--- 1/draft-ietf-teep-architecture-05.txt 2020-02-08 15:13:15.664860104 -0800
+++ 2/draft-ietf-teep-architecture-06.txt 2020-02-08 15:13:15.728861733 -0800
@@ -1,53 +1,53 @@
TEEP M. Pei
Internet-Draft Symantec
Intended status: Informational H. Tschofenig
-Expires: June 14, 2020 Arm Limited
+Expires: August 11, 2020 Arm Limited
D. Thaler
Microsoft
D. Wheeler
Intel
- December 12, 2019
+ February 08, 2020
Trusted Execution Environment Provisioning (TEEP) Architecture
- draft-ietf-teep-architecture-05
+ draft-ietf-teep-architecture-06
Abstract
A Trusted Execution Environment (TEE) is an environment that enforces
- that only authorized code can execute with that environment, and that
- any data used by such code cannot be read or tampered with by any
- code outside that environment. This architecture document motivates
- the design and standardization of a protocol for managing the
- lifecycle of trusted applications running inside a TEE.
+ that only authorized code can execute within that environment, and
+ that any data used by such code cannot be read or tampered with by
+ any code outside that environment. This architecture document
+ motivates the design and standardization of a protocol for managing
+ the lifecycle of trusted applications running inside such a TEE.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
- This Internet-Draft will expire on June 14, 2020.
+ This Internet-Draft will expire on August 11, 2020.
Copyright Notice
- Copyright (c) 2019 IETF Trust and the persons identified as the
+ Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
@@ -66,206 +66,201 @@
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7
3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 7
- 3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 7
+ 3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 8
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. System Components . . . . . . . . . . . . . . . . . . . . 8
- 4.2. Different Renditions of TEEP Architecture . . . . . . . . 10
+ 4.2. Multiple TEEs in a Device . . . . . . . . . . . . . . . . 10
4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 12
4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 13
- 4.5. Examples of Application Delivery Mechanisms in Existing
- TEEs . . . . . . . . . . . . . . . . . . . . . . . . . . 14
- 4.6. Entity Relations . . . . . . . . . . . . . . . . . . . . 15
+ 4.4.1. Examples of Application Delivery Mechanisms in
+ Existing TEEs . . . . . . . . . . . . . . . . . . . . 14
+ 4.5. Entity Relations . . . . . . . . . . . . . . . . . . . . 16
5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 17
- 5.1. Trust Anchors in TEE . . . . . . . . . . . . . . . . . . 18
- 5.2. Trust Anchors in TAM . . . . . . . . . . . . . . . . . . 19
- 5.3. Scalability . . . . . . . . . . . . . . . . . . . . . . . 19
- 5.4. Message Security . . . . . . . . . . . . . . . . . . . . 19
- 6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 19
+ 5.1. Trust Anchors in a TEEP Agent . . . . . . . . . . . . . . 18
+ 5.2. Trust Anchors in a TEE . . . . . . . . . . . . . . . . . 19
+ 5.3. Trust Anchors in a TAM . . . . . . . . . . . . . . . . . 19
+ 5.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 19
+ 5.5. Message Security . . . . . . . . . . . . . . . . . . . . 20
+ 6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. Role of the TEEP Broker . . . . . . . . . . . . . . . . . 20
- 6.2. TEEP Broker Implementation Consideration . . . . . . . . 20
- 6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 20
- 6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 21
- 6.2.3. Number of TEEP Brokers . . . . . . . . . . . . . . . 21
+ 6.2. TEEP Broker Implementation Consideration . . . . . . . . 21
+ 6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 21
+ 6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 22
7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 22
- 7.1. Information Required in TEEP Claims . . . . . . . . . . . 23
+ 7.1. Information Required in TEEP Claims . . . . . . . . . . . 24
8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 24
9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
- 9.1. TA Trust Check at TEE . . . . . . . . . . . . . . . . . . 25
- 9.2. One TA Multiple SP Case . . . . . . . . . . . . . . . . . 25
- 9.3. Broker Trust Model . . . . . . . . . . . . . . . . . . . 25
- 9.4. Data Protection at TAM and TEE . . . . . . . . . . . . . 25
- 9.5. Compromised CA . . . . . . . . . . . . . . . . . . . . . 26
- 9.6. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 26
- 9.7. Certificate Renewal . . . . . . . . . . . . . . . . . . . 26
- 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 26
+ 9.1. Broker Trust Model . . . . . . . . . . . . . . . . . . . 25
+ 9.2. Data Protection at TAM and TEE . . . . . . . . . . . . . 25
+ 9.3. Compromised REE . . . . . . . . . . . . . . . . . . . . . 25
+ 9.4. Compromised CA . . . . . . . . . . . . . . . . . . . . . 26
+ 9.5. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 26
+ 9.6. Malicious TA Removal . . . . . . . . . . . . . . . . . . 26
+ 9.7. Certificate Renewal . . . . . . . . . . . . . . . . . . . 27
+ 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 27
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
- 13. Informative References . . . . . . . . . . . . . . . . . . . 27
+ 13. Informative References . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
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
attacks increase with the number of other applications on the device,
with such other applications coming from potentially untrustworthy
- sources. The potential for attacks further increase with the
+ sources. The potential for attacks further increases with the
complexity of features and applications on devices, and the
unintended interactions among those features and applications. The
danger of attacks on a system increases as the sensitivity of the
applications or data on the device increases. As an example,
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
greater concerns.
The Trusted Execution Environment (TEE) concept is designed to
execute applications in a protected environment that enforces that
- only authorized code can execute with that environment, and that any
- data used by such code cannot be read or tampered with by any code
- outside that environment, including a commodity operating system (if
- present).
+ only authorized code can execute within that environment, and that
+ any data used by such code cannot be read or tampered with by any
+ code outside that environment, including by a commodity operating
+ system (if present).
This separation reduces the possibility of a successful attack on
application components and the data contained inside the TEE.
Typically, application components are chosen to execute inside a TEE
because those application components perform security sensitive
operations or operate on sensitive data. An application component
running inside a TEE is referred to as a Trusted Application (TA),
while an application running outside any TEE is referred to as an
- Untrusted Application (UA).
+ Untrusted Application.
TEEs use hardware enforcement combined with software protection to
secure TAs and its data. TEEs typically offer a more limited set of
services to TAs than is normally available to Untrusted Applications.
- But not all TEEs are the same, 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 features, and different control mechanisms to operate on
TAs. Some vendors may themselves market multiple different TEEs with
different properties attuned to different markets. A device vendor
may integrate one or more TEEs into their devices depending on market
needs.
- To simplify the life of developers and service providers interacting
- with TAs in a TEE, an interoperable protocol for managing TAs running
- in different TEEs of various devices is needed. In this TEE
- ecosystem, there often arises a need for an external trusted party to
- verify the identity, claims, and rights of Service Providers (SP),
- devices, and their TEEs. This trusted third party is the Trusted
- Application Manager (TAM).
+ To simplify the life of TA developers interacting with TAs in a TEE,
+ an interoperable protocol for managing TAs running in different TEEs
+ of various devices is needed. In this TEE ecosystem, there often
+ arises a need for an external trusted party to verify the identity,
+ claims, and rights of TA developers, devices, and their TEEs. This
+ trusted third party is the Trusted Application Manager (TAM).
- The Trusted Execution Provisioning (TEEP) protocol addresses the
- following problems:
+ The Trusted Execution Environment Provisioning (TEEP) protocol
+ addresses the following problems:
- - A Service Provider (SP) intending to provide services through a TA
- to users of a device needs to determine security-relevant
- information of a device before provisioning their TA to the TEE
+ - 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
+ that the Untrusted Application can complete, but the TEE needs to
+ verify whether such a TA is actually authorized to run in the TEE
+ and consume potentially scarce TEE resources.
+
+ - A TA developer providing a TA whose code itself is considered
+ confidential wants to determine security-relevant information of a
+ device before allowing their TA to be provisioned to the TEE
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
- security protections required by a particular TA.
+ security protections required.
- - A TEE in a device needs to determine whether a Service Provider
- (SP) that wants to manage a TA in the device is authorized to
- manage TAs in the TEE, and what TAs the SP is permitted to manage.
+ - 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
+ TEE, and what TAs the entity is permitted to manage.
- - A Service Provider (SP) must be able to determine if a TA exists
- (is installed) on a device (in the TEE), and if not, install the
- TA in the TEE.
+ - A TAM (e.g., operated by 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 the TEE.
- - A Service Provider (SP) must be able to check whether a TA in a
- device's TEE is the most up-to-date version, and if not, update
- the TA in the TEE.
+ - A TAM 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 the TEE.
- - A Service Provider (SP) must be able to remove a TA in a device's
- TEE if the SP is no longer offering such services or the services
+ - A TA developer wants to remove a confidential TA from a device's
+ TEE if the TA developer is no longer offering such TAs or the TAs
are being revoked from a particular user (or device). For
example, if a subscription or contract for a particular service
has expired, or a payment by the user has not been completed or
has been rescinded.
- - A Service Provider (SP) must be able to define the relationship
- between cooperating TAs under the SP's control, and specify
+ - A TA developer wants to define the relationship between
+ cooperating TAs under the TA developer's control, and specify
whether the TAs can communicate, share data, and/or share key
material.
- Note: The Service Provider requires the help of a TAM to provision
- the Trusted Applications to remote devices and the TEEP protocol
- exchanges messages between a Trusted Application Manager (TAM) and a
- TEEP Agent via a TEEP Broker.
+ Note: The TA developer requires the help of a TAM to provision the
+ Trusted Applications to remote devices and the TEEP protocol
+ exchanges messages between a TAM and a TEEP Agent via a TEEP Broker.
2. Terminology
The following terms are used:
- - Untrusted Application: An application running in a Rich Execution
- Environment, such as an Android, Windows, or iOS application.
-
- - Trusted Application Manager (TAM): An entity that manages Trusted
- Applications (TAs) running in different TEEs of various devices.
-
- Device: A physical piece of hardware that hosts one or more TEEs,
- often along with a Rich Execution Environment. A Device contains
+ often along with a Rich Execution Environment. A device contains
a default list of Trust Anchors that identify entities (e.g.,
- TAMs) that are trusted by the Device. This list is normally set
- by the Device Manufacturer, and may be governed by the Device's
- network carrier. The list of Trust Anchors is normally modifiable
- by the Device's owner or Device Administrator. However the Device
- manufacturer and network carrier may restrict some modifications,
- for example, by not allowing the manufacturer or carrier's Trust
+ TAMs) that are trusted by the device. This list is normally set
+ by the device manufacturer, and may be governed by the device's
+ network carrier when it is a mobile device. The list of Trust
+ Anchors is normally modifiable by the device's owner or Device
+ Administrator. However the device manufacturer or network carrier
+ (in the mobile device case) may restrict some modifications, for
+ example, by not allowing the manufacturer or carrier's Trust
Anchor to be removed or disabled.
- - Rich Execution Environment (REE): An environment that is provided
- and governed by a typical OS (e.g., Linux, Windows, Android, iOS),
- potentially in conjunction with other supporting operating systems
- and hypervisors; it is outside of any TEE. This environment and
- applications running on it are considered untrusted.
+ - Device Administrator: An entity that is responsible for
+ administration of a device, which could be the device owner. A
+ Device Administrator has privileges on the device to install and
+ remove Untrusted Applications and TAs, approve or reject Trust
+ Anchors, and approve or reject TA developers, among possibly other
+ privileges on the device. A Device Administrator can manage the
+ list of allowed TAMs by modifying the list of Trust Anchors on the
+ device. Although a Device Administrator may have privileges and
+ device-specific controls to locally administer a device, the
+ Device Administrator may choose to remotely administer a device
+ through a TAM.
- - Service Provider (SP): An entity that wishes to provide a service
- on Devices that requires the use of one or more Trusted
- Applications.
+ - 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,
+ making the device user/owner also the Device Administrator. In
+ enterprise environments it is more common for the enterprise to
+ own the device, and any device user has no or limited
+ administration rights. In this case, the enterprise appoints a
+ Device Administrator that is not the device owner.
- Device User: A human being that uses a device. Many devices have
a single device user. Some devices have a primary device user
with other human beings as secondary device users (e.g., parent
allowing children to use their tablet or laptop). Other devices
are not used by a human being and hence have no device user.
Relates to Device Owner and Device Administrator.
- - 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,
- making the device user/owner also the device administrator. In
- enterprise environments it is more common for the enterprise to
- own the device, and any device user has no or limited
- administration rights. In this case, the enterprise appoints a
- device administrator that is not the device owner.
-
- - Device Administrator (DA): An entity that is responsible for
- administration of a Device, which could be the device owner. A
- Device Administrator has privileges on the Device to install and
- remove applications and TAs, approve or reject Trust Anchors, and
- approve or reject Service Providers, among possibly other
- privileges on the Device. A Device Administrator can manage the
- list of allowed TAMs by modifying the list of Trust Anchors on the
- Device. Although a Device Administrator may have privileges and
- Device-specific controls to locally administer a device, the
- Device Administrator may choose to remotely administrate a device
- through a TAM.
+ - Rich Execution Environment (REE): An environment that is provided
+ and governed by a typical OS (e.g., Linux, Windows, Android, iOS),
+ potentially in conjunction with other supporting operating systems
+ and hypervisors; it is outside of any TEE. This environment and
+ applications running on it are considered untrusted (or more
+ precisely, less trusted than the TEE).
- Trust Anchor: As defined in [RFC6024] and
[I-D.ietf-suit-manifest], "A trust anchor represents an
authoritative entity via a public key and associated data. The
public key is used to verify digital signatures, and the
associated data is used to constrain the types of information for
which the trust anchor is authoritative." The Trust Anchor may be
a certificate or it may be a raw public key along with additional
data if necessary such as its public key algorithm and parameters.
@@ -273,31 +268,41 @@
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
may be used by one or more applications." As noted in
[I-D.ietf-suit-manifest], a trust anchor store must resist
modification against unauthorized insertion, deletion, and
modification.
- Trusted Application (TA): An application component that runs in a
TEE.
+ - Trusted Application (TA) Developer: An entity that wishes to
+ provide functionality on devices that requires the use of one or
+ more Trusted Applications.
+
+ - Trusted Application Manager (TAM): An entity that manages Trusted
+ Applications (TAs) running in TEEs of various devices.
+
- Trusted Execution Environment (TEE): An execution environment that
enforces that only authorized code can execute within the TEE, and
data used by that code cannot be read or tampered with by code
outside the TEE. A TEE also generally has a device unique
credential that cannot be cloned. There are multiple technologies
that can be used to implement a TEE, and the level of security
achieved varies accordingly. In addition, TEEs typically use an
isolation mechanism between Trusted Applications to ensure that
one TA cannot read, modify or delete the data and code of another
TA.
+ - Untrusted Application: An application running in a Rich Execution
+ Environment.
+
3. Use Cases
3.1. Payment
A payment application in a mobile device requires high security and
trust about the hosting device. Payments initiated from a mobile
device can use a Trusted Application to provide strong identification
and proof of transaction.
For a mobile payment application, some biometric identification
@@ -326,549 +331,575 @@
such as authentication credentials in the device. A TEE can be the
best way to implement such IoT security functions.
3.4. Confidential Cloud Computing
A tenant can store sensitive data in a TEE in a cloud computing
server such that only the tenant can access the data, preventing the
cloud hosting provider from accessing the data. A tenant can run TAs
inside a server TEE for secure operation and enhanced data security.
This provides benefits not only to tenants with better data security
- but also to cloud hosting provider for reduced liability and
+ but also to cloud hosting providers for reduced liability and
increased cloud adoption.
4. Architecture
4.1. System Components
- The following are the main components in the system. Full
- descriptions of components not previously defined are provided below.
- Interactions of all components are further explained in the following
- paragraphs.
+ Figure 1 shows the main components in a typical device with an REE.
+ Full descriptions of components not previously defined are provided
+ below. Interactions of all components are further explained in the
+ following paragraphs.
+-------------------------------------------+
| Device |
- | +--------+ | Service Provider
- | +-------------+ | |----------+ |
+ | +--------+ | TA Developer
+ | +-------------+ | |-----------+ |
| | TEE-1 | | TEEP |---------+| |
| | +--------+ | +----| Broker | | || +--------+ |
- | | | TEEP | | | | |<---+ | |+-->| |<-+
+ | | | TEEP | | | | |<---+ | | +->| |<-+
| | | Agent |<----+ | | | | | +-| TAM-1 |
| | +--------+ | | |<-+ | | +->| | |<-+
| | | +--------+ | | | | +--------+ |
| | +---+ +---+ | | | | | TAM-2 | |
| +-->|TA1| |TA2| | +-------+ | | | +--------+ |
| | | | | | |<---------| App-2 |--+ | | |
| | | +---+ +---+ | +-------+ | | | Device Administrator
| | +-------------+ | App-1 | | | |
| | | | | | |
| +--------------------| |---+ | |
| | |--------+ |
| +-------+ |
+-------------------------------------------+
Figure 1: Notional Architecture of TEEP
- - Service Providers (SP) and Device Administrators (DA) utilize the
- services of a TAM to manage TAs on Devices. SPs do not directly
- interact with devices. DAs may elect to use a TAM for remote
- administration of TAs instead of managing each device directly.
+ - TA developers and Device Administrators utilize the services of a
+ TAM to manage TAs on devices. TA developers do not directly
+ interact with devices. Device Administators may elect to use a
+ TAM for remote administration of TAs instead of managing each
+ device directly.
- Trusted Application Manager (TAM): A TAM is responsible for
- performing lifecycle management activity on TA's on behalf of
- Service Providers and Device Administrators. This includes
- creation and deletion of TA's, and may include, for example, over-
- the-air updates to keep an SP's TAs up-to-date and clean up when a
- version should be removed. TAMs may provide services that make it
- easier for SPs or DAs to use the TAM's service to manage multiple
- devices, although that is not required of a TAM.
+ performing lifecycle management activity on TAs on behalf of TA
+ developers and Device Administrators. This includes creation and
+ deletion of TAs, and may include, for example, over-the-air
+ updates to keep TAs up-to-date and clean up when a version should
+ be removed. TAMs may provide services that make it easier for TA
+ developers or Device Administators to use the TAM's service to
+ manage multiple devices, although that is not required of a TAM.
- The TAM performs its management of TA's through an interaction
- with a Device's TEEP Broker. As shown in Figure 1, the TAM cannot
- directly contact a TEEP Agent, but must wait for the TEEP Broker
- to contact the TAM requesting a particular service. This
- architecture is intentional in order to accommodate network and
- application firewalls that normally protect user and enterprise
- devices from arbitrary connections from external network entities.
+ The TAM performs its management of TAs on the device through
+ interactions with a device's TEEP Broker, which relays messages
+ between a TAM and a TEEP Agent running inside the TEE. As shown
+ in Figure 1, the TAM cannot directly contact a TEEP Agent, but
+ must wait for the TEEP Broker to contact the TAM requesting a
+ particular service. This architecture is intentional in order to
+ accommodate network and application firewalls that normally
+ protect user and enterprise devices from arbitrary connections
+ from external network entities.
- A TAM may be publicly available for use by many SPs, or a TAM may
- be private, and accessible by only one or a limited number of SPs.
- It is expected that manufacturers and carriers will run their own
- private TAM. Another example of a private TAM is a TAM running as
- a Software-as-a-Service (SaaS) within an SP.
+ A TAM may be publicly available for use by many TA developers, or
+ a TAM may be private, and accessible by only one or a limited
+ number of TA developers. It is expected that many manufacturers
+ and network carriers will run their own private TAM.
- A SP or Device Administrator chooses a 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 public key is an authorized
- Trust Anchor in the Device. A SP or Device Administrator may run
- their own TAM, however the Devices they wish to manage must
- include this TAM's pubic key in the Trust Anchor list.
+ A TA developer or Device Administrator chooses a 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 public key is, or
+ chains up to, an authorized Trust Anchor in the device. A TA
+ developer or Device Administrator may run their own TAM, but the
+ devices they wish to manage must include this TAM's public key/
+ certificate, or a certificate it chains up to, in the Trust Anchor
+ list.
- A SP or Device Administrator is free to utilize multiple TAMs.
- This may be required for a SP to manage multiple different types
- of devices from different manufacturers, or devices on different
- carriers, since the Trust Anchor list on these different devices
- may contain different TAMs. A Device Administrator may be able to
- add their own TAM's public key or certificate to the Trust Anchor
- list on all their devices, overcoming this limitation.
+ A TA developer or Device Administrator is free to utilize multiple
+ TAMs. This may be required for a TA developer to manage multiple
+ different types of devices from different manufacturers, or to
+ manage mobile devices on different network carriers, since the
+ Trust Anchor list on these different devices may contain different
+ TAMs. A Device Administrator may be able to add their own TAM's
+ public key or certificate to the Trust Anchor list on all their
+ devices, overcoming this limitation.
Any entity is free to operate a TAM. For a TAM to be successful,
- it must have its public key or certificate installed in Devices
+ it must have its public key or certificate installed in a device's
Trust Anchor list. A TAM may set up a relationship with device
- manufacturers or carriers to have them install the TAM's keys in
- their device's Trust Anchor list. Alternatively, a TAM may
- publish its certificate and allow Device Administrators to install
- the TAM's certificate in their devices as an after-market-action.
+ manufacturers or network carriers to have them install the TAM's
+ keys in their device's Trust Anchor list. Alternatively, a TAM
+ may publish its certificate and allow Device Administrators to
+ install the TAM's certificate in their devices as an after-market-
+ action.
- - TEEP Broker: The TEEP Broker is an application component running
- in a Rich Execution Environment (REE) that enables the message
- protocol exchange between a TAM and a TEE in a device. The TEEP
+ - TEEP Broker: A TEEP Broker is an application component running in
+ a Rich Execution Environment (REE) that enables the message
+ 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
responsible for relaying messages from the TAM to the TEE, and for
- returning the TEE's responses to the TAM.
+ returning the TEE's responses to the TAM. In devices with no REE,
+ the TEEP Broker would be absent and instead the TEEP protocol
+ transport would be implemented inside the TEE itself.
- - TEEP Agent: the TEEP Agent is a processing module running inside a
- TEE that receives TAM requests that are relayed via a TEEP 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, which is
- up to a TEE provider's implementation. A response message
- corresponding to a TAM request is sent by a TEEP Agent back to a
- TEEP Broker.
+ - TEEP Agent: The TEEP Agent is a processing module running inside a
+ TEE that receives TAM requests (typically relayed via a TEEP
+ 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,
+ which is up to a TEE provider's implementation. A response
+ message corresponding to a TAM request is sent back to the TAM,
+ again typically relayed via a TEEP Broker.
- Certification Authority (CA): Certificate-based credentials used
- for authenticating a device, a TAM and an SP. A device embeds a
- list of root certificates (Trust Anchors), from trusted CAs that a
- TAM will be validated against. A TAM will remotely attest a
- device by checking whether a device comes with a certificate from
- a CA that the TAM trusts. The CAs do not need to be the same;
- different CAs can be chosen by each TAM, and different device CAs
- can be used by different device manufacturers.
+ for authenticating a device, a TAM and a TA developer. A device
+ embeds a list of root certificates (Trust Anchors), from trusted
+ CAs that a TAM will be validated against. A TAM will remotely
+ attest a device by checking whether a device comes with a
+ certificate from a CA that the TAM trusts. The CAs do not need to
+ be the same; different CAs can be chosen by each TAM, and
+ different device CAs can be used by different device
+ manufacturers.
-4.2. Different Renditions of TEEP Architecture
+4.2. Multiple TEEs in a Device
- There is nothing prohibiting a device from implementing multiple
- TEEs. In addition, some TEEs (for example, SGX) present themselves
+ Some devices might implement multiple TEEs. In these cases, there
+ might be one shared TEEP Broker that interacts with all the TEEs in
+ the device. However, some TEEs (for example, SGX) present themselves
as separate containers within memory without a controlling manager
- within the TEE. In these cases, the Rich Execution Environment hosts
- multiple TEEP brokers, where each Broker manages a particular TEE or
- set of TEEs. Enumeration and access to the appropriate TEEP Broker
- is up to the Rich Execution Environment and the Untrusted
- Applications. Verification that the correct TA has been reached then
- becomes a matter of properly verifying TA attestations, which are
- unforgeable. The multiple TEEP Broker approach is shown in the
- diagram below. For brevity, TEEP Broker 2 is shown interacting with
- only one TAM and UA, but no such limitation is intended to be implied
- in the architecture.
+ within the TEE. As such, there might be multiple TEEP Brokers in the
+ Rich Execution Environment, where each TEEP Broker communicates with
+ one or more TEEs associated with it.
+
+ It is up to the Rich Execution Environment and the Untrusted
+ Applications how they select the correct TEEP Broker. Verification
+ that the correct TA has been reached then becomes a matter of
+ properly verifying TA attestations, which are unforgeable.
+
+ The multiple TEEP Broker approach is shown in the diagram below. For
+ brevity, TEEP Broker 2 is shown interacting with only one TAM and
+ Untrusted Application and only one TEE, but no such limitations are
+ intended to be implied in the architecture.
+-------------------------------------------+
| Device |
- | +--------+ | Service Provider
- | | |----------+ |
- | +-------------+ | TEEP |---------+| |
- | | TEE-1 | +---| Broker | | || +--------+ |
- | | | | | 1 |<---+ | |+-->| |<-+
- | | +-------+ | | | | | | | | |
- | | | TEEP | | | | | | | | | |
- | | | Agent |<------+ | | | | | | |
- | | | 1 | | | | | | | | |
- | | +-------+ | | | | | | | |
- | | | | | | | | | |
+ | | TA Developer
+ | +-------------+ | |
+ | | TEE-1 | | |
+ | | +-------+ | +--------+ | +--------+ |
+ | | | TEEP | | | TEEP |------------->| |<-+
+ | | | Agent |<----------| Broker | | | |
+ | | | 1 | | | 1 |---------+ | |
+ | | +-------+ | | | | | | |
+ | | | | |<---+ | | | |
| | +---+ +---+ | | | | | | +-| TAM-1 |
| | |TA1| |TA2| | | |<-+ | | +->| | |<-+
| +-->| | | |<---+ +--------+ | | | | +--------+ |
| | | +---+ +---+ | | | | | | TAM-2 | |
| | | | | +-------+ | | | +--------+ |
| | +-------------+ +-----| App-2 |--+ | | ^ |
| | +-------+ | | | | Device
| +--------------------| App-1 | | | | | Administrator
| +------| | | | | |
| +-----------|-+ | |---+ | | |
| | TEE-2 | | | |--------+ | |
| | +------+ | | | |------+ | |
| | | TEEP | | | +-------+ | | |
| | | Agent|<-----+ | | |
| | | 2 | | | | | | |
| | +------+ | | | | | |
| | | | | | | |
| | +---+ | | | | | |
| | |TA3|<----+ | | +----------+ | | |
| | | | | | | TEEP |<--+ | |
- | | +---+ | +--| Broker |----------------+
- | | | | 2 | |
+ | | +---+ | +--| Broker | | |
+ | | | | 2 |----------------+
| +-------------+ +----------+ |
| |
+-------------------------------------------+
Figure 2: Notional Architecture of TEEP with multiple TEEs
In the diagram above, TEEP Broker 1 controls interactions with the
- TA's in TEE-1, and TEEP Broker 2 controls interactions with the TA's
- in TEE-2. This presents some challenges for a TAM in completely
+ 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
managing the device, since a TAM may not interact with all the TEEP
- Brokers on a particular platform. In addition, since TEE's may be
+ Brokers on a particular platform. In addition, since TEEs may be
physically separated, with wholly different resources, there may be
no need for TEEP Brokers to share information on installed TAs or
- resource usage. However, the architecture guarantees that the TAM
- will receive all the relevant information from the TEEP Broker to
- which it communicates.
+ resource usage.
4.3. Multiple TAMs and Relationship to TAs
- As shown in Figure 2, the TEEP Broker provides connections from the
- TEE and the Untrusted Application to one or more TAMs. The selection
- of which TAM to communicate with is dependent on information from the
- Untrusted Application and is directly related to the TA.
+ 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
+ TAM to communicate with might be made with or without input from an
+ Untrusted Application, but is ultimately the decision of a TEEP
+ Agent.
- When a SP offers a service which requires a TA, the SP associates
- that service with a specific TA. The TA itself is digitally signed,
- protecting its integrity, but the signature also links the TA back to
- the signer. The signer is usually the SP, but in some cases may be
- another party that the SP trusts. The SP selects one or more TAMs
- through which to offer their service, and communicates the
- information of the service and the specific Untrusted Applications
- and TAs to the TAM.
+ Each TA is digitally signed, protecting its integrity, and linking
+ the TA back to the signer. The signer is usually the TA software
+ author, but in some cases might be another party that the TA software
+ author trusts, or a party to whom the code has been licensed (in
+ which case the same code might be signed by multiple licensees and
+ distributed as if it were different TAs).
- The SP chooses TAMs based upon the markets into which the TAM can
- provide access. There may be TAMs that provide services to specific
- types of mobile devices, or mobile device operating systems, or
- specific geographical regions or network carriers. A SP may be
+ A TA author or signer selects one or more TAMs through which to offer
+ their TA(s), and communicates the TA(s) to the TAM. In this
+ document, we use the term "TA developer" to refer to the entity that
+ selects a TAM and publishes a signed TA to it, independent of whether
+ the publishing entity is the TA software author or the signer or
+ both.
+
+ The TA developer chooses TAMs based upon the markets into which the
+ TAM can provide access. There may be TAMs that provide services to
+ specific types of devices, or device operating systems, or specific
+ geographical regions or network carriers. A TA developer may be
motivated to utilize multiple TAMs for its service in order to
maximize market penetration and availability on multiple types of
- devices. This likely means that the same service will be available
+ devices. This likely means that the same TA will be available
through multiple TAMs.
- When the SP publishes the Untrusted Application to an app store or
- other app repositories, the SP binds the Untrusted Application with a
- manifest that identifies what TAMs can be contacted for the TA. In
- some situations, an SP may use only a single TAM - this is likely the
- case for enterprise applications or SPs serving a closed community.
- For broad public apps, there will likely be multiple TAMs in the
- manifest - one servicing one brand of mobile device and another
- servicing a different manufacturer, etc. Because different devices
- and different manufacturers trust different TAMs, the manifest will
- include different TAMs that support this SP's Untrusted Application
- and TA. Multiple TAMs allow the SP to provide their service and this
- app (and TA) to multiple different devices.
+ When the developer of an Untrusted Application that depends on a TA
+ publishes the Untrusted Application to an app store or other app
+ repository, the developer optionally binds the Untrusted Application
+ with a manifest that identifies what TAMs can be contacted for the
+ TA. In some situations, a TA may only be available via a single TAM
+ - this is likely the case for enterprise applications or TA
+ developers serving a closed community. For broad public apps, there
+ will likely be multiple TAMs in the manifest - one servicing one
+ brand of mobile device and another servicing a different
+ manufacturer, etc. Because different devices and different
+ manufacturers trust different TAMs, the manifest can include multiple
+ TAMs that support the required TA.
When a TEEP Broker receives a request from an Untrusted Application
to install a TA, a list of TAM URIs may be provided for that TA, and
the request is passed to the TEEP Agent. If the TEEP Agent decides
that the TA needs to be installed, the TEEP Agent selects a single
TAM URI that is consistent with the list of trusted TAMs provisioned
- on the device invokes the HTTP transport for TEEP to connect to the
- TAM URI and begins a TEEP protocol exchange. When the TEEP Agent
+ on the device, invokes the HTTP transport for TEEP to connect to the
+ TAM URI, and begins a TEEP protocol exchange. When the TEEP Agent
subsequently receives the TA to install and the TA's manifest
indicates dependencies on any other trusted components, each
dependency can include a list of TAM URIs for the relevant
dependency. If such dependencies exist that are prerequisites to
install the TA, then the TEEP Agent recursively follows the same
procedure for each dependency that needs to be installed or updated,
including selecting a TAM URI that is consistent with the list of
trusted TAMs provisioned on the device, and beginning a TEEP
exchange. If multiple TAM URIs are considered trusted, only one
needs to be contacted and they can be attempted in some order until
one responds.
Separate from the Untrusted Application's manifest, this framework
relies on the use of the manifest format in [I-D.ietf-suit-manifest]
- for expressing how to install the TA as well as dependencies on other
- TEE components and versions. That is, dependencies from TAs on other
- TEE components can be expressed in a SUIT manifest, including
+ for expressing how to install a TA, as well as any dependencies on
+ other TEE components and versions. That is, dependencies from TAs on
+ other TEE components can be expressed in a SUIT manifest, including
dependencies on any other TAs, or trusted OS code (if any), or
trusted firmware. Installation steps can also be expressed in a SUIT
manifest.
- For example, TEE's compliant with Global Platform may have a notion
- of a "security domain" (which is a grouping of one or more TAs
- installed on a device, that can share information within such a
- group) that must be created and into which one or more TAs can then
- be installed. It is thus up to the SUIT manifest to express a
- dependency on having such a security domain existing or being created
- first, as appropriate.
+ For example, TEEs compliant with GlobalPlatform may have a notion of
+ a "security domain" (which is a grouping of one or more TAs installed
+ on a device, that can share information within such a group) that
+ must be created and into which one or more TAs can then be installed.
+ It is thus up to the SUIT manifest to express a dependency on having
+ such a security domain existing or being created first, as
+ appropriate.
Updating a TA may cause compatibility issues with any Untrusted
Applications or other components that depend on the updated TA, just
like updating the OS or a shared library could impact an Untrusted
Application. Thus, an implementation needs to take into account such
issues.
4.4. Untrusted Apps, Trusted Apps, and Personalization Data
- In TEEP, there is an explicit relationship and dependence between the
- Untrusted Application in the REE and one or more TAs in the TEE, as
- shown in Figure 2. For most purposes, an Untrusted Application that
- uses one or more TA's in a TEE appears no different from any other
+ In TEEP, there is an explicit relationship and dependence between an
+ Untrusted Application in a REE and one or more TAs in a TEE, as shown
+ in Figure 2. For most purposes, an Untrusted Application that uses
+ one or more TAs in a TEE appears no different from any other
Untrusted Application in the REE. However, the way the Untrusted
- Application and its corresponding TA's are packaged, delivered, and
+ Application and its corresponding TAs are packaged, delivered, and
installed on the device can vary. The variations depend on whether
the Untrusted Application and TA are bundled together or are provided
separately, and this has implications to the management of the TAs in
- the TEE. In addition to the Untrusted Application and TA, the TA
+ a TEE. In addition to the Untrusted Application and TA(s), the TA(s)
and/or TEE may require some additional data to personalize the TA to
- the service provider or the device or a user. This personalization
- data is dependent on the TEE, the TA and the SP; an example of
+ the TA developer or the device or a user. This personalization data
+ is dependent on the TEE, the TA, and the TA developer; an example of
personalization data might be a secret symmetric key used by the TA
- to communicate with the SP. The personalization data must be
- encrypted to preserve the confidentiality of potentially sensitive
+ to communicate with the TA developer. The personalization data must
+ be encrypted to preserve the confidentiality of potentially sensitive
data contained within it. Other than this requirement to support
- confidentiality, TEEP place no limitations or requirements on the
- personalization data.
+ confidentiality, the TEEP architecture places no limitations or
+ requirements on the personalization data.
- There are three possible cases for bundling of the Untrusted
- Application, TA, and personalization data:
+ There are three possible cases for bundling of an Untrusted
+ Application, TA(s), and personalization data:
- 1. The Untrusted Application, TA, and personalization data are all
- bundled together in a single package by the SP and provided to
- the TEEP Broker through the TAM.
+ 1. The Untrusted Application, TA(s), and personalization data are
+ all bundled together in a single package by a TA developer and
+ provided to the TEEP Broker through the TAM.
- 2. The Untrusted Application and the TA 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
maintains, and the personalization data is separately provided by
- the SP's TAM.
+ the TA developer's TAM.
3. All components are independent. The Untrusted Application is
installed through some independent or device-specific mechanism,
- and the TAM provides the TA and personalization data from the SP.
- Delivery of the TA and personalization data may be combined or
- separate.
+ and the TAM provides the TA and personalization data from the TA
+ developer. Delivery of the TA and personalization data may be
+ combined or separate.
- The TEEP protocol treats the TA, any dependencies the TA has, and
+ The TEEP protocol treats each TA, any dependencies the TA has, and
personalization data as separate components with separate
installation steps that are expressed in SUIT manifests, and a SUIT
- manifest might contain or reference multiple binaries (see {{I-
- D.ietf-suit-manifest} for more details). The TEEP Agent is
+ manifest might contain or reference multiple binaries (see
+ [I-D.ietf-suit-manifest] for more details). The TEEP Agent is
responsible for handling any installation steps that need to be
- performed inside the TEE, such as decryption of private TA bianries
+ performed inside the TEE, such as decryption of private TA binaries
or personalization data.
-4.5. Examples of Application Delivery Mechanisms in Existing TEEs
+4.4.1. Examples of Application Delivery Mechanisms in Existing TEEs
In order to better understand these cases, it is helpful to review
actual implementations of TEEs and their application delivery
mechanisms.
In Intel Software Guard Extensions (SGX), the Untrusted Application
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
Untrusted Application loads the TA into an SGX enclave when the
Untrusted Application needs the TA. This organization makes it easy
to maintain compatibility between the Untrusted Application and the
TA, since they are updated together. It is entirely possible to
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 (Case 3). In this case, the Untrusted
Application would require a reference to an external file or download
such a file dynamically, place the contents of the file into memory,
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
SGX TEE. In SGX, for Case 2 and Case 3, the personalization data is
normally loaded into the SGX enclave (the TA) after the TA has
started. Although Case 1 is possible with SGX, there are no
instances of this known to be in use at this time, since such a
construction would require a special installation program and SGX TA
to receive the encrypted binary, decrypt it, separate it into the
three different elements, and then install all three. This
- installation is complex, because the Untrusted Application decrypted
+ installation is complex because the Untrusted Application decrypted
inside the TEE must be passed out of the TEE to an installer in the
REE which would install the Untrusted Application; this assumes that
the Untrusted Application package includes the TA code also, since
otherwise there is a significant problem in getting the SGX enclave
- code (the TA) from the TEE, through the installer and into the
+ code (the TA) from the TEE, through the installer, and into the
Untrusted Application in a trusted fashion. Finally, the
personalization data would need to be sent out of the TEE (encrypted
- in an SGX encalve-to-enclave manner) to the REE's installation app,
+ in an SGX enclave-to-enclave manner) to the REE's installation app,
which would pass this data to the installed Untrusted Application,
which would in turn send this data to the SGX enclave (TA). This
complexity is due to the fact that each SGX enclave is separate and
does not have direct communication to other SGX enclaves.
In Arm TrustZone for A- and R-class devices, the Untrusted
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
a specific Untrused Application process lifetime as occurs in SGX. A
TA is loaded by a trusted OS running in the TEE, where the trusted OS
is separate from the OS in the REE. Thus Cases 2 and 3 are equally
applicable. In addition, it is possible for TAs to communicate with
- each other without involving the Untrusted Application, and so the
- complexity of Case 1 is lower than in the SGX example, and so Case 1
- is possible as well though still more complex than Cases 2 and 3.
+ each other without involving any Untrusted Application, and so the
+ complexity of Case 1 is lower than in the SGX example. Thus, Case 1
+ is possible as well, though still more complex than Cases 2 and 3.
-4.6. Entity Relations
+4.5. Entity Relations
This architecture leverages asymmetric cryptography to authenticate a
- device to a TAM. Additionally, a TEE in a device authenticates a TAM
- and TA signer. The provisioning of Trust Anchors to a device may be
- different from one use case to the other. A device administrator may
- want to have the capability to control what TAs are allowed. A
- device manufacturer enables verification of the TA signers and TAM
- providers; it may embed a list of default Trust Anchors that the
- signer of an allowed TA's signer certificate should chain to. A
- device administrator may choose to accept a subset of the allowed TAs
- via consent or action of downloading.
+ device to a TAM. Additionally, a TEEP Agent in a device
+ authenticates a TAM. The provisioning of Trust Anchors to a device
+ may be different from one use case to the other. A Device
+ Administrator may want to have the capability to control what TAs are
+ allowed. A device manufacturer enables verification of the TAM
+ providers and TA binary signers; it may embed a list of default Trust
+ Anchors into the TEEP Agent and TEE for TAM trust verification and TA
+ signer verification.
- (App Developer) (App Store) (TAM) (Device with TEE) (CAs)
- | |
- | --> (Embedded TEE cert) <--
- | |
- | <------------------------------ Get an app cert ----- |
- | | <-- Get a TAM cert ------ |
- |
- 1. Build two apps:
- Untrusted Application
- TA
- |
- |
- Untrusted Application -- 2a. --> | ----- 3. Install -------> |
- TA ----------------- 2b. Supply ------> | 4. Messaging-->|
+ (App Developers) (App Store) (TAM) (Device with TEE) (CAs)
+ | | | | |
+ | | | (Embedded TEE cert) <--|
+ | | | | |
+ | <--- Get an app cert -----------------------------------|
+ | | | | |
+ | | | <-- Get a TAM cert ---------|
+ | | | | |
+ 1. Build two apps: | | | |
+ | | | |
+ (a) Untrusted | | | |
+ App - 2a. Supply --> | --- 3. Install ------> | |
+ | | | |
+ (b) TA -- 2b. Supply ----------> | 4. Messaging-->| |
| | | |
Figure 3: Developer Experience
- Note that Figure 3 shows the app developer as a TA signer and not the
- SP. However, the App Developer is either closely associated with the
- SP or the SP delegates the signing authority to the app developer.
- For the purpose of this document there is no difference between the
- SP and the app developer.
+ Note that Figure 3 shows the TA developer as a TA signer. The TA
+ signer is either the same as the TA developer, or is a related entity
+ trusted to sign the developer's TAs.
- Figure 3 shows an application developer building two applications: 1)
- an Untrusted Application; 2) a TA that provides some security
- functions to be run inside a TEE. At step 2, the application
+ Figure 3 shows an example where the same developer builds two
+ applications: 1) an Untrusted Application; 2) a TA that provides some
+ security functions to be run inside a TEE. At step 2, the TA
developer uploads the Untrusted Application (2a) to an Application
Store. The Untrusted Application may optionally bundle the TA
- binary. Meanwhile, the application developer may provide its TA to a
- TAM provider that will be managing the TA in various devices. 3. A
- user will go to an Application Store to download the Untrusted
- Application. The Untrusted Application will trigger TA installation
- by initiating communication with a TAM. This is the step 4. The
- Untrusted Application will get messages from TAM, and interacts with
- device TEE via an Agent.
+ binary. Meanwhile, the TA developer may provide its TA to a TAM that
+ will be managing the TA in various devices. At step 3, a user will
+ go to an Application Store to download the Untrusted Application.
+ Since the Untrusted Application depends on the TA, installing the
+ Untrusted Application will trigger TA installation by initiating
+ communication with a TAM. This is step 4. The TEEP Agent will
+ interact with TAM via a TEEP Broker that faciliates communications
+ between a TAM and the TEEP Agent in TEE.
+
+ Some TA installation implementations might ask for a user's consent.
+ In other implementations, a Device Administrator might choose what
+ Untrusted Applications and related TAs to be installed. A user
+ consent flow is out of scope of the TEEP architecture.
The main components consist of a set of standard messages created by
a TAM to deliver TA management commands to a device, and device
attestation and response messages created by a TEE that responds to a
TAM's message.
It should be noted that network communication capability is generally
- not available in TAs in today's TEE-powered devices. Trusted
- Applications need to rely on a broker in the REE to interact with a
- TEE for network message exchanges. Consequently, a TAM generally
- communicates with an Untrusted Application about how it gets messages
- that originate from a TEE inside a device. Similarly, a TA or TEE
- generally gets messages from a TAM via a TEEP Broker in this protocol
- architecture, not directly from the network.
+ not available in TAs in today's TEE-powered devices. Consequently,
+ Trusted Applications generally rely on broker in the REE to provide
+ access to nnetwork functionality in the REE. A broker does not need
+ to know the actual content of messages to facilitate such access.
- It is imperative to have an interoperable protocol to communicate
- with different TAMs and different TEEs in different devices. This is
- the role of the Broker, which is a software component that bridges
- communication between a TAM and a TEE. Furthermore the Broker
- communicates with a Agent inside a TEE that is responsible to process
- TAM requests. The Broker in REE does not need to know the actual
- content of messages except for the TEE routing information.
+ Similarly, since the TEEP Agent runs inside a TEE, the TEEP Agent
+ generally relies on a TEEP Broker in the REE to provide network
+ access, and relay TAM requests to the TEEP Agent and relay the
+ responses back to the TAM.
5. Keys and Certificate Types
This architecture leverages the following credentials, which allow
delivering end-to-end security between a TAM and a TEEP Agent.
Figure 4 summarizes the relationships between various keys and where
- they are stored. Each public/private key identifies an SP, TAM, or
- TEE, and gets a certificate that chains up to some CA. A list of
- trusted certificates is then used to check a presented certificate
- against.
+ they are stored. Each public/private key identifies a TA developer,
+ TAM, or TEE, and gets a certificate that chains up to some CA. A
+ list of trusted certificates is then used to check a presented
+ certificate against.
Different CAs can be used for different types of certificates. TEEP
messages are always signed, where the signer key is the message
- originator's private key such as that of a TAM, or a TEE's private
- key. In addition to the keys shown in Figure 4, there may be
- additional keys used for attestation. Refer to the RATS Architecture
- for more discussion.
+ 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
+ used for attestation. Refer to the RATS Architecture
+ [I-D.ietf-rats-architecture] for more discussion.
Cardinality & Location of
- Location of Private Key Corresponding
- Purpose Private Key Signs CA Certs
+ Location of Private Key Trust Anchor
+ Purpose Private Key Signs Store
------------------ ----------- ------------- -------------
Authenticating TEE 1 per TEE TEEP responses TAM
Authenticating TAM 1 per TAM TEEP requests TEEP Agent
- Code Signing 1 per SP TA binary TEE
+ Code Signing 1 per TA TA binary TEE
+ developer
Figure 4: Keys
Note that personalization data is not included in the table above.
The use of personalization data is dependent on how TAs are used and
what their security requirements are.
The TEE key pair and certificate are used for authenticating the TEE
to a remote TAM. Often, 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 the TEE. A TAM provider is responsible for
- configuring its TAM with the manufacturer certificates or CAs that
- are used to sign TEE keys.
+ configuring the TAM's Trust Anchor Store with the manufacturer
+ certificates or CAs that are used to sign TEE keys. This is
+ discussed further in Section 5.3 below.
The TAM key pair and certificate are used for authenticating a TAM to
a remote TEE. A TAM provider is responsible for acquiring a
- certificate from a CA that is trusted by the TEEs it manages.
+ certificate from a CA that is trusted by the TEEs it manages. This
+ is discussed further in Section 5.1 below.
- The SP key pair and certificate are used to sign TAs that the TEE
- will consider authorized to execute. TEEs must be configured with
- the CAs that it considers authorized to sign TAs that it will
- execute.
+ The TA developer key pair and certificate are used to sign TAs that
+ the TEE will consider authorized to execute. TEEs must be configured
+ with the certificates or keys that it considers authorized to sign
+ TAs that it will execute. This is discussed further in Section 5.2
+ below.
-5.1. Trust Anchors in TEE
+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
list is typically preloaded at manufacturing time, and can be updated
using the TEEP protocol if the TEE has some form of "Trust Anchor
Manager TA" that has Trust Anchors in its configuration data. Thus,
Trust Anchors can be updated similar to updating the configuration
data for any other TA.
When Trust Anchor update is carried out, it is imperative that any
- update must maintain integrity where only authentic Trust Anchor list
- from a device manufacturer or a Device Administrator is accepted.
- This calls for a complete lifecycle flow in authorizing who can make
- Trust Anchor update and whether a given Trust Anchor list are non-
- tampered from the original provider. The signing of a Trust Anchor
- list for integrity check and update authorization methods are
- desirable to be developed. This can be addressed outside of this
- architecture document.
+ update must maintain integrity where only an authentic Trust Anchor
+ list from a device manufacturer or a Device Administrator is
+ accepted. Details are out of scope of the architecture and can be
+ addressed in a protocol document.
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
- CA that is listed in the Trust Anchor store of the TEE.
+ CA that is listed in the Trust Anchor Store of the TEEP Agent.
-5.2. Trust Anchors in TAM
+5.2. Trust Anchors in a TEE
- The Trust Anchor store in a TAM consists of a list of Trust Anchors,
- which are CA certificates that sign various device TEE certificates.
- A TAM will accept a device for TA management if the TEE in the device
- uses a TEE certificate that is chained to a CA that the TAM trusts.
+ A TEE determines whether TA binaries are allowed to execute by
+ verifying whether the TA's signer chains up to a certificate in the
+ TEE's Trust Anchor Store. The list is typically preloaded at
+ manufacturing time, and can be updated using the TEEP protocol if the
+ TEE has some form of "Trust Anchor Manager TA" that has Trust Anchors
+ in its configuration data. Thus, Trust Anchors can be updated
+ similar to updating the configuration data for any other TA, as
+ discussed in Section 5.1.
-5.3. Scalability
+5.3. Trust Anchors in a TAM
- This architecture uses a PKI. Trust Anchors exist on the devices to
- enable the TEE to authenticate TAMs, and TAMs use Trust Anchors to
- authenticate TEEs. Since a PKI is used, many intermediate CA
+ The Trust Anchor Store in a TAM consists of a list of Trust Anchors,
+ which are certificates that sign various device TEE certificates. A
+ TAM will accept a device for TA management if the TEE in the device
+ uses a TEE certificate that is chained to a certificate that the TAM
+ trusts.
+
+5.4. Scalability
+
+ This architecture uses a PKI, although self-signed certificates are
+ also permitted. Trust Anchors exist on the devices to enable the TEE
+ to authenticate TAMs and TA signers, and TAMs use Trust Anchors to
+ authenticate TEEs. When a PKI is used, many intermediate CA
certificates can chain to a root certificate, each of which can issue
many certificates. This makes the protocol highly scalable. New
factories that produce TEEs can join the ecosystem. In this case,
such a factory can get an intermediate CA certificate from one of the
existing roots without requiring that TAMs are updated with
information about the new device factory. Likewise, new TAMs can
join the ecosystem, providing they are issued a TAM certificate that
chains to an existing root whereby existing TEEs will be allowed to
be personalized by the TAM without requiring changes to the TEE
itself. This enables the ecosystem to scale, and avoids the need for
- centralized databases of all TEEs produced or all TAMs that exist.
+ centralized databases of all TEEs produced or all TAMs that exist or
+ all TA developers that exist.
-5.4. Message Security
+5.5. Message Security
Messages created by a TAM are used to deliver TA management commands
to a device, and device attestation and messages created by the
device TEE to respond to TAM messages.
These messages are signed end-to-end between a TEEP Agent and a TAM,
and are typically encrypted such that only the targeted device TEE or
TAM is able to decrypt and view the actual content.
6. TEEP Broker
@@ -877,180 +908,162 @@
communicate outside of the hosting device. For example,
GlobalPlatform [GPTEE] specifies one such architecture. This calls
for a software module in the REE world to handle network
communication with a TAM.
A TEEP Broker is an application component running in the REE of the
device or an SDK that facilitates communication between a TAM and a
TEE. It also provides interfaces for Untrusted Applications to query
and trigger TA installation that the application needs to use.
- An Untrusted Application might communicate with the TEEP Broker at
- runtime to trigger TA installation itself. Or an Untrusted
+ An Untrusted Application might communicate with a TEEP Broker at
+ runtime to trigger TA installation itself, or an Untrusted
Application might simply have a metadata file that describes the TAs
it depends on and the associated TAM(s) for each TA, and an REE
Application Installer can inspect this application metadata file and
invoke the TEEP Broker to trigger TA installation on behalf of the
Untrusted Application without requiring the Untrusted Application to
run first.
6.1. Role of the TEEP Broker
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
call to trigger a TA installation.
The Broker doesn't need to parse a message content received from a
TAM that should be processed by a TEE. When a device has more than
- one TEE, one TEEP Broker per TEE could be present in REE. A TEEP
+ one TEE, one TEEP Broker per TEE could be present in the REE. A TEEP
Broker interacts with a TEEP Agent inside a TEE.
A TAM message may indicate the target TEE where a TA 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
- in a TEE to the TAM. The Broker is not expected to handle any
- network connection with an application or TAM.
+ in a TEE to the TAM.
- The Broker only needs to return an error message if the TEE is not
- reachable for some reason. Other errors are represented as response
- messages returned from the TEE which will then be passed to the TAM.
+ The Broker only needs to return a (transport) error message if the
+ TEE is not reachable for some reason. Other errors are represented
+ as response messages returned from the TEE which will then be passed
+ to the TAM.
6.2. TEEP Broker Implementation Consideration
- A Provider should consider methods of distribution, scope and
- concurrency on devices and runtime options when implementing a TEEP
- Broker. Several non-exhaustive options are discussed below.
- Providers are encouraged to take advantage of the latest
- communication and platform capabilities to offer the best user
- experience.
+ TEEP Broker implementers should consider methods of distribution,
+ scope and concurrency on devices and runtime options. Several non-
+ exhaustive options are discussed below.
6.2.1. TEEP Broker APIs
The following conceptual APIs exist from a TEEP Broker to a TEEP
Agent:
1. RequestTA: A notification from an REE application (e.g., an
- installer, or a normal application) that it depends on a given
- TA, which may or may not already be installed in the TEE.
+ installer, or an Untrusted Application) that it depends on a
+ given TA, which may or may not already be installed in the TEE.
2. ProcessTeepMessage: A message arriving from the network, to be
delivered to the TEEP Agent for processing.
3. RequestPolicyCheck: A hint (e.g., based on a timer) that the TEEP
Agent may wish to contact the TAM for any changes, without the
device itself needing any particular change.
4. ProcessError: A notification that the TEEP Broker could not
deliver an outbound TEEP message to a TAM.
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
- or not):
+ Broker may or may not exist, depending on whether the TAM uses a TEE
+ or not:
1. ProcessConnect: A notification that an incoming TEEP session is
being requested by a TEEP Agent.
2. ProcessTeepMessage: A message arriving from the network, to be
delivered to the TAM for processing.
For further discussion on these APIs, see
[I-D.ietf-teep-otrp-over-http].
6.2.2. TEEP Broker Distribution
The Broker installation is commonly carried out at OEM time. A user
can dynamically download and install a Broker on-demand.
-6.2.3. Number of TEEP Brokers
-
- There should be generally only one shared TEEP Broker in a device.
- The device's TEE vendor will most probably supply one Broker. When
- multiple TEEs are present in a device, one TEEP Broker per TEE may be
- used.
-
- When only one Broker is used per device, the Broker provider is
- responsible to allow multiple TAMs and TEE providers to achieve
- interoperability. With a standard Broker interface, each TAM can
- implement its own SDK for its SP Untrusted Applications to work with
- this Broker.
-
- Multiple independent Broker providers can be used as long as they
- have standard interface to an Untrusted Application or TAM SDK. Only
- one Broker is generally expected in a device.
-
7. Attestation
Attestation is the process through which one entity (an Attester)
presents "evidence", in the form of a series of claims, to another
entity (a Verifier), and provides sufficient proof that the claims
- are true. Different verifiers may have different standards for
+ are true. Different Verifiers may have different standards for
attestation proofs and not all attestations are acceptable to every
verifier. A third entity (a Relying Party) can then use "attestation
results", in the form of another series of claims, from a Verifier to
- make authorization decisions.
+ make authorization decisions. (See [I-D.ietf-rats-architecture] for
+ more discussion.)
In TEEP, as depicted in Figure 5, the primary purpose of an
- attestation is to allow a device (the Attester) to prove to TAMs (the
- Relying Parties) that a TEE in the device has particular properties,
- was built by a particular manufacturer, or is executing a particular
- TA. Other claims are possible; TEEP does not limit the claims that
- may appear in evidence or attestation results, but defines a minimal
- set of attestation result claims required for TEEP to operate
- properly. Extensions to these claims are possible. Other standards
- or groups may define the format and semantics of extended claims.
+ attestation is to allow a device (the Attester) to prove to a TAM
+ (the Relying Party) that a TEE in the device has particular
+ properties, was built by a particular manufacturer, and/or is
+ executing a particular TA. Other claims are possible; TEEP does not
+ limit the claims that may appear in evidence or attestation results,
+ but defines a minimal set of attestation result claims required for
+ TEEP to operate properly. Extensions to these claims are possible.
+ Other standards or groups may define the format and semantics of
+ extended claims.
+----------------+
| Device | +----------+
| +------------+ | Evidence | TAM | Evidence +----------+
| | TEE |------------->| (Relying |-------------->| Verifier |
| | (Attester) | | | Party) |<--------------| |
| +------------+ | +----------+ Attestation +----------+
+----------------+ Result
Figure 5: TEEP Attestation Roles
As of the writing of this specification, device and TEE attestations
have not been standardized across the market. Different devices,
manufacturers, and TEEs support different attestation algorithms and
mechanisms. In order for TEEP to be inclusive, it is agnostic to the
format of evidence, allowing proprietary or standardized formats to
be used between a TEE and a verifier (which may or may not be
colocated in the TAM). However, it should be recognized that not all
- verifiers may be able to process all proprietary forms of attestation
+ Verifiers may be able to process all proprietary forms of attestation
evidence. Similarly, the TEEP protocol is agnostic as to the format
of attestation 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 in some format.
- The assumptions which may apply to an attestation have to do with the
+ The assumptions that may apply to an attestation have to do with the
quality of the attestation and the quality and security provided by
the TEE, the device, the manufacturer, or others involved in the
device or TEE ecosystem. Some of the assumptions that might apply to
an attestations include (this may not be a comprehensive list):
- Assumptions regarding the security measures a manufacturer takes
when provisioning keys into devices/TEEs;
- Assumptions regarding what hardware and software components have
- access to the Attestation keys of the TEE;
+ access to the attestation keys of the TEE;
- Assumptions related to the source or local verification of claims
within an attestation prior to a TEE signing a set of claims;
- Assumptions regarding the level of protection afforded to
attestation keys against exfiltration, modification, and side
channel attacks;
- Assumptions regarding the limitations of use applied to TEE
- Attestation keys;
+ attestation keys;
- Assumptions regarding the processes in place to discover or detect
TEE breeches; and
- Assumptions regarding the revocation and recovery process of TEE
attestation keys.
TAMs must be comfortable with the assumptions that are inherently
part of any attestation result they accept. Alternatively, any TAM
may choose not to accept an attestation result generated using
@@ -1061,196 +1074,226 @@
Some TAMs may require additional claims in order to properly
authorize a device or TEE. These additional claims may help clear up
any assumptions for which the TAM wants to alleviate. The specific
format for these additional claims are outside the scope of this
specification, but the TEEP protocol allows these additional claims
to be included in the attestation messages.
7.1. Information Required in TEEP Claims
- Device Identifying Info: TEEP attestations may need to uniquely
- identify a device to the TAM and SP. Unique device identification
- allows the TAM to provide services to the device, such as managing
- installed TAs, and providing subscriptions to services, and
- locating device-specific keying material to communicate with or
- authenticate the device. In some use cases it may be sufficient
- to identify only the class of the device. The security and
- privacy requirements regarding device identification will vary
- with the type of TA provisioned to the TEE.
+ identify a device to the TAM and TA developer. Unique device
+ identification allows the TAM to provide services to the device,
+ such as managing installed TAs, and providing subscriptions to
+ services, and locating device-specific keying material to
+ communicate with or authenticate the device. In some use cases it
+ may be sufficient to identify only the class of the device. The
+ security and privacy requirements regarding device identification
+ will vary with the type of TA provisioned to the TEE.
- TEE Identifying info: The type of TEE that generated this
- attestation must be identified. Standard TEE types are identified
- by an IANA number, but also must include version identification
+ attestation must be identified, including version identification
information such as the hardware, firmware, and software version
of the TEE, as applicable by the TEE type. TEE manufacturer
information for the TEE is required in order to disambiguate the
same TEE type created by different manufacturers and resolve
potential assumptions around manufacturer provisioning, keying and
support for the TEE.
- - Liveness Proof: A claim that includes liveness information must be
- included, such as a nonce or timestamp.
+ - Freshness Proof: A claim that includes freshness information must
+ be included, such as a nonce or timestamp.
- Requested Components: A list of zero or more components (TAs or
other dependencies needed by a TEE) that are requested by some
depending app, but which are not currently installed in the TEE.
8. Algorithm and Attestation Agility
RFC 7696 [RFC7696] outlines the requirements to migrate from one
mandatory-to-implement algorithm suite to another over time. This
feature is also known as crypto agility. Protocol evolution is
- greatly simplified when crypto agility is already considered during
- the design of the protocol. In the case of the Trusted Execution
- Provisioning (TEEP) Protocol the diverse range of use cases, from
- trusted app updates for smart phones and tablets to updates of code
- on higher-end IoT devices, creates the need for different mandatory-
- to-implement algorithms already from the start.
+ greatly simplified when crypto agility is considered 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 phones and
+ tablets to updates of code on higher-end IoT devices, creates the
+ need for different mandatory-to-implement algorithms already from the
+ start.
Crypto agility in TEEP concerns the use of symmetric as well as
asymmetric algorithms. Symmetric algorithms are used for encryption
of content whereas the asymmetric algorithms are mostly used for
signing messages.
- In addition to the use of cryptographic algorithms in TEEP there is
+ In addition to the use of cryptographic algorithms in TEEP, there is
also the need to make use of different attestation technologies. A
- Device must provide techniques to inform a TAM about the attestation
+ device must provide techniques to inform a TAM about the attestation
technology it supports. For many deployment cases it is more likely
for the TAM to support one or more attestation techniques whereas the
- Device may only support one.
+ device may only support one.
9. Security Considerations
-9.1. TA Trust Check at TEE
-
- A TA binary is signed by a TA signer certificate. This TA signing
- certificate/private key belongs to the SP, and may be self-signed
- (i.e., it need not participate in a trust hierarchy). It is the
- responsibility of the TAM to only allow verified TAs from trusted SPs
- into the system. Delivery of that TA to the TEE is then the
- responsibility of the TEE, using the security mechanisms provided by
- the protocol.
+9.1. Broker Trust Model
- We allow a way for an Untrusted Application to check the
- trustworthiness of a TA. A TEEP Broker has a function to allow an
- application to query the information about a TA.
+ The architecture enables the TAM to communicate, via a TEEP Broker,
+ with the device's TEE to manage TAs. Since the TEEP Broker runs in a
+ potentially vulnerable REE, the TEEP Broker could, however, be (or be
+ infected by) malware. As such, all TAM messages are signed and
+ sensitive data is encrypted such that the TEEP Broker cannot modify
+ or capture sensitive data.
- An Untrusted Application may perform verification of the TA by
- verifying the signature of the TA. An application can do additional
- trust checks on the certificate returned for this TA. It might trust
- the TAM, or require additional SP signer trust chaining.
+ A TEEP Agent in a TEE is responsible for protecting against potential
+ 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
+ launch a DoS attack by sending a flood of TEEP protocol requests.
+ The TEEP Agent validates the signature of each TEEP protocol request
+ and checks the signing certificate against its Trust Anchors. To
+ mitigate DoS attacks, it might also add some protection scheme such
+ as a threshold on repeated requests or number of TAs that can be
+ installed.
-9.2. One TA Multiple SP Case
+9.2. Data Protection at TAM and TEE
- A TA for multiple SPs must have a different identifier per SP. They
- should appear as different TAs when they are installed in the same
- device.
+ The TEE implementation provides protection of data on the device. It
+ is the responsibility of the TAM to protect data on its servers.
-9.3. Broker Trust Model
+9.3. Compromised REE
- A TEEP Broker could be malware in the vulnerable REE. An Untrusted
- Application will connect its TAM provider for required TA
- installation. It gets command messages from the TAM, and passes the
- message to the Broker.
+ It is possible that the REE of a device is compromised. If the REE
+ is compromised, several DoS attacks may be launched. The compromised
+ REE may terminate the TEEP Broker such that TEEP transactions cannot
+ reach the TEE. However, while a DoS attack cannot be prevented, the
+ REE cannot access anything in the TEE if it is implemented correctly.
+ Some TEEs may have some watchdog scheme to observe REE state and
+ mitigate DoS attacks against it but most TEEs don't have have such
+ capability.
- The architecture enables the TAM to communicate with the device's TEE
- to manage TAs. All TAM messages are signed and sensitive data is
- encrypted such that the TEEP Broker cannot modify or capture
- sensitive data.
+ 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
+ uninstall a TA. A TA installation or uninstallation 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 a TAM
+ to pass the request signature validation.
-9.4. Data Protection at TAM and TEE
+ This can become a DoS attack by exhausting resources in a TEE with
+ repeated requests. In general, a DoS attack threat exists when the
+ REE is compromised, and a DoS attack can happen to other resources.
+ The TEEP architecture doesn't change this.
- The TEE implementation provides protection of data on the device. It
- is the responsibility of the TAM to protect data on its servers.
+ A compromised REE might also request initiating the full flow of
+ installation of TAs that are not necessary. It may also repeat a
+ prior legitimate TA installation request. A TEEP Agent
+ implementation is responsible for ensuring that it can recognize and
+ decline such repeated requests. It is also responsible for
+ protecting the resource usage allocated for TA management.
-9.5. Compromised CA
+9.4. Compromised CA
A root CA for TAM certificates might get compromised. Some TEE Trust
Anchor update mechanism is expected from device OEMs. TEEs are
responsible for validating certificate revocation about a TAM
certificate chain.
If the root CA of some TEE device certificates is compromised, these
devices might be rejected by a TAM, which is a decision of the TAM
implementation and policy choice. TAMs are responsible for
validating any intermediate CA for TEE device certificates.
-9.6. Compromised TAM
+9.5. Compromised TAM
Device TEEs are responsible for validating the supplied TAM
certificates to determine that the TAM is trustworthy.
+9.6. Malicious TA Removal
+
+ It is possible that a rogue developer distributes a malicious
+ Untrusted Application and intends to get a malicious TA installed.
+ It's the responsibility of the TAM to not install malicious trusted
+ apps in the first place. The TEEP architecture allows a TEEP Agent
+ to decide which TAMs it trusts via Trust Anchors, and delegates the
+ TA authenticity check to the TAMs it trusts.
+
+ It may happen that a TA was previously considered trustworthy but is
+ later found to be buggy or compromised. In this case, the TAM can
+ initiate the removal of the TA by notifying devices to remove the TA
+ (and potentially the REE or device owner to remove any Untrusted
+ Application that depend on the TA). If the TAM does not currently
+ have a connection to the TEEP Agent on a device, such a notification
+ would occur the next time connectivity does exist.
+
+ Furthermore the policy in the Verifier in an attestation process can
+ be updated so that any evidence that includes the malicious TA would
+ result in an attestation failure.
+
9.7. Certificate Renewal
TEE device certificates are expected to be long lived, longer than
the lifetime of a device. A TAM certificate usually has a moderate
lifetime of 2 to 5 years. A TAM should get renewed or rekeyed
certificates. The root CA certificates for a TAM, which are embedded
into the Trust Anchor store in a device, should have long lifetimes
that don't require device Trust Anchor update. On the other hand, it
is imperative that OEMs or device providers plan for support of Trust
Anchor update in their shipped devices.
9.8. Keeping Secrets from the TAM
In some scenarios, it is desirable to protect the TA binary or
configuration from being disclosed to the TAM that distributes them.
- In such a scenario, the files can be encrypted end-to-end between an
- SP and a TEE. However, there must be some means of provisioning the
- decryption key into the TEE and/or some means of the SP securely
- learning a public key of the TEE that it can use to encrypt. One way
- to do this is for the SP to run its own TAM, merely to distribute the
- decryption key via the TEEP protocol, and the key file can be a
- dependency in the manifest of the encrypted TA. Thus, the TEEP Agent
- would look at the TA manifest, determine there is a dependency with a
- TAM URI of the SP's TAM. The Agent would then install the
- dependency, and then continue with the TA installation steps,
- including decrypting the TA binary with the relevant key.
+ In such a scenario, the files can be encrypted end-to-end between a
+ TA developer and a TEE. However, there must be some means of
+ provisioning the decryption key into the TEE and/or some means of the
+ TA developer securely learning a public key of the TEE that it can
+ use to encrypt. One way to do this is for the TA developer to run
+ its own TAM so that it can distribute the decryption key via the TEEP
+ protocol, and the key file can be a dependency in the manifest of the
+ encrypted TA. Thus, the TEEP Agent would look at the TA manifest,
+ determine there is a dependency with a TAM URI of the TA developer's
+ TAM. The Agent would then install the dependency, and then continue
+ with the TA installation steps, including decrypting the TA binary
+ with the relevant key.
10. IANA Considerations
This document does not require actions by IANA.
11. Contributors
- - Andrew Atyeo
-
- - Intercede
-
- - andrew.atyeo@intercede.com
-
- - Liu Dapeng
-
- - Alibaba Group
+ - Andrew Atyeo, Intercede (andrew.atyeo@intercede.com)
- - maxpassion@gmail.com
+ - Liu Dapeng, Alibaba Group (maxpassion@gmail.com)
12. Acknowledgements
We would like to thank Nick Cook, Minho Yoo, Brian Witten, Tyler Kim,
Alin Mutu, Juergen Schoenwaelder, Nicolae Paladi, Sorin Faibish, Ned
Smith, Russ Housley, Jeremy O'Donoghue, and Anders Rundgren for their
feedback.
13. Informative References
[GPTEE] Global Platform, "GlobalPlatform Device Technology: TEE
System Architecture, v1.1", Global Platform GPD_SPE_009,
January 2017, .
+ [I-D.ietf-rats-architecture]
+ Birkholz, H., Thaler, D., Richardson, M., and N. Smith,
+ "Remote Attestation Procedures Architecture", draft-ietf-
+ rats-architecture-01 (work in progress), February 2020.
+
[I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., and H. Birkholz, "A Concise
Binary Object Representation (CBOR)-based Serialization
Format for the Software Updates for Internet of Things
- (SUIT) Manifest", draft-ietf-suit-manifest-02 (work in
- progress), November 2019.
+ (SUIT) Manifest", draft-ietf-suit-manifest-03 (work in
+ progress), February 2020.
[I-D.ietf-teep-otrp-over-http]
Thaler, D., "HTTP Transport for Trusted Execution
Environment Provisioning: Agent-to- TAM Communication",
draft-ietf-teep-otrp-over-http-03 (work in progress),
November 2019.
[RFC6024] Reddy, R. and C. Wallace, "Trust Anchor Management
Requirements", RFC 6024, DOI 10.17487/RFC6024, October
2010, .