@peculiar/asn1-android

• Android key attestation schema
• Key attestation extension data schema
• AttestationApplicationId

KeyDescription and NonStandardKeyDescription

The KeyDescription class in this library represents the ASN.1 schema for the Android Keystore Key Description structure. However, in practice, there are cases where the AuthorizationList fields in the softwareEnforced and teeEnforced fields are not strictly ordered, which can lead to ASN.1 structure reading errors.

To address this issue, this library provides a NonStandardKeyDescription class that can read such structures. However, when creating extensions, it is recommended to use KeyDescription, as it guarantees the order of object fields according to the specification.

Here are simplified TypeScript examples:

Example of creating a KeyDescription object in TypeScript for the Android Keystore system

const attestation = new android.AttestationApplicationId({
  packageInfos: [
    new android.AttestationPackageInfo({
      packageName: new OctetString(Buffer.from("123", "utf8")),
      version: 1,
    }),
  ],
  signatureDigests: [
    new OctetString(Buffer.from("123", "utf8")),
  ],
});

const keyDescription = new KeyDescription({
  attestationVersion: android.Version.v200,
  attestationSecurityLevel: android.SecurityLevel.software,
  keymasterVersion: 1,
  keymasterSecurityLevel: android.SecurityLevel.software,
  attestationChallenge: new OctetString(Buffer.from("123", "utf8")),
  uniqueId: new OctetString(Buffer.from("123", "utf8")),
  softwareEnforced: new android.AuthorizationList({
    creationDateTime: 1506793476000,
    attestationApplicationId: new OctetString(AsnConvert.serialize(attestation)),
  }),
  teeEnforced: new android.AuthorizationList({
    purpose: new android.IntegerSet([1]),
    algorithm: 1,
    keySize: 1,
    digest: new android.IntegerSet([1]),
    ecCurve: 1,
    userAuthType: 1,
    origin: 1,
    rollbackResistant: null,
  }),
});

const raw = AsnConvert.serialize(keyDescription);

Example of reading a NonStandardKeyDescription object in TypeScript

const keyDescription = AsnConvert.parse(raw, NonStandardKeyDescription);

console.log(keyDescription.attestationVersion); // 100
console.log(keyDescription.attestationSecurityLevel); // 1
console.log(keyDescription.keymasterVersion); // 100
console.log(keyDescription.keymasterSecurityLevel); // 1
console.log(keyDescription.attestationChallenge.byteLength); // 32
console.log(keyDescription.uniqueId.byteLength); // 0
console.log(keyDescription.softwareEnforced.findProperty("attestationApplicationId")?.byteLength); // 81
console.log(keyDescription.teeEnforced.findProperty("attestationIdBrand")?.byteLength); // 8