The Android Profile for DICE is a specialization of the Open Profile for DICE that provides additional detail around algorithms, certificates, and configuration descriptor. The choices are made to meet the needs of the Android ecosystem.
This profile is not always a strict refinement of the Open Profile for DICE as it also forced to address practical concerns such as workarounds for errata in ROMs that require a relaxation of the base specification. However, the objective is to avoid these where practical.
The choice of algorithm must remain consistent with any given certificate e.g. if SHA-256 is the hash algorithm used for the code hash then the authority hash, config hash, etc. must also use SHA-256.
See the Open Profile for DICE's acceptable cryptographic algorithms for more detail on specific algorithms.
Acceptable hash algorithms are:
Unlike the Open Profile for DICE, digests can be used as DICE inputs at their output size without needing to be resized to 64 bytes. The value that is used as the DICE input must be listed in the certificate. E.g. SHA-256 digests can be used as 32-byte DICE inputs with the same 32 bytes encoded as a byte string in the certificate.
HKDF with a supported hash algorithm, or CKDF for all key derivation.
Ed25519 is recommended for performance and memory usage reasons. ECDSA with curves P-256 or P-384 are acceptable.
Only CBOR certificates are allowed by this profile. Other certificate types, such as X.509, must not be used.
A certificate must only set the mode to normal when all of the following conditions are met when loading and verifying the software component that is being described by the certificate:
The mode should never be not configured.
The configuration descriptor is a CBOR map. Only key values less than -65536 are used as this is conventionally reserved for private use in IANA assignments. The key value range [-70000, -70999] is reserved for use by this profile. Implementation-specific fields may be added using key values outside of the reserved range.
Unless explicitly stated as required in the versions section, each field is optional. If no fields are relevant, an empty map should be encoded.
| Name | Key | Value type | Meaning |
|---|---|---|---|
| Component name | -70002 | tstr | Name of the component |
| Component version | -70003 | int / tstr | Version of the component |
| Resettable | -70004 | null | If present, key changes on factory |
| : : : : reset : | |||
| Security version | -70005 | uint | Machine-comparable, monotonically |
| : : : : increasing version of the component: | |||
| : : : : where a greater value indicates a : | |||
| : : : : newer version, for example, the : | |||
| : : : : anti-rollback counter : |
Android is an evolving ecosystem with compatibility requirements that enable devices to continue being updated. Explicit versioning of certificates in the DICE chain allows continued compatibility between higher-level software that updates and lower-level software (such as ROM) that might not update.
Versions of this profile are identified by their profile name which is composed of the prefix "android." followed by the Android version number it aligns with. Certificates declare which profile they are following in the profileName field defined by the Open Profile for DICE. If no profile name is included in the certificate, "android.14" is assumed.
Within a DICE chain, the version of the profile used in each certificate must be the same or greater than the version used in the previous certificate. This ensures the all certificates are aware of, and can maintain, any chain invariants that can be added in any version of the profile.
Android provides the hwtrust tool which can validate that certificate chains conform to this profile and can assist in diagnosing problems.
The version-specific details listed below are non-cumulative so only apply to the version they are listed under.
"android.14"The profile named "android.14" aligns with Android 14.
configurationHash field is permitted to be missing rather than being required, as specified by the Open Profile for DICE.mode field is permitted to be encoded as an integer rather than the byte string that is specified by the Open Profile for DICE.keyUsage field is permitted to be encoded in big-endian byte order as well as the little-endian byte order that is specified by the Open Profile for DICE. As a result of this erratum workaround, the value is ambiguous and verifiers might not be able to rely on this value."android.15"The profile named "android.15" aligns with Android 15. It is backwards compatible with the previous versions of the Andorid Profile for DICE.
configurationHash field is permitted to be missing rather than being required, as specified by the Open Profile for DICE."android.16"The profile named "android.16" aligns with Android 16 and is still subject to change. It is backwards compatible with the previous versions of the Android Profile for DICE.