< draft-ietf-teep-architecture-03.txt   draft-ietf-teep-architecture-04.txt >
TEEP M. Pei TEEP M. Pei
Internet-Draft Symantec Internet-Draft Symantec
Intended status: Informational H. Tschofenig Intended status: Informational H. Tschofenig
Expires: January 9, 2020 Arm Limited Expires: June 8, 2020 Arm Limited
D. Wheeler D. Wheeler
Intel Intel
A. Atyeo A. Atyeo
Intercede Intercede
L. Dapeng L. Dapeng
Alibaba Group Alibaba Group
July 08, 2019 December 06, 2019
Trusted Execution Environment Provisioning (TEEP) Architecture Trusted Execution Environment Provisioning (TEEP) Architecture
draft-ietf-teep-architecture-03 draft-ietf-teep-architecture-04
Abstract Abstract
A Trusted Execution Environment (TEE) is designed to provide a A Trusted Execution Environment (TEE) is an environment that enforces
hardware-isolation mechanism to separate a regular operating system that only authorized code can execute with that environment, and that
from security-sensitive application components. any data used by such code cannot be read or tampered with by any
code outside that environment. This architecture document motivates
This architecture document motivates the design and standardization the design and standardization of a protocol for managing the
of a protocol for managing the lifecycle of trusted applications lifecycle of trusted applications running inside a TEE.
running inside a TEE.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 9, 2020. This Internet-Draft will expire on June 8, 2020.
Copyright Notice Copyright Notice
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Payment . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Authentication . . . . . . . . . . . . . . . . . . . . . 7
4.2. Authentication . . . . . . . . . . . . . . . . . . . . . 9 3.3. Internet of Things . . . . . . . . . . . . . . . . . . . 7
4.3. Internet of Things . . . . . . . . . . . . . . . . . . . 9 3.4. Confidential Cloud Computing . . . . . . . . . . . . . . 8
4.4. Confidential Cloud Computing . . . . . . . . . . . . . . 9 4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. System Components . . . . . . . . . . . . . . . . . . . . 8
5.1. System Components . . . . . . . . . . . . . . . . . . . . 9 4.2. Different Renditions of TEEP Architecture . . . . . . . . 10
5.2. Different Renditions of TEEP Architecture . . . . . . . . 12 4.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 12
5.3. Multiple TAMs and Relationship to TAs . . . . . . . . . . 14 4.4. Untrusted Apps, Trusted Apps, and Personalization Data . 13
5.4. Client Apps, Trusted Apps, and Personalization Data . . . 15 4.5. Examples of Application Delivery Mechanisms in Existing
5.5. Examples of Application Delivery Mechanisms in Existing TEEs . . . . . . . . . . . . . . . . . . . . . . . . . . 14
TEEs . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.6. Entity Relations . . . . . . . . . . . . . . . . . . . . 15
5.6. TEEP Architectural Support for Client App, TA, and 5. Keys and Certificate Types . . . . . . . . . . . . . . . . . 17
Personalization Data Delivery . . . . . . . . . . . . . . 17 5.1. Trust Anchors in TEE . . . . . . . . . . . . . . . . . . 18
5.7. Entity Relations . . . . . . . . . . . . . . . . . . . . 17 5.2. Trust Anchors in TAM . . . . . . . . . . . . . . . . . . 18
5.8. Trust Anchors in TEE . . . . . . . . . . . . . . . . . . 20 5.3. Scalability . . . . . . . . . . . . . . . . . . . . . . . 18
5.9. Trust Anchors in TAM . . . . . . . . . . . . . . . . . . 20 5.4. Message Security . . . . . . . . . . . . . . . . . . . . 19
5.10. Keys and Certificate Types . . . . . . . . . . . . . . . 21 6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.11. Scalability . . . . . . . . . . . . . . . . . . . . . . . 23 6.1. Role of the TEEP Broker . . . . . . . . . . . . . . . . . 20
5.12. Message Security . . . . . . . . . . . . . . . . . . . . 23 6.2. TEEP Broker Implementation Consideration . . . . . . . . 20
5.13. Security Domain . . . . . . . . . . . . . . . . . . . . . 23 6.2.1. TEEP Broker APIs . . . . . . . . . . . . . . . . . . 20
5.14. A Sample Device Setup Flow . . . . . . . . . . . . . . . 23 6.2.2. TEEP Broker Distribution . . . . . . . . . . . . . . 21
6. TEEP Broker . . . . . . . . . . . . . . . . . . . . . . . . . 24 6.2.3. Number of TEEP Brokers . . . . . . . . . . . . . . . 21
6.1. Role of the TEEP Broker . . . . . . . . . . . . . . . . . 25 7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.2. TEEP Broker Implementation Consideration . . . . . . . . 25 7.1. Information Required in TEEP Claims . . . . . . . . . . . 23
6.2.1. TEEP Broker Distribution . . . . . . . . . . . . . . 26 8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 24
6.2.2. Number of TEEP Brokers . . . . . . . . . . . . . . . 26 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
7. Attestation . . . . . . . . . . . . . . . . . . . . . . . . . 26 9.1. TA Trust Check at TEE . . . . . . . . . . . . . . . . . . 24
7.1. Attestation Cryptographic Properties . . . . . . . . . . 28 9.2. One TA Multiple SP Case . . . . . . . . . . . . . . . . . 25
7.2. TEEP Attestation Structure . . . . . . . . . . . . . . . 29 9.3. Broker Trust Model . . . . . . . . . . . . . . . . . . . 25
7.3. TEEP Attestation Claims . . . . . . . . . . . . . . . . . 31 9.4. Data Protection at TAM and TEE . . . . . . . . . . . . . 25
7.4. TEEP Attestation Flow . . . . . . . . . . . . . . . . . . 31 9.5. Compromised CA . . . . . . . . . . . . . . . . . . . . . 25
7.5. Attestation Key Example . . . . . . . . . . . . . . . . . 31 9.6. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 25
7.5.1. Attestation Hierarchy Establishment: Manufacture . . 32 9.7. Certificate Renewal . . . . . . . . . . . . . . . . . . . 26
7.5.2. Attestation Hierarchy Establishment: Device Boot . . 32 9.8. Keeping Secrets from the TAM . . . . . . . . . . . . . . 26
7.5.3. Attestation Hierarchy Establishment: TAM . . . . . . 32 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
8. Algorithm and Attestation Agility . . . . . . . . . . . . . . 32 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
9. Security Considerations . . . . . . . . . . . . . . . . . . . 33 12. Informative References . . . . . . . . . . . . . . . . . . . 26
9.1. TA Trust Check at TEE . . . . . . . . . . . . . . . . . . 33 Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 28
9.2. One TA Multiple SP Case . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
9.3. Broker Trust Model . . . . . . . . . . . . . . . . . . . 34
9.4. Data Protection at TAM and TEE . . . . . . . . . . . . . 34
9.5. Compromised CA . . . . . . . . . . . . . . . . . . . . . 34
9.6. Compromised TAM . . . . . . . . . . . . . . . . . . . . . 34
9.7. Certificate Renewal . . . . . . . . . . . . . . . . . . . 34
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
12.1. Normative References . . . . . . . . . . . . . . . . . . 35
12.2. Informative References . . . . . . . . . . . . . . . . . 35
Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
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 increase with the sources. The potential for attacks further increase with the
complexity of features and applications on devices, and the complexity of features and applications on devices, and the
unintended interactions among those features and applications. The unintended interactions among those features and applications. The
danger of attacks on a system increases as the sensitivity of the danger of attacks on a system increases as the sensitivity of the
applications or data on the device increases. As an example, applications or data on the device increases. As an example,
exposure of emails from a mail client is likely to be of concern to exposure of emails from a mail client is likely to be of concern to
its owner, but a compromise of a banking application raises even its owner, but a compromise of a banking application raises even
greater concerns. greater concerns.
The Trusted Execution Environment (TEE) concept is designed to The Trusted Execution Environment (TEE) concept is designed to
execute applications in a protected environment that separates execute applications in a protected environment that enforces that
applications inside the TEE from the regular operating system and only authorized code can execute with that environment, and that any
from other applications on the device. This separation reduces the data used by such code cannot be read or tampered with by any code
possibility of a successful attack on application components and the outside that environment, including a commodity operating system (if
data contained inside the TEE. Typically, application components are present).
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 a normal application running in the
regular operating system is referred to as an Untrusted Application
(UA).
The TEE uses hardware to enforce protections on the TA and its data, This separation reduces the possibility of a successful attack on
but also presents a more limited set of services to applications application components and the data contained inside the TEE.
inside the TEE than is normally available to UA's running in the Typically, application components are chosen to execute inside a TEE
normal operating system. 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).
The TEE typically uses hardware to enforce protections on the TA and
its data, but also presents a more limited set of services to
applications inside the TEE than is normally available to Untrusted
Applications.
But not all TEEs are the same, and different vendors may have But not all TEEs are the same, and different vendors may have
different implementations of TEEs with different security properties, different implementations of TEEs with different security properties,
different features, and different control mechanisms to operate on different features, and different control mechanisms to operate on
TAs. Some vendors may themselves market multiple different TEEs with TAs. Some vendors may themselves market multiple different TEEs with
different properties attuned to different markets. A device vendor different properties attuned to different markets. A device vendor
may integrate one or more TEEs into their devices depending on market may integrate one or more TEEs into their devices depending on market
needs. needs.
To simplify the life of developers and service providers interacting To simplify the life of developers and service providers interacting
with TAs in a TEE, an interoperable protocol for managing TAs running with TAs in a TEE, an interoperable protocol for managing TAs running
in different TEEs of various devices is needed. In this TEE in different TEEs of various devices is needed. In this TEE
ecosystem, there often arises a need for an external trusted party to ecosystem, there often arises a need for an external trusted party to
verify the identity, claims, and rights of Service Providers(SP), verify the identity, claims, and rights of Service Providers (SP),
devices, and their TEEs. This trusted third party is the Trusted devices, and their TEEs. This trusted third party is the Trusted
Application Manager (TAM). Application Manager (TAM).
This protocol addresses the following problems: The Trusted Execution Provisioning (TEEP) protocol addresses the
following problems:
- A Service Provider (SP) intending to provide services through a TA - A Service Provider (SP) intending to provide services through a TA
to users of a device needs to determine security-relevant to users of a device needs to determine security-relevant
information of a device before provisioning their TA to the TEE information of a device before provisioning their TA to the TEE
within the device. Examples include the verification of the within the device. An example is the verification of the type of
device 'root of trust' and the type of TEE included in a device. TEE included in a device.
- A TEE in a device needs to determine whether a Service Provider - 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 (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. manage TAs in the TEE, and what TAs the SP is permitted to manage.
- The parties involved in the protocol must be able to attest that a - The parties involved in the protocol must be able to attest that a
TEE is genuine and capable of providing the security protections TEE is genuine and capable of providing the security protections
required by a particular TA. required by a particular TA.
- A Service Provider (SP) must be able to determine if a TA exists - A Service Provider (SP) must be able to determine if a TA exists
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has expired, or a payment by the user has not been completed or has expired, or a payment by the user has not been completed or
has been rescinded. has been rescinded.
- A Service Provider (SP) must be able to define the relationship - A Service Provider (SP) must be able to define the relationship
between cooperating TAs under the SP's control, and specify between cooperating TAs under the SP'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 key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The following terms are used: The following terms are used:
- Client Application: An application running in a Rich Execution - Untrusted Application: An application running in a Rich Execution
Environment, such as an Android, Windows, or iOS application. We Environment, such as an Android, Windows, or iOS application.
sometimes refer to this as the 'Client App'.
- Device: A physical piece of hardware that hosts a TEE along with a - Trusted Application Manager (TAM): An entity that manages Trusted
Rich Execution Environment. A Device contains a default list of Applications (TAs) running in different TEEs of various devices.
Trust Anchors that identify entities (e.g., TAMs) that are trusted
by the Device. This list is normally set by the Device - Device: A physical piece of hardware that hosts one or more TEEs,
Manufacturer, and may be governed by the Device's network carrier. often along with a Rich Execution Environment. A Device contains
The list of Trust Anchors is normally modifiable by the Device's a default list of Trust Anchors that identify entities (e.g.,
owner or Device Administrator. However the Device manufacturer TAMs) that are trusted by the Device. This list is normally set
and network carrier may restrict some modifications, for example, by the Device Manufacturer, and may be governed by the Device's
by not allowing the manufacturer or carrier's Trust Anchor to be network carrier. The list of Trust Anchors is normally modifiable
removed or disabled. 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
Anchor to be removed or disabled.
- 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 the TEE. This environment and and hypervisors; it is outside of any TEE. This environment and
applications running on it are considered un-trusted. applications running on it are considered untrusted.
- Service Provider (SP): An entity that wishes to provide a service - Service Provider (SP): An entity that wishes to provide a service
on Devices that requires the use of one or more Trusted on Devices that requires the use of one or more Trusted
Applications. A Service Provider requires the help of a TAM in Applications. A Service Provider requires the help of a TAM in
order to provision the Trusted Applications to remote devices. order to provision the Trusted Applications to remote devices.
- 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). Relates to allowing children to use their tablet or laptop). Other devices
Device Owner and Device Administrator. 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. It is common - Device Owner: A device is always owned by someone. In some cases,
for the (primary) device user to also own the device, making the it is common for the (primary) device user to also own the device,
device user/owner also the device administrator. In enterprise making the device user/owner also the device administrator. In
environments it is more common for the enterprise to own the enterprise environments it is more common for the enterprise to
device, and device users have no or limited administration rights. own the device, and any device user has no or limited
In this case, the enterprise appoints a device administrator that administration rights. In this case, the enterprise appoints a
is not the device owner. device administrator that is not the device owner.
- Device Administrator (DA): An entity that is responsible for - Device Administrator (DA): 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 applications and TAs, approve or reject Trust Anchors, and remove applications and TAs, approve or reject Trust Anchors, and
approve or reject Service Providers, among possibly other approve or reject Service Providers, among possibly other
privileges on the Device. A Device Administrator can manage the privileges on the Device. A Device Administrator can manage the
list of allowed TAMs by modifying the list of Trust Anchors on the list of allowed TAMs by modifying the list of Trust Anchors on the
Device. Although a Device Administrator may have privileges and Device. Although a Device Administrator may have privileges and
Device-specific controls to locally administer a device, the Device-specific controls to locally administer a device, the
Device Administrator may choose to remotely administrate a device Device Administrator may choose to remotely administrate a device
through a TAM. through a TAM.
- Trust Anchor: A public key in a device whose corresponding private - Trust Anchor: As defined in [RFC6024] and
key is held by an entity implicitly trusted by the device. The [I-D.ietf-suit-manifest], "A trust anchor represents an
Trust Anchor may be a certificate or it may be a raw public key authoritative entity via a public key and associated data. The
along with additional data if necessary such as its public key public key is used to verify digital signatures, and the
algorithm and parameters. The Trust Anchor is normally stored in associated data is used to constrain the types of information for
a location that resists unauthorized modification, insertion, or which the trust anchor is authoritative." The Trust Anchor may be
replacement. The digital fingerprint of a Trust Anchor may be a certificate or it may be a raw public key along with additional
stored along with the Trust Anchor certificate or public key. A data if necessary such as its public key algorithm and parameters.
device can use the fingerprint to uniquely identify a Trust
Anchor. The Trust Anchor private key owner can sign certificates - Trust Anchor Store: As defined in [RFC6024], "A trust anchor store
of other public keys, which conveys trust about those keys to the is a set of one or more trust anchors stored in a device. A
device. A certificate signed by the Trust Anchor communicates device may have more than one trust anchor store, each of which
that the private key holder of the signed certificate is trusted may be used by one or more applications." As noted in
by the Trust Anchor holder, and can therefore be trusted by the [I-D.ietf-suit-manifest], a trust anchor store must resist
device. Trust Anchors in a device may be updated by an authorized modification against unauthorized insertion, deletion, and
party when a Trust Anchor should be deprecated or a new Trust modification.
Anchor should be added.
- Trusted Application (TA): An application component that runs in a - Trusted Application (TA): An application component that runs in a
TEE. TEE.
- Trusted Execution Environment (TEE): An execution environment that - Trusted Execution Environment (TEE): An execution environment that
runs alongside of, but is isolated from, an REE. A TEE has enforces that only authorized code can execute within the TEE, and
security capabilities and meets certain security-related data used by that code cannot be read or tampered with by code
requirements. It protects TEE assets from general software outside the TEE. A TEE also generally has a device unique
attacks, defines rigid safeguards as to data and functions that a credential that cannot be cloned. There are multiple technologies
program can access, and resists a set of defined threats. It that can be used to implement a TEE, and the level of security
should have at least the following three properties: achieved varies accordingly. In addition, TEEs typically use an
isolation mechanism between Trusted Applications to ensure that
(a) A device unique credential that cannot be cloned; one TA cannot read, modify or delete the data and code of another
TA.
(b) Assurance that only authorized code can run in the TEE;
(c) Memory that cannot be read by code outside the TEE.
There are multiple technologies that can be used to implement a
TEE, and the level of security achieved varies accordingly.
- Root-of-Trust (RoT): A hardware or software component in a device
that is inherently trusted to perform a certain security-critical
function. A RoT should be secure by design, small, and protected
by hardware against modification or interference. Examples of
RoTs include software/firmware measurement and verification using
a Trust Anchor (RoT for Verification), provide signed assertions
using a protected attestation key (RoT for Reporting), or protect
the storage and/or use of cryptographic keys (RoT for Storage).
Other RoTs are possible, including RoT for Integrity, and RoT for
Measurement. Reference: NIST SP800-164 (Draft).
- Trusted Firmware (TFW): A firmware in a device that can be
verified with a Trust Anchor by RoT for Verification.
- Bootloader key: This symmetric key is protected by
electronic fuse (eFUSE) technology. In this context it is used to
decrypt a
TFW private key, which belongs to a device-unique private/public
key pair. Not every device is equipped with a bootloader key.
This document uses the following abbreviations:
- CA: Certificate Authority
- REE: Rich Execution Environment
- RoT: Root of Trust
- SD: Security Domain
- SP: Service Provider
- TA: Trusted Application
- TAM: Trusted Application Manager
- TEE: Trusted Execution Environment
- TFW: Trusted Firmware
3. Assumptions
This specification assumes that an applicable device is equipped with
one or more TEEs and each TEE is pre-provisioned with a device-unique
public/private key pair, which is securely stored.
A TEE uses an isolation mechanism between Trusted Applications to
ensure that one TA cannot read, modify or delete the data and code of
another TA.
4. Use Cases 3. Use Cases
4.1. Payment 3.1. Payment
A payment application in a mobile device requires high security and A payment application in a mobile device requires high security and
trust about the hosting device. Payments initiated from a mobile trust about the hosting device. Payments initiated from a mobile
device can use a Trusted Application to provide strong identification device can use a Trusted Application to provide strong identification
and proof of transaction. and 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 authentication. application can use such information for authentication.
A secure user interface (UI) may be used in a mobile device to A secure 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 application implementation often relies on a TEE for user Such an application implementation often relies on a TEE for user
input protection. input protection.
4.2. Authentication 3.2. Authentication
For better security of authentication, a device may store its For better security of authentication, a device may store its
sensitive authentication keys inside a TEE, providing hardware- sensitive authentication keys inside a TEE, providing TEE-protected
protected security key strength and trusted code execution. security key strength and trusted code execution.
4.3. Internet of Things 3.3. Internet of Things
The Internet of Things (IoT) has been posing threats to networks and The Internet of Things (IoT) has been posing threats to networks and
national infrastructures because of existing weak security in national infrastructures because of existing weak security in
devices. It is very desirable that IoT devices can prevent malware devices. It is very desirable that IoT devices can prevent malware
from manipulating actuators (e.g., unlocking a door), or stealing or from manipulating actuators (e.g., unlocking a door), or stealing or
modifying sensitive data such as authentication credentials in the modifying sensitive data such as authentication credentials in the
device. A TEE can be the best way to implement such IoT security device. A TEE can be the best way to implement such IoT security
functions. functions.
TEEs could be used to store variety of sensitive data for IoT TEEs could be used to store variety of sensitive data for IoT
devices. For example, a TEE could be used in smart door locks to devices. For example, a TEE could be used in smart door locks to
store a user's biometric information for identification, and for store a user's biometric information for identification, and for
protecting access the locking mechanism. protecting access the locking mechanism.
4.4. Confidential Cloud Computing 3.4. Confidential Cloud Computing
A tenant can store sensitive data in a TEE in a 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 server such that only the tenant can access the data, preventing the
cloud hosting provider from accessing the data. A tenant can run TAs cloud hosting provider from accessing the data. A tenant can run TAs
inside a server TEE for secure operation and enhanced data security. inside a server TEE for secure operation and enhanced data security.
This provides benefits not only to tenants with better 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 provider for reduced liability and
increased cloud adoption. increased cloud adoption.
5. Architecture 4. Architecture
5.1. System Components 4.1. System Components
The following are the main components in the system. Full The following are the main components in the system. Full
descriptions of components not previously defined are provided below. descriptions of components not previously defined are provided below.
Interactions of all components are further explained in the following Interactions of all components are further explained in the following
paragraphs. paragraphs.
+-------------------------------------------+ +-------------------------------------------+
| Device | | Device |
| +--------+ | Service Provider | +--------+ | Service Provider
| +-------------+ | |----------+ | | +-------------+ | |----------+ |
skipping to change at page 10, line 33 skipping to change at page 9, line 7
| +-------+ | | +-------+ |
+-------------------------------------------+ +-------------------------------------------+
Figure 1: Notional Architecture of TEEP Figure 1: Notional Architecture of TEEP
- Service Providers (SP) and Device Administrators (DA) utilize the - Service Providers (SP) and Device Administrators (DA) utilize the
services of a TAM to manage TAs on Devices. SPs do not directly 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 interact with devices. DAs may elect to use a TAM for remote
administration of TAs instead of managing each device directly. administration of TAs instead of managing each device directly.
- TAM: A TAM is responsible for performing lifecycle management - Trusted Application Manager (TAM): A TAM is responsible for
activity on TA's on behalf of Service Providers and Device performing lifecycle management activity on TA's on behalf of
Administrators. This includes creation and deletion of TA's, and Service Providers and Device Administrators. This includes
may include, for example, over-the-air updates to keep an SP's TAs creation and deletion of TA's, and may include, for example, over-
up-to-date and clean up when a version should be removed. TAMs the-air updates to keep an SP's TAs up-to-date and clean up when a
may provide services that make it easier for SPs or DAs to use the version should be removed. TAMs may provide services that make it
TAM's service to manage multiple devices, although that is not easier for SPs or DAs to use the TAM's service to manage multiple
required of a TAM. devices, although that is not required of a TAM.
The TAM performs its management of TA's through an interaction The TAM performs its management of TA's through an interaction
with a Device's TEEP Broker. As shown in #notionalarch, the TAM with a Device's TEEP Broker. As shown in Figure 1, the TAM cannot
cannot directly contact a Device, but must wait for a the TEEP directly contact a Device, but must wait for the TEEP Broker to
Broker or a Client Application to contact the TAM requesting a contact the TAM requesting a particular service. This
particular service. This architecture is intentional in order to architecture is intentional in order to accommodate network and
accommodate network and application firewalls that normally application firewalls that normally protect user and enterprise
protect user and enterprise devices from arbitrary connections devices from arbitrary connections from external network entities.
from external network entities.
A TAM may be publicly available for use by many SPs, or a TAM may 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. be private, and accessible by only one or a limited number of SPs.
It is expected that manufacturers and carriers will run their own It is expected that manufacturers and carriers will run their own
private TAM. Another example of a private TAM is a TAM running as private TAM. Another example of a private TAM is a TAM running as
a Software-as-a-Service (SaaS) within an SP. a Software-as-a-Service (SaaS) within an SP.
A SP or Device Administrator chooses a particular TAM based on 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 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 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 Trust Anchor in the Device. A SP or Device Administrator may run
their own TAM, however the Devices they wish to manage must their own TAM, however the Devices they wish to manage must
include this TAM's pubic key in the Trust Anchor list. include this TAM's pubic key in the Trust Anchor list.
skipping to change at page 11, line 32 skipping to change at page 10, line 5
list on all their devices, overcoming this limitation. list on all their devices, overcoming this limitation.
Any entity is free to operate a TAM. For a TAM to be successful, Any entity is free to operate a TAM. For a TAM to be successful,
it must have its public key or certificate installed in Devices it must have its public key or certificate installed in Devices
Trust Anchor list. A TAM may set up a relationship with device Trust Anchor list. A TAM may set up a relationship with device
manufacturers or carriers to have them install the TAM's keys in manufacturers or carriers to have them install the TAM's keys in
their device's Trust Anchor list. Alternatively, a TAM may their device's Trust Anchor list. Alternatively, a TAM may
publish its certificate and allow Device Administrators to install publish its certificate and allow Device Administrators to install
the TAM's certificate in their devices as an after-market-action. the TAM's certificate in their devices as an after-market-action.
- TEEP Broker: The TEEP Broker is an application running in a Rich - TEEP Broker: The TEEP Broker is an application component running
Execution Environment (REE) that enables the message protocol in a Rich Execution Environment (REE) that enables the message
exchange between a TAM and a TEE in a device. The TEEP Broker protocol exchange between a TAM and a TEE in a device. The TEEP
does not process messages on behalf of a TEE, but merely is Broker does not process messages on behalf of a TEE, but merely is
responsible for relaying messages from the TAM to the TEE, and for responsible for relaying messages from the TAM to the TEE, and for
returning the TEE's responses to the TAM. returning the TEE's responses to the TAM.
A Client Application is expected to communicate with a TAM to
request TAs that it needs to use. The Client Application needs to
pass the messages from the TAM to TEEs in the device. This calls
for a component in the REE that Client Applications can use to
pass messages to TEEs. The TEEP Broker is thus an application in
the REE or software library that can relay messages from a Client
Application to a TEE in the device. A device usually comes with
only one active TEE. A TEE may provide such a Broker to the
device manufacturer to be bundled in devices. Such a TEE must
also include a Broker counterpart, namely, a TEEP Agent inside the
TEE, to parse TAM messages sent through the Broker. A TEEP Broker
is generally acting as a dummy relaying box with just the TEE
interacting capability; it doesn't need and shouldn't parse
protocol messages.
- TEEP Agent: the TEEP Agent is a processing module running inside a - TEEP Agent: the TEEP Agent is a processing module running inside a
TEE that receives TAM requests that are relayed via a TEEP Broker 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 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 or forward requests to other processing modules in a TEE, which is
up to a TEE provider's implementation. A response message up to a TEE provider's implementation. A response message
corresponding to a TAM request is sent by a TEEP Agent back to a corresponding to a TAM request is sent by a TEEP Agent back to a
TEEP Broker. TEEP Broker.
- Certification Authority (CA): Certificate-based credentials used - Certification Authority (CA): Certificate-based credentials used
for authenticating a device, a TAM and an SP. A device embeds a for authenticating a device, a TAM and an SP. A device embeds a
list of root certificates (Trust Anchors), from trusted CAs that a list of root certificates (Trust Anchors), from trusted CAs that a
TAM will be validated against. A TAM will remotely attest a TAM will be validated against. A TAM will remotely attest a
device by checking whether a device comes with a certificate from 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; 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 different CAs can be chosen by each TAM, and different device CAs
can be used by different device manufacturers. can be used by different device manufacturers.
5.2. Different Renditions of TEEP Architecture 4.2. Different Renditions of TEEP Architecture
There is nothing prohibiting a device from implementing multiple There is nothing prohibiting a device from implementing multiple
TEEs. In addition, some TEEs (for example, SGX) present themselves TEEs. In addition, some TEEs (for example, SGX) present themselves
as separate containers within memory without a controlling manager as separate containers within memory without a controlling manager
within the TEE. In these cases, the rich operating system hosts within the TEE. In these cases, the Rich Execution Environment hosts
multiple TEEP brokers, where each broker manages a particular TEE or multiple TEEP brokers, where each Broker manages a particular TEE or
set of TEEs. Enumeration and access to the appropriate broker is up set of TEEs. Enumeration and access to the appropriate TEEP Broker
to the rich OS and the applications. Verification that the correct is up to the Rich Execution Environment and the Untrusted
TA has been reached then becomes a matter of properly verifying TA Applications. Verification that the correct TA has been reached then
attestations, which are unforgeable. The multiple TEE approach is becomes a matter of properly verifying TA attestations, which are
shown in the diagram below. For brevity, TEEP Broker 2 is shown unforgeable. The multiple TEE approach is shown in the diagram
interacting with only one TAM and UA, but no such limitation is below. For brevity, TEEP Broker 2 is shown interacting with only one
intended to be implied in the architecture. TAM and UA, but no such limitation is intended to be implied in the
architecture.
+-------------------------------------------+ +-------------------------------------------+
| Device | | Device |
| +--------+ | Service Provider | +--------+ | Service Provider
| | |----------+ | | | |----------+ |
| +-------------+ | TEEP |---------+| | | +-------------+ | TEEP |---------+| |
| | TEE-1 | +---| Broker | | || +--------+ | | | TEE-1 | +---| Broker | | || +--------+ |
| | | | | 1 |<---+ | |+-->| |<-+ | | | | | 1 |<---+ | |+-->| |<-+
| | +-------+ | | | | | | | | | | | +-------+ | | | | | | | | |
| | | TEEP | | | | | | | | | | | | | TEEP | | | | | | | | | |
skipping to change at page 13, line 31 skipping to change at page 11, line 31
| | | +---+ +---+ | | | | | | TAM-2 | | | | | +---+ +---+ | | | | | | TAM-2 | |
| | | | | +-------+ | | | +--------+ | | | | | | +-------+ | | | +--------+ |
| | +-------------+ +-----| App-2 |--+ | | ^ | | | +-------------+ +-----| App-2 |--+ | | ^ |
| | +-------+ | | | | Device | | +-------+ | | | | Device
| +--------------------| App-1 | | | | | Administrator | +--------------------| App-1 | | | | | Administrator
| +------| | | | | | | +------| | | | | |
| +-----------|-+ | |---+ | | | | +-----------|-+ | |---+ | | |
| | TEE-2 | | | |--------+ | | | | TEE-2 | | | |--------+ | |
| | +------+ | | | |------+ | | | | +------+ | | | |------+ | |
| | | TEEP | | | +-------+ | | | | | | TEEP | | | +-------+ | | |
| | | Agent|<-----+ | | | | | | Agent|<-----+ | | |
| | | 2 | | | | | | | | | | 2 | | | | | | |
| | +------+ | | | | | | | | +------+ | | | | | |
| | | | | | | | | | | | | | | |
| | +---+ | | | | | | | | +---+ | | | | | |
| | |TA3|<----+ | | +----------+ | | | | | |TA3|<----+ | | +----------+ | | |
| | | | | | | TEEP |<--+ | | | | | | | | | TEEP |<--+ | |
| | +---+ | +--| Broker |----------------+ | | +---+ | +--| Broker |----------------+
| | | | 2 | | | | | | 2 | |
| +-------------+ +----------+ | | +-------------+ +----------+ |
| | | |
+-------------------------------------------+ +-------------------------------------------+
Figure 2: Notional Architecture of TEEP wtih multiple TEEs Figure 2: Notional Architecture of TEEP with multiple TEEs
In the diagram above, TEEP Broker 1 controls interactions with the In the diagram above, TEEP Broker 1 controls interactions with the
TA's in TEE-1, and TEEP Broker 2 controls interactions with the TA's 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 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 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 TEE's may be
physically separated, with wholly different resources, there may be physically separated, with wholly different resources, there may be
no need for TEEP Brokers to share information on installed TAs or no need for TEEP Brokers to share information on installed TAs or
resource usage. However, the architecture guarantees that the TAM resource usage. However, the architecture guarantees that the TAM
will receive all the relevant information from the TEEP Broker to will receive all the relevant information from the TEEP Broker to
which it communicates. which it communicates.
5.3. Multiple TAMs and Relationship to TAs 4.3. Multiple TAMs and Relationship to TAs
As shown in Figure 2, the TEEP Broker provides connections from the As shown in Figure 2, the TEEP Broker provides connections from the
TEE and the Client App to one or more TAMs. The selection of which TEE and the Untrusted Application to one or more TAMs. The selection
TAM to communicate with is dependent on information from the Client of which TAM to communicate with is dependent on information from the
App and is directly related to the TA. Untrusted Application and is directly related to the TA.
When a SP offers a service which requires a TA, the SP associates 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, that service with a specific TA. The TA itself is digitally signed,
protecting its integrity, but the signature also links the TA back to 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 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 another party that the SP trusts. The SP selects one or more TAMs
through which to offer their service, and communicates the through which to offer their service, and communicates the
information of the service and the specific client apps and TAs to information of the service and the specific Untrusted Applications
the TAM. and TAs to the TAM.
The SP chooses TAMs based upon the markets into which the TAM can The SP chooses TAMs based upon the markets into which the TAM can
provide access. There may be TAMs that provide services to specific provide access. There may be TAMs that provide services to specific
types of mobile devices, or mobile device operating systems, or types of mobile devices, or mobile device operating systems, or
specific geographical regions or network carriers. A SP may be specific geographical regions or network carriers. A SP may be
motivated to utilize multiple TAMs for its service in order to motivated to utilize multiple TAMs for its service in order to
maximize market penetration and availability on multiple types of 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 service will be available
through multiple TAMs. through multiple TAMs.
When the SP publishes the Client App to an app store or other app When the SP publishes the Untrusted Application to an app store or
repositories, the SP binds the Client App with a manifest that other app repositories, the SP binds the Untrusted Application with a
identifies what TAMs can be contacted for the TA. In some manifest that identifies what TAMs can be contacted for the TA. In
situations, an SP may use only a single TAM - this is likely the case some situations, an SP may use only a single TAM - this is likely the
for enterprise applications or SPs serving a closed community. For case for enterprise applications or SPs serving a closed community.
broad public apps, there will likely be multiple TAMs in the manifest For broad public apps, there will likely be multiple TAMs in the
- one servicing one brand of mobile device and another servicing a manifest - one servicing one brand of mobile device and another
different manufacturer, etc. Because different devices and different servicing a different manufacturer, etc. Because different devices
manufacturers trust different TAMs, the manifest will include and different manufacturers trust different TAMs, the manifest will
different TAMs that support this SP's client app and TA. Multiple include different TAMs that support this SP's Untrusted Application
TAMs allow the SP to provide thier service and this app (and TA) to and TA. Multiple TAMs allow the SP to provide their service and this
multiple different devices. app (and TA) to multiple different devices.
When the TEEP Broker receives a request to contact the TAM for a When a TEEP Broker receives a request from an Untrusted Application
Client App in order to install a TA, a list of TAMs may be provided. to install a TA, a list of TAM URIs may be provided for that TA, and
The TEEP Broker selects a single TAM that is consistent with the list the request is passed to the TEEP Agent. If the TEEP Agent decides
of trusted TAMs (trust anchors) provisioned on the device. For any that the TA needs to be installed, the TEEP Agent selects a single
client app, there should be only a single TAM for the TEEP Broker to TAM URI that is consistent with the list of trusted TAMs provisioned
contact. This is also the case when a Client App uses multiple TAs, on the device invokes the HTTP transport for TEEP to connect to the
or when one TA depends on anther TA in a software dependency (see TAM URI and begins a TEEP protocol exchange. When the TEEP Agent
section TBD). The reason is that the SP should provide each TAM that subsequently receives the TA to install and the TA's manifest
it places in the Client App's manifest all the TAs that the app indicates dependencies on any other trusted components, each
requires. There is no benefit to going to multiple different TAMs, dependency can include a list of TAM URIs for the relevant
and there is no need for a special TAM to be contacted for a specific dependency. If such dependencies exist that are prerequisites to
TA. 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.
[Note: This should always be the case. When a particular device or Separate from the Untrusted Application's manifest, this framework
TEE supports only a special proprietary attestation mechanism, then a relies on the use of the manifest format in [I-D.ietf-suit-manifest]
specific TAM will be needed that supports that attestation scheme. for expressing how to install the TA as well as dependencies on other
The TAM should also support standard atttestation signatures as well. TEE components and versions. That is, dependencies from TAs on other
It is highly unlikely that a set of TAs would use different TEE components can be expressed in a SUIT manifest, including
proprietary attestation mechanisms since a TEE is likley to support dependencies on any other TAs, or trusted OS code (if any), or
only one such proprietary scheme.] trusted firmware. Installation steps can also be expressed in a SUIT
manifest.
[Note: This situation gets more complex in situations where a Client For example, TEE's compliant with Global Platform may have a notion
App expects another application or a device to already have a of a "security domain" (which is a grouping of one or more TAs
specific TA installed. This situation does not occur with SGX, but installed on a device, that can share information within such a
could occur in situations where the secure world maintains an trusted group) that must be created and into which one or more TAs can then
operating system and runs an entire trusted system with multiple TAs be installed. It is thus up to the SUIT manifest to express a
running. This requires more discussion.] dependency on having such a security domain existing or being created
first, as appropriate.
5.4. Client Apps, Trusted Apps, and Personalization Data 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 In TEEP, there is an explicit relationship and dependence between the
client app in the REE and one or more TAs in the TEE, as shown in Untrusted Application in the REE and one or more TAs in the TEE, as
Figure 2. From the perspective of a device user, a client app that 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 uses one or more TA's in a TEE appears no different from any other
untrusted application in the REE. However, the way the client app Untrusted Application in the REE. However, the way the Untrusted
and its corresponding TA's are packaged, delivered, and installed on Application and its corresponding TA's are packaged, delivered, and
the device can vary. The variations depend on whether the client app installed on the device can vary. The variations depend on whether
and TA are bundled together or are provided separately, and this has the Untrusted Application and TA are bundled together or are provided
implications to the management of the TAs in the TEE. In addition to separately, and this has implications to the management of the TAs in
the client app and TA, the TA and/or TEE may require some additional the TEE. In addition to the Untrusted Application and TA, the TA
data to personalize the TA to the service provider or the device and/or TEE may require some additional data to personalize the TA to
user. This personalization data is dependent on the TEE, the TA and the service provider or the device or a user. This personalization
the SP; an example of personalization data might be username and data is dependent on the TEE, the TA and the SP; an example of
password of the device user's account with the SP, or a secret personalization data might be username and password of an account
symmetric key used to by the TA to communicate with the SP. The with the SP, or a secret symmetric key used by the TA to communicate
personalization data must be encrypted to preserve the with the SP. The personalization data must be encrypted to preserve
confidentiality of potentially sensitive data contained within it. the confidentiality of potentially sensitive data contained within
Other than this requirement to support confidentiality, TEEP place no it. Other than this requirement to support confidentiality, TEEP
limitations or requirements on the personalization data. place no limitations or requirements on the personalization data.
There are three possible cases for bundling of the Client App, TA, There are three possible cases for bundling of the Untrusted
and personalization data: Application, TA, and personalization data:
1. The Client App, TA, and personalization data are all bundled 1. The Untrusted Application, TA, and personalization data are all
together in a single package by the SP and provided to the TEEP bundled together in a single package by the SP and provided to
Broker through the TAM. the TEEP Broker through the TAM.
2. The Client App and the TA are bundled together in a single 2. The Untrusted Application and the TA are bundled together in a
binary, which the TAM or a publicly accessible app store single package, which a TAM or a publicly accessible app store
maintains in repository, and the personalization data is maintains, and the personalization data is separately provided by
separately provided by the SP. In this case, the personalization the SP's TAM.
data is collected by the TAM and included in the InstallTA
message to the TEEP Broker.
3. All components are independent. The device user installs the 3. All components are independent. The Untrusted Application is
Client App 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 SP. and the TAM provides the TA and personalization data from the SP.
Delivery of the TA and personalization data may be combined or Delivery of the TA and personalization data may be combined or
separate. separate.
5.5. Examples of Application Delivery Mechanisms in Existing TEEs The TEEP protocol treats the 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
responsible for handling any installation steps that need to be
performed inside the TEE, such as decryption of private TA bianries
or personalization data.
4.5. Examples of Application Delivery Mechanisms in Existing TEEs
In order to better understand these cases, it is helpful to review In order to better understand these cases, it is helpful to review
actual implementations of TEEs and their application delivery actual implementations of TEEs and their application delivery
mechanisms. mechanisms.
In Intel Software Guard Extensions (SGX), the Client App and TA are In Intel Software Guard Extensions (SGX), the Untrusted Application
typically bound into the same binary (Case 2). The TA is compiled and TA are typically bundled into the same package (Case 2). The TA
into the Client App binary using SGX tools, and exists in the binary exists in the package as a shared library (.so or .dll). The
as a shared library (.so or .dll). The Client App loads the TA into Untrusted Application loads the TA into an SGX enclave when the
an SGX enclave when the client needs the TA. This organization makes Untrusted Application needs the TA. This organization makes it easy
it easy to maintain compatibility between the Client App and the TA, to maintain compatibility between the Untrusted Application and the
since they are updated together. It is entirely possible to create a TA, since they are updated together. It is entirely possible to
Client App that loads an external TA into an SGX enclave and use that create an Untrusted Application that loads an external TA into an SGX
TA (Case 3). In this case, the Client App would require a reference enclave and use that TA (Case 3). In this case, the Untrusted
to an external file or download such a file dynamically, place the Application would require a reference to an external file or download
contents of the file into memory, and load that as a TA. Obviously, such a file dynamically, place the contents of the file into memory,
such file or downloaded content must be properly formatted and signed and load that as a TA. Obviously, such file or downloaded content
for it to be accepted by the SGX TEE. In SGX, for Case 2 and Case 3, must be properly formatted and signed for it to be accepted by the
the personalization data is normally loaded into the SGX enclave (the SGX TEE. In SGX, for Case 2 and Case 3, the personalization data is
TA) after the TA has started. Although Case 1 is possible with SGX, normally loaded into the SGX enclave (the TA) after the TA has
there are no instances of this known to be in use at this time, since started. Although Case 1 is possible with SGX, there are no
such a construction would required a special installation program and instances of this known to be in use at this time, since such a
SGX TA to recieve the encrypted binary, decrypt it, separate it into construction would require a special installation program and SGX TA
the three different elements, and then install all three. This to receive the encrypted binary, decrypt it, separate it into the
installation is complex, because the Client App decrypted inside the three different elements, and then install all three. This
TEE must be passed out of the TEE to an installer in the REE which installation is complex, because the Untrusted Application decrypted
would install the Client App; this assumes that the Client App binary inside the TEE must be passed out of the TEE to an installer in the
includes the TA code also, otherwise there is a significant problem REE which would install the Untrusted Application; this assumes that
in getting the SGX encalve code (the TA) from the TEE, through the the Untrusted Application package includes the TA code also, since
installer and into the Client App in a trusted fashion. Finally, the otherwise there is a significant problem in getting the SGX enclave
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 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 encalve-to-enclave manner) to the REE's installation app,
which would pass this data to the installed Client App, which would which would pass this data to the installed Untrusted Application,
in turn send this data to the SGX enclave (TA). This complexity is which would in turn send this data to the SGX enclave (TA). This
due to the fact that each SGX enclave is separate and does not have complexity is due to the fact that each SGX enclave is separate and
direct communication to one another. does not have direct communication to other SGX enclaves.
[NOTE: Need to add an equivalent discussion for an ARM/TZ
implementation]
5.6. TEEP Architectural Support for Client App, TA, and Personalization
Data Delivery
This section defines TEEP support for the three different cases for
delivery of the Client App, TA, and personalization data.
[Note: discussion of format of this single binary, and who/what is In ARM TrustZone based environments, the Untrusted Application and TA
responsible for splitting these things apart, and installing the may or may not be bundled together. This differs from SGX since in
client app into the REE, the TA into the TEE, and the personalization TrustZone the TA lifetime is not inherently tied to a specific
data into the TEE or TA. Obviously the decryption must be done by Untrused Application process lifetime as occurs in SGX. A TA is
the TEE but this may not be supported by all TAs.] 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.
5.7. Entity Relations 4.6. Entity Relations
This architecture leverages asymmetric cryptography to authenticate a This architecture leverages asymmetric cryptography to authenticate a
device to a TAM. Additionally, a TEE in a device authenticates a TAM 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 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 different from one use case to the other. A device administrator may
want to have the capability to control what TAs are allowed. A want to have the capability to control what TAs are allowed. A
device manufacturer enables verification of the TA signers and TAM device manufacturer enables verification of the TA signers and TAM
providers; it may embed a list of default Trust Anchors that the providers; it may embed a list of default Trust Anchors that the
signer of an allowed TA's signer certificate should chain to. A signer of an allowed TA's signer certificate should chain to. A
device administrator may choose to accept a subset of the allowed TAs device administrator may choose to accept a subset of the allowed TAs
via consent or action of downloading. via consent or action of downloading.
PKI CA -- CA CA --
| | |
| | |
| | |
Device | | --- Agent / Client App --- |
SW | | | | |
| | | | |
| | | | |
| -- TEE TAM-------
|
|
FW
Figure 3: Entities
(App Developer) (App Store) (TAM) (Device with TEE) (CAs) (App Developer) (App Store) (TAM) (Device with TEE) (CAs)
| | | |
| --> (Embedded TEE cert) <-- | --> (Embedded TEE cert) <--
| | | |
| <------------------------------ Get an app cert ----- | | <------------------------------ Get an app cert ----- |
| | <-- Get a TAM cert ------ | | | <-- Get a TAM cert ------ |
| |
1. Build two apps: 1. Build two apps:
Client App Untrusted Application
TA TA
| |
| |
Client App -- 2a. --> | ----- 3. Install -------> | Untrusted Application -- 2a. --> | ----- 3. Install -------> |
TA ------- 2b. Supply ------> | 4. Messaging-->| TA ----------------- 2b. Supply ------> | 4. Messaging-->|
| | | | | | | |
Figure 4: Developer Experience Figure 3: Developer Experience
Figure 4 shows an application developer building two applications: 1) Figure 3 shows an application developer building two applications: 1)
a rich Client Application; 2) a TA that provides some security an Untrusted Application; 2) a TA that provides some security
functions to be run inside a TEE. At step 2, the application functions to be run inside a TEE. At step 2, the application
developer uploads the Client Application (2a) to an Application developer uploads the Untrusted Application (2a) to an Application
Store. The Client Application may optionally bundle the TA binary. Store. The Untrusted Application may optionally bundle the TA
Meanwhile, the application developer may provide its TA to a TAM binary. Meanwhile, the application developer may provide its TA to a
provider that will be managing the TA in various devices. 3. A user TAM provider that will be managing the TA in various devices. 3. A
will go to an Application Store to download the Client Application. user will go to an Application Store to download the Untrusted
The Client Application will trigger TA installation by initiating Application. The Untrusted Application will trigger TA installation
communication with a TAM. This is the step 4. The Client by initiating communication with a TAM. This is the step 4. The
Application will get messages from TAM, and interacts with device TEE Untrusted Application will get messages from TAM, and interacts with
via an Agent. device TEE via an Agent.
The following diagram shows a system diagram about the entity
relationships between CAs, TAMs, SPs and devices.
------- Message Protocol -----
| |
| |
-------------------- --------------- ----------
| REE | TEE | | TAM | | SP |
| --- | --- | | --- | | -- |
| | | | | | |
| Client | TEEP | | TA | | TA |
| Apps | Agent | | Mgmt | | |
| | | | | | | |
| | | TAs | | | | |
| TEEP | | | | | |
| Broker | List of | | List of | | |
| | Trusted | | Trusted | | |
| | TAM/SP | | FW/TEE | | |
| | CAs | | CAs | | |
| | | | | | |
| |TEE Key/ | | TAM Key/ | |SP Key/ |
| | Cert | | Cert | | Cert |
| | FW Key/ | | | | |
| | Cert | | | | |
-------------------- --------------- ----------
| | |
| | |
------------- ---------- ---------
| TEE CA | | TAM CA | | SP CA |
------------- ---------- ---------
Figure 5: Keys
In the previous diagram, different CAs can be used for different
types of certificates. Messages are always signed, where the signer
key is the message originator's private key such as that of a TAM,
the private key of trusted firmware (TFW), or a TEE's private key.
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.
It should be noted that network communication capability is generally It should be noted that network communication capability is generally
not available in TAs in today's TEE-powered devices. The networking not available in TAs in today's TEE-powered devices. Trusted
functionality must be delegated to a rich Client Application. Client Applications need to rely on a broker in the REE to interact with a
Applications will need to rely on an agent in the REE to interact TEE for network message exchanges. Consequently, a TAM generally
with a TEE for message exchanges. Consequently, a TAM generally communicates with an Untrusted Application about how it gets messages
communicates with a Client Application about how it gets messages
that originate from a TEE inside a device. Similarly, a TA or TEE that originate from a TEE inside a device. Similarly, a TA or TEE
generally gets messages from a TAM via some Client Application, generally gets messages from a TAM via a TEEP Broker in this protocol
namely, a TEEP Broker in this protocol architecture, not directly architecture, not directly from the network.
from the network.
It is imperative to have an interoperable protocol to communicate It is imperative to have an interoperable protocol to communicate
with different TAMs and different TEEs in different devices. This is with different TAMs and different TEEs in different devices. This is
the role of the Broker, which is a software component that bridges the role of the Broker, which is a software component that bridges
communication between a TAM and a TEE. Furthermore the Broker communication between a TAM and a TEE. Furthermore the Broker
communicates with a Agent inside a TEE that is responsible to process 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 TAM requests. The Broker in REE does not need to know the actual
content of messages except for the TEE routing information. content of messages except for the TEE routing information.
5.8. Trust Anchors in TEE 5. Keys and Certificate Types
Each TEE comes with a trust store that contains a whitelist of Trust
Anchors that are used to validate a TAM's certificate. A TEE will
accept a TAM to create new Security Domains and install new TAs on
behalf of an SP only if the TAM's certificate is chained to one of
the root CA certificates in the TEE's trust store.
A TEE's trust store is typically preloaded at manufacturing time. It
is out of the scope in this document to specify how the trust anchors
should be updated when a new root certificate should be added or
existing one should be updated or removed. A device manufacturer is
expected to provide its TEE trust anchors live update or out-of-band
update to Device Administrators.
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.
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 store of the TEE.
5.9. Trust Anchors in TAM
The Trust Anchor store in a TAM consists of a list of 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.
5.10. Keys and Certificate Types
This architecture leverages the following credentials, which allow This architecture leverages the following credentials, which allow
delivering end-to-end security without relying on any transport delivering end-to-end security between a TAM and a TEEP Agent,
security. without relying on any transport security.
+-------------+----------+--------+-------------------+-------------+
| Key Entity | Location | Issuer | Checked Against | Cardinality |
| Name | | | | |
+-------------+----------+--------+-------------------+-------------+
| 1. TFW key | Device | FW CA | A whitelist of | 1 per |
| pair and | secure | | FW root CA | device |
| certificate | storage | | trusted by TAMs | |
| | | | | |
| 2. TEE key | Device | TEE CA | A whitelist of | 1 per |
| pair and | TEE | under | TEE root CA | device |
| certificate | | a root | trusted by TAMs | |
| | | CA | | |
| | | | | |
| 3. TAM key | TAM | TAM CA | A whitelist of | 1 or |
| pair and | provider | under | TAM root CA | multiple |
| certificate | | a root | embedded in TEE | can be used |
| | | CA | | by a TAM |
| | | | | |
| 4. SP key | SP | SP | A SP uses a TAM. | 1 or |
| pair and | | signer | TA is signed by a | multiple |
| certificate | | CA | SP signer. TEE | can be used |
| | | | delegates trust | by a TAM |
| | | | of TA to TAM. SP | |
| | | | signer is | |
| | | | associated with a | |
| | | | TA as the owner. | |
+-------------+----------+--------+-------------------+-------------+
Figure 6: Key and Certificate Types
1. TFW key pair and certificate: A key pair and certificate for
evidence of trustworthy firmware in a device. This key pair is
optional for TEEP architecture. Some TEE may present its trusted
attributes to a TAM using signed attestation with a TFW key. For
example, a platform that uses a hardware based TEE can have
attestation data signed by a hardware protected TFW key.
o Location: Device secure storage
o Supported Key Type: RSA and ECC
o Issuer: OEM CA
o Checked Against: A whitelist of FW root CA trusted by TAMs
o Cardinality: One per device
2. TEE key pair and certificate: It is used for device attestation
to a remote TAM and SP.
o This key pair is burned into the device by the device
manufacturer. The key pair and its certificate are valid for
the expected lifetime of the device.
o Location: Device TEE
o Supported Key Type: RSA and ECC
o Issuer: A CA that chains to a TEE root CA
o Checked Against: A whitelist of TEE root CAs trusted by TAMs 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.
o Cardinality: One per device 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.
3. TAM key pair and certificate: A TAM provider acquires a Cardinality & Location of
certificate from a CA that a TEE trusts. Location of Private Key Corresponding
Purpose Private Key Signs CA Certs
------------------ ----------- ------------- -------------
Authenticating TEE 1 per TEE TEEP responses TAM
o Location: TAM provider Authenticating TAM 1 per TAM TEEP requests TEEP Agent
o Supported Key Type: RSA and ECC. Code Signing 1 per SP TA binary TEE
o Supported Key Size: RSA 2048-bit, ECC P-256 and P-384. Other Figure 4: Keys
sizes should be anticipated in future.
o Issuer: TAM CA that chains to a root CA 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.
o Checked Against: A whitelist of TAM root CAs embedded in a TEE 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.
o Cardinality: One or multiple can be used by a TAM 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.
4. SP key pair and certificate: An SP uses its own key pair and 5.1. Trust Anchors in TEE
certificate to sign a TA.
o Location: SP 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.
o Supported Key Type: RSA and ECC 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.
o Supported Key Size: RSA 2048-bit, ECC P-256 and P-384. Other Before a TAM can begin operation in the marketplace to support a
sizes should be anticipated in future. 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.
o Issuer: An SP signer CA that chains to a root CA 5.2. Trust Anchors in TAM
o Checked Against: An SP uses a TAM. A TEE trusts an SP by
validating trust against a TAM that the SP uses. A TEE trusts
a TAM to ensure that a TA is trustworthy.
o Cardinality: One or multiple can be used by an SP 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.
5.11. Scalability 5.3. Scalability
This architecture uses a PKI. Trust Anchors exist on the devices to This architecture uses a PKI. Trust Anchors exist on the devices to
enable the TEE to authenticate TAMs, and TAMs use Trust Anchors to enable the TEE to authenticate TAMs, and TAMs use Trust Anchors to
authenticate TEEs. Since a PKI is used, many intermediate CA authenticate TEEs. Since a PKI is used, many intermediate CA
certificates can chain to a root certificate, each of which can issue certificates can chain to a root certificate, each of which can issue
many certificates. This makes the protocol highly scalable. New many certificates. This makes the protocol highly scalable. New
factories that produce TEEs can join the ecosystem. In this case, factories that produce TEEs can join the ecosystem. In this case,
such a factory can get an intermediate CA certificate from one of the such a factory can get an intermediate CA certificate from one of the
existing roots without requiring that TAMs are updated with existing roots without requiring that TAMs are updated with
information about the new device factory. Likewise, new TAMs can information about the new device factory. Likewise, new TAMs can
join the ecosystem, providing they are issued a TAM certificate that join the ecosystem, providing they are issued a TAM certificate that
chains to an existing root whereby existing TEEs will be allowed to chains to an existing root whereby existing TEEs will be allowed to
be personalized by the TAM without requiring changes to the TEE be personalized by the TAM without requiring changes to the TEE
itself. This enables the ecosystem to scale, and avoids the need for 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.
5.12. Message Security 5.4. Message Security
Messages created by a TAM are used to deliver TA management commands Messages created by a TAM are used to deliver TA management commands
to a device, and device attestation and messages created by the to a device, and device attestation and messages created by the
device TEE to respond to TAM messages. device TEE to respond to TAM messages.
These messages are signed end-to-end and are typically encrypted such These messages are signed end-to-end between a TEEP Agent and a TAM,
that only the targeted device TEE or TAM is able to decrypt and view and are typically encrypted such that only the targeted device TEE or
the actual content. TAM is able to decrypt and view the actual content.
5.13. Security Domain
No security domain (SD) is explicitly assumed in a TEE for TA
management. Some TEE, for example, some TEE compliant with Global
Platform (GP), may continue to choose to use SD to organize resource
partition and security boundaries. It is up to a TEE implementation
to decide how a SD is attached to a TA installation, for example, one
SD could be created per TA.
5.14. A Sample Device Setup Flow
Step 1: Prepare Images for Devices
1. [TEE vendor] Deliver TEE Image (CODE Binary) to device OEM
2. [CA] Deliver root CA Whitelist
3. [Soc] Deliver TFW Image
Step 2: Inject Key Pairs and Images to Devices
1. [OEM] Generate TFW Key Pair (May be shared among multiple
devices)
2. [OEM] Flash signed TFW Image and signed TEE Image onto devices
(signed by TFW Key)
Step 3: Set up attestation key pairs in devices
1. [OEM] Flash TFW Public Key and a bootloader key.
2. [TFW/TEE] Generate a unique attestation key pair and get a
certificate for the device.
Step 4: Set up Trust Anchors in devices
1. [TFW/TEE] Store the key and certificate encrypted with the
bootloader key
2. [TEE vendor or OEM] Store trusted CA certificate list into
devices
6. TEEP Broker 6. TEEP Broker
A TEE and TAs do not generally have the capability to communicate to A TEE and TAs often do not have the capability to directly
the outside of the hosting device. For example, GlobalPlatform communicate outside of the hosting device. For example,
[GPTEE] specifies one such architecture. This calls for a software GlobalPlatform [GPTEE] specifies one such architecture. This calls
module in the REE world to handle the network communication. Each for a software module in the REE world to handle network
Client Application in the REE might carry this communication communication with a TAM.
functionality but such functionality must also interact with the TEE
for the message exchange.
The TEE interaction will vary according to different TEEs. In order
for a Client Application to transparently support different TEEs, it
is imperative to have a common interface for a Client Application to
invoke for exchanging messages with TEEs.
A shared module in REE comes to meet this need. A TEEP broker is an A TEEP Broker is an application component running in the REE of the
application running in the REE of the device or an SDK that device or an SDK that facilitates communication between a TAM and a
facilitates communication between a TAM and a TEE. It also provides TEE. It also provides interfaces for Untrusted Applications to query
interfaces for Client Applications to query and trigger TA and trigger TA installation that the application needs to use.
installation that the application needs to use.
It isn't always that a Client Application directly calls such a An Untrusted Application might communicate with the TEEP Broker at
Broker to interact with a TEE. A REE Application Installer might runtime to trigger TA installation itself. Or an Untrusted
carry out TEE and TAM interaction to install all required TAs that a Application might simply have a metadata file that describes the TAs
Client Application depends. A Client Application may have a metadata it depends on and the associated TAM(s) for each TA, and an REE
file that describes the TAs it depends on and the associated TAM that Application Installer can inspect this application metadata file and
each TA installation goes to use. The REE Application Installer can invoke the TEEP Broker to trigger TA installation on behalf of the
inspect the application metadata file and installs TAs on behalf of Untrusted Application without requiring the Untrusted Application to
the Client Application without requiring the Client Application to
run first. run first.
This interface for Client Applications or Application Installers may
be commonly in a form of an OS service call for an REE OS. A Client
Application or an Application Installer interacts with the device TEE
and the TAMs.
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. 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 REE. A TEEP
Broker interacts with a TEEP Agent inside a TEE. Broker interacts with a TEEP Agent inside a TEE.
skipping to change at page 26, line 5 skipping to change at page 20, line 37
6.2. TEEP Broker Implementation Consideration 6.2. TEEP Broker Implementation Consideration
A Provider should consider methods of distribution, scope and A Provider should consider methods of distribution, scope and
concurrency on devices and runtime options when implementing a TEEP concurrency on devices and runtime options when implementing a TEEP
Broker. Several non-exhaustive options are discussed below. Broker. Several non-exhaustive options are discussed below.
Providers are encouraged to take advantage of the latest Providers are encouraged to take advantage of the latest
communication and platform capabilities to offer the best user communication and platform capabilities to offer the best user
experience. experience.
6.2.1. TEEP Broker Distribution 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.
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):
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 The Broker installation is commonly carried out at OEM time. A user
can dynamically download and install a Broker on-demand. can dynamically download and install a Broker on-demand.
6.2.2. Number of TEEP Brokers 6.2.3. Number of TEEP Brokers
There should be generally only one shared TEEP Broker in a device. There should be generally only one shared TEEP Broker in a device.
The device's TEE vendor will most probably supply one Broker. When 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 multiple TEEs are present in a device, one TEEP Broker per TEE may be
used. used.
When only one Broker is used per device, the Broker provider is When only one Broker is used per device, the Broker provider is
responsible to allow multiple TAMs and TEE providers to achieve responsible to allow multiple TAMs and TEE providers to achieve
interoperability. With a standard Broker interface, each TAM can interoperability. With a standard Broker interface, each TAM can
implement its own SDK for its SP Client Applications to work with implement its own SDK for its SP Untrusted Applications to work with
this Broker. this Broker.
Multiple independent Broker providers can be used as long as they Multiple independent Broker providers can be used as long as they
have standard interface to a Client Application or TAM SDK. Only one have standard interface to an Untrusted Application or TAM SDK. Only
Broker is generally expected in a device. one Broker is generally expected in a device.
7. Attestation 7. Attestation
Attestation is the process through which one entity (an attestor) Attestation is the process through which one entity (an Attester)
presents a series of claims to another entity (a verifier), and presents "evidence", in the form of a series of claims, to another
provides sufficient proof that the claims are true. Different entity (a Verifier), and provides sufficient proof that the claims
verifiers may have different standards for attestation proofs and not are true. Different verifiers may have different standards for
all attestations are acceptable to every verifier. TEEP attestations attestation proofs and not all attestations are acceptable to every
are based upon the use of an asymmetric key pair under the control of verifier. A third entity (a Relying Party) can then use "attestation
the TEE to create digital signatures across a well-defined claim set. results", in the form of another series of claims, from a Verifier to
make authorization decisions.
In TEEP, the primary purpose of an attestation is to allow a device In TEEP, as depicted in Figure 5, the primary purpose of an
to prove to TAMs and SPs that a TEE in the device has particular attestation is to allow a device (the Attester) to prove to TAMs (the
properties, was built by a particular manufacturer, or is executing a Relying Parties) that a TEE in the device has particular properties,
particular TA. Other claims are possible; this architecture was built by a particular manufacturer, or is executing a particular
specification does not limit the attestation claims, but defines a TA. Other claims are possible; TEEP does not limit the claims that
minimal set of claims required for TEEP to operate properly. may appear in evidence or attestation results, but defines a minimal
Extensions to these claims are possible, but are not defined in the set of attestation result claims required for TEEP to operate
TEEP specifications. Other standards or groups may define the format properly. Extensions to these claims are possible. Other standards
and semantics of extended claims. The TEEP specification defines the or groups may define the format and semantics of extended claims.
claims format such that these extended claims may be easily included
in a TEEP attestation message. +----------------+
| 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 As of the writing of this specification, device and TEE attestations
have not been standardized across the market. Different devices, have not been standardized across the market. Different devices,
manufacturers, and TEEs support different attestation algorithms and manufacturers, and TEEs support different attestation algorithms and
mechanisms. In order for TEEP to be inclusive, the attestation mechanisms. In order for TEEP to be inclusive, it is agnostic to the
format shall allow for both proprietary attestation signatures, as format of evidence, allowing proprietary or standardized formats to
well as a standardized form of attestation signature. Either form of be used between a TEE and a verifier (which may or may not be
attestation signature may be applied to a set of TEEP claims, and colocated in the TAM). However, it should be recognized that not all
both forms of attestation shall be considered conformant with TEEP. verifiers may be able to process all proprietary forms of attestation
However, it should be recognized that not all TAMs or SPs may be able evidence. Similarly, the TEEP protocol is agnostic as to the format
to process all proprietary forms of attestations. All TAMs and SPs of attestation results, and the protocol (if any) used between the
MUST be able to process the TEEP standard attestation format and TAM and a verifier, as long as they convey at least the required set
attached signature. of claims in some format.
The attestation formats and mechanisms described and mandated by TEEP
shall convey a particular set of cryptographic properties based on
minimal assumptions. The cryptographic properties are conveyed by
the attestation; however the assumptions are not conveyed within the
attestation itself.
The assumptions which may apply to an attestation have to do with the The assumptions which may apply to an attestation have to do with the
quality of the attestation and the quality and security provided by quality of the attestation and the quality and security provided by
the TEE, the device, the manufacturer, or others involved in the the TEE, the device, the manufacturer, or others involved in the
device or TEE ecosystem. Some of the assumptions that might apply to device or TEE ecosystem. Some of the assumptions that might apply to
an attestations include (this may not be a comprehensive list): an attestations include (this may not be a comprehensive list):
- Assumptions regarding the security measures a manufacturer takes - Assumptions regarding the security measures a manufacturer takes
when provisioning keys into devices/TEEs; when provisioning keys into devices/TEEs;
skipping to change at page 27, line 47 skipping to change at page 23, line 18
- Assumptions regarding the limitations of use applied to TEE - Assumptions regarding the limitations of use applied to TEE
Attestation keys; Attestation keys;
- Assumptions regarding the processes in place to discover or detect - Assumptions regarding the processes in place to discover or detect
TEE breeches; and TEE breeches; and
- Assumptions regarding the revocation and recovery process of TEE - Assumptions regarding the revocation and recovery process of TEE
attestation keys. attestation keys.
TAMs and SPs must be comfortable with the assumptions that are TAMs must be comfortable with the assumptions that are inherently
inherently part of any attestation they accept. Alternatively, any part of any attestation result they accept. Alternatively, any TAM
TAM or SP may choose not to accept an attestation generated from a may choose not to accept an attestation result generated using
particular manufacturer or device's TEE based on the inherent evidence from a particular manufacturer or device's TEE based on the
assumptions. The choice and policy decisions are left up to the inherent assumptions. The choice and policy decisions are left up to
particular TAM/SP. the particular TAM.
Some TAMs or SPs may require additional claims in order to properly Some TAMs may require additional claims in order to properly
authorize a device or TEE. These additional claims may help clear up authorize a device or TEE. These additional claims may help clear up
any assumptions for which the TAM/SP wants to alleviate. The any assumptions for which the TAM wants to alleviate. The specific
specific format for these additional claims are outside the scope of format for these additional claims are outside the scope of this
this specification, but the OTrP protocol SHALL allow these specification, but the TEEP protocol allows these additional claims
additional claims to be included in the attestation messages. to be included in the attestation messages.
The following sub-sections define the cryptographic properties
conveyed by the TEEP attestation, the basic set of TEEP claims
required in a TEEP attestation, the TEEP attestation flow between the
TAM the device TEE, and some implementation examples of how an
attestation key may be realized in a real TEEP device.
7.1. Attestation Cryptographic Properties
The attestation constructed by TEEP must convey certain cryptographic
properties from the attestor to the verifier; in the case of TEEP,
the attestation must convey properties from the device to the TAM
and/or SP. The properties required by TEEP include:
- Non-repudiation, Unique Proof of Source - the cryptographic
digital signature across the attestation, and optionally along
with information in the attestion itself SHALL uniquely identify a
specific TEE in a specific device.
- Integrity of claims - the cryptographic digital signature across
the attestation SHALL cover the entire attestation including all
meta data and all the claims in the attestation, ensuring that the
attestation has not be modified since the TEE signed the
attestation.
Standard public key algorithms such as RSA and ECDSA digital
signatures convey these properties. Group public key algorithms such
as EPID can also convey these properties, if the attestation includes
a unique device identifier and an identifier for the TEE. Other
cryptographic operations used in other attestation schemes may also
convey these properties.
The TEEP standard attestation format SHALL use one of the following
digital signature formats:
- RSA-2048 with SHA-256 or SHA-384 in RSASSA-PKCS1-v1_5 or PSS
format
- RSA-3072 with SHA-256 or SHA-384 in RSASSA-PKCS1-v1_5 or PSS
format
- ECDSA-256 using NIST P256 curve using SHA-256
- ECDSA-384 using NIST P384 curve using SHA-384
- HashEdDSA using Ed25519 with SHA-512 (Ed25519ph in RFC8032) and
context="TEEP Attestation"
- EdDSA using Ed448 with SHAK256 (Ed448ph in RFC8032) and
context="TEEP Attestation"
All TAMs and SPs MUST be able to accept attestations using these
algorithms, contingent on their acceptance of the assumptions implied
by the attestations.
7.2. TEEP Attestation Structure
For a TEEP attestation to be useful, it must contain an information
set allowing the TAM and/or SP to assess the attestation and make a
related security policy decision. The structure of the TEEP
attestation is shown in the diagram below.
+------(Signed By)-----------+
| |
/--------------------------\ V
+---------------+-------------+--------------------------+
| Attestation | The | The |
| Header | Claims | Attestation Signature(s) |
+---------------+-------------+--------------------------+
|
|
+------------+--(Contains)------+-----------------+--------------+
| | | | |
V V V V V
+-------------+ +-------------+ +----------+ +-----------------+ +------------+
| Device | | TEE | | | | Action or | | Additional |
| Identifying | | Identifying | | Liveness | | Operation | | or optional|
| Info | | Info | | Proof | | Specific claims | | Claims |
+-------------+ +-------------+ +----------+ +-----------------+ +------------+
Figure 7: Structure of TEEP Attestation
The Attestation Header SHALL identify the "Attestation Type" and the
"Attestation Signature Type" along with an "Attestation Format
Version Number." The "Attestation Type" identifies the minimal set
of claims that MUST be included in the attestation; this is an
identifier for a profile that defines the claims that should be
included in the attestation as part of the "Action or Operation
Specific Claims." The "Attestation Signature Type" identifies the
type of attestation signature that is attached. The type of
attestation signature SHALL be one of the standard signatures types
identified by an IANA number, a proprietary signature type identified
by an IANA number, or the generic "Proprietary Signature" with an
accompanying proprietary identifier. Not all TAMs may be able to
process proprietary signatures.
The claims in the attestation are set of mandatory and optional 7.1. Information Required in TEEP Claims
claims. The claims themselves SHALL be defined in an attestation
claims dictionary. See the next section on TEEP Attestation Claims.
Claims are grouped in profiles under an identifier (Attestation
Type), however all attestations require a minimal set of claims which
includes:
- Device Identifying Info: TEEP attestations must uniquely identify - Device Identifying Info: TEEP attestations must uniquely identify
a device to the TAM and SP. This identifier allows the TAM/SP to a device to the TAM and SP. This identifier allows the TAM to
provide services unique to the device, such as managing installed provide services unique to the device, such as managing installed
TAs, and providing subscriptions to services, and locating device- TAs, and providing subscriptions to services, and locating device-
specific keying material to communicate wiht or authenticate the specific keying material to communicate with or authenticate the
device. Additionally, device manufacturer information must be device. Additionally, device manufacturer information must be
provided to provide better universal uniqueness qualities without provided to provide better universal uniqueness qualities without
requiring globally unique identifiers for all devices. requiring globally unique identifiers for all devices.
- TEE Identifying info: The type of TEE that generated this - TEE Identifying info: The type of TEE that generated this
attestation must be identified. Standard TEE types are identified attestation must be identified. Standard TEE types are identified
by an IANA number, but also must include version identification by an IANA number, but also must include version identification
information such as the hardware, firmware, and software version information such as the hardware, firmware, and software version
of the TEE, as applicable by the TEE type. Structure to the of the TEE, as applicable by the TEE type. TEE manufacturer
version number is required.TEE manufacturer information for the information for the TEE is required in order to disambiguate the
TEE is required in order to disambiguate the same TEE type created same TEE type created by different manufacturers and resolve
by different manufacturers and resolve potential assumptions potential assumptions around manufacturer provisioning, keying and
around manufacturer provisioning, keying and support for the TEE. support for the TEE.
- Liveness Proof: a claim that includes liveness information SHALL
be included which may be a large nonce or may be a timestamp and
short nonce.
- Action Specific Claims: Certain attestation types shall include
specific claims. For example an attestation from a specific TA
shall include a measurement, version and signing public key for
the TA.
- Additional Claims: (Optional - May be empty set) A TAM or SP may
require specific additional claims in order to address potential
assumptions, such as the requirement that a device's REE performed
a secure boot, or that the device is not currenlty in a debug or
non-productions state. A TAM may require a device to provide a
device health attestation that may include some claims or
measurements about the REE. These claims are TAM specific.
7.3. TEEP Attestation Claims
TEEP requires a set of attestation claims that provide sufficient
evidence to the TAM and/or SP that the device and its TEE meet
certain minimal requirements. Because attestation formats are not
yet broadly standardized across the industry, standardization work is
currently ongoing, and it is expected that extensions to the
attestation claims will be required as new TEEs and devices are
created, the set of attestation claims required by TEEP SHALL be
defined in an IANA registry. That registry SHALL be defined in the
OTrP protocol with sufficient elements to address basic TEEP claims,
expected new standard claims (for example from
https://www.ietf.org/id/draft-mandyam-eat-01.txt), and proprietary
claim sets.
7.4. TEEP Attestation Flow
Attesations are required in TEEP under the following flows:
- When a TEE responds with device state information (dsi) to the TAM
or SP, including a "GetDeviceState" response, "InstallTA"
response, etc.
- When a new key pair is generated for a TA-to-TAM or TA-to-SP
communication, the keypair must be covered by an attestation,
including "CreateSecurityDomain" response, "UpdateSecurityDomain"
response, etc.
7.5. Attestation Key Example
The attestation hierarchy and seed required for TAM protocol
operation must be built into the device at manufacture. Additional
TEEs can be added post-manufacture using the scheme proposed, but it
is outside of the current scope of this document to detail that.
It should be noted that the attestation scheme described is based on
signatures. The only decryption that may take place is through the
use of a bootloader key.
A boot module generated attestation can be optional where the
starting point of device attestation can be at TEE certificates. A
TAM can define its policies on what kinds of TEE it trusts if TFW
attestation is not included during the TEE attestation.
7.5.1. Attestation Hierarchy Establishment: Manufacture
During manufacture the following steps are required:
1. A device-specific TFW key pair and certificate are burnt into the
device. This key pair will be used for signing operations
performed by the boot module.
2. TEE images are loaded and include a TEE instance-specific key
pair and certificate. The key pair and certificate are included
in the image and covered by the code signing hash.
3. The process for TEE images is repeated for any subordinate TEEs,
which are additional TEEs after the root TEE that some devices
have.
7.5.2. Attestation Hierarchy Establishment: Device Boot
During device boot the following steps are required:
1. The boot module releases the TFW private key by decrypting it
with the bootloader key.
2. The boot module verifies the code-signing signature of the active
TEE and places its TEE public key into a signing buffer, along
with its identifier for later access. For a TEE non-compliant to
this architecture, the boot module leaves the TEE public key
field blank.
3. The boot module signs the signing buffer with the TFW private
key.
4. Each active TEE performs the same operation as the boot module,
building up their own signed buffer containing subordinate TEE
information.
7.5.3. Attestation Hierarchy Establishment: TAM - Liveness Proof: A claim that includes liveness information must be
included, such as a nonce or timestamp.
Before a TAM can begin operation in the marketplace, it must obtain a - Requested Components: A list of zero or more components (TAs or
TAM certificate from a CA that is registered in the trust store of other dependencies needed by a TEE) that are requested by some
devices. In this way, the TEE can check the intermediate and root CA depending app, but which are not currently installed in the TEE.
and verify that it trusts this TAM to perform operations on the TEE.
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 algorithm suite to another over time. This mandatory-to-implement algorithm suite to another over time. This
feature is also known as crypto agility. Protocol evolution is feature is also known as crypto agility. Protocol evolution is
greatly simplified when crypto agility is already considered during greatly simplified when crypto agility is already considered during
the design of the protocol. In the case of the Open Trust Protocol the design of the protocol. In the case of the Trusted Execution
(OTrP) the diverse range of use cases, from trusted app updates for Provisioning (TEEP) Protocol the diverse range of use cases, from
smart phones and tablets to updates of code on higher-end IoT trusted app updates for smart phones and tablets to updates of code
devices, creates the need for different mandatory-to-implement on higher-end IoT devices, creates the need for different mandatory-
algorithms already from the start. to-implement algorithms already from the start.
Crypto agility in the OTrP concerns the use of symmetric as well as Crypto agility in TEEP concerns the use of symmetric as well as
asymmetric algorithms. Symmetric algorithms are used for encryption asymmetric algorithms. Symmetric algorithms are used for encryption
of content whereas the asymmetric algorithms are mostly used for of content whereas the asymmetric algorithms are mostly used for
signing messages. signing messages.
In addition to the use of cryptographic algorithms in OTrP 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.
9. Security Considerations 9. Security Considerations
9.1. TA Trust Check at TEE 9.1. TA Trust Check at TEE
A TA binary is signed by a TA signer certificate. This TA signing 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 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 (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 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 into the system. Delivery of that TA to the TEE is then the
responsibility of the TEE, using the security mechanisms provided by responsibility of the TEE, using the security mechanisms provided by
the protocol. the protocol.
We allow a way for an (untrusted) application to check the We allow a way for an Untrusted Application to check the
trustworthiness of a TA. A TEEP Broker has a function to allow an trustworthiness of a TA. A TEEP Broker has a function to allow an
application to query the information about a TA. application to query the information about a TA.
An application in the Rich O/S may perform verification of the TA by An Untrusted Application may perform verification of the TA by
verifying the signature of the TA. The GetTAInformation function is verifying the signature of the TA. An application can do additional
available to return the TEE supplied TA signer and TAM signer
information to the application. An application can do additional
trust checks on the certificate returned for this TA. It might trust trust checks on the certificate returned for this TA. It might trust
the TAM, or require additional SP signer trust chaining. the TAM, or require additional SP signer trust chaining.
9.2. One TA Multiple SP Case 9.2. One TA Multiple SP Case
A TA for multiple SPs must have a different identifier per SP. They 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 should appear as different TAs when they are installed in the same
device. device.
9.3. Broker Trust Model 9.3. Broker Trust Model
A TEEP Broker could be malware in the vulnerable REE. A Client A TEEP Broker could be malware in the vulnerable REE. An Untrusted
Application will connect its TAM provider for required TA Application will connect its TAM provider for required TA
installation. It gets command messages from the TAM, and passes the installation. It gets command messages from the TAM, and passes the
message to the Broker. message to the Broker.
The architecture enables the TAM to communicate with the device's TEE The architecture enables the TAM to communicate with the device's TEE
to manage TAs. All TAM messages are signed and sensitive data is to manage TAs. All TAM messages are signed and sensitive data is
encrypted such that the TEEP Broker cannot modify or capture encrypted such that the TEEP Broker cannot modify or capture
sensitive data. sensitive data.
9.4. Data Protection at TAM and TEE 9.4. Data Protection at TAM and TEE
The TEE implementation provides protection of data on the device. It The TEE implementation provides protection of data on the device. 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.
9.5. Compromised CA 9.5. Compromised CA
A root CA for TAM certificates might get compromised. Some TEE trust A root CA for TAM certificates might get compromised. Some TEE Trust
anchor update mechanism is expected from device OEMs. A compromised Anchor update mechanism is expected from device OEMs. TEEs are
intermediate CA is covered by OCSP stapling and OCSP validation check responsible for validating certificate revocation about a TAM
in the protocol. A TEE should validate certificate revocation about certificate chain.
a TAM certificate chain.
If the root CA of some TEE device certificates is compromised, these 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 devices might be rejected by a TAM, which is a decision of the TAM
implementation and policy choice. Any intermediate CA for TEE device implementation and policy choice. TAMs are responsible for
certificates SHOULD be validated by TAM with a Certificate Revocation validating any intermediate CA for TEE device certificates.
List (CRL) or Online Certificate Status Protocol (OCSP) method.
9.6. Compromised TAM 9.6. Compromised TAM
The TEE SHOULD use validation of the supplied TAM certificates and Device TEEs are responsible for validating the supplied TAM
OCSP stapled data to validate that the TAM is trustworthy. certificates to determine that the TAM is trustworthy.
Since PKI is used, the integrity of the clock within the TEE
determines the ability of the TEE to reject an expired TAM
certificate, or revoked TAM certificate. Since OCSP stapling
includes signature generation time, certificate validity dates are
compared to the current time.
9.7. Certificate Renewal 9.7. Certificate Renewal
TFW and TEE device certificates are expected to be long lived, longer TEE device certificates are expected to be long lived, longer than
than the lifetime of a device. A TAM certificate usually has a the lifetime of a device. A TAM certificate usually has a moderate
moderate lifetime of 2 to 5 years. A TAM should get renewed or lifetime of 2 to 5 years. A TAM should get renewed or rekeyed
rekeyed certificates. The root CA certificates for a TAM, which are certificates. The root CA certificates for a TAM, which are embedded
embedded into the Trust Anchor store in a device, should have long into the Trust Anchor store in a device, should have long lifetimes
lifetimes that don't require device Trust Anchor update. On the that don't require device Trust Anchor update. On the other hand, it
other hand, it is imperative that OEMs or device providers plan for is imperative that OEMs or device providers plan for support of Trust
support of Trust Anchor update in their shipped devices. 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.
10. IANA Considerations 10. IANA Considerations
This document does not require actions by IANA. This document does not require actions by IANA.
11. Acknowledgements 11. Acknowledgements
The authors thank Dave Thaler for his very thorough review and many Some content of this document is based on text in a previous OTrP
important suggestions. Most content of this document is split from a protocol document [I-D.ietf-teep-opentrustprotocol]. We thank the
previously combined OTrP protocol document former co-authors Nick Cook and Minho Yoo for the initial document
[I-D.ietf-teep-opentrustprotocol]. We thank the former co-authors content, and contributors Brian Witten, Tyler Kim, and Alin Mutu.
Nick Cook and Minho Yoo for the initial document content, and
contributors Brian Witten, Tyler Kim, and Alin Mutu.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References 12. Informative References
[GPTEE] Global Platform, "GlobalPlatform Device Technology: TEE [GPTEE] Global Platform, "GlobalPlatform Device Technology: TEE
System Architecture, v1.1", Global Platform GPD_SPE_009, System Architecture, v1.1", Global Platform 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-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.
[I-D.ietf-teep-opentrustprotocol] [I-D.ietf-teep-opentrustprotocol]
Pei, M., Atyeo, A., Cook, N., Yoo, M., and H. Tschofenig, Pei, M., Atyeo, A., Cook, N., Yoo, M., and H. Tschofenig,
"The Open Trust Protocol (OTrP)", draft-ietf-teep- "The Open Trust Protocol (OTrP)", draft-ietf-teep-
opentrustprotocol-03 (work in progress), May 2019. opentrustprotocol-03 (work in progress), May 2019.
[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 [RFC6024] Reddy, R. and C. Wallace, "Trust Anchor Management
Requirements", RFC 6024, DOI 10.17487/RFC6024, October Requirements", RFC 6024, DOI 10.17487/RFC6024, October
2010, <https://www.rfc-editor.org/info/rfc6024>. 2010, <https://www.rfc-editor.org/info/rfc6024>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms", Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>. <https://www.rfc-editor.org/info/rfc7696>.
Appendix A. History Appendix A. History
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