RATS H. Tschofenig
Internet-Draft S. Frost
Intended status: Informational M. Brossard
Expires: 25 September 2021 A. Shaw
T. Fossati
Arm Limited
24 March 2021
Arm's Platform Security Architecture (PSA) Attestation Token
draft-tschofenig-rats-psa-token-08
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.
The PSA attestation token is a profiled Entity Attestation Token
(EAT).
This specification describes what claims are used in an attestation
token generated by PSA compliant systems, how these claims get
serialized to the wire, and how they are cryptographically protected.
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/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 25 September 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2.1. Glossary . . . . . . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . 7
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. Backwards Compatibility Considerations . . . . . . . . . . . 12
5. Token Encoding and Signing . . . . . . . . . . . . . . . . . 12
6. Freshness Model . . . . . . . . . . . . . . . . . . . . . . . 12
7. Collated CDDL . . . . . . . . . . . . . . . . . . . . . . . . 13
8. Security and Privacy Considerations . . . . . . . . . . . . . 15
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9. Verification . . . . . . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10.1. Media Type Registration . . . . . . . . . . . . . . . . 16
10.2. CoAP Content-Formats Registration . . . . . . . . . . . 17
10.2.1. Registry Contents . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Reference Implementation . . . . . . . . . . . . . . 20
Appendix B. Example . . . . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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.
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
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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 used to carry the challenge provided by the caller
to demonstrate freshness of the generated token.
The EAT [I-D.ietf-rats-eat] "nonce" (claim key 10) is used. The
following constraints apply to the "nonce-type":
* The length MUST be either 32, 48, or 64 bytes.
* Only a single nonce value is conveyed. Per [I-D.ietf-rats-eat]
the array notation is not used for encoding the nonce value.
This claim MUST be present in a PSA attestation token.
psa-nonce = (
10 => 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 Initial
Attestation Key (IAK). The full definition is in [PSA-SM].
The EAT "ueid" (claim key 11) of type RAND is used. The following
constraints apply to the "ueid-type":
* The length MUST be 33 bytes.
* The first byte MUST be 0x01 (RAND) followed by the 32-bytes key
hash.
This claim MUST be present in a PSA attestation token.
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psa-instance-id-type = bytes .size 33
psa-instance-id = (
11 => psa-instance-id-type
)
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
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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
* 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 encodes the unique identifier that
corresponds to the EAT profile described by this document. This
allows a receiver to assign the intended semantics to the rest of the
claims found in the token.
The EAT "profile" (claim key 18) is used. The following constraints
apply to its type:
* The URI encoding MUST be used.
* The value MUST be "http://arm.com/psa/2.0.0".
This claim MUST be present in a PSA attestation token.
See Section 4, for considerations about backwards compatibility with
previous versions of the PSA attestation token format.
psa-profile-type = "http://arm.com/psa/2.0.0"
psa-profile = (
18 => psa-profile-type
)
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4. Backwards Compatibility Considerations
Previous versions of this specification used different claim key
values for the following claims:
* Nonce (claim key -75008);
* Instance ID (claim key -75009);
* Profile Description (claim key -75000 and value
"PSA_IOT_PROFILE_1").
These claim keys have been retired and their use is deprecated.
Unless compatibility with existing infrastructure is a concern,
emitters (e.g., devices that implement the PSA Attestation API)
SHOULD produce tokens with their standard equivalent instead, as
described in Section 3.1.1, Section 3.2.1 and Section 3.5.2
respectively.
To simplify the transition to the token format described in this
document it is RECOMMENDED that receivers (e.g., PSA Attestation
Verifiers) accept tokens encoded according to the old profile
("PROFILE_IOT_1") as well as to the new profile ("http://arm.com/
psa/2.0.0"), at least for the time needed to their clients to
upgrade.
5. Token Encoding and Signing
The PSA attestation token is encoded in CBOR [RFC7049] format. Only
definite-length string, arrays, and maps are allowed.
Cryptographic protection is obtained by wrapping the "psa-token" map
in a COSE Web Token (CWT) [RFC8392]. For asymmetric key algorithms,
the signature structure MUST be COSE_Sign1. For symmetric key
algorithms, the signature structure MUST be COSE_Mac0.
The CWT CBOR tag (61) is not used. An application that needs to
exchange PSA attestation tokens can use the media type defined in
Section 10.1 or the CoAP Content-Format defined in Section 10.2.
6. Freshness Model
The PSA Token supports the freshness models for attestation Evidence
based on nonces and epoch handles (Section 10.2 and 10.3 of
[I-D.ietf-rats-architecture]) using the "nonce" claim to convey the
nonce or epoch handle supplied by the Verifier. No further
assumption on the specific remote attestation protocol is made.
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7. Collated CDDL
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 =>
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psa-certification-reference-type
)
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 = (
11 => 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 = (
10 => psa-hash-type
)
psa-profile-type = "http://arm.com/psa/2.0.0"
psa-profile = (
18 => 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
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psa-lifecycle = (
psa-lifecycle-key => psa-lifecycle-type
)
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
)
8. 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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9. 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.
10. IANA Considerations
10.1. 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
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* Optional parameters: n/a
* Encoding considerations: binary
* Security considerations: See the Security Considerations section
of [[this RFC]]
* Interoperability considerations: n/a
* 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
10.2. 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].
10.2.1. Registry Contents
* Media Type: application/psa-attestation-token
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* Encoding: -
* Id: [[To-be-assigned by IANA]]
* Reference: [[this RFC]]
11. References
11.1. Normative References
[EAN-13] GS1, "International Article Number - EAN/UPC barcodes",
2019, <https://www.gs1.org/standards/barcodes/ean-upc>.
[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>.
[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>.
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[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>.
[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>.
11.2. 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>.
[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/>.
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Appendix A. Reference Implementation
A reference implementation is provided by the Trusted Firmware
project [TF-M].
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:
{
/ profile / 18: "http://arm.com/psa/2.0.0",
/ 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'
}
],
/ nonce / 10: h'00010203000102030001020300010203
00010203000102030001020300010203',
/ ueid / 11: 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'AD127818687474703A2F2F61726D2E636F6D2F7073
612F322E302E303A000124F8013A000124F91930003A000124FA582050515253
545556575051525354555657505152535455565750515253545556573A000124
FB5820DEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDEADBEEFDE
ADBEEF3A000124FC6D313233343536373839303132333A000124FD82A3016242
4C02582000010204000102040001020400010204000102040001020400010204
00010204055820519200FF519200FF519200FF519200FF519200FF519200FF51
9200FF519200FFA3016450526F54025820050607080506070805060708050607
0805060708050607080506070805060708055820519200FF519200FF519200FF
519200FF519200FF519200FF519200FF519200FF0A5820000102030001020300
01020300010203000102030001020300010203000102030B582101A0A1A2A3A0
A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A3A0A1A2A33A00012501
781868747470733A2F2F7073612D76657269666965722E6F72673A00012500F6
3A000124F7F63A000124FFF6',
/ signature / h'8C92FDC99CFDB0016F27008744B3730266342D2881
861DC9A3F89E02394DE7F906EE2D1A3C164A59D580CDD7DFA077290CBFB55069
C55A5D9A2AE17FA31D2108'
]
)
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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