Arm's Platform Security Architecture (PSA) Attestation Token
draft-tschofenig-rats-psa-token-07
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Hannes Tschofenig , Simon Frost , Mathias Brossard , Adrian L. Shaw , Thomas Fossati | ||
| Last updated | 2021-02-01 | ||
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draft-tschofenig-rats-psa-token-07
RATS H. Tschofenig
Internet-Draft S. Frost
Intended status: Informational M. Brossard
Expires: 5 August 2021 A. Shaw
T. Fossati
Arm Limited
1 February 2021
Arm's Platform Security Architecture (PSA) Attestation Token
draft-tschofenig-rats-psa-token-07
Abstract
The Platform Security Architecture (PSA) is a family of hardware and
firmware security specifications, as well as open-source reference
implementations, to help device makers and chip manufacturers build
best-practice security into products. Devices that are PSA compliant
are able to produce attestation tokens as described in this memo,
which are the basis for a number of different protocols, including
secure provisioning and network access control. This document
specifies the PSA attestation token structure and semantics.
At its core, the CWT (COSE Web Token) format is used and populated
with a set of claims in a way similar to EAT (Entity Attestation
Token). This specification describes what claims are used by PSA
compliant systems.
Note to Readers
Source for this draft and an issue tracker can be found at
https://github.com/thomas-fossati/draft-psa-token
(https://github.com/thomas-fossati/draft-psa-token).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 5 August 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2.1. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 4
3. PSA Claims . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Caller Claims . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Nonce . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.2. Client ID . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Target Identification Claims . . . . . . . . . . . . . . 5
3.2.1. Instance ID . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. Implementation ID . . . . . . . . . . . . . . . . . . 6
3.2.3. Certification Reference . . . . . . . . . . . . . . . 6
3.3. Target State Claims . . . . . . . . . . . . . . . . . . . 6
3.3.1. Security Lifecycle . . . . . . . . . . . . . . . . . 6
3.3.2. Boot Seed . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Software Inventory Claims . . . . . . . . . . . . . . . . 8
3.4.1. Software Components . . . . . . . . . . . . . . . . . 8
3.4.2. No Software Measurements . . . . . . . . . . . . . . 10
3.5. Verification Claims . . . . . . . . . . . . . . . . . . . 11
3.5.1. Verification Service Indicator . . . . . . . . . . . 11
3.5.2. Profile Definition . . . . . . . . . . . . . . . . . 11
4. Token Encoding and Signing . . . . . . . . . . . . . . . . . 11
5. Collated CDDL . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Security and Privacy Considerations . . . . . . . . . . . . . 14
7. Verification . . . . . . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8.1. CBOR Web Token Claims Registration . . . . . . . . . . . 15
8.1.1. Nonce Claim . . . . . . . . . . . . . . . . . . . . . 15
8.1.2. Client ID Claim . . . . . . . . . . . . . . . . . . . 16
8.1.3. Instance ID Claim . . . . . . . . . . . . . . . . . . 16
8.1.4. Implementation ID Claim . . . . . . . . . . . . . . . 16
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8.1.5. Certification Reference Claim . . . . . . . . . . . . 17
8.1.6. Security Lifecycle Claim . . . . . . . . . . . . . . 17
8.1.7. Boot Seed Claim . . . . . . . . . . . . . . . . . . . 17
8.1.8. Software Components Claim . . . . . . . . . . . . . . 18
8.1.9. No Software Measurements Claim . . . . . . . . . . . 18
8.1.10. Verification Service Indicator Claim . . . . . . . . 18
8.1.11. Profile Definition Claim . . . . . . . . . . . . . . 19
8.2. Media Type Registration . . . . . . . . . . . . . . . . . 19
8.3. CoAP Content-Formats Registration . . . . . . . . . . . . 20
8.3.1. Registry Contents . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Reference Implementation . . . . . . . . . . . . . . 22
Appendix B. Example . . . . . . . . . . . . . . . . . . . . . . 23
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
Trusted execution environments are now present in many devices, which
provide a safe environment to place security sensitive code such as
cryptography, secure boot, secure storage, and other essential
security functions. These security functions are typically exposed
through a narrow and well-defined interface, and can be used by
operating system libraries and applications. Various APIs have been
developed by Arm as part of the Platform Security Architecture [PSA]
framework. This document focuses on the output provided by PSA's
Initial Attestation API. Since the tokens are also consumed by
services outside the device, there is an actual need to ensure
interoperability. Interoperability needs are addressed here by
describing the exact syntax and semantics of the attestation claims,
and defining the way these claims are encoded and cryptographically
protected.
Further details on concepts expressed below can be found in the PSA
Security Model documentation [PSA-SM].
2. Conventions and Definitions
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.
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2.1. Glossary
RoT Root of Trust, the minimal set of software, hardware and data
that has to be implicitly trusted in the platform - there is no
software or hardware at a deeper level that can verify that the
Root of Trust is authentic and unmodified. An example of RoT is
an initial bootloader in ROM, which contains cryptographic
functions and credentials, running on a specific hardware
platform.
SPE Secure Processing Environment, a platform's processing
environment for software that provides confidentiality and
integrity for its runtime state, from software and hardware,
outside of the SPE. Contains trusted code and trusted hardware.
(Equivalent to Trusted Execution Environment (TEE), or "secure
world".)
NSPE Non Secure Processing Environment, the security domain outside
of the SPE, the Application domain, typically containing the
application firmware, operating systems, and general hardware.
(Equivalent to Rich Execution Environment (REE), or "normal
world".)
3. PSA Claims
This section describes the claims to be used in a PSA attestation
token.
CDDL [RFC8610] along with text descriptions is used to define each
claim independent of encoding. The following CDDL type(s) are reused
by different claims:
psa-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64
3.1. Caller Claims
3.1.1. Nonce
The Nonce claim is a challenge from the caller. The length must be
32, 48, or 64 bytes.
This claim MUST be present in a PSA attestation token.
psa-nonce = (
psa-nonce-key => psa-hash-type
)
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3.1.2. Client ID
The Client ID claim represents the security domain of the caller.
In PSA, a security domain is represented by a signed integer whereby
negative values represent callers from the NSPE and where positive
IDs represent callers from the SPE. The value 0 is not permitted.
For an example definition of client IDs, see the PSA Firmware
Framework [PSA-FF].
It is essential that this claim is checked in the verification
process to ensure that a security domain, i.e., an attestation
endpoint, cannot spoof a report from another security domain.
This claim MUST be present in a PSA attestation token.
Note that the CDDL label used to be called arm_psa_partition_id.
psa-client-id-nspe-type = -2147483648...0
psa-client-id-spe-type = 1..2147483647
psa-client-id-type = psa-client-id-nspe-type / psa-client-id-spe-type
psa-client-id = (
psa-client-id-key => psa-client-id-type
)
3.2. Target Identification Claims
3.2.1. Instance ID
The Instance ID claim represents the unique identifier of the device
instance. It is a 32 bytes hash of the public key corresponding to
the Initial Attestation Key (IAK). If the IAK is a symmetric key
then the Instance ID is a hash of the hash of the IAK itself. It is
encoded as a Universal Entity ID of type RAND [I-D.ietf-rats-eat],
i.e., prepending a 0x01 type byte to the key hash. The full
definition is in [PSA-SM].
This claim MUST be present in a PSA attestation token.
psa-instance-id-type = bytes .size 33
psa-instance-id = (
psa-instance-id-key => psa-instance-id-type
)
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3.2.2. Implementation ID
The Implementation ID claim uniquely identifies the underlying
immutable PSA RoT. A verification service can use this claim to
locate the details of the verification process. Such details include
the implementation's origin and associated certification state. The
full definition is in [PSA-SM].
This claim MUST be present in a PSA attestation token.
psa-implementation-id-type = bytes .size 32
psa-implementation-id = (
psa-implementation-id-key => psa-implementation-id-type
)
3.2.3. Certification Reference
The Certification Reference claim is used to link the class of chip
and PSA RoT of the attesting device to an associated entry in the PSA
Certification database. It MUST be represented as a thirteen-digit
[EAN-13].
Linking to the PSA Certification entry can still be achieved if this
claim is not present in the token by making an association at a
Verifier between the reference value and other token claim values -
for example, the Implementation ID.
psa-certification-reference-type = text .regexp "[0-9]{13}"
psa-certification-reference = (
? psa-certification-reference-key =>
psa-certification-reference-type
)
3.3. Target State Claims
3.3.1. Security Lifecycle
The Security Lifecycle claim represents the current lifecycle state
of the PSA RoT. The state is represented by an integer that is
divided to convey a major state and a minor state. A major state is
mandatory and defined by [PSA-SM]. A minor state is optional and
'IMPLEMENTATION DEFINED'. The PSA security lifecycle state and
implementation state are encoded as follows:
* version[15:8] - PSA security lifecycle state, and
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* version[7:0] - IMPLEMENTATION DEFINED state.
The PSA lifecycle states are illustrated in Figure 1. For PSA, a
remote verifier can only trust reports from the PSA RoT when it is in
SECURED or NON_PSA_ROT_DEBUG major states.
This claim MUST be present in a PSA attestation token.
.----------------------.
.--- Enrol ---+ Provisioning Lockdown |
| '-----------+----------'
| | .------------------.
| | | |
* v v |
.--------------. .---------. |
| Verifier | .---------+ Secured +-----------. |
'--------------' | '-+-------' | |
* | | ^ | |
| | v | v |
Blacklist | .------------+------. .----------+----.
| | | Non-PSA RoT Debug | | Recoverable |
| | '---------+---------' | PSA RoT Debug |
.-+-----------+-. | '------+--------'
| Terminate +------------+-------------------'
'------+--------'
| .----------------.
'------------>| Decommissioned |
'----------------'
Figure 1: PSA Lifecycle States
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psa-lifecycle-unknown-type = 0x0000..0x00ff
psa-lifecycle-assembly-and-test-type = 0x1000..0x10ff
psa-lifecycle-psa-rot-provisioning-type = 0x2000..0x20ff
psa-lifecycle-secured-type = 0x3000..0x30ff
psa-lifecycle-non-psa-rot-debug-type = 0x4000..0x40ff
psa-lifecycle-recoverable-psa-rot-debug-type = 0x5000..0x50ff
psa-lifecycle-decommissioned-type = 0x6000..0x60ff
psa-lifecycle-type =
psa-lifecycle-unknown-type /
psa-lifecycle-assembly-and-test-type /
psa-lifecycle-psa-rot-provisioning-type /
psa-lifecycle-secured-type /
psa-lifecycle-non-psa-rot-debug-type /
psa-lifecycle-recoverable-psa-rot-debug-type /
psa-lifecycle-decommissioned-type
psa-lifecycle = (
psa-lifecycle-key => psa-lifecycle-type
)
3.3.2. Boot Seed
The Boot Seed claim represents a random value created at system boot
time that will allow differentiation of reports from different boot
sessions.
This claim MUST be present in a PSA attestation token.
psa-boot-seed-type = bytes .size 32
psa-boot-seed = (
psa-boot-seed-key => psa-boot-seed-type
)
3.4. Software Inventory Claims
3.4.1. Software Components
The Software Components claim is a list of software components that
includes all the software loaded by the PSA RoT. This claim SHALL be
included in attestation tokens produced by an implementation
conformant with [PSA-SM]. If the Software Components claim is
present, then the No Software Measurement claim (Section 3.4.2) MUST
NOT be present.
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Each entry in the Software Components list describes one software
component using the attributes described in the following
subsections. Unless explicitly stated, the presence of an attribute
is OPTIONAL.
Note that, as described in [I-D.ietf-rats-architecture], a relying
party will typically see the result of the verification process from
the Verifier in form of an attestation result, rather than the
"naked" PSA token from the attesting endpoint. Therefore, a relying
party is not expected to understand the Software Components claim.
Instead, it is for the Verifier to check this claim against the
available endorsements and provide an answer in form of an "high
level" attestation result, which may or may not include the original
Software Components claim.
psa-software-component = {
? 1 => text, ; measurement type
2 => psa-hash-type, ; measurement value
? 4 => text, ; version
5 => psa-hash-type, ; signer id
? 6 => text, ; measurement description
}
psa-software-components = (
psa-software-components-key => [ + psa-software-component ]
)
3.4.1.1. Measurement Type
The Measurement Type attribute (key=1) is short string representing
the role of this software component.
The following measurement types MAY be used:
* "BL": a Boot Loader
* "PRoT": a component of the PSA Root of Trust
* "ARoT": a component of the Application Root of Trust
* "App": a component of the NSPE application
* "TS": a component of a Trusted Subsystem
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3.4.1.2. Measurement Value
The Measurement Value attribute (key=2) represents a hash of the
invariant software component in memory at startup time. The value
MUST be a cryptographic hash of 256 bits or stronger.
This attribute MUST be present in a PSA software component.
3.4.1.3. Version
The Version attribute (key=4) is the issued software version in the
form of a text string. The value of this attribute will correspond
to the entry in the original signed manifest of the component.
3.4.1.4. Signer ID
The Signer ID attribute (key=5) is the hash of a signing authority
public key for the software component. The value of this attribute
will correspond to the entry in the original manifest for the
component. This can be used by a verifier to ensure the components
were signed by an expected trusted source.
This attribute MUST be present in a PSA software component to be
compliant with [PSA-SM].
3.4.1.5. Measurement Description
The Measurement Description attribute (key=6) is the description of
the way in which the measurement value of the software component is
computed. The value will be a text string containing an abbreviated
description (or name) of the measurement method which can be used to
lookup the details of the method in a profile document. This
attribute will normally be excluded, unless there was an exception to
the default measurement described in the profile for a specific
component.
3.4.2. No Software Measurements
In the event that the implementation does not contain any software
measurements then the Software Components claim Section 3.4.1 can be
omitted but instead the token MUST include this claim to indicate
this is a deliberate state. The value SHOULD be 1. This claim is
intended for devices that are not compliant with [PSA-SM].
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psa-no-sw-measurements-type = 1
psa-no-sw-measurement = (
psa-no-sw-measurement-key => psa-no-sw-measurements-type
)
3.5. Verification Claims
3.5.1. Verification Service Indicator
The Verification Service Indicator claim is a hint used by a relying
party to locate a validation service for the token. The value is a
text string that can be used to locate the service or a URL
specifying the address of the service. A verifier may choose to
ignore this claim in favor of other information.
psa-verification-service-indicator-type = text
psa-verification-service-indicator = (
? psa-verification-service-indicator-key =>
psa-verification-service-indicator-type
)
3.5.2. Profile Definition
The Profile Definition claim contains the name of a document that
describes the "profile" of the report. The document name may include
versioning. The value for this specification MUST be
PSA_IOT_PROFILE_1.
psa-profile-type = "PSA_IOT_PROFILE_1"
psa-profile = (
? psa-profile-key => psa-profile-type
)
4. Token Encoding and Signing
The report is encoded as a COSE Web Token (CWT) [RFC8392], similar to
the Entity Attestation Token (EAT) [I-D.ietf-rats-eat]. The token
consists of a series of claims declaring evidence as to the nature of
the instance of hardware and software. The claims are encoded in
CBOR [RFC7049] format. For asymmetric key algorithms, the signature
structure MUST be COSE_Sign1. For symmetric key algorithms, the
structure MUST be COSE_Mac0.
5. Collated CDDL
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psa-token = {
psa-nonce,
psa-instance-id,
psa-verification-service-indicator,
psa-profile,
psa-implementation-id,
psa-client-id,
psa-lifecycle,
psa-certification-reference,
psa-boot-seed,
( psa-software-components // psa-no-sw-measurement ),
}
psa-profile-key = -75000
psa-client-id-key = -75001
psa-lifecycle-key = -75002
psa-implementation-id-key = -75003
psa-boot-seed-key = -75004
psa-certification-reference-key = -75005
psa-software-components-key = -75006
psa-no-sw-measurement-key = -75007
psa-nonce-key = -75008
psa-instance-id-key = -75009
psa-verification-service-indicator-key = -75010
psa-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64
psa-boot-seed-type = bytes .size 32
psa-boot-seed = (
psa-boot-seed-key => psa-boot-seed-type
)
psa-client-id-nspe-type = -2147483648...0
psa-client-id-spe-type = 1..2147483647
psa-client-id-type = psa-client-id-nspe-type / psa-client-id-spe-type
psa-client-id = (
psa-client-id-key => psa-client-id-type
)
psa-certification-reference-type = text .regexp "[0-9]{13}"
psa-certification-reference = (
? psa-certification-reference-key =>
psa-certification-reference-type
)
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psa-implementation-id-type = bytes .size 32
psa-implementation-id = (
psa-implementation-id-key => psa-implementation-id-type
)
psa-instance-id-type = bytes .size 33
psa-instance-id = (
psa-instance-id-key => psa-instance-id-type
)
psa-no-sw-measurements-type = 1
psa-no-sw-measurement = (
psa-no-sw-measurement-key => psa-no-sw-measurements-type
)
psa-nonce = (
psa-nonce-key => psa-hash-type
)
psa-profile-type = "PSA_IOT_PROFILE_1"
psa-profile = (
? psa-profile-key => psa-profile-type
)
psa-lifecycle-unknown-type = 0x0000..0x00ff
psa-lifecycle-assembly-and-test-type = 0x1000..0x10ff
psa-lifecycle-psa-rot-provisioning-type = 0x2000..0x20ff
psa-lifecycle-secured-type = 0x3000..0x30ff
psa-lifecycle-non-psa-rot-debug-type = 0x4000..0x40ff
psa-lifecycle-recoverable-psa-rot-debug-type = 0x5000..0x50ff
psa-lifecycle-decommissioned-type = 0x6000..0x60ff
psa-lifecycle-type =
psa-lifecycle-unknown-type /
psa-lifecycle-assembly-and-test-type /
psa-lifecycle-psa-rot-provisioning-type /
psa-lifecycle-secured-type /
psa-lifecycle-non-psa-rot-debug-type /
psa-lifecycle-recoverable-psa-rot-debug-type /
psa-lifecycle-decommissioned-type
psa-lifecycle = (
psa-lifecycle-key => psa-lifecycle-type
)
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psa-software-component = {
? 1 => text, ; measurement type
2 => psa-hash-type, ; measurement value
? 4 => text, ; version
5 => psa-hash-type, ; signer id
? 6 => text, ; measurement description
}
psa-software-components = (
psa-software-components-key => [ + psa-software-component ]
)
psa-verification-service-indicator-type = text
psa-verification-service-indicator = (
? psa-verification-service-indicator-key =>
psa-verification-service-indicator-type
)
6. Security and Privacy Considerations
This specification re-uses the CWT and the EAT specification. Hence,
the security and privacy considerations of those specifications apply
here as well.
Since CWTs offer different ways to protect the token, this
specification profiles those options and allows signatures based on
use of public key cryptography as well as MAC authentication. The
token MUST be signed following the structure of the COSE
specification [RFC8152]. The COSE type MUST be COSE_Sign1 for public
key signatures or COSE_Mac0 for MAC authentication. Note however
that use of MAC authentication is NOT RECOMMENDED due to the
associated infrastructure costs for key management and protocol
complexities. It may also restrict the ability to interoperate with
third parties.
Attestation tokens contain information that may be unique to a device
and therefore they may allow to single out an individual device for
tracking purposes. Implementations that have privacy requirements
must take appropriate measures to ensure that the token is only used
to provision anonymous/pseudonym keys.
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7. Verification
To verify the token, the primary need is to check correct formation
and signing as for any CWT token. In addition though, the verifier
can operate a policy where values of some of the claims in this
profile can be compared to reference values, registered with the
verifier for a given deployment, in order to confirm that the device
is endorsed by the manufacturer supply chain. The policy may require
that the relevant claims must have a match to a registered reference
value. All claims may be worthy of additional appraisal. It is
likely that most deployments would include a policy with appraisal
for the following claims:
* Instance ID - the value of the Instance ID can be used (together
with the kid in the token COSE header, if present) to assist in
locating the public key used to verify the token signature.
* Implementation ID - the value of the Implementation ID can be used
to identify the verification requirements of the deployment.
* Software Component, Measurement Value - this value can uniquely
identify a firmware release from the supply chain. In some cases,
a verifier may maintain a record for a series of firmware
releases, being patches to an original baseline release. A
verification policy may then allow this value to match any point
on that release sequence or expect some minimum level of maturity
related to the sequence.
* Software Component, Signer ID - where present in a deployment,
this could allow a verifier to operate a more general policy than
that for Measurement Value as above, by allowing a token to
contain any firmware entries signed by a known Signer ID, without
checking for a uniquely registered version.
8. IANA Considerations
8.1. CBOR Web Token Claims Registration
This specification registers the following claims in the IANA "CBOR
Web Token (CWT) Claims" registry [IANA-CWT], established by
[RFC8392].
8.1.1. Nonce Claim
* Claim Name: "psa-nonce"
* Claim Description: Nonce
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* JWT Claim Name: "psa-nonce"
* Claim Key: [[Proposed: -75008]]
* Claim Value Type(s): bytes (32, 48, or 64 bytes in length)
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.1.1 of [[this RFC]]
8.1.2. Client ID Claim
* Claim Name: "psa-client-id"
* Claim Description: Client ID
* JWT Claim Name: "psa-client-id"
* Claim Key: [[Proposed: -75001]]
* Claim Value Type(s): signed integer
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.1.2 of [[this RFC]]
8.1.3. Instance ID Claim
* Claim Name: "psa-instance-id"
* Claim Description: Instance ID
* JWT Claim Name: "psa-instance-id"
* Claim Key: [[Proposed: -75009]]
* Claim Value Type(s): bytes (33 bytes in length)
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.2.1 of [[this RFC]]
8.1.4. Implementation ID Claim
* Claim Name: "psa-implementation-id"
* Claim Description: Implementation ID
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* JWT Claim Name: "psa-implementation-id"
* Claim Key: [[Proposed: -75003]]
* Claim Value Type(s): bytes (32 bytes in length)
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.2.2 of [[this RFC]]
8.1.5. Certification Reference Claim
* Claim Name: "psa-certification-reference"
* Claim Description: Certification Reference
* JWT Claim Name: "psa-certification-reference"
* Claim Key: [[Proposed: -75005]]
* Claim Value Type(s): text
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.2.3 of [[this RFC]]
8.1.6. Security Lifecycle Claim
* Claim Name: "psa-lifecycle"
* Claim Description: Security Lifecycle
* JWT Claim Name: "psa-lifecycle"
* Claim Key: [[Proposed: -75002]]
* Claim Value Type(s): unsigned integer
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.3.1 of [[this RFC]]
8.1.7. Boot Seed Claim
* Claim Name: "psa-boot-seed"
* Claim Description: Boot Seed
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* JWT Claim Name: "psa-boot-seed"
* Claim Key: [[Proposed: -75004]]
* Claim Value Type(s): bytes (32 bytes in length)
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.3.2 of [[this RFC]]
8.1.8. Software Components Claim
* Claim Name: "psa-software-components"
* Claim Description: Software Components
* JWT Claim Name: "psa-software-components"
* Claim Key: [[Proposed: -75006]]
* Claim Value Type(s): array
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.4.1 of [[this RFC]]
8.1.9. No Software Measurements Claim
* Claim Name: "psa-no-sw-measurement"
* Claim Description: No Software Measurements
* JWT Claim Name: "psa-no-sw-measurement"
* Claim Key: [[Proposed: -75007]]
* Claim Value Type(s): unsigned integer
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.4.2 of [[this RFC]]
8.1.10. Verification Service Indicator Claim
* Claim Name: "psa-verification-service-indicator"
* Claim Description: Verification Service Indicator
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* JWT Claim Name: "psa-verification-service-indicator"
* Claim Key: [[Proposed: -75010]]
* Claim Value Type(s): text
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.5.1 of [[this RFC]]
8.1.11. Profile Definition Claim
* Claim Name: "psa-profile"
* Claim Description: Profile Definition
* JWT Claim Name: "psa-profile"
* Claim Key: [[Proposed: -75000]]
* Claim Value Type(s): text
* Change Controller: [[Authors of this RFC]]
* Specification Document(s): Section 3.5.2 of [[this RFC]]
8.2. Media Type Registration
IANA is requested to register the "application/psa-attestation-token"
media type [RFC2046] in the "Media Types" registry [IANA-MediaTypes]
in the manner described in RFC 6838 [RFC6838], which can be used to
indicate that the content is a PSA Attestation Token.
* Type name: application
* Subtype name: psa-attestation-token
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: binary
* Security considerations: See the Security Considerations section
of [[this RFC]]
* Interoperability considerations: n/a
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* Published specification: [[this RFC]]
* Applications that use this media type: Attesters and Relying
Parties sending PSA attestation tokens over HTTP(S), CoAP(S), and
other transports.
* Fragment identifier considerations: n/a
* Additional information:
- Magic number(s): n/a
- File extension(s): n/a
- Macintosh file type code(s): n/a
* Person & email address to contact for further information: Hannes
Tschofenig, Hannes.Tschofenig@arm.com
* Intended usage: COMMON
* Restrictions on usage: none
* Author: Hannes Tschofenig, Hannes.Tschofenig@arm.com
* Change controller: IESG
* Provisional registration? No
8.3. CoAP Content-Formats Registration
IANA is requested to register the CoAP Content-Format ID for the
"application/psa-attestation-token" media type in the "CoAP Content-
Formats" registry [IANA-CoAP-Content-Formats].
8.3.1. Registry Contents
* Media Type: application/psa-attestation-token
* Encoding: -
* Id: [[To-be-assigned by IANA]]
* Reference: [[this RFC]]
9. References
9.1. Normative References
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[EAN-13] GS1, "International Article Number - EAN/UPC barcodes",
2019, <https://www.gs1.org/standards/barcodes/ean-upc>.
[PSA-FF] Arm, "Platform Security Architecture Firmware Framework
1.0 (PSA-FF)", February 2019, <https://developer.arm.com/-
/media/Files/pdf/PlatformSecurityArchitecture/Architect/
DEN0063-PSA_Firmware_Framework-1.0.0-2.pdf>.
[PSA-SM] Arm, "Platform Security Architecture Security Model 1.0
(PSA-SM)", February 2019, <https://developer.arm.com/-
/media/Files/pdf/PlatformSecurityArchitecture/Architect/
DEN0079_PSA_SM_ALPHA-03_RC01.pdf>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[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>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
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[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
9.2. Informative References
[I-D.ietf-rats-architecture]
Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote Attestation Procedures Architecture", Work
in Progress, Internet-Draft, draft-ietf-rats-architecture-
08, 8 December 2020, <http://www.ietf.org/internet-drafts/
draft-ietf-rats-architecture-08.txt>.
[I-D.ietf-rats-eat]
Mandyam, G., Lundblade, L., Ballesteros, M., and J.
O'Donoghue, "The Entity Attestation Token (EAT)", Work in
Progress, Internet-Draft, draft-ietf-rats-eat-06, 2
December 2020, <http://www.ietf.org/internet-drafts/draft-
ietf-rats-eat-06.txt>.
[IANA-CoAP-Content-Formats]
IANA, "CoAP Content-Formats", 2021,
<https://www.iana.org/assignments/core-parameters>.
[IANA-CWT] IANA, "CBOR Web Token (CWT) Claims", 2021,
<https://www.iana.org/assignments/cwt/cwt.xhtml>.
[IANA-MediaTypes]
IANA, "Media Types", 2021,
<http://www.iana.org/assignments/media-types>.
[PSA] Arm, "Platform Security Architecture Resources", 2021,
<https://developer.arm.com/architectures/security-
architectures/platform-security-architecture/
documentation>.
[TF-M] Linaro, "Trusted Firmware-M", 2021,
<https://www.trustedfirmware.org/projects/tf-m/>.
Appendix A. Reference Implementation
A reference implementation is provided by the Trusted Firmware
project [TF-M].
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Appendix B. Example
The following example shows a PSA attestation token for an
hypothetical system comprising two measured software components (a
boot loader and a trusted RTOS). The attesting device is in a
lifecycle state Section 3.3.1 of SECURED. The attestation has been
requested from a client residing in the SPE:
{
/ psa-profile / -75000: "PSA_IOT_PROFILE_1",
/ psa-client-id / -75001: 1,
/ psa-lifecycle / -75002: 12288,
/ psa-implementation-id / -75003: h'50515253545556575051
52535455565750515253545556575051525354555657',
/ psa-boot-seed / -75004: h'DEADBEEFDEADBEEFDEAD
BEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEF',
/ psa-certification-reference / -75005: "1234567890123",
/ psa-software-components / -75006: [
{
/ measurement type / 1: "BL",
/ measurement value / 2: h'0001020400010204000102040001020
400010204000102040001020400010204',
/ signer ID / 5: h'519200FF519200FF519200FF519200F
F519200FF519200FF519200FF519200FF'
},
{
/ measurement type / 1: "PRoT",
/ measurement value / 2: h'0506070805060708050607080506070
805060708050607080506070805060708',
/ signer ID / 5: h'519200FF519200FF519200FF519200F
F519200FF519200FF519200FF519200FF'
}
],
/ psa-nonce / -75008: h'00010203000102030001020300010203
00010203000102030001020300010203',
/ psa-instance-id / -75009: h'01A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2
A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3',
/ psa-verification-service-indicator / -75010: "https://psa-ve
rifier.org"
}
The JWK representation of the IAK used for creating the COSE Sign1
signature over the PSA token is:
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{
"kty": "EC",
"crv": "P-256",
"x": "MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4",
"y": "4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM",
"d": "870MB6gfuTJ4HtUnUvYMyJpr5eUZNP4Bk43bVdj3eAE",
"use": "enc",
"kid": "1"
}
The resulting COSE object is:
18(
[
/ protected / h'A10126',
/ unprotected / {},
/ payload / h'AA3A000124F7715053415F494F545F50524F46494C
455F313A000124F8013A000124F91930003A000124FA58205051525354555657
5051525354555657505152535455565750515253545556573A000124FB5820DE
ADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEF3A
000124FC6D313233343536373839303132333A000124FD82A30162424C025820
0001020400010204000102040001020400010204000102040001020400010204
055820519200FF519200FF519200FF519200FF519200FF519200FF519200FF51
9200FFA3016450526F5402582005060708050607080506070805060708050607
08050607080506070805060708055820519200FF519200FF519200FF519200FF
519200FF519200FF519200FF519200FF3A000124FF5820000102030001020300
01020300010203000102030001020300010203000102033A00012500582101A0
A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A33A
00012501781868747470733A2F2F7073612D76657269666965722E6F7267',
/ signature / h'7C0FA38F80E5EA2A5C710A4BB37ABE63B26B25F17D
B6BE9489587F9B3F8FEB80E0E410D8CDAAFAE5588024CB3E18D60C1F96CED9E0
6743824614019E99BF13FE'
]
)
Contributors
We would like to thank the following colleagues for their
contributions:
* Laurence Lundblade
Security Theory LLC
lgl@securitytheory.com
* Tamas Ban
Arm Limited
Tamas.Ban@arm.com
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* Sergei Trofimov
Arm Limited
Sergei.Trofimov@arm.com
Acknowledgments
Thanks to Carsten Bormann for help with the CDDL and Nicholas Wood
for ideas and comments.
Authors' Addresses
Hannes Tschofenig
Arm Limited
Email: Hannes.Tschofenig@arm.com
Simon Frost
Arm Limited
Email: Simon.Frost@arm.com
Mathias Brossard
Arm Limited
Email: Mathias.Brossard@arm.com
Adrian Shaw
Arm Limited
Email: Adrian.Shaw@arm.com
Thomas Fossati
Arm Limited
Email: Thomas.Fossati@arm.com
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