A CoRIM Profile for Arm's Confidential Computing Architecture (CCA) Endorsements

Arm CCA Endorsements The Arm CCA Attester is a layered Attester comprising separate yet linked Platform and Realm Attesters. For the details, see . Appraising Arm CCA Evidence requires Endorsements for both the Platform and Realm. This document outlines the Platform and Realm Endorsements in and , respectively. It also provides the Evidence transformation logic for conducting appraisals using the CoRIM processor (see ) for both platform and realm claim sets, which are covered in and , respectively.

Arm CCA Platform Endorsements There are two types of CCA Platform Endorsements:

Reference Values (), i.e., measurements of the CCA Platform firmware.
Attestation Verification Keys (), i.e., cryptographic keys that can be used to verify Evidence produced by the CCA Platform, along with the identifiers that link the keys to their platform instances.

Arm CCA Platform Endorsement Profile Arm CCA Platform Endorsements are carried in one or more CoMIDs within a CoRIM. The profile attribute in the CoRIM MUST be present and MUST be the URI tag:arm.com,2025:endorsements/cca_platform#1.0.0, as shown in .

CoRIM profile for CCA Platform Endorsements version 1.0.0

Arm CCA Platform Endorsements linkage to CCA Platform Each CCA Platform Endorsement, be it a Reference Value or an Attestation Verification Key, is associated with a unique identifier known as CCA Platform Implementation ID (see ). The Implementation ID uniquely identifies a given implementation of a CCA Platform and it is used by the Endorser or Reference Value Provider as an anchor to which Reference Values and Attestation Verification Keys for a CCA Platform are linked. To encode an Implementation ID, the tagged-bytes variant of the $class-id-type-choice is used, as described in . The length of the byte string MUST be exactly 32.

CCA Platform Implementation ID encoding Besides, a CCA Endorsement can be associated with a specific instance of a certain CCA Platform implementation - as is the case of Attestation Verification Keys. The Instance ID (see ) provides a unique identifier for a given CCA Platform instance. To encode an Instance ID, the tagged-ueid-type variant of the $instance-id-type-choice is used, as described in . The first byte MUST be 0x01 (RAND) followed by the 32-byte unique instance identifier.

CCA Platform Instance ID encoding CCA Attestation Verification Keys are associated with a CCA Platform instance by means of the Instance ID and the corresponding Implementation ID. These identifiers are typically found in the subject of a CoMID triple, encoded in an environment-map as shown in .

Example CCA Platform Identification Together, they are interpreted as a unique identifier of the CCA Platform.

Reference Values Reference Values carry measurements and other metadata associated with the updatable firmware of the CCA Platform. CCA Platform is a collective term used to identify all the hardware and firmware components that comprise a CCA system. Specifically these include the following:

CCA system security domain
Monitor security domain
Realm Management Security domain

When appraising Evidence, the Verifier compares Reference Values against:

The values found in the Software Components of the CCA Platform token (see ).
The value set in the platform configuration of the CCA Platform token (see ).

Each measurement is encoded in a measurement-map of a CoMID reference-triple-record. Since a measurement-map can encode one or more measurements, a single reference-triple-record can carry as many measurements as needed, provided they belong to the same CCA Platform identified in the subject of the triple. A single reference-triple-record MUST completely describe the CCA Platform measurements.

CCA Platform Software Components Each CCA Platform software component (called arm-platform-sw-component in ) is encoded in a measurement-values-map as defined in .

CCA Platform Software Component encoding cca-swcomp-version-map &(digests: 2) => cca-swcomp-digests-type ? &(name: 11) => cca-swcomp-name &(cryptokeys: 13) => [ cca-swcomp-signer-id ] } cca-swcomp-version-map = { &(version: 0) => text } cca-swcomp-digests-type = [ + cca-digest ] cca-digest = [ alg: text val: cca-hash-type ] cca-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64 cca-swcomp-name = text cca-swcomp-signer-id = #6.560(cca-hash-type) ]]>

version (key 0):: A version-map with its version field containing the version (key 4) of the arm-platform-sw-component. The version-scheme field of the version-map MUST NOT be present. This field is optional.
digests (key 2):: Each array element encodes the "measurement value" (key 2) and "hash algorithm identifier" (key 6) of the arm-platform-sw-component in the val and alg entries, respectively. The alg entry MUST use the text encoding. The digests array MUST contain at least one entry and MAY contain more than one entry if multiple digests (obtained with different hash algorithms) of the same measured component exist. If multiple entries exist, they MUST have different alg values. This field is mandatory.
name (key 11):: A text value containing the "component type" (key 1) of the arm-platform-sw-component. This field is optional.
cryptokeys (key 13):: An array with only one entry using the tagged-bytes variant of the $crypto-key-type-choice. The entry contains the "signer id" (key 5) of the arm-platform-sw-component. This field is mandatory.

Each measurement-values-map for a CCA Platform software component is wrapped in a measurement-map with an mkey using the text variant of the $measured-element-type-choice. The value of the mkey MUST be "cca.software-component". The authorized-by field of the measurement-map MUST NOT be present. Find the related CDDL definitions in .

CCA Platform Software Component measurement-map "cca.software-component" &(mval: 1) => cca-swcomp-measurement-values-map } ]]>

CCA Platform Configuration The CCA Platform configuration describes the set of chosen implementation options of the CCA Platform. For example, this may include a description of the level of physical memory protection provided. CCA Platform configuration is vendor-specific variable-length data. Only some of the data may be security-relevant. For these reasons, it is represented in a raw-value of the measurement-values-map, using the tagged-masked-raw-value variant of the $raw-values-type-choice. Refer to for the details about the comparison algorithm.

CCA Platform Configuration measurement-values-map cca-tagged-masked-raw-value } cca-config-tagged-masked-raw-value = #6.563([ value: bytes mask: bytes ]) ]]> The measurement-values-map for a CCA Platform configuration is wrapped in a measurement-map with an mkey using the text variant of the $measured-element-type-choice. The value of the mkey MUST be "cca.platform-config". There MUST be only one measurement-map with mkey "cca.platform-config" in the triple. The authorized-by field of the measurement-map MUST NOT be present. Find the related CDDL definitions in .

CCA Platform Configuration measurement-map "cca.platform-config" &(mval: 1) => cca-config-measurement-values-map } ]]>

CCA Platform Trusted Board Boot ROTPK When an implementation of the CCA Platform follows the Trusted Board Boot specification, the platform will include several provisioned public key identifiers to establish a chain of trust. Each public key identifier is expressed as a hash of the corresponding public key. For CCA Implementation, the public key identifiers are provisioned as a number of array entries, with each array entry containing a list of key identifiers. For CCA Implementation, there MUST be only two types of arrays: 1. Chip Manufacturing array - known as "CM" 2. Device Manufacturing array - known as "DM" In CCA Implementation, for a particular type of array, the maximum number of array entries SHALL be 8, while the maximum entries in a single array SHALL be 6. CCA Platform public key identifiers are encoded in a CoMID using Reference Value triples. Each array entry is encoded in a single Reference Value Triple. Each public key identifier is encoded in a single measurement-map.

mkey uniquely identifies the position of each key identifier, using the text variant of $measured-element-type-choice. The encoding follows a consistent pattern: the prefix "cca.rotpk", followed by the set name ("CM" or "DM"), then the array index (starting from zero), and finally the entry position within the array (starting from zero). The parts are separated by ".". For example, to encode a "CM" key identifier for an active array index of 2 at position 3 in the array, mkey will be set to "cca.rotpk.CM.2.3".
The public key identifier is encoded using cryptokeys (key 13). The array MUST have only one entry encoded using the tagged-bytes variant of the $crypto-key-type-choice. The length of the tagged-bytes MUST be 32, 48 or 64 bytes.
The authorized-by field of the measurement-map MUST NOT be present.

Find the related CDDL definition of Measurement Values Map in and the associated measurement map in .

CCA Platform ROTPK measurement-values-map [ cca-rotpk-id ] } cca-hash-type = bytes .size 32 / bytes .size 48 / bytes .size 64 cca-rotpk-id = #6.560(cca-hash-type) ]]>

CCA ROTPK measurement-map text .regexp "cca.rotpk.[CD]M\\.[0-7]\\.[0-5]" &(mval: 1) => cca-rotpk-measurement-values-map } ]]> An Endorser may choose to provision either the entire set of entries or the single active entry currently in use on the platform.

CCA Platform Manufacturing Configuration The CCA Platform Manufacturing Configuration represents a record of production phases and testing conducted during the manufacturing process for the platform instance. CCA Platform Manufacturing Configuration is vendor-specific variable-length data. It is represented in a raw-value of the measurement-values-map, using the tagged-masked-raw-value variant of the $raw-values-type-choice. Refer to for the details about the comparison algorithm.

CCA Platform Manufacturing Configuration measurement-values-map cca-tagged-masked-raw-value } cca-config-tagged-masked-raw-value = #6.563([ value: bytes mask: bytes ]) ]]> The measurement-values-map for a CCA Platform manufacturing configuration is wrapped in a measurement-map with an mkey using the text variant of the $measured-element-type-choice. The value of the mkey MUST be "cca.platform-manufacturing-config". There MUST be only one measurement-map with mkey "cca.platform-manufacturing-config" in the triple. The authorized-by field of the measurement-map MUST NOT be present. Find the related CDDL definitions in and in .

CCA Platform Manufacturing Configuration measurement-map "cca.platform-manufacturing-config" &(mval: 1) => cca-manufacturing-config-measurement-values-map } ]]>

CoMID Example An example CoMID containing one Reference Values triple with the expected values for both software components and platform configuration is given in .

Example CCA Platform Reference Values

Attestation Verification Keys An Attestation Verification Key contains the public key associated with the CCA Platform Attestation Key (CPAK). When appraising Platform Evidence, the Verifier uses the Implementation ID and Instance ID claims found in the Platform Token to identify the key that it shall use to verify the signature on the CCA Platform token. This allows the Verifier to prove (or disprove) the Attester's claimed identity. Each verification key is provided with the corresponding CCA Platform Instance and Implementation IDs in an attest-key-triple-record. Specifically:

The Instance and Implementation IDs are encoded in the environment-map as described in ;
The CPAK public key uses the tagged-pkix-base64-key-type variant of the $crypto-key-type-choice.

The CPAK public key is a SubjectPublicKeyInfo using the encoding defined in . There MUST be only one key in an attest-key-triple-record.

CoMID Example The example in shows the CCA Endorsement of type Attestation Verification Key carrying a secp256r1 EC public CPAK associated with Instance ID 4ca3...d296.

Example CCA Platform Attestation Verification Key

Evidence Transformations This section describes the transformations required to map a CCA Platform Token to its equivalent CoRIM internal representation. shows the complete transformation.

Platform Identification The CCA Implementation and Instance IDs are used together to provide a unique identifer for the CCA platform. The following function maps these IDs onto a CoRIM environment-map.

Transform CCA Platform IDs into Environment Map environment-map { env := environment-map::NEW() env.class.class-id = tagged-bytes(impl-id) env.instance = tagged-ueid-type(inst-id) RETURN env } ]]>

Software Components The following function maps a single CCA software component to a CoRIM element map. The element identifier is "cca.software-component", and the element claims are synthesized from the CCA software component attributes using only the following default CoRIM element-map attributes: name, version, digests and cryptokeys.

Transform a CCA Software Component into an Element Map element-map { em := element-map::NEW() em.element-id = tstr("cca.software-component") em.element-claims.name = C.measurement-type em.element-claims.version.version = C.version digest := eatmc.digest(C.measurement-desc, C.measurement-value) em.element-claims.digests::APPEND(digest) signer := tagged-bytes(C.signer-id) em.element-claims.cryptokeys::APPEND(signer) RETURN em } ]]>

Platform Configuration The following function maps the CCA platform configuration claim to a CoRIM element map. The element identifier is "cca.platform-config", and the element claims use the standard raw-values attribute to represent the platform configuration value as tagged-bytes.

Transform a CCA Plaform Config into an Element Map element-map { em := element-map::NEW() em.element-id = tstr("cca.platform-config") em.element-claims.raw-values = tagged-bytes(C) RETURN em } ]]>

Platform TBB ROTPK The following function maps a CCA TBB ROTPK to a CoRIM element map. The element identifier is created from the claim as shown below, following the same encoding pattern for the mkey described in . The element claims use the standard raw-values attribute to represent the ROTPK hash value as tagged-bytes.

Transform a CCA Platform TBB ROTPK into an Element Map element-map { em := element-map::NEW() em.element-id = tstr( "cca.rotpk." + C.life-cycle + "." + C.active-rotpk-array + "." + C.active-rotpk-index ) em.element-claims.raw-values = tagged-bytes(C.pk-hash) RETURN em } ]]>

Platform Manufacturing Configuration The following function maps the CCA platform manufacturing configuration claim to a CoRIM element map. The element identifier is "cca.platform-manufacturing-config", and the element claims use the standard raw-values attribute to represent the platform manufacturing configuration value as tagged-bytes.

Transform a CCA Plaform Manufacturing Config into an Element Map element-map { em := element-map::NEW() em.element-id = tstr("cca.platform-manufacturing-config") em.element-claims.raw-values = tagged-bytes(C) RETURN em } ]]>

Platform Token The following function maps the CCA platform's claims set to a single CoRIM ae-item. The environment is synthesized from instance and implementation identifiers. Each software component is mapped to an element-map entry with identifier "cca.software-component". The platform configuration is mapped to an element-map entry with identifier "cca.platform-config". The Platform TBB ROTPK is mapped to an element-map entry, the identifier of which is computed by concatenating the cca.lifecycle claim with the string representations of the integer indices of the active ROTPK array and the active array entry. The platform manufacturing configuration is mapped to an element-map entry with identifier "cca.platform-manufacturing-config". The process uses the functions defined in , , , and . The process assumes that the profile of the CCA Platform claims-set is "tag:arm.com,2024:cca_platform#2.0.0".

Transform a CCA Plaform into a CoRIM `ae` Relation ae-item { ASSERT::Equal( P.arm-platform-profile-label, "tag:arm.com,2024:cca_platform#2.0.0" ) item := ae-item::NEW() item.addition.cmtype = evidence # map platform identifiers to environment item.addition.environment = cca_platform_id_to_env( P.arm-platform-instance-id-label, P.arm-platform-implementation-id-label ) element-list = [ + element-map ]::NEW() # map software components to elements FOREACH c IN P.arm-platform-sw-components: e := element-from-sw-component(c) element-list::APPEND(e) # map platform config to element e := element-from-platform-config(P.arm-platform-config-label) element-list::APPEND(e) item.addition.element-list = element-list item.addition.profile = "tag:arm.com,2025:endorsements/cca_platform#1.0.0" item.addition.authority::APPEND(cpak_pub) # map platform tbb rotpk to elements FOREACH pk IN P.arm-platform-tbb-rotpk: e := element-from-tbb-rotpk(pk) element-list::APPEND(e) # map platform manufacturing config to element e := element-from-platform-manufacturing-config( P.arm-platform-manufacturing-config-label ) element-list::APPEND(e) item.addition.element-list = element-list item.addition.profile = "tag:arm.com,2025:endorsements/cca_platform#1.0.0" item.addition.authority::APPEND(cpak_pub) RETURN item } ]]>

Arm CCA Realm Endorsements Arm CCA provides confidential computing environments, known as Realms, that enable application workloads requiring confidential execution to operate in isolation from the host hypervisor and any other concurrent workload. Arm CCA allows the initial and run-time state of a Realm to be attested (). Realm Endorsements consist of Reference Values (), which are measurements of the configuration and contents of a Realm at the time of its activation, along with measurements of the software operating within the Realm, which can be extended throughout the Realm's lifetime. Unlike the Platform, Realm Attestation Verification Key Endorsements are not necessary as the key material needed to verify the Realm Evidence is inline in the CCA Token ().

Arm CCA Realm Endorsement Profile Arm CCA Realm Endorsements are carried in a CoMID within a CoRIM. The profile attribute in the CoRIM MUST be present and MUST be the URI tag:arm.com,2025:endorsements/cca_realm#1.0.0 as shown in .

CoRIM profile for CCA Realm Endorsements version 1.0.0

Realm Endorsements linkage to Realm Realms do not have explicit class or instance identifiers. However, the Realm Initial Measurement (RIM) is unique and stable enough to serve as an identifier for the Realm Target Environment. Therefore, this profile employs an environment-map with a class identifier that uses the tagged-bytes variant of the $class-id-type-choice to encode the RIM value ().

CCA Realm Identification

Reference Values Reference Values carry measurements and other metadata associated with the CCA Realm. Realm Reference Values comprise:

Realm Initial Measurements (RIM)
Realm Extended Measurements (REMs)
Realm Personalization Value (RPV)

All Realm Reference Values are carried in a reference-triple-record whose environment-map is as described in The triple includes as many measurement-maps as needed to fully describe the Realm. The measurement-map contents depend on the type of Reference Value. For all, the mkey uses the text variant of the $measured-element-type-choice. The value of the mkey MUST be "cca.rim" for the RIM measurement, "cca.rpv" for the RPV measurement, and "cca.rem0".."cca.rem3" for the REM measurements. The authorized-by field of the measurement-map MUST NOT be present. RIM and REMs are encoded as digests (key 2). RPV is encoded using a raw-value (key 4) using the tagged bytes variant of the $raw-value-type-choice. All the Realm Reference Values are optional except RIM, which is mandatory.

CoMID Example An example CoMID containing one Reference Values triple with the expected values for a Realm is given in .

CCA realm identifiers

Evidence Transformations This section describes the transformations required to map a CCA Realm Token to its equivalent CoRIM internal representation. shows the complete transformation.

Realm Identification The following function maps the CCA Realm Initial Measurement - which, as discussed in , provides a stable identifier for the Realm - onto a CoRIM environment-map.

Transform a CCA Realm Initial Measurement into an Element Map environment-map { env := environment-map::NEW() env.class.class-id = tagged-bytes(rim) RETURN env } ]]>

Realm Initial Measurements The following function maps the CCA Realm Initial Measurement claim to a CoRIM element map. The element identifier is "cca.rim", and the element claims use the standard digests attribute to represent the RIM value, using the digest algorithm taken from the Realm hash algorithm ID claim.

Transform a CCA Realm Initial Measurement into an Element Map element-map { em := element-map::NEW() em.element-id = tstr("cca.rim") digest := eatmc.digest(rim-algo, rim-value) em.element-claims.digests::APPEND(digest) RETURN em } ]]>

Realm Extended Measurements The following function maps the i-th (0..3) bank of a CCA Realm Extended Measurements claim to a CoRIM element map. The element identifier is one of "cca.rem0".."cca.rem3", depending on the bank index, and the element claims use the standard digests attribute to represent the REM value, using the digest algorithm taken from the Realm hash algorithm ID claim.

Transform a CCA Realm Extended Measurement Bank into an Element Map element-map { em := element-map::NEW() em.element-id = tstr("cca.rem" + rem-index) digest := eatmc.digest(rem-algo, rem-value) em.element-claims.digests::APPEND(digest) RETURN em } ]]>

Realm Personalization Value The following function maps the CCA realm personalization value claim to a CoRIM element map. The element identifier is "cca.rpv", and the element claims use the standard raw-values attribute to represent the personalization value as tagged-bytes.

Transform a CCA Realm Personalization Value into an Element Map element-map { em := element-map::NEW() em.element-id = tstr("cca.rpv") em.element-claims.raw-values = tagged-bytes(rpv) RETURN em } ]]>

Realm Token The following function maps the CCA realm's claims set to a single CoRIM ae-item. The environment is synthesized from the RIM. Each REM bank, if present, is mapped to an element-map entry with identifier "cca.rem0".."cca.rem3". The personalization value, if present, is mapped to an element-map entry with identifier "cca.rpv". The process uses the functions defined in , , , and . The process assumes that the profile of the CCA Realm claims-set is "tag:arm.com,2024:realm#2.0.0".

Transform a CCA Realm into a CoRIM `ae` Relation ae-item { ASSERT::Equal( R.cca-realm-profile-label, "tag:arm.com,2024:realm#2.0.0" ) item := ae-item::NEW() item.addition.cmtype = evidence # map platform identifiers to environment item.addition.environment = cca_realm_id_to_env( R.cca-realm-initial-measurement-label ) element-list = [ + element-map ]::NEW() # map realm initial measurement to element e := element-from-rim(R.cca-realm-profile-label) element-list::APPEND(e) # map optional REMs IF R.cca-realm-extensible-measurements: FOREACH idx, r IN R.cca-realm-extensible-measurements: e := element-from-rem(idx, r, R.cca-realm-hash-algo-id-label) element-list::APPEND(e) # map optional RVP IF R.cca-realm-personalization-value: e := element-from-rpv(R.arm-platform-config-label) element-list::APPEND(e) item.addition.element-list = element-list item.addition.profile = "tag:arm.com,2025:endorsements/cca_realm#1.0.0" item.addition.authority::APPEND(R.cca-realm-public-key-label) RETURN item } ]]>