--- 1/draft-ietf-teep-architecture-11.txt 2020-07-13 16:26:27.276100947 -0700 +++ 2/draft-ietf-teep-architecture-12.txt 2020-07-13 16:26:27.364103172 -0700 @@ -1,23 +1,23 @@ TEEP M. Pei Internet-Draft Broadcom Intended status: Informational H. Tschofenig -Expires: January 3, 2021 Arm Limited +Expires: January 14, 2021 Arm Limited D. Thaler Microsoft D. Wheeler Intel - July 02, 2020 + July 13, 2020 Trusted Execution Environment Provisioning (TEEP) Architecture - draft-ietf-teep-architecture-11 + draft-ietf-teep-architecture-12 Abstract A Trusted Execution Environment (TEE) is an environment that enforces 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 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. @@ -29,21 +29,21 @@ 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 January 3, 2021. + This Internet-Draft will expire on January 14, 2021. Copyright Notice 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 @@ -64,29 +64,29 @@ not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 8 + 3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7 3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 8 3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 8 4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. System Components . . . . . . . . . . . . . . . . . . . . 8 4.2. Multiple TEEs in a Device . . . . . . . . . . . . . . . . 11 4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 13 4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 14 - 4.4.1. Example: Application Delivery Mechanisms in Intel SGX 15 + 4.4.1. Example: Application Delivery Mechanisms in Intel SGX 16 4.4.2. Example: Application Delivery Mechanisms in Arm TrustZone . . . . . . . . . . . . . . . . . . . . . . 16 4.5. Entity Relations . . . . . . . . . . . . . . . . . . . . 17 5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 18 5.1. Trust Anchors in a TEEP Agent . . . . . . . . . . . . . . 20 5.2. Trust Anchors in a TEE . . . . . . . . . . . . . . . . . 20 5.3. Trust Anchors in a TAM . . . . . . . . . . . . . . . . . 20 5.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 20 5.5. Message Security . . . . . . . . . . . . . . . . . . . . 21 6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 21 @@ -95,30 +95,30 @@ 6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 22 6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 23 7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.1. Information Required in TEEP Claims . . . . . . . . . . . 25 8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 25 9. Security Considerations . . . . . . . . . . . . . . . . . . . 26 9.1. Broker Trust Model . . . . . . . . . . . . . . . . . . . 26 9.2. Data Protection . . . . . . . . . . . . . . . . . . . . . 26 9.3. Compromised REE . . . . . . . . . . . . . . . . . . . . . 27 - 9.4. Compromised CA . . . . . . . . . . . . . . . . . . . . . 27 + 9.4. Compromised CA . . . . . . . . . . . . . . . . . . . . . 28 9.5. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 28 9.6. Malicious TA Removal . . . . . . . . . . . . . . . . . . 28 - 9.7. Certificate Expiry and Renewal . . . . . . . . . . . . . 28 - 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 29 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 - 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29 - 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 + 9.7. Certificate Expiry and Renewal . . . . . . . . . . . . . 29 + 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 30 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 + 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 30 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30 13. Informative References . . . . . . . . . . . . . . . . . . . 30 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 1. Introduction Applications executing in a device are exposed to many different 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 increases with the complexity of features and applications on devices, and the @@ -190,51 +190,44 @@ 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. - 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 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 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 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 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 + the TEE. - 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 been revoked or is not used for other reasons anymore (e.g., due to an expired subscription). - 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. 2. Terminology The following terms are used: - Device: A physical piece of hardware that hosts one or more TEEs, - often along with a REE. 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 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. + often along with an REE. - 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 @@ -249,21 +242,21 @@ 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. - - Raw Public Key (RPK): The RPK only consists of the + - Raw Public Key: The raw public key only consists of the SubjectPublicKeyInfo structure of a PKIX certificate that carries the parameters necessary to describe the public key. Other serialization formats that do not rely on ASN.1 may also be used. - 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 a TEE). @@ -325,21 +318,22 @@ proof of transaction. For a mobile payment application, some biometric identification information could also be stored in a TEE. The mobile payment application can use such information for unlocking the device and for local identification of the user. A trusted user interface (UI) may be used in a mobile device to prevent malicious software from stealing sensitive user input data. Such an implementation often relies on a TEE for providing access to - peripherals, such as PIN input. + peripherals, such as PIN input or a trusted display, so that the REE + cannot observe or tamper with the user input or output. 3.2. Authentication For better security of authentication, a device may store its keys and cryptographic libraries inside a TEE limiting access to cryptographic functions via a well-defined interface and thereby reducing access to keying material. 3.3. Internet of Things @@ -393,36 +387,38 @@ Figure 1: Notional Architecture of TEEP - TA Signers and Device Administrators utilize the services of a TAM to manage TAs on devices. TA Signers 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 TAs on behalf of TA - Signers and Device Administrators. This includes creation and + Signers and Device Administrators. This includes installation 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 Signers 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 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. + between a TAM and a TEEP Agent running inside the TEE. TEEP + authentication is performed between a TAM and a TEEP Agent. + + 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 TA Signers, or a TAM may be private, and accessible by only one or a limited number of TA Signers. It is expected that many manufacturers and network carriers will run their own private TAM. A TA Signer 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 Signer or @@ -464,28 +460,24 @@ 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): A CA is an entity that issues digital certificates (especially X.509 certificates) and vouches for the binding between the data items in a certificate [RFC4949]. - Certificates are then used for authenticating a device, a TAM and - a TA Signer. 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. + Certificates are then used for authenticating a device, a TAM, or + a TA Signer, as discussed in Section 5. 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. Multiple TEEs in a Device 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 [SGX]) present themselves as separate containers within memory without a controlling manager within the TEE. As such, there might be multiple TEEP Brokers in the REE, where each TEEP Broker communicates with one or more TEEs associated with it. @@ -582,38 +574,38 @@ 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 Signers 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 - 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. + When a TEEP Broker receives a request (see the RequestTA API in + Section 6.2.1) 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 in the TEEP Agent, 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 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. @@ -627,23 +619,23 @@ 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 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 an 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 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 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 device or a user. This personalization data may depend on the type of TEE, a particular TEE instance, the TA, and even the user of the device; an example of personalization data might be a secret @@ -653,21 +645,24 @@ within it and support integrity protection of the personalization data. Other than the requirement to support confidentiality and integrity protection, the TEEP architecture places no limitations or requirements on the personalization data. There are three possible cases for bundling of an Untrusted Application, TA(s), and personalization data: 1. The Untrusted Application, TA(s), and personalization data are all bundled together in a single package by a TA Signer and - provided to the TEEP Broker through the TAM. + either provided to the TEEP Broker through the TAM, or provided + separately (with encrypted personalization data), with key + material needed to decrypt and install the personalization data + and TA provided by a TAM. 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 TA Signer'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 TA Signer. Delivery of the TA and personalization data may be @@ -760,36 +755,43 @@ | | | | (a) Untrusted | | | | App - 2a. Supply --> | --- 3. Install ------> | | | | | | (b) TA -- 2b. Supply ----------> | 4. Messaging-->| | | | | | Figure 3: Example Developer Experience Figure 3 shows an example where the same developer builds and signs - two applications: 1) an Untrusted Application; 2) a TA that provides - some security functions to be run inside a TEE. + two applications: (a) an Untrusted Application; (b) a TA that + provides some security functions to be run inside a TEE. This + example assumes that the developer, the TEE, and the TAM have + previously been provisioned with certificates. + + At step 1, the developer authors the two applications. At step 2, the developer uploads the Untrusted Application (2a) to an Application Store. In this example, the developer is also the TA Signer, and so generates a signed TA. The developer can then either bundle the signed TA with the Untrusted Application, or the developer can provide the signed 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. + Untrusted Application (where the arrow indicates the direction of + data transfer). + + At step 4, since the Untrusted Application depends on the TA, + installing the Untrusted Application will trigger TA installation by + initiating communication with a TAM. 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. @@ -962,23 +964,24 @@ 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 the REE. A TEEP - Broker interacts with a TEEP Agent inside a TEE. + 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 + 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 only needs to return a (transport) error message if the TEE is not reachable for some reason. Other errors are represented @@ -1129,35 +1132,38 @@ same TEE type created by different manufacturers and address considerations around manufacturer provisioning, keying and support for the TEE. - 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. + The claims also need to specify for each component, whether the TA + binary is needed, or whether the TA binary is already available + and only permission to install is needed. 8. Algorithm and Attestation Agility RFC 7696 [RFC7696] outlines the requirements to migrate from one mandatory-to-implement cryptographic algorithm suite to another over time. This feature is also known as crypto agility. Protocol evolution is 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. In the context of TEEP symmetric algorithms + asymmetric algorithms. In the context of TEEP, symmetric algorithms are used for encryption of TA binaries and personalization data whereas the asymmetric algorithms are mostly used for signing messages. 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 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. @@ -1179,22 +1185,28 @@ 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. Data Protection - The TEE implementation provides protection of data on the device. 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 + provides protection of data against integrity and confidentiality + attacks from outside the TEE. TEEs that provide isolation among TAs + within the TEE are likewise responsible for protecting TA data + 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/ + tenant, even if the attacker has TAs. The protocol between TEEP Agents and TAMs similarly is responsible for securely providing integrity and confidentiality protection against adversaries between them. Since the transport protocol under the TEEP protocol might be implemented outside a TEE, as discussed in Section 6, it cannot be relied upon for sufficient protection. The TEEP protocol provides integrity protection, but confidentiality must be provided by payload security, i.e., using encrypted TA binaries and encrypted attestation information. See [I-D.ietf-teep-protocol] for more discussion. @@ -1225,48 +1237,69 @@ 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. 9.4. Compromised CA - A root CA for TAM certificates might get compromised. A Trust Anchor - other than a root CA certificate may also be compromised. Some TEE - Trust Anchor update mechanism is expected from device OEMs. + A root CA for TAM certificates might get compromised or its + certificate might expire, or a Trust Anchor other than a root CA + certificate may also expire or be compromised. TEEs are responsible + for validating the entire TAM certificate chain, including the TAM + certificate and any intermediate certificates up to the root + certificate. Such validation includes checking for certificate + revocation. - TEEs are responsible for validating certificate revocation about a - TAM certificate chain, including the TAM certificate and the - intermediate CA certificates up to the root certificate. This will - detect a compromised TAM certificate and also any compromised - intermediate CA certificate. + If a TAM certificate chain validation fails, the TAM might be + rejected by a TEEP Agent. To address this, some certificate chain + update mechanism is expected from TAM operators, so that the TAM can + get a new certificate chain that can be validated by a TEEP Agent. + In addition, the Trust Anchor in the TEEP Agent's Trust Anchor Store + may need to be updated. To address this, some TEE Trust Anchor + update mechanism is expected from device OEMs. - 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. + Similarly, a root CA for TEE certificates might get compromised or + its certificate might expire, or a Trust Anchor other than a root CA + certificate may also expire or be compromised. TAMs are responsible + for validating the entire TEE certificate chain, including the TEE + certificate and any intermediate certificates up to the root + certificate. Such validation includes checking for certificate + revocation. + + If a TEE certificate chain validation fails, the TEE might be + rejected by a TAM, subject to the TAM's policy. To address this, + some certificate chain update mechanism is expected from device OEMs, + so that the TEE can get a new certificate chain that can be validated + by a TAM. In addition, the Trust Anchor in the TAM's Trust Anchor + Store may need to be updated. 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. + Such a TA might be able to escape from malware detection by the REE, + or access trusted resources within the TEE (but could not access + other TEEs, or access other TA's if the TEE provides isolation + between TAs). + + It is the responsibility of the TAM to not install malicious TAs 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. That is, to recover, the TEEP Agent must be able to reach out to the TAM, for example whenever the RequestPolicyCheck API (Section 6.2.1) is @@ -1291,21 +1324,21 @@ 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 updates. On the other hand, it is imperative that OEMs or device providers plan for support of Trust Anchor update in their shipped devices. For those cases where TEE devices are given certificates for which no good expiration date can be assigned the recommendations in - Section 4.1.2.5 of RFC 5280 [RFC5280] are applicable. + Section 4.1.2.5 of [RFC5280] are applicable. 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 a TA Signer and a TEE. However, there must be some means of provisioning the decryption key into the TEE and/or some means of the TA Signer securely learning a public key of the TEE that it can use to encrypt. One way to do this is for the TA Signer to run its own @@ -1337,29 +1370,29 @@ 13. Informative References [GPTEE] GlobalPlatform, "GlobalPlatform Device Technology: TEE System Architecture, v1.1", GlobalPlatform GPD_SPE_009, January 2017, . [I-D.ietf-rats-architecture] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and W. Pan, "Remote Attestation Procedures Architecture", - draft-ietf-rats-architecture-04 (work in progress), May + draft-ietf-rats-architecture-05 (work in progress), July 2020. [I-D.ietf-suit-manifest] Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg, "A Concise Binary Object Representation (CBOR)-based Serialization Format for the Software Updates for Internet - of Things (SUIT) Manifest", draft-ietf-suit-manifest-07 - (work in progress), June 2020. + of Things (SUIT) Manifest", draft-ietf-suit-manifest-08 + (work in progress), July 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-06 (work in progress), April 2020. [I-D.ietf-teep-protocol] Tschofenig, H., Pei, M., Wheeler, D., Thaler, D., and A. Tsukamoto, "Trusted Execution Environment Provisioning