< draft-ietf-teep-architecture-11.txt   draft-ietf-teep-architecture-12.txt >
TEEP M. Pei TEEP M. Pei
Internet-Draft Broadcom Internet-Draft Broadcom
Intended status: Informational H. Tschofenig Intended status: Informational H. Tschofenig
Expires: January 3, 2021 Arm Limited Expires: January 14, 2021 Arm Limited
D. Thaler D. Thaler
Microsoft Microsoft
D. Wheeler D. Wheeler
Intel Intel
July 02, 2020 July 13, 2020
Trusted Execution Environment Provisioning (TEEP) Architecture Trusted Execution Environment Provisioning (TEEP) Architecture
draft-ietf-teep-architecture-11 draft-ietf-teep-architecture-12
Abstract Abstract
A Trusted Execution Environment (TEE) is an environment that enforces A Trusted Execution Environment (TEE) is an environment that enforces
that any code within that environment cannot be tampered with, and that any code within that environment cannot be tampered with, and
that any data used by such code cannot be read or tampered with by that any data used by such code cannot be read or tampered with by
any code outside that environment. This architecture document any code outside that environment. This architecture document
motivates the design and standardization of a protocol for managing motivates the design and standardization of a protocol for managing
the lifecycle of trusted applications running inside such a TEE. the lifecycle of trusted applications running inside such a TEE.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2021. This Internet-Draft will expire on January 14, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 8 3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7
3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 8 3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 8
3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 8 3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 8
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. System Components . . . . . . . . . . . . . . . . . . . . 8 4.1. System Components . . . . . . . . . . . . . . . . . . . . 8
4.2. Multiple TEEs in a Device . . . . . . . . . . . . . . . . 11 4.2. Multiple TEEs in a Device . . . . . . . . . . . . . . . . 11
4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 13 4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 13
4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 14 4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 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 4.4.2. Example: Application Delivery Mechanisms in Arm
TrustZone . . . . . . . . . . . . . . . . . . . . . . 16 TrustZone . . . . . . . . . . . . . . . . . . . . . . 16
4.5. Entity Relations . . . . . . . . . . . . . . . . . . . . 17 4.5. Entity Relations . . . . . . . . . . . . . . . . . . . . 17
5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 18 5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 18
5.1. Trust Anchors in a TEEP Agent . . . . . . . . . . . . . . 20 5.1. Trust Anchors in a TEEP Agent . . . . . . . . . . . . . . 20
5.2. Trust Anchors in a TEE . . . . . . . . . . . . . . . . . 20 5.2. Trust Anchors in a TEE . . . . . . . . . . . . . . . . . 20
5.3. Trust Anchors in a TAM . . . . . . . . . . . . . . . . . 20 5.3. Trust Anchors in a TAM . . . . . . . . . . . . . . . . . 20
5.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 20 5.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 20
5.5. Message Security . . . . . . . . . . . . . . . . . . . . 21 5.5. Message Security . . . . . . . . . . . . . . . . . . . . 21
6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 21 6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 21
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6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 22 6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 22
6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 23 6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 23
7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 23 7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.1. Information Required in TEEP Claims . . . . . . . . . . . 25 7.1. Information Required in TEEP Claims . . . . . . . . . . . 25
8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 25 8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26 9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
9.1. Broker Trust Model . . . . . . . . . . . . . . . . . . . 26 9.1. Broker Trust Model . . . . . . . . . . . . . . . . . . . 26
9.2. Data Protection . . . . . . . . . . . . . . . . . . . . . 26 9.2. Data Protection . . . . . . . . . . . . . . . . . . . . . 26
9.3. Compromised REE . . . . . . . . . . . . . . . . . . . . . 27 9.3. Compromised REE . . . . . . . . . . . . . . . . . . . . . 27
9.4. Compromised CA . . . . . . . . . . . . . . . . . . . . . 27 9.4. Compromised CA . . . . . . . . . . . . . . . . . . . . . 28
9.5. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 28 9.5. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 28
9.6. Malicious TA Removal . . . . . . . . . . . . . . . . . . 28 9.6. Malicious TA Removal . . . . . . . . . . . . . . . . . . 28
9.7. Certificate Expiry and Renewal . . . . . . . . . . . . . 28 9.7. Certificate Expiry and Renewal . . . . . . . . . . . . . 29
9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 29 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 30
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 30
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
13. Informative References . . . . . . . . . . . . . . . . . . . 30 13. Informative References . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction 1. Introduction
Applications executing in a device are exposed to many different Applications executing in a device are exposed to many different
attacks intended to compromise the execution of the application or attacks intended to compromise the execution of the application or
reveal the data upon which those applications are operating. These reveal the data upon which those applications are operating. These
attacks increase with the number of other applications on the device, attacks increase with the number of other applications on the device,
with such other applications coming from potentially untrustworthy with such other applications coming from potentially untrustworthy
sources. The potential for attacks further increases with the sources. The potential for attacks further increases with the
complexity of features and applications on devices, and the complexity of features and applications on devices, and the
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confidential wants to determine security-relevant information of a confidential wants to determine security-relevant information of a
device before allowing their TA to be provisioned to the TEE device before allowing their TA to be provisioned to the TEE
within the device. An example is the verification of the type of within the device. An example is the verification of the type of
TEE included in a device and that it is capable of providing the TEE included in a device and that it is capable of providing the
security protections required. security protections required.
- A TEE in a device wants to determine whether an entity that wants - A TEE in a device wants to determine whether an entity that wants
to manage a TA in the device is authorized to manage TAs in the to manage a TA in the device is authorized to manage TAs in the
TEE, and what TAs the entity is permitted to manage. TEE, and what TAs the entity is permitted to manage.
- A TAM (e.g., operated by a device administrator) wants to - A Device Administrator wants to determine if a TA exists (is
determine if a TA exists (is installed) on a device (in the TEE), installed) on a device (in the TEE), and if not, install the TA in
and if not, install the TA in the TEE. the TEE.
- A TAM wants to check whether a TA in a device's TEE is the most - A Device Administrator wants to check whether a TA in a device's
up-to-date version, and if not, update the TA in the TEE. 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 - A Device Administrator wants to remove a TA from a device's TEE if
the TA developer is no longer maintaining that TA, when the TA has the TA developer is no longer maintaining that TA, when the TA has
been revoked or is not used for other reasons anymore (e.g., due been revoked or is not used for other reasons anymore (e.g., due
to an expired subscription). to an expired subscription).
- A TA developer wants to define the relationship between - A TA developer wants to define the relationship between
cooperating TAs under the TA developer's control, and specify cooperating TAs under the TA developer's control, and specify
whether the TAs can communicate, share data, and/or share key whether the TAs can communicate, share data, and/or share key
material. material.
2. Terminology 2. Terminology
The following terms are used: The following terms are used:
- Device: A physical piece of hardware that hosts one or more TEEs, - Device: A physical piece of hardware that hosts one or more TEEs,
often along with a REE. A device contains a default list of Trust often along with an REE.
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.
- Device Administrator: An entity that is responsible for - Device Administrator: An entity that is responsible for
administration of a device, which could be the Device Owner. A administration of a device, which could be the Device Owner. A
Device Administrator has privileges on the device to install and Device Administrator has privileges on the device to install and
remove Untrusted Applications and TAs, approve or reject Trust remove Untrusted Applications and TAs, approve or reject Trust
Anchors, and approve or reject TA developers, among possibly other Anchors, and approve or reject TA developers, among possibly other
privileges on the device. A Device Administrator can manage the privileges on the device. A Device Administrator can manage the
list of allowed TAMs by modifying the list of Trust Anchors on the list of allowed TAMs by modifying the list of Trust Anchors on the
device. Although a Device Administrator may have privileges and device. Although a Device Administrator may have privileges and
device-specific controls to locally administer a device, the device-specific controls to locally administer a device, the
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administration rights. In this case, the enterprise appoints a administration rights. In this case, the enterprise appoints a
Device Administrator that is not the device owner. Device Administrator that is not the device owner.
- Device User: A human being that uses a device. Many devices have - Device User: A human being that uses a device. Many devices have
a single device user. Some devices have a primary device user a single device user. Some devices have a primary device user
with other human beings as secondary device users (e.g., parent with other human beings as secondary device users (e.g., parent
allowing children to use their tablet or laptop). Other devices allowing children to use their tablet or laptop). Other devices
are not used by a human being and hence have no device user. are not used by a human being and hence have no device user.
Relates to Device Owner and Device Administrator. Relates to Device Owner and Device Administrator.
- 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 SubjectPublicKeyInfo structure of a PKIX certificate that carries
the parameters necessary to describe the public key. Other the parameters necessary to describe the public key. Other
serialization formats that do not rely on ASN.1 may also be used. serialization formats that do not rely on ASN.1 may also be used.
- Rich Execution Environment (REE): An environment that is provided - Rich Execution Environment (REE): An environment that is provided
and governed by a typical OS (e.g., Linux, Windows, Android, iOS), and governed by a typical OS (e.g., Linux, Windows, Android, iOS),
potentially in conjunction with other supporting operating systems potentially in conjunction with other supporting operating systems
and hypervisors; it is outside of any TEE. This environment and and hypervisors; it is outside of any TEE. This environment and
applications running on it are considered untrusted (or more applications running on it are considered untrusted (or more
precisely, less trusted than a TEE). precisely, less trusted than a TEE).
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proof of transaction. proof of transaction.
For a mobile payment application, some biometric identification For a mobile payment application, some biometric identification
information could also be stored in a TEE. The mobile payment information could also be stored in a TEE. The mobile payment
application can use such information for unlocking the device and for application can use such information for unlocking the device and for
local identification of the user. local identification of the user.
A trusted user interface (UI) may be used in a mobile device to A trusted user interface (UI) may be used in a mobile device to
prevent malicious software from stealing sensitive user input data. prevent malicious software from stealing sensitive user input data.
Such an implementation often relies on a TEE for providing access to 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 3.2. Authentication
For better security of authentication, a device may store its keys For better security of authentication, a device may store its keys
and cryptographic libraries inside a TEE limiting access to and cryptographic libraries inside a TEE limiting access to
cryptographic functions via a well-defined interface and thereby cryptographic functions via a well-defined interface and thereby
reducing access to keying material. reducing access to keying material.
3.3. Internet of Things 3.3. Internet of Things
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Figure 1: Notional Architecture of TEEP Figure 1: Notional Architecture of TEEP
- TA Signers and Device Administrators utilize the services of a TAM - TA Signers and Device Administrators utilize the services of a TAM
to manage TAs on devices. TA Signers do not directly interact to manage TAs on devices. TA Signers do not directly interact
with devices. Device Administators may elect to use a TAM for with devices. Device Administators may elect to use a TAM for
remote administration of TAs instead of managing each device remote administration of TAs instead of managing each device
directly. directly.
- Trusted Application Manager (TAM): A TAM is responsible for - Trusted Application Manager (TAM): A TAM is responsible for
performing lifecycle management activity on TAs on behalf of TA 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 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 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 be removed. TAMs may provide services that make it easier for TA
Signers or Device Administators to use the TAM's service to manage Signers or Device Administators to use the TAM's service to manage
multiple devices, although that is not required of a TAM. multiple devices, although that is not required of a TAM.
The TAM performs its management of TAs on the device through The TAM performs its management of TAs on the device through
interactions with a device's TEEP Broker, which relays messages interactions with a device's TEEP Broker, which relays messages
between a TAM and a TEEP Agent running inside the TEE. As shown between a TAM and a TEEP Agent running inside the TEE. TEEP
in Figure 1, the TAM cannot directly contact a TEEP Agent, but authentication is performed between a TAM and a TEEP Agent.
must wait for the TEEP Broker to contact the TAM requesting a
particular service. This architecture is intentional in order to As shown in Figure 1, the TAM cannot directly contact a TEEP
accommodate network and application firewalls that normally Agent, but must wait for the TEEP Broker to contact the TAM
protect user and enterprise devices from arbitrary connections requesting a particular service. This architecture is intentional
from external network entities. 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 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 TAM may be private, and accessible by only one or a limited number
of TA Signers. It is expected that many manufacturers and network of TA Signers. It is expected that many manufacturers and network
carriers will run their own private TAM. carriers will run their own private TAM.
A TA Signer or Device Administrator chooses a particular TAM based 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 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 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 up to, an authorized Trust Anchor in the device. A TA Signer or
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TEE that receives TAM requests (typically relayed via a TEEP TEE that receives TAM requests (typically relayed via a TEEP
Broker that runs in an REE). A TEEP Agent in the TEE may parse Broker that runs in an REE). A TEEP Agent in the TEE may parse
requests or forward requests to other processing modules in a TEE, requests or forward requests to other processing modules in a TEE,
which is up to a TEE provider's implementation. A response which is up to a TEE provider's implementation. A response
message corresponding to a TAM request is sent back to the TAM, message corresponding to a TAM request is sent back to the TAM,
again typically relayed via a TEEP Broker. again typically relayed via a TEEP Broker.
- Certification Authority (CA): A CA is an entity that issues - Certification Authority (CA): A CA is an entity that issues
digital certificates (especially X.509 certificates) and vouches digital certificates (especially X.509 certificates) and vouches
for the binding between the data items in a certificate [RFC4949]. for the binding between the data items in a certificate [RFC4949].
Certificates are then used for authenticating a device, a TAM and Certificates are then used for authenticating a device, a TAM, or
a TA Signer. A device embeds a list of root certificates (Trust a TA Signer, as discussed in Section 5. The CAs do not need to be
Anchors), from trusted CAs that a TAM will be validated against. the same; different CAs can be chosen by each TAM, and different
A TAM will remotely attest a device by checking whether a device device CAs can be used by different device manufacturers.
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. Multiple TEEs in a Device 4.2. Multiple TEEs in a Device
Some devices might implement multiple TEEs. In these cases, there Some devices might implement multiple TEEs. In these cases, there
might be one shared TEEP Broker that interacts with all the TEEs in might be one shared TEEP Broker that interacts with all the TEEs in
the device. However, some TEEs (for example, SGX [SGX]) present the device. However, some TEEs (for example, SGX [SGX]) present
themselves as separate containers within memory without a controlling themselves as separate containers within memory without a controlling
manager within the TEE. As such, there might be multiple TEEP manager within the TEE. As such, there might be multiple TEEP
Brokers in the REE, where each TEEP Broker communicates with one or Brokers in the REE, where each TEEP Broker communicates with one or
more TEEs associated with it. more TEEs associated with it.
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repository, the developer optionally binds the Untrusted Application repository, the developer optionally binds the Untrusted Application
with a manifest that identifies what TAMs can be contacted for the 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 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 - this is likely the case for enterprise applications or TA Signers
serving a closed community. For broad public apps, there will likely serving a closed community. For broad public apps, there will likely
be multiple TAMs in the manifest - one servicing one brand of mobile be multiple TAMs in the manifest - one servicing one brand of mobile
device and another servicing a different manufacturer, etc. Because device and another servicing a different manufacturer, etc. Because
different devices and different manufacturers trust different TAMs, different devices and different manufacturers trust different TAMs,
the manifest can include multiple TAMs that support the required TA. the manifest can include multiple TAMs that support the required TA.
When a TEEP Broker receives a request from an Untrusted Application When a TEEP Broker receives a request (see the RequestTA API in
to install a TA, a list of TAM URIs may be provided for that TA, and Section 6.2.1) from an Untrusted Application to install a TA, a list
the request is passed to the TEEP Agent. If the TEEP Agent decides of TAM URIs may be provided for that TA, and the request is passed to
that the TA needs to be installed, the TEEP Agent selects a single the TEEP Agent. If the TEEP Agent decides that the TA needs to be
TAM URI that is consistent with the list of trusted TAMs provisioned installed, the TEEP Agent selects a single TAM URI that is consistent
on the device, invokes the HTTP transport for TEEP to connect to the with the list of trusted TAMs provisioned in the TEEP Agent, invokes
TAM URI, and begins a TEEP protocol exchange. When the TEEP Agent the HTTP transport for TEEP to connect to the TAM URI, and begins a
subsequently receives the TA to install and the TA's manifest TEEP protocol exchange. When the TEEP Agent subsequently receives
indicates dependencies on any other trusted components, each the TA to install and the TA's manifest indicates dependencies on any
dependency can include a list of TAM URIs for the relevant other trusted components, each dependency can include a list of TAM
dependency. If such dependencies exist that are prerequisites to URIs for the relevant dependency. If such dependencies exist that
install the TA, then the TEEP Agent recursively follows the same are prerequisites to install the TA, then the TEEP Agent recursively
procedure for each dependency that needs to be installed or updated, follows the same procedure for each dependency that needs to be
including selecting a TAM URI that is consistent with the list of installed or updated, including selecting a TAM URI that is
trusted TAMs provisioned on the device, and beginning a TEEP consistent with the list of trusted TAMs provisioned on the device,
exchange. If multiple TAM URIs are considered trusted, only one and beginning a TEEP exchange. If multiple TAM URIs are considered
needs to be contacted and they can be attempted in some order until trusted, only one needs to be contacted and they can be attempted in
one responds. some order until one responds.
Separate from the Untrusted Application's manifest, this framework Separate from the Untrusted Application's manifest, this framework
relies on the use of the manifest format in [I-D.ietf-suit-manifest] relies on the use of the manifest format in [I-D.ietf-suit-manifest]
for expressing how to install a TA, as well as any dependencies on 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 and versions. That is, dependencies from TAs on
other TEE components can be expressed in a SUIT manifest, including other TEE components can be expressed in a SUIT manifest, including
dependencies on any other TAs, or trusted OS code (if any), or dependencies on any other TAs, or trusted OS code (if any), or
trusted firmware. Installation steps can also be expressed in a SUIT trusted firmware. Installation steps can also be expressed in a SUIT
manifest. manifest.
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Updating a TA may cause compatibility issues with any Untrusted Updating a TA may cause compatibility issues with any Untrusted
Applications or other components that depend on the updated TA, just Applications or other components that depend on the updated TA, just
like updating the OS or a shared library could impact an Untrusted like updating the OS or a shared library could impact an Untrusted
Application. Thus, an implementation needs to take into account such Application. Thus, an implementation needs to take into account such
issues. issues.
4.4. Untrusted Apps, Trusted Apps, and Personalization Data 4.4. Untrusted Apps, Trusted Apps, and Personalization Data
In TEEP, there is an explicit relationship and dependence between an In TEEP, there is an explicit relationship and dependence between an
Untrusted Application in a REE and one or more TAs in a TEE, as shown Untrusted Application in an REE and one or more TAs in a TEE, as
in Figure 2. For most purposes, an Untrusted Application that uses shown in Figure 2. For most purposes, an Untrusted Application that
one or more TAs in a TEE appears no different from any other uses one or more TAs in a TEE appears no different from any other
Untrusted Application in the REE. However, the way the Untrusted Untrusted Application in the REE. However, the way the Untrusted
Application and its corresponding TAs are packaged, delivered, and Application and its corresponding TAs are packaged, delivered, and
installed on the device can vary. The variations depend on whether installed on the device can vary. The variations depend on whether
the Untrusted Application and TA are bundled together or are provided the Untrusted Application and TA are bundled together or are provided
separately, and this has implications to the management of the TAs in separately, and this has implications to the management of the TAs in
a TEE. In addition to the Untrusted Application and TA(s), the TA(s) a TEE. In addition to the Untrusted Application and TA(s), the TA(s)
and/or TEE may require some additional data to personalize the TA to 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 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 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 the device; an example of personalization data might be a secret
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within it and support integrity protection of the personalization within it and support integrity protection of the personalization
data. Other than the requirement to support confidentiality and data. Other than the requirement to support confidentiality and
integrity protection, the TEEP architecture places no limitations or integrity protection, the TEEP architecture places no limitations or
requirements on the personalization data. requirements on the personalization data.
There are three possible cases for bundling of an Untrusted There are three possible cases for bundling of an Untrusted
Application, TA(s), and personalization data: Application, TA(s), and personalization data:
1. The Untrusted Application, TA(s), and personalization data are 1. The Untrusted Application, TA(s), and personalization data are
all bundled together in a single package by a TA Signer and 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 2. The Untrusted Application and the TA(s) are bundled together in a
single package, which a TAM or a publicly accessible app store single package, which a TAM or a publicly accessible app store
maintains, and the personalization data is separately provided by maintains, and the personalization data is separately provided by
the TA Signer's TAM. the TA Signer's TAM.
3. All components are independent. The Untrusted Application is 3. All components are independent. The Untrusted Application is
installed through some independent or device-specific mechanism, installed through some independent or device-specific mechanism,
and the TAM provides the TA and personalization data from the TA and the TAM provides the TA and personalization data from the TA
Signer. Delivery of the TA and personalization data may be Signer. Delivery of the TA and personalization data may be
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| | | | | | | |
(a) Untrusted | | | | (a) Untrusted | | | |
App - 2a. Supply --> | --- 3. Install ------> | | App - 2a. Supply --> | --- 3. Install ------> | |
| | | | | | | |
(b) TA -- 2b. Supply ----------> | 4. Messaging-->| | (b) TA -- 2b. Supply ----------> | 4. Messaging-->| |
| | | | | | | |
Figure 3: Example Developer Experience Figure 3: Example Developer Experience
Figure 3 shows an example where the same developer builds and signs Figure 3 shows an example where the same developer builds and signs
two applications: 1) an Untrusted Application; 2) a TA that provides two applications: (a) an Untrusted Application; (b) a TA that
some security functions to be run inside a TEE. 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 At step 2, the developer uploads the Untrusted Application (2a) to an
Application Store. In this example, the developer is also the TA Application Store. In this example, the developer is also the TA
Signer, and so generates a signed TA. The developer can then either Signer, and so generates a signed TA. The developer can then either
bundle the signed TA with the Untrusted Application, or the developer 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 can provide the signed TA to a TAM that will be managing the TA in
various devices. various devices.
At step 3, a user will go to an Application Store to download the At step 3, a user will go to an Application Store to download the
Untrusted Application. Since the Untrusted Application depends on Untrusted Application (where the arrow indicates the direction of
the TA, installing the Untrusted Application will trigger TA data transfer).
installation by initiating communication with a TAM. This is step 4.
The TEEP Agent will interact with TAM via a TEEP Broker that At step 4, since the Untrusted Application depends on the TA,
faciliates communications between a TAM and the TEEP Agent in TEE. 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. Some TA installation implementations might ask for a user's consent.
In other implementations, a Device Administrator might choose what In other implementations, a Device Administrator might choose what
Untrusted Applications and related TAs to be installed. A user Untrusted Applications and related TAs to be installed. A user
consent flow is out of scope of the TEEP architecture. consent flow is out of scope of the TEEP architecture.
The main components consist of a set of standard messages created by The main components consist of a set of standard messages created by
a TAM to deliver TA management commands to a device, and device a TAM to deliver TA management commands to a device, and device
attestation and response messages created by a TEE that responds to a attestation and response messages created by a TEE that responds to a
TAM's message. TAM's message.
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Untrusted Application without requiring the Untrusted Application to Untrusted Application without requiring the Untrusted Application to
run first. run first.
6.1. Role of the TEEP Broker 6.1. Role of the TEEP Broker
A TEEP Broker abstracts the message exchanges with a TEE in a device. A TEEP Broker abstracts the message exchanges with a TEE in a device.
The input data is originated from a TAM or the first initialization The input data is originated from a TAM or the first initialization
call to trigger a TA installation. call to trigger a TA installation.
The Broker doesn't need to parse a message content received from a 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 TAM that should be processed by a TEE (see the ProcessTeepMessage API
one TEE, one TEEP Broker per TEE could be present in the REE. A TEEP in Section 6.2.1). When a device has more than one TEE, one TEEP
Broker interacts with a TEEP Agent inside a TEE. 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 A TAM message may indicate the target TEE where a TA should be
installed. A compliant TEEP protocol should include a target TEE installed. A compliant TEEP protocol should include a target TEE
identifier for a TEEP Broker when multiple TEEs are present. identifier for a TEEP Broker when multiple TEEs are present.
The Broker relays the response messages generated from a TEEP Agent The Broker relays the response messages generated from a TEEP Agent
in a TEE to the TAM. in a TEE to the TAM.
The Broker only needs to return a (transport) error message if the The Broker only needs to return a (transport) error message if the
TEE is not reachable for some reason. Other errors are represented TEE is not reachable for some reason. Other errors are represented
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same TEE type created by different manufacturers and address same TEE type created by different manufacturers and address
considerations around manufacturer provisioning, keying and considerations around manufacturer provisioning, keying and
support for the TEE. support for the TEE.
- Freshness Proof: A claim that includes freshness information must - Freshness Proof: A claim that includes freshness information must
be included, such as a nonce or timestamp. be included, such as a nonce or timestamp.
- Requested Components: A list of zero or more components (TAs or - Requested Components: A list of zero or more components (TAs or
other dependencies needed by a TEE) that are requested by some other dependencies needed by a TEE) that are requested by some
depending app, but which are not currently installed in the TEE. 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 8. Algorithm and Attestation Agility
RFC 7696 [RFC7696] outlines the requirements to migrate from one RFC 7696 [RFC7696] outlines the requirements to migrate from one
mandatory-to-implement cryptographic algorithm suite to another over mandatory-to-implement cryptographic algorithm suite to another over
time. This feature is also known as crypto agility. Protocol time. This feature is also known as crypto agility. Protocol
evolution is greatly simplified when crypto agility is considered evolution is greatly simplified when crypto agility is considered
during the design of the protocol. In the case of the TEEP protocol during the design of the protocol. In the case of the TEEP protocol
the diverse range of use cases, from trusted app updates for smart the diverse range of use cases, from trusted app updates for smart
phones and tablets to updates of code on higher-end IoT devices, phones and tablets to updates of code on higher-end IoT devices,
creates the need for different mandatory-to-implement algorithms creates the need for different mandatory-to-implement algorithms
already from the start. already from the start.
Crypto agility in TEEP concerns the use of symmetric as well as 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 are used for encryption of TA binaries and personalization data
whereas the asymmetric algorithms are mostly used for signing whereas the asymmetric algorithms are mostly used for signing
messages. 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 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 technology it supports. For many deployment cases it is more likely
for the TAM to support one or more attestation techniques whereas the for the TAM to support one or more attestation techniques whereas the
device may only support one. device may only support one.
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A rogue TEEP Broker might send corrupted data to the TEEP Agent, or A rogue TEEP Broker might send corrupted data to the TEEP Agent, or
launch a DoS attack by sending a flood of TEEP protocol requests. launch a DoS attack by sending a flood of TEEP protocol requests.
The TEEP Agent validates the signature of each TEEP protocol request The TEEP Agent validates the signature of each TEEP protocol request
and checks the signing certificate against its Trust Anchors. To and checks the signing certificate against its Trust Anchors. To
mitigate DoS attacks, it might also add some protection scheme such mitigate DoS attacks, it might also add some protection scheme such
as a threshold on repeated requests or number of TAs that can be as a threshold on repeated requests or number of TAs that can be
installed. installed.
9.2. Data Protection 9.2. Data Protection
The TEE implementation provides protection of data on the device. It It is the responsibility of the TAM to protect data on its servers.
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 The protocol between TEEP Agents and TAMs similarly is responsible
for securely providing integrity and confidentiality protection for securely providing integrity and confidentiality protection
against adversaries between them. Since the transport protocol under against adversaries between them. Since the transport protocol under
the TEEP protocol might be implemented outside a TEE, as discussed in the TEEP protocol might be implemented outside a TEE, as discussed in
Section 6, it cannot be relied upon for sufficient protection. The Section 6, it cannot be relied upon for sufficient protection. The
TEEP protocol provides integrity protection, but confidentiality must TEEP protocol provides integrity protection, but confidentiality must
be provided by payload security, i.e., using encrypted TA binaries be provided by payload security, i.e., using encrypted TA binaries
and encrypted attestation information. See [I-D.ietf-teep-protocol] and encrypted attestation information. See [I-D.ietf-teep-protocol]
for more discussion. for more discussion.
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A compromised REE might also request initiating the full flow of A compromised REE might also request initiating the full flow of
installation of TAs that are not necessary. It may also repeat a installation of TAs that are not necessary. It may also repeat a
prior legitimate TA installation request. A TEEP Agent prior legitimate TA installation request. A TEEP Agent
implementation is responsible for ensuring that it can recognize and implementation is responsible for ensuring that it can recognize and
decline such repeated requests. It is also responsible for decline such repeated requests. It is also responsible for
protecting the resource usage allocated for TA management. protecting the resource usage allocated for TA management.
9.4. Compromised CA 9.4. Compromised CA
A root CA for TAM certificates might get compromised. A Trust Anchor A root CA for TAM certificates might get compromised or its
other than a root CA certificate may also be compromised. Some TEE certificate might expire, or a Trust Anchor other than a root CA
Trust Anchor update mechanism is expected from device OEMs. 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 If a TAM certificate chain validation fails, the TAM might be
TAM certificate chain, including the TAM certificate and the rejected by a TEEP Agent. To address this, some certificate chain
intermediate CA certificates up to the root certificate. This will update mechanism is expected from TAM operators, so that the TAM can
detect a compromised TAM certificate and also any compromised get a new certificate chain that can be validated by a TEEP Agent.
intermediate CA certificate. 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 Similarly, a root CA for TEE certificates might get compromised or
devices might be rejected by a TAM, which is a decision of the TAM its certificate might expire, or a Trust Anchor other than a root CA
implementation and policy choice. TAMs are responsible for certificate may also expire or be compromised. TAMs are responsible
validating any intermediate CA for TEE device certificates. 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 9.5. Compromised TAM
Device TEEs are responsible for validating the supplied TAM Device TEEs are responsible for validating the supplied TAM
certificates to determine that the TAM is trustworthy. certificates to determine that the TAM is trustworthy.
9.6. Malicious TA Removal 9.6. Malicious TA Removal
It is possible that a rogue developer distributes a malicious It is possible that a rogue developer distributes a malicious
Untrusted Application and intends to get a malicious TA installed. Untrusted Application and intends to get a malicious TA installed.
It's the responsibility of the TAM to not install malicious trusted Such a TA might be able to escape from malware detection by the REE,
apps in the first place. The TEEP architecture allows a TEEP Agent or access trusted resources within the TEE (but could not access
to decide which TAMs it trusts via Trust Anchors, and delegates the other TEEs, or access other TA's if the TEE provides isolation
TA authenticity check to the TAMs it trusts. 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 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 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 initiate the removal of the TA by notifying devices to remove the TA
(and potentially the REE or Device Owner to remove any Untrusted (and potentially the REE or Device Owner to remove any Untrusted
Application that depend on the TA). If the TAM does not currently 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 have a connection to the TEEP Agent on a device, such a notification
would occur the next time connectivity does exist. That is, to 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 recover, the TEEP Agent must be able to reach out to the TAM, for
example whenever the RequestPolicyCheck API (Section 6.2.1) is example whenever the RequestPolicyCheck API (Section 6.2.1) is
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the lifetime of a device. A TAM certificate usually has a moderate 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 lifetime of 2 to 5 years. A TAM should get renewed or rekeyed
certificates. The root CA certificates for a TAM, which are embedded certificates. The root CA certificates for a TAM, which are embedded
into the Trust Anchor Store in a device, should have long lifetimes into the Trust Anchor Store in a device, should have long lifetimes
that don't require device Trust Anchor updates. On the other hand, that don't require device Trust Anchor updates. On the other hand,
it is imperative that OEMs or device providers plan for support of it is imperative that OEMs or device providers plan for support of
Trust Anchor update in their shipped devices. Trust Anchor update in their shipped devices.
For those cases where TEE devices are given certificates for which no For those cases where TEE devices are given certificates for which no
good expiration date can be assigned the recommendations in 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 9.8. Keeping Secrets from the TAM
In some scenarios, it is desirable to protect the TA binary or In some scenarios, it is desirable to protect the TA binary or
configuration from being disclosed to the TAM that distributes them. configuration from being disclosed to the TAM that distributes them.
In such a scenario, the files can be encrypted end-to-end between a 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 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 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 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 to encrypt. One way to do this is for the TA Signer to run its own
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13. Informative References 13. Informative References
[GPTEE] GlobalPlatform, "GlobalPlatform Device Technology: TEE [GPTEE] GlobalPlatform, "GlobalPlatform Device Technology: TEE
System Architecture, v1.1", GlobalPlatform GPD_SPE_009, System Architecture, v1.1", GlobalPlatform GPD_SPE_009,
January 2017, <https://globalplatform.org/specs-library/ January 2017, <https://globalplatform.org/specs-library/
tee-system-architecture-v1-1/>. tee-system-architecture-v1-1/>.
[I-D.ietf-rats-architecture] [I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture", W. Pan, "Remote Attestation Procedures Architecture",
draft-ietf-rats-architecture-04 (work in progress), May draft-ietf-rats-architecture-05 (work in progress), July
2020. 2020.
[I-D.ietf-suit-manifest] [I-D.ietf-suit-manifest]
Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg, Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg,
"A Concise Binary Object Representation (CBOR)-based "A Concise Binary Object Representation (CBOR)-based
Serialization Format for the Software Updates for Internet Serialization Format for the Software Updates for Internet
of Things (SUIT) Manifest", draft-ietf-suit-manifest-07 of Things (SUIT) Manifest", draft-ietf-suit-manifest-08
(work in progress), June 2020. (work in progress), July 2020.
[I-D.ietf-teep-otrp-over-http] [I-D.ietf-teep-otrp-over-http]
Thaler, D., "HTTP Transport for Trusted Execution Thaler, D., "HTTP Transport for Trusted Execution
Environment Provisioning: Agent-to- TAM Communication", Environment Provisioning: Agent-to- TAM Communication",
draft-ietf-teep-otrp-over-http-06 (work in progress), draft-ietf-teep-otrp-over-http-06 (work in progress),
April 2020. April 2020.
[I-D.ietf-teep-protocol] [I-D.ietf-teep-protocol]
Tschofenig, H., Pei, M., Wheeler, D., Thaler, D., and A. Tschofenig, H., Pei, M., Wheeler, D., Thaler, D., and A.
Tsukamoto, "Trusted Execution Environment Provisioning Tsukamoto, "Trusted Execution Environment Provisioning
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