TEE, where the trusted OS is
the OS in the REE. Thus Cases 2 and 3 are equally applicable. In separate from the OS in the REE. Thus Cases 2-4 are equally
addition, it is possible for TAs to communicate with each other applicable. In addition, it is possible for TAs to communicate with
without involving any Untrusted Application, and so the complexity of each other without involving any Untrusted Application, and so the
Case 1 is lower than in the SGX example. Thus, Case 1 is possible as complexity of Cases 1 and 5 are lower than in the SGX example, though
well, though still more complex than Cases 2 and 3. still more complex than Cases 2-4.
A trusted OS running in the TEE (e.g., OP-TEE) that supports loading A trusted OS running in the TEE (e.g., OP-TEE) that supports loading
and verifying signed TAs from an untrusted filesystem can, like SGX, and verifying signed TAs from an untrusted filesystem can, like SGX,
use classic file distribution mechanisms. If secure TA storage is use classic file distribution mechanisms. If secure TA storage is
used (e.g., a Replay-Protected Memory Block device) on the other used (e.g., a Replay-Protected Memory Block device) on the other
hand, the TEEP protocol can be used to manage such storage. hand, the TEEP protocol can be used to manage such storage.
4.5. Entity Relations 4.5. Entity Relations
This architecture leverages asymmetric cryptography to authenticate a This architecture leverages asymmetric cryptography to authenticate a
skipping to change at page 18, line 21 skipping to change at page 18, line 24
| | | <-- Get a TAM cert ---------| | | | <-- Get a TAM cert ---------|
| | | | | | | | | |
1. Build two apps: | | | | 1. Build two apps: | | | |
| | | | | | | |
(a) Untrusted | | | | (a) Untrusted | | | |
App - 2a. Supply --> | --- 3. Install ------> | | App - 2a. Supply --> | --- 3. Install ------> | |
| | | | | | | |
(b) TA -- 2b. Supply ----------> | 4. Messaging-->| | (b) TA -- 2b. Supply ----------> | 4. Messaging-->| |
| | | | | | | |
Figure 3: Example Developer Experience Figure 3: Example Developer Experience
Figure 3 shows an example where the same developer builds and signs Figure 3 shows an example where the same developer builds and signs
two applications: (a) an Untrusted Application; (b) a TA that two applications: (a) an Untrusted Application; (b) a TA that
provides some security functions to be run inside a TEE. This provides some security functions to be run inside a TEE. This
example assumes that the developer, the TEE, and the TAM have example assumes that the developer, the TEE, and the TAM have
previously been provisioned with certificates. previously been provisioned with certificates.
At step 1, the developer authors the two applications. At step 1, the developer authors the two applications.
At step 2, the developer uploads the Untrusted Application (2a) to an At step 2, the developer uploads the Untrusted Application (2a) to an
skipping to change at page 18, line 44 skipping to change at page 18, line 47
developer can then either bundle the signed TA with the Untrusted developer can then either bundle the signed TA with the Untrusted
Application, or the developer can provide a signed Trusted Component Application, or the developer can provide a signed Trusted Component
containing the TA to a TAM that will be managing the TA in various containing the TA to a TAM that will be managing the TA in various
devices. devices.
At step 3, a user will go to an Application Store to download the At step 3, a user will go to an Application Store to download the
Untrusted Application (where the arrow indicates the direction of Untrusted Application (where the arrow indicates the direction of
data transfer). data transfer).
At step 4, since the Untrusted Application depends on the TA, At step 4, since the Untrusted Application depends on the TA,
installing the Untrusted Application will trigger TA installation by installing the Untrusted Application will trigger TA installation via
initiating communication with a TAM. The TEEP Agent will interact communication with a TAM. The TEEP Agent will interact with the TAM
with TAM via a TEEP Broker that faciliates communications between a via a TEEP Broker that faciliates communications between the TAM and
TAM and the TEEP Agent in TEE. the TEEP Agent.
Some Trusted Component installation implementations might ask for a Some Trusted Component installation implementations might ask for a
user's consent. In other implementations, a Device Administrator user's consent. In other implementations, a Device Administrator
might choose what Untrusted Applications and related Trusted might choose what Untrusted Applications and related Trusted
Components to be installed. A user consent flow is out of scope of Components to be installed. A user consent flow is out of scope of
the TEEP architecture. the TEEP architecture.
The main components consist of a set of standard messages created by The main components of the TEEP protocol consist of a set of standard
a TAM to deliver Trusted Component management commands to a device, messages created by a TAM to deliver Trusted Component management
and device attestation and response messages created by a TEE that commands to a device, and device attestation and response messages
responds to a TAM's message. created by a TEE that responds to a TAM's message.
It should be noted that network communication capability is generally It should be noted that network communication capability is generally
not available in TAs in today's TEE-powered devices. Consequently, not available in TAs in today's TEE-powered devices. Consequently,
Trusted Applications generally rely on broker in the REE to provide Trusted Applications generally rely on a broker in the REE to provide
access to network functionality in the REE. A broker does not need access to network functionality in the REE. A broker does not need
to know the actual content of messages to facilitate such access. to know the actual content of messages to facilitate such access.
Similarly, since the TEEP Agent runs inside a TEE, the TEEP Agent Similarly, since the TEEP Agent runs inside a TEE, the TEEP Agent
generally relies on a TEEP Broker in the REE to provide network generally relies on a TEEP Broker in the REE to provide network
access, and relay TAM requests to the TEEP Agent and relay the access, and relay TAM requests to the TEEP Agent and relay the
responses back to the TAM. responses back to the TAM.
5. Keys and Certificate Types 5. Keys and Certificate Types
This architecture leverages the following credentials, which allow This architecture leverages the following credentials, which allow
delivering end-to-end security between a TAM and a TEEP Agent. achieving end-to-end security between a TAM and a TEEP Agent.
Figure 4 summarizes the relationships between various keys and where Figure 4 summarizes the relationships between various keys and where
they are stored. Each public/private key identifies a Trusted they are stored. Each public/private key identifies a Trusted
Component Signer, TAM, or TEE, and gets a certificate that chains up Component Signer, TAM, or TEE, and gets a certificate that chains up
to some trust anchor. A list of trusted certificates is then used to to some trust anchor. A list of trusted certificates is used to
check a presented certificate against. check a presented certificate against.
Different CAs can be used for different types of certificates. TEEP Different CAs can be used for different types of certificates. TEEP
messages are always signed, where the signer key is the message messages are always signed, where the signer key is the message
originator's private key, such as that of a TAM or a TEE. In originator's private key, such as that of a TAM or a TEE. In
addition to the keys shown in Figure 4, there may be additional keys addition to the keys shown in Figure 4, there may be additional keys
used for attestation. Refer to the RATS Architecture used for attestation or encryption. Refer to the RATS Architecture
[I-D.ietf-rats-architecture] for more discussion. [I-D.ietf-rats-architecture] for more discussion.
Cardinality & Location of Cardinality & Location of
Location of Private Key Trust Anchor Location of Private Key Trust Anchor
Purpose Private Key Signs Store Purpose Private Key Signs Store
------------------ ----------- ------------- ------------- ------------------ ----------- ------------- -------------
Authenticating 1 per TEE TEEP responses TAM Authenticating 1 per TEE TEEP responses TAM
TEEP Agent TEEP Agent
Authenticating TAM 1 per TAM TEEP requests TEEP Agent Authenticating TAM 1 per TAM TEEP requests TEEP Agent
Code Signing 1 per Trusted TA binary TEE Code Signing 1 per Trusted TA binary TEE
Component Component
Signer Signer
Figure 4: Signature Keys Figure 4: Signature Keys
Note that Personalization Data is not included in the table above. Note that Personalization Data is not included in the table above.
The use of Personalization Data is dependent on how TAs are used and The use of Personalization Data is dependent on how TAs are used and
what their security requirements are. what their security requirements are.
TEEP requests from a TAM to a TEEP Agent are signed with the TAM TEEP requests from a TAM to a TEEP Agent are signed with the TAM
private key (for authentication and integrity protection). private key (for authentication and integrity protection).
Personalization Data and TA binaries can be encrypted with a key that Personalization Data and TA binaries can be encrypted with a key that
is established with a content-encryption key established with the TEE is established with a content-encryption key established with the TEE
public key (to provide confidentiality). Conversely, TEEP responses public key (to provide confidentiality). Conversely, TEEP responses
from a TEEP Agent to a TAM can be signed with the TEE private key. from a TEEP Agent to a TAM can be signed with the TEE private key.
The TEE key pair and certificate are thus used for authenticating the The TEE key pair and certificate are thus used for authenticating the
TEE to a remote TAM, and for sending private data to the TEE. Often, TEE to a remote TAM, and for sending private data to the TEE. Often,
the key pair is burned into the TEE by the TEE manufacturer and the the key pair is burned into the TEE by the TEE manufacturer and the
key pair and its certificate are valid for the expected lifetime of key pair and its certificate are valid for the expected lifetime of
the TEE. A TAM provider is responsible for configuring the TAM's the TEE. A TAM provider is responsible for configuring the TAM's
Trust Anchor Store with the manufacturer certificates or CAs that are Trust Anchor Store with the manufacturer certificates or CAs that are
used to sign TEE keys. This is discussed further in Section 5.3 used to sign TEE keys. This is discussed further in Section 5.3
below. below. Typically the same key TEE pair is used for both signing and
encryption, though separate key pairs might also be used in the
future, as the joint security of encryption and signature with a
single key remains to some extent an open question in academic
cryptography.
The TAM key pair and certificate are used for authenticating a TAM to The TAM key pair and certificate are used for authenticating a TAM to
a remote TEE, and for sending private data to the TAM. A TAM a remote TEE, and for sending private data to the TAM (separate key
provider is responsible for acquiring a certificate from a CA that is pairs for authentication vs. encryption could also be used in the
trusted by the TEEs it manages. This is discussed further in future). A TAM provider is responsible for acquiring a certificate
Section 5.1 below. from a CA that is trusted by the TEEs it manages. This is discussed
further in Section 5.1 below.
The Trusted Component Signer key pair and certificate are used to The Trusted Component Signer key pair and certificate are used to
sign Trusted Components that the TEE will consider authorized to sign Trusted Components that the TEE will consider authorized to
execute. TEEs must be configured with the certificates or keys that execute. TEEs must be configured with the certificates or keys that
it considers authorized to sign TAs that it will execute. This is it considers authorized to sign TAs that it will execute. This is
discussed further in Section 5.2 below. discussed further in Section 5.2 below.
5.1. Trust Anchors in a TEEP Agent 5.1. Trust Anchors in a TEEP Agent
A TEEP Agent's Trust Anchor Store contains a list of Trust Anchors, A TEEP Agent's Trust Anchor Store contains a list of Trust Anchors,
which are CA certificates that sign various TAM certificates. The which are typically CA certificates that sign various TAM
list is typically preloaded at manufacturing time, and can be updated certificates. The list is typically preloaded at manufacturing time,
using the TEEP protocol if the TEE has some form of "Trust Anchor and can be updated using the TEEP protocol if the TEE has some form
Manager TA" that has Trust Anchors in its configuration data. Thus, of "Trust Anchor Manager TA" that has Trust Anchors in its
Trust Anchors can be updated similar to updating the Personalization configuration data. Thus, Trust Anchors can be updated similarly to
Data for any other TA. the Personalization Data for any other TA.
When Trust Anchor update is carried out, it is imperative that any When Trust Anchor update is carried out, it is imperative that any
update must maintain integrity where only an authentic Trust Anchor update must maintain integrity where only an authentic Trust Anchor
list from a device manufacturer or a Device Administrator is list from a device manufacturer or a Device Administrator is
accepted. Details are out of scope of the architecture and can be accepted. Details are out of scope of the architecture and can be
addressed in a protocol document. addressed in a protocol document.
Before a TAM can begin operation in the marketplace to support a Before a TAM can begin operation in the marketplace to support a
device with a particular TEE, it must obtain a TAM certificate from a device with a particular TEE, it must be able to get its raw public
CA or the raw public key of a TAM that is listed in the Trust Anchor key, or its certificate, or a certificate it chains up to, listed in
Store of the TEEP Agent. the Trust Anchor Store of the TEEP Agent.
5.2. Trust Anchors in a TEE 5.2. Trust Anchors in a TEE
A TEE determines whether TA binaries are allowed to execute by The Trust Anchor Store in a TEE contains a list of Trust Anchors (raw
verifying whether their signature can be verified using public keys or certificates) that are used to determine whether TA
certificate(s) or raw public key(s) in the TEE's Trust Anchor Store. binaries are allowed to execute by checking if their signatures can
The list is typically preloaded at manufacturing time, and can be be verified. The list is typically preloaded at manufacturing time,
updated using the TEEP protocol if the TEE has some form of "Trust and can be updated using the TEEP protocol if the TEE has some form
Anchor Manager TA" that has Trust Anchors in its configuration data. of "Trust Anchor Manager TA" that has Trust Anchors in its
Thus, Trust Anchors can be updated similar to updating the configuration data. Thus, Trust Anchors can be updated similarly to
Personalization Data for any other TA, as discussed in Section 5.1. the Personalization Data for any other TA, as discussed in
Section 5.1.
5.3. Trust Anchors in a TAM 5.3. Trust Anchors in a TAM
The Trust Anchor Store in a TAM consists of a list of Trust Anchors, The Trust Anchor Store in a TAM consists of a list of Trust Anchors,
which are certificates that sign various device TEE certificates. A which are certificates that sign various device TEE certificates. A
TAM will accept a device for Trusted Component management if the TEE TAM will accept a device for Trusted Component management if the TEE
in the device uses a TEE certificate that is chained to a certificate in the device uses a TEE certificate that is chained to a certificate
or raw public key that the TAM trusts, is contained in an allow list, or raw public key that the TAM trusts, is contained in an allow list,
is not found on a block list, and/or fulfills any other policy is not found on a block list, and/or fulfills any other policy
criteria. criteria.
5.4. Scalability 5.4. Scalability
This architecture uses a PKI (including self-signed certificates). This architecture uses a PKI (including self-signed certificates).
Trust Anchors exist on the devices to enable the TEE to authenticate Trust Anchors exist on the devices to enable the TEEP Agent to
TAMs and Trusted Component Signers, and TAMs use Trust Anchors to authenticate TAMs and the TEE to authenticate Trusted Component
authenticate TEEs. When a PKI is used, many intermediate CA Signers, and TAMs use Trust Anchors to authenticate TEEP Agents.
certificates can chain to a root certificate, each of which can issue When a PKI is used, many intermediate CA certificates can chain to a
many certificates. This makes the protocol highly scalable. New root certificate, each of which can issue many certificates. This
factories that produce TEEs can join the ecosystem. In this case, makes the protocol highly scalable. New factories that produce TEEs
such a factory can get an intermediate CA certificate from one of the can join the ecosystem. In this case, such a factory can get an
existing roots without requiring that TAMs are updated with intermediate CA certificate from one of the existing roots without
information about the new device factory. Likewise, new TAMs can requiring that TAMs are updated with information about the new device
join the ecosystem, providing they are issued a TAM certificate that factory. Likewise, new TAMs can join the ecosystem, providing they
chains to an existing root whereby existing TEEs will be allowed to are issued a TAM certificate that chains to an existing root whereby
be personalized by the TAM without requiring changes to the TEE existing TEEs will be allowed to be personalized by the TAM without
itself. This enables the ecosystem to scale, and avoids the need for requiring changes to the TEE itself. This enables the ecosystem to
centralized databases of all TEEs produced or all TAMs that exist or scale, and avoids the need for centralized databases of all TEEs
all Trusted Component Signers that exist. produced or all TAMs that exist or all Trusted Component Signers that
exist.
5.5. Message Security 5.5. Message Security
Messages created by a TAM are used to deliver Trusted Component Messages created by a TAM are used to deliver Trusted Component
management commands to a device, and device attestation and messages management commands to a device, and device attestation and messages
created by the device TEE to respond to TAM messages. are created by the device TEE to respond to TAM messages.
These messages are signed end-to-end between a TEEP Agent and a TAM. These messages are signed end-to-end between a TEEP Agent and a TAM.
Confidentiality is provided by encrypting sensitive payloads (such as Confidentiality is provided by encrypting sensitive payloads (such as
Personalization Data and attestation evidence), rather than Personalization Data and attestation evidence), rather than
encrypting the messages themselves. Using encrypted payloads is encrypting the messages themselves. Using encrypted payloads is
important to ensure that only the targeted device TEE or TAM is able important to ensure that only the targeted device TEE or TAM is able
to decrypt and view the actual content. to decrypt and view the actual content.
6. TEEP Broker 6. TEEP Broker
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can inspect this application metadata file and invoke the TEEP Broker can inspect this application metadata file and invoke the TEEP Broker
to trigger Trusted Component installation on behalf of the Untrusted to trigger Trusted Component installation on behalf of the Untrusted
Application without requiring the Untrusted Application to run first. Application without requiring the Untrusted Application to run first.
6.1. Role of the TEEP Broker 6.1. Role of the TEEP Broker
A TEEP Broker abstracts the message exchanges with a TEE in a device. A TEEP Broker abstracts the message exchanges with a TEE in a device.
The input data is originated from a TAM or the first initialization The input data is originated from a TAM or the first initialization
call to trigger a Trusted Component installation. call to trigger a Trusted Component installation.
The Broker doesn't need to parse a message content received from a The Broker doesn't need to parse TEEP message content received from a
TAM that should be processed by a TEE (see the ProcessTeepMessage API TAM that should be processed by a TEE (see the ProcessTeepMessage API
in Section 6.2.1). When a device has more than one TEE, one TEEP in Section 6.2.1). When a device has more than one TEE, one TEEP
Broker per TEE could be present in the REE. A TEEP Broker interacts Broker per TEE could be present in the REE or a common TEEP Broker
with a TEEP Agent inside a TEE. could be used by multiple TEEs where the transport protocol (e.g.,
[I-D.ietf-teep-otrp-over-http]) allows the TEEP Broker to distinguish
A TAM message may indicate the target TEE where a Trusted Component which TEE is relevant for each message from a TAM.
should be installed. A compliant TEEP protocol should include a
target TEE identifier for a TEEP Broker when multiple TEEs are
present.
The Broker relays the response messages generated from a TEEP Agent The TEEP Broker interacts with a TEEP Agent inside a TEE, and relays
in a TEE to the TAM. the response messages generated from the TEEP Agent back to the TAM.
The Broker only needs to return a (transport) error message if the The Broker only needs to return a (transport) error message to the
TEE is not reachable for some reason. Other errors are represented TAM if the TEE is not reachable for some reason. Other errors are
as response messages returned from the TEE which will then be passed represented as TEEP response messages returned from the TEE which
to the TAM. will then be passed to the TAM.
6.2. TEEP Broker Implementation Consideration 6.2. TEEP Broker Implementation Consideration
As depicted in Figure 5, there are multiple ways in which a TEEP As depicted in Figure 5, there are multiple ways in which a TEEP
Broker can be implemented, with more or fewer layers being inside the Broker can be implemented, with more or fewer layers being inside the
TEE. For example, in model A, the model with the smallest TEE TEE. For example, in model A, the model with the smallest TEE
footprint, only the TEEP implementation is inside the TEE, whereas footprint, only the TEEP implementation is inside the TEE, whereas
the TEEP/HTTP implementation is in the TEEP Broker outside the TEE. the TEEP/HTTP implementation is in the TEEP Broker outside the TEE.
Model: A B C ... Model: A B C ...
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| HTTP(S) | | | | | HTTP(S) | | | |
| implementation | | | | | implementation | | | |
+----------------+ | | v +----------------+ | | v
| | | | | |
+----------------+ | | ^ +----------------+ | | ^
| TCP or QUIC | | | | Broker | TCP or QUIC | | | | Broker
| implementation | | | | | implementation | | | |
+----------------+ | | | +----------------+ | | |
REE REE REE REE REE REE
Figure 5: TEEP Broker Models Figure 5: TEEP Broker Models
In other models, additional layers are moved into the TEE, increasing In other models, additional layers are moved into the TEE, increasing
the TEE footprint, with the Broker either containing or calling the the TEE footprint, with the Broker either containing or calling the
topmost protocol layer outside of the TEE. An implementation is free topmost protocol layer outside of the TEE. An implementation is free
to choose any of these models. to choose any of these models.
TEEP Broker implementers should consider methods of distribution, TEEP Broker implementers should consider methods of distribution,
scope and concurrency on devices and runtime options. scope and concurrency on devices and runtime options.
6.2.1. TEEP Broker APIs 6.2.1. TEEP Broker APIs
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Agent may wish to contact the TAM for any changes, without the Agent may wish to contact the TAM for any changes, without the
device itself needing any particular change. device itself needing any particular change.
5. ProcessError: A notification that the TEEP Broker could not 5. ProcessError: A notification that the TEEP Broker could not
deliver an outbound TEEP message to a TAM. deliver an outbound TEEP message to a TAM.
For comparison, similar APIs may exist on the TAM side, where a For comparison, similar APIs may exist on the TAM side, where a
Broker may or may not exist, depending on whether the TAM uses a TEE Broker may or may not exist, depending on whether the TAM uses a TEE
or not: or not:
1. ProcessConnect: A notification that an incoming TEEP session is 1. ProcessConnect: A notification that a new TEEP session is being
being requested by a TEEP Agent. requested by a TEEP Agent.
2. ProcessTeepMessage: A message arriving from the network, to be 2. ProcessTeepMessage: A message arriving on an existing TEEP
delivered to the TAM for processing. session, to be delivered to the TAM for processing.
For further discussion on these APIs, see For further discussion on these APIs, see
[I-D.ietf-teep-otrp-over-http]. [I-D.ietf-teep-otrp-over-http].
6.2.2. TEEP Broker Distribution 6.2.2. TEEP Broker Distribution
The Broker installation is commonly carried out at OEM time. A user The Broker installation is commonly carried out at OEM time. A user
can dynamically download and install a Broker on-demand. can dynamically download and install a Broker on-demand.
7. Attestation 7. Attestation
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extended claims. extended claims.
+----------------+ +----------------+
| Device | +----------+ | Device | +----------+
| +------------+ | Evidence | TAM | Evidence +----------+ | +------------+ | Evidence | TAM | Evidence +----------+
| | TEE |------------->| (Relying |-------------->| Verifier | | | TEE |------------->| (Relying |-------------->| Verifier |
| | (Attester) | | | Party) |<--------------| | | | (Attester) | | | Party) |<--------------| |
| +------------+ | +----------+ Attestation +----------+ | +------------+ | +----------+ Attestation +----------+
+----------------+ Result +----------------+ Result
Figure 6: TEEP Attestation Roles Figure 6: TEEP Attestation Roles
As of the writing of this specification, device and TEE attestations As of the writing of this specification, device and TEE attestations
have not been standardized across the market. Different devices, have not been standardized across the market. Different devices,
manufacturers, and TEEs support different attestation protocols. In manufacturers, and TEEs support different attestation protocols. In
order for TEEP to be inclusive, it is agnostic to the format of order for TEEP to be inclusive, it is agnostic to the format of
evidence, allowing proprietary or standardized formats to be used evidence, allowing proprietary or standardized formats to be used
between a TEE and a verifier (which may or may not be colocated in between a TEE and a verifier (which may or may not be colocated in
the TAM), as long as the format supports encryption of any the TAM), as long as the format supports encryption of any
information that is considered sensitive. information that is considered sensitive.
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results, and the protocol (if any) used between the TAM and a results, and the protocol (if any) used between the TAM and a
verifier, as long as they convey at least the required set of claims verifier, as long as they convey at least the required set of claims
in some format. Note that the respective attestation algorithms are in some format. Note that the respective attestation algorithms are
not defined in the TEEP protocol itself; see not defined in the TEEP protocol itself; see
[I-D.ietf-rats-architecture] and [I-D.ietf-teep-protocol] for more [I-D.ietf-rats-architecture] and [I-D.ietf-teep-protocol] for more
discussion. discussion.
There are a number of considerations that need to be considered when There are a number of considerations that need to be considered when
appraising evidence provided by a TEE, including: appraising evidence provided by a TEE, including:
- What security measures a manufacturer takes when provisioning keys * What security measures a manufacturer takes when provisioning keys
into devices/TEEs; into devices/TEEs;
- What hardware and software components have access to the * What hardware and software components have access to the
attestation keys of the TEE; attestation keys of the TEE;
- The source or local verification of claims within an attestation * The source or local verification of claims within an attestation
prior to a TEE signing a set of claims; prior to a TEE signing a set of claims;
- The level of protection afforded to attestation keys against * The level of protection afforded to attestation keys against
exfiltration, modification, and side channel attacks; exfiltration, modification, and side channel attacks;
- The limitations of use applied to TEE attestation keys; * The limitations of use applied to TEE attestation keys;
- The processes in place to discover or detect TEE breaches; and * The processes in place to discover or detect TEE breaches; and
- The revocation and recovery process of TEE attestation keys. * The revocation and recovery process of TEE attestation keys.
Some TAMs may require additional claims in order to properly Some TAMs may require additional claims in order to properly
authorize a device or TEE. The specific format for these additional authorize a device or TEE. The specific format for these additional
claims are outside the scope of this specification, but the TEEP claims are outside the scope of this specification, but the TEEP
protocol allows these additional claims to be included in the protocol allows these additional claims to be included in the
attestation messages. attestation messages.
For more discussion of the attestation and appraisal process, see the For more discussion of the attestation and appraisal process, see the
RATS Architecture [I-D.ietf-rats-architecture]. RATS Architecture [I-D.ietf-rats-architecture].
The following information is required for TEEP attestation: The following information is required for TEEP attestation:
- Device Identifying Information: Attestation information may need * Device Identifying Information: Attestation information may need
to uniquely identify a device to the TAM. Unique device to uniquely identify a device to the TAM. Unique device
identification allows the TAM to provide services to the device, identification allows the TAM to provide services to the device,
such as managing installed TAs, and providing subscriptions to such as managing installed TAs, and providing subscriptions to
services, and locating device-specific keying material to services, and locating device-specific keying material to
communicate with or authenticate the device. In some use cases it communicate with or authenticate the device. In some use cases it
may be sufficient to identify only the class of the device. The may be sufficient to identify only the class of the device. The
security and privacy requirements regarding device identification security and privacy requirements regarding device identification
will vary with the type of TA provisioned to the TEE. will vary with the type of TA provisioned to the TEE.
- TEE Identifying Information: The type of TEE that generated this * TEE Identifying Information: The type of TEE that generated this
attestation must be identified. This includes version attestation must be identified. This includes version
identification information for hardware, firmware, and software identification information for hardware, firmware, and software
version of the TEE, as applicable by the TEE type. TEE version of the TEE, as applicable by the TEE type. TEE
manufacturer information for the TEE is required in order to manufacturer information for the TEE is required in order to
disambiguate the same TEE type created by different manufacturers disambiguate the same TEE type created by different manufacturers
and address considerations around manufacturer provisioning, and address considerations around manufacturer provisioning,
keying and support for the TEE. keying and support for the TEE.
- Freshness Proof: A claim that includes freshness information must * Freshness Proof: A claim that includes freshness information must
be included, such as a nonce or timestamp. be included, such as a nonce or timestamp.
8. Algorithm and Attestation Agility 8. Algorithm and Attestation Agility
RFC 7696 [RFC7696] outlines the requirements to migrate from one RFC 7696 [RFC7696] outlines the requirements to migrate from one
mandatory-to-implement cryptographic algorithm suite to another over mandatory-to-implement cryptographic algorithm suite to another over
time. This feature is also known as crypto agility. Protocol time. This feature is also known as crypto agility. Protocol
evolution is greatly simplified when crypto agility is considered evolution is greatly simplified when crypto agility is considered
during the design of the protocol. In the case of the TEEP protocol during the design of the protocol. In the case of the TEEP protocol
the diverse range of use cases, from trusted app updates for smart the diverse range of use cases, from trusted app updates for smart
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with the device's TEE to manage Trusted Components. Since the TEEP with the device's TEE to manage Trusted Components. Since the TEEP
Broker runs in a potentially vulnerable REE, the TEEP Broker could, Broker runs in a potentially vulnerable REE, the TEEP Broker could,
however, be (or be infected by) malware. As such, all TAM messages however, be (or be infected by) malware. As such, all TAM messages
are signed and sensitive data is encrypted such that the TEEP Broker are signed and sensitive data is encrypted such that the TEEP Broker
cannot modify or capture sensitive data, but the TEEP Broker can cannot modify or capture sensitive data, but the TEEP Broker can
still conduct DoS attacks as discussed in Section 9.3. still conduct DoS attacks as discussed in Section 9.3.
A TEEP Agent in a TEE is responsible for protecting against potential A TEEP Agent in a TEE is responsible for protecting against potential
attacks from a compromised TEEP Broker or rogue malware in the REE. attacks from a compromised TEEP Broker or rogue malware in the REE.
A rogue TEEP Broker might send corrupted data to the TEEP Agent, or A rogue TEEP Broker might send corrupted data to the TEEP Agent, or
launch a DoS attack by sending a flood of TEEP protocol requests. launch a DoS attack by sending a flood of TEEP protocol requests, or
The TEEP Agent validates the signature of each TEEP protocol request simply drop or delay notifications to a TEE. The TEEP Agent
and checks the signing certificate against its Trust Anchors. To validates the signature of each TEEP protocol request and checks the
mitigate DoS attacks, it might also add some protection scheme such signing certificate against its Trust Anchors. To mitigate DoS
as a threshold on repeated requests or number of TAs that can be attacks, it might also add some protection scheme such as a threshold
installed. on repeated requests or number of TAs that can be installed.
Some implementations might rely on (due to lack of any available
alternative) the use of an untrusted timer or other event to call the
RequestPolicyCheck API (Section 6.2.1), which means that a
compromised REE can cause a TEE to not receive policy changes and
thus be out of date with respect to policy. The same can potentially
be done by any other man-in-the-middle simply by blocking
communication with a TAM. Ultimately such outdated compliance could
be addressed by using attestation in secure communication, where the
attestation evidence reveals what state the TEE is in, so that
communication (other than remediation such as via TEEP) from an out-
of-compliance TEE can be rejected.
Similarly, in most implementations the REE is involved in the
mechanics of installing new TAs. However, the authority for what TAs
are running in a given TEE is between the TEEP Agent and the TAM.
While a TEEP Broker broker can in effect make suggestions, it cannot
decide or enforce what runs where. The TEEP Broker can also control
which TEE a given installation request is directed at, but a TEEP
Agent will only accept TAs that are actually applicable to it and
where installation instructions are received by a TAM that it trusts.
The authorization model for the UnrequestTA operation is, however,
weaker in that it expresses the removal of a dependency from an
application that was untrusted to begin with. This means that a
compromised REE could remove a valid dependency from an Untrusted
Application on a TA. Normal REE security mechanisms should be used
to protect the REE and Untrusted Applications.
9.2. Data Protection 9.2. Data Protection
It is the responsibility of the TAM to protect data on its servers. It is the responsibility of the TAM to protect data on its servers.
Similarly, it is the responsibility of the TEE implementation to Similarly, it is the responsibility of the TEE implementation to
provide protection of data against integrity and confidentiality provide protection of data against integrity and confidentiality
attacks from outside the TEE. TEEs that provide isolation among TAs attacks from outside the TEE. TEEs that provide isolation among TAs
within the TEE are likewise responsible for protecting TA data within the TEE are likewise responsible for protecting TA data
against the REE and other TAs. For example, this can be used to against the REE and other TAs. For example, this can be used to
protect one user's or tenant's data from compromise by another user protect one user's or tenant's data from compromise by another user
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confidentiality protection to secure data end-to-end. For example, confidentiality protection to secure data end-to-end. For example,
confidentiality protection for payloads may be provided by utilizing confidentiality protection for payloads may be provided by utilizing
encrypted TA binaries and encrypted attestation information. See encrypted TA binaries and encrypted attestation information. See
[I-D.ietf-teep-protocol] for how a specific solution addresses the [I-D.ietf-teep-protocol] for how a specific solution addresses the
design question of how to provide integrity and confidentiality design question of how to provide integrity and confidentiality
protection. protection.
9.3. Compromised REE 9.3. Compromised REE
It is possible that the REE of a device is compromised. We have It is possible that the REE of a device is compromised. We have
already seen examples of attacks on the public Internet of billions already seen examples of attacks on the public Internet with billions
of compromised devices being used to mount DDoS attacks. A of compromised devices being used to mount DDoS attacks. A
compromised REE can be used for such an attack but it cannot tamper compromised REE can be used for such an attack but it cannot tamper
with the TEE's code or data in doing so. A compromised REE can, with the TEE's code or data in doing so. A compromised REE can,
however, launch DoS attacks against the TEE. however, launch DoS attacks against the TEE.
The compromised REE may terminate the TEEP Broker such that TEEP The compromised REE may terminate the TEEP Broker such that TEEP
transactions cannot reach the TEE, or might drop or delay messages transactions cannot reach the TEE, or might drop or delay messages
between a TAM and a TEEP Agent. However, while a DoS attack cannot between a TAM and a TEEP Agent. However, while a DoS attack cannot
be prevented, the REE cannot access anything in the TEE if it is be prevented, the REE cannot access anything in the TEE if the TEE is
implemented correctly. Some TEEs may have some watchdog scheme to implemented correctly. Some TEEs may have some watchdog scheme to
observe REE state and mitigate DoS attacks against it but most TEEs observe REE state and mitigate DoS attacks against it but most TEEs
don't have such a capability. don't have such a capability.
In some other scenarios, the compromised REE may ask a TEEP Broker to In some other scenarios, the compromised REE may ask a TEEP Broker to
make repeated requests to a TEEP Agent in a TEE to install or make repeated requests to a TEEP Agent in a TEE to install or
uninstall a Trusted Component. An installation or uninstallation uninstall a Trusted Component. An installation or uninstallation
request constructed by the TEEP Broker or REE will be rejected by the request constructed by the TEEP Broker or REE will be rejected by the
TEEP Agent because the request won't have the correct signature from TEEP Agent because the request won't have the correct signature from
a TAM to pass the request signature validation. a TAM to pass the request signature validation.
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responsible for protecting the resource usage allocated for Trusted responsible for protecting the resource usage allocated for Trusted
Component management. Component management.
9.4. CA Compromise or Expiry of CA Certificate 9.4. CA Compromise or Expiry of CA Certificate
A root CA for TAM certificates might get compromised or its A root CA for TAM certificates might get compromised or its
certificate might expire, or a Trust Anchor other than a root CA certificate might expire, or a Trust Anchor other than a root CA
certificate may also expire or be compromised. TEEs are responsible certificate may also expire or be compromised. TEEs are responsible
for validating the entire TAM certificate path, including the TAM for validating the entire TAM certificate path, including the TAM
certificate and any intermediate certificates up to the root certificate and any intermediate certificates up to the root
certificate. Such validation includes checking for certificate certificate. See Section 6 of [RFC5280] for details. Such
revocation. See Section 6 of [RFC5280] for details. validation generally includes checking for certificate revocation,
but certificate status check protocols may not scale down to
constrained devices that use TEEP.
If a TAM certificate path validation fails, the TAM might be rejected To address the above issues, a certificate path update mechanism is
by a TEEP Agent. To address this, some certificate path update expected from TAM operators, so that the TAM can get a new
mechanism is expected from TAM operators, so that the TAM can get a certificate path that can be validated by a TEEP Agent. In addition,
new certificate path that can be validated by a TEEP Agent. In the Trust Anchor in the TEEP Agent's Trust Anchor Store may need to
addition, the Trust Anchor in the TEEP Agent's Trust Anchor Store may be updated. To address this, some TEE Trust Anchor update mechanism
need to be updated. To address this, some TEE Trust Anchor update is expected from device OEMs, such as using the TEEP protocol to
mechanism is expected from device OEMs. distribute new Trust Anchors.
Similarly, a root CA for TEE certificates might get compromised or Similarly, a root CA for TEE certificates might get compromised or
its certificate might expire, or a Trust Anchor other than a root CA its certificate might expire, or a Trust Anchor other than a root CA
certificate may also expire or be compromised. TAMs are responsible certificate may also expire or be compromised. TAMs are responsible
for validating the entire TEE certificate path, including the TEE for validating the entire TEE certificate path, including the TEE
certificate and any intermediate certificates up to the root certificate and any intermediate certificates up to the root
certificate. Such validation includes checking for certificate certificate. Such validation includes checking for certificate
revocation. revocation.
If a TEE certificate path validation fails, the TEE might be rejected If a TEE certificate path validation fails, the TEE might be rejected
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Section 4.1.2.5 of [RFC5280] are applicable. Section 4.1.2.5 of [RFC5280] are applicable.
9.8. Keeping Secrets from the TAM 9.8. Keeping Secrets from the TAM
In some scenarios, it is desirable to protect the TA binary or In some scenarios, it is desirable to protect the TA binary or
Personalization Data from being disclosed to the TAM that distributes Personalization Data from being disclosed to the TAM that distributes
them. In such a scenario, the files can be encrypted end-to-end them. In such a scenario, the files can be encrypted end-to-end
between a Trusted Component Signer and a TEE. However, there must be between a Trusted Component Signer and a TEE. However, there must be
some means of provisioning the decryption key into the TEE and/or some means of provisioning the decryption key into the TEE and/or
some means of the Trusted Component Signer securely learning a public some means of the Trusted Component Signer securely learning a public
key of the TEE that it can use to encrypt. One way to do this is for key of the TEE that it can use to encrypt. The Trusted Component
the Trusted Component Signer to run its own TAM so that it can Signer cannot necessarily even trust the TAM to report the correct
distribute the decryption key via the TEEP protocol, and the key file public key of a TEE for use with encryption, since the TAM might
can be a dependency in the manifest of the encrypted TA. Thus, the instead provide the public key of a TEE that it controls.
TEEP Agent would look at the Trusted Component manifest, determine
there is a dependency with a TAM URI of the Trusted Component One way to solve this is for the Trusted Component Signer to run its
Signer's TAM. The Agent would then install the dependency, and then own TAM that is only used to distribute the decryption key via the
continue with the Trusted Component installation steps, including TEEP protocol, and the key file can be a dependency in the manifest
decrypting the TA binary with the relevant key. of the encrypted TA. Thus, the TEEP Agent would look at the Trusted
Component manifest, determine there is a dependency with a TAM URI of
the Trusted Component Signer's TAM. The Agent would then install the
dependency, and then continue with the Trusted Component installation
steps, including decrypting the TA binary with the relevant key.
9.9. REE Privacy
The TEEP architecture is applicable to cases where devices have a TEE
that protects data and code from the REE administrator. In such
cases, the TAM administrator, not the REE administrator, controls the
TEE in the devices. As some examples:
* a cloud hoster may be the REE administrator where a customer
administrator controls the TEE hosted in the cloud.
* a device manufacturer might control the TEE in a device purchased
by a customer
The privacy risk is that data in the REE might be susceptible to
disclosure to the TEE administrator. This risk is not introduced by
the TEEP architecture, but is inherent in most uses of TEEs. This
risk can be mitigated by making sure the REE administrator is aware
of and explicitly chooses to have a TEE that is managed by another
party. In the cloud hoster example, this choice is made by
explicitly offering a service to customers to provide TEEs for them
to administer. In the device manufacturer example, this choice is
made by the customer choosing to buy a device made by a given
manufacturer.
10. IANA Considerations 10. IANA Considerations
This document does not require actions by IANA. This document does not require actions by IANA.
11. Contributors 11. Contributors
- Andrew Atyeo, Intercede (andrew.atyeo@intercede.com) * Andrew Atyeo, Intercede (andrew.atyeo@intercede.com)
- Liu Dapeng, Alibaba Group (maxpassion@gmail.com) * Liu Dapeng, Alibaba Group (maxpassion@gmail.com)
12. Acknowledgements 12. Acknowledgements
We would like to thank Nick Cook, Minho Yoo, Brian Witten, Tyler Kim, We would like to thank Nick Cook, Minho Yoo, Brian Witten, Tyler Kim,
Alin Mutu, Juergen Schoenwaelder, Nicolae Paladi, Sorin Faibish, Ned Alin Mutu, Juergen Schoenwaelder, Nicolae Paladi, Sorin Faibish, Ned
Smith, Russ Housley, Jeremy O'Donoghue, and Anders Rundgren for their Smith, Russ Housley, Jeremy O'Donoghue, and Anders Rundgren for their
feedback. feedback.
13. Informative References 13. Informative References
[CC-Overview]
Confidential Computing Consortium, "Confidential
Computing: Hardware-Based Trusted Execution for
Applications and Data", January 2021,
<https://confidentialcomputing.io/wp-
content/uploads/sites/85/2021/03/
confidentialcomputing_outreach_whitepaper-8-5x11-1.pdf>.
[CC-Technical-Analysis]
Confidential Computing Consortium, "A Technical Analysis
of Confidential Computing, v1.2", October 2021,
<https://confidentialcomputing.io/wp-
content/uploads/sites/85/2022/01/CCC-A-Technical-Analysis-
of-Confidential-Computing-v1.2.pdf>.
[GPTEE] GlobalPlatform, "GlobalPlatform Device Technology: TEE [GPTEE] GlobalPlatform, "GlobalPlatform Device Technology: TEE
System Architecture, v1.1", GlobalPlatform GPD_SPE_009, System Architecture, v1.1", GlobalPlatform GPD_SPE_009,
January 2017, <https://globalplatform.org/specs-library/ January 2017, <https://globalplatform.org/specs-library/
tee-system-architecture-v1-1/>. tee-system-architecture-v1-1/>.
[GSMA] GSM Association, "GP.22 RSP Technical Specification, [GSMA] GSM Association, "GP.22 RSP Technical Specification,
Version 2.2.2", June 2020, <https://www.gsma.com/esim/wp- Version 2.2.2", June 2020, <https://www.gsma.com/esim/wp-
content/uploads/2020/06/SGP.22-v2.2.2.pdf>. content/uploads/2020/06/SGP.22-v2.2.2.pdf>.
[I-D.ietf-rats-architecture] [I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture", W. Pan, "Remote Attestation Procedures Architecture", Work
draft-ietf-rats-architecture-12 (work in progress), April in Progress, Internet-Draft, draft-ietf-rats-architecture-
2021. 15, 8 February 2022, <https://www.ietf.org/archive/id/
draft-ietf-rats-architecture-15.txt>.
[I-D.ietf-suit-architecture]
Moran, B., Tschofenig, H., Brown, D., and M. Meriac, "A
Firmware Update Architecture for Internet of Things", Work
in Progress, Internet-Draft, draft-ietf-suit-architecture-
16, 27 January 2021, <https://www.ietf.org/archive/id/
draft-ietf-suit-architecture-16.txt>.
[I-D.ietf-suit-manifest] [I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg, Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"A Concise Binary Object Representation (CBOR)-based "A Concise Binary Object Representation (CBOR)-based
Serialization Format for the Software Updates for Internet Serialization Format for the Software Updates for Internet
of Things (SUIT) Manifest", draft-ietf-suit-manifest-14 of Things (SUIT) Manifest", Work in Progress, Internet-
(work in progress), July 2021. Draft, draft-ietf-suit-manifest-16, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-suit-manifest-
16.txt>.
[I-D.ietf-teep-otrp-over-http] [I-D.ietf-teep-otrp-over-http]
Thaler, D., "HTTP Transport for Trusted Execution Thaler, D., "HTTP Transport for Trusted Execution
Environment Provisioning: Agent-to- TAM Communication", Environment Provisioning: Agent Initiated Communication",
draft-ietf-teep-otrp-over-http-11 (work in progress), July Work in Progress, Internet-Draft, draft-ietf-teep-otrp-
2021. over-http-13, 28 February 2022,
<https://www.ietf.org/archive/id/draft-ietf-teep-otrp-
over-http-13.txt>.
[I-D.ietf-teep-protocol] [I-D.ietf-teep-protocol]
Tschofenig, H., Pei, M., Wheeler, D., Thaler, D., and A. Tschofenig, H., Pei, M., Wheeler, D., Thaler, D., and A.
Tsukamoto, "Trusted Execution Environment Provisioning Tsukamoto, "Trusted Execution Environment Provisioning
(TEEP) Protocol", draft-ietf-teep-protocol-05 (work in (TEEP) Protocol", Work in Progress, Internet-Draft, draft-
progress), February 2021. ietf-teep-protocol-07, 25 October 2021,
<https://www.ietf.org/archive/id/draft-ietf-teep-protocol-
07.txt>.
[OTRP] GlobalPlatform, "Open Trust Protocol (OTrP) Profile v1.1", [OTRP] GlobalPlatform, "Open Trust Protocol (OTrP) Profile v1.1",
GlobalPlatform GPD_SPE_123, July 2020, GlobalPlatform GPD_SPE_123, July 2020,
<https://globalplatform.org/specs-library/tee-management- <https://globalplatform.org/specs-library/tee-management-
framework-open-trust-protocol/>. framework-open-trust-protocol/>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>. <https://www.rfc-editor.org/info/rfc4949>.
skipping to change at page 34, line 25 skipping to change at page 36, line 35
[TrustZone] [TrustZone]
Arm, "Arm TrustZone Technology", n.d., Arm, "Arm TrustZone Technology", n.d.,
<https://developer.arm.com/ip-products/security-ip/ <https://developer.arm.com/ip-products/security-ip/
trustzone>. trustzone>.
Authors' Addresses Authors' Addresses
Mingliang Pei Mingliang Pei
Broadcom Broadcom
EMail: mingliang.pei@broadcom.com Email: mingliang.pei@broadcom.com
Hannes Tschofenig Hannes Tschofenig
Arm Limited Arm Limited
EMail: hannes.tschofenig@arm.com Email: hannes.tschofenig@arm.com
Dave Thaler Dave Thaler
Microsoft Microsoft
EMail: dthaler@microsoft.com Email: dthaler@microsoft.com
David Wheeler David Wheeler
Amazon Amazon
Email: davewhee@amazon.com
EMail: davewhee@amazon.com
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