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import type { Base64URLString } from '../deps.ts';
import type { AlgSign, MetadataStatement } from '../metadata/mdsTypes.ts';
import { convertCertBufferToPEM } from '../helpers/convertCertBufferToPEM.ts';
import { validateCertificatePath } from '../helpers/validateCertificatePath.ts';
import { decodeCredentialPublicKey } from '../helpers/decodeCredentialPublicKey.ts';
import { COSEALG, COSECRV, COSEKEYS, COSEKTY, isCOSEPublicKeyEC2 } from '../helpers/cose.ts';
/**
* Match properties of the authenticator's attestation statement against expected values as
* registered with the FIDO Alliance Metadata Service
*/
export async function verifyAttestationWithMetadata({
statement,
credentialPublicKey,
x5c,
attestationStatementAlg,
}: {
statement: MetadataStatement;
credentialPublicKey: Uint8Array;
x5c: Uint8Array[] | Base64URLString[];
attestationStatementAlg?: number;
}): Promise<boolean> {
const {
authenticationAlgorithms,
authenticatorGetInfo,
attestationRootCertificates,
} = statement;
// Make sure the alg in the attestation statement matches one of the ones specified in metadata
const keypairCOSEAlgs: Set<COSEInfo> = new Set();
authenticationAlgorithms.forEach((algSign) => {
// Map algSign string to { kty, alg, crv }
const algSignCOSEINFO = algSignToCOSEInfoMap[algSign];
// Keeping this statement here just in case MDS returns something unexpected
if (algSignCOSEINFO) {
keypairCOSEAlgs.add(algSignCOSEINFO);
}
});
// Extract the public key's COSE info for comparison
const decodedPublicKey = decodeCredentialPublicKey(credentialPublicKey);
const kty = decodedPublicKey.get(COSEKEYS.kty);
const alg = decodedPublicKey.get(COSEKEYS.alg);
if (!kty) {
throw new Error('Credential public key was missing kty');
}
if (!alg) {
throw new Error('Credential public key was missing alg');
}
if (!kty) {
throw new Error('Credential public key was missing kty');
}
// Assume everything is a number because these values should be
const publicKeyCOSEInfo: COSEInfo = { kty, alg };
if (isCOSEPublicKeyEC2(decodedPublicKey)) {
const crv = decodedPublicKey.get(COSEKEYS.crv);
publicKeyCOSEInfo.crv = crv;
}
/**
* Attempt to match the credential public key's algorithm to one specified in the device's
* metadata
*/
let foundMatch = false;
for (const keypairAlg of keypairCOSEAlgs) {
// Make sure algorithm and key type match
if (
keypairAlg.alg === publicKeyCOSEInfo.alg &&
keypairAlg.kty === publicKeyCOSEInfo.kty
) {
// If not an RSA keypair then make sure curve numbers match too
if (
(keypairAlg.kty === COSEKTY.EC2 || keypairAlg.kty === COSEKTY.OKP) &&
keypairAlg.crv === publicKeyCOSEInfo.crv
) {
foundMatch = true;
} else {
// We've matched an RSA public key's properties
foundMatch = true;
}
}
if (foundMatch) {
break;
}
}
// Make sure the public key is one of the allowed algorithms
if (!foundMatch) {
/**
* Craft some useful error output from the MDS algorithms
*
* Example:
*
* ```
* [
* 'rsassa_pss_sha256_raw' (COSE info: { kty: 3, alg: -37 }),
* 'secp256k1_ecdsa_sha256_raw' (COSE info: { kty: 2, alg: -47, crv: 8 })
* ]
* ```
*/
const debugMDSAlgs = authenticationAlgorithms.map(
(algSign) => `'${algSign}' (COSE info: ${stringifyCOSEInfo(algSignToCOSEInfoMap[algSign])})`,
);
const strMDSAlgs = JSON.stringify(debugMDSAlgs, null, 2).replace(/"/g, '');
/**
* Construct useful error output about the public key
*/
const strPubKeyAlg = stringifyCOSEInfo(publicKeyCOSEInfo);
throw new Error(
`Public key parameters ${strPubKeyAlg} did not match any of the following metadata algorithms:\n${strMDSAlgs}`,
);
}
/**
* Confirm the attestation statement's algorithm is one supported according to metadata
*/
if (
attestationStatementAlg !== undefined &&
authenticatorGetInfo?.algorithms !== undefined
) {
const getInfoAlgs = authenticatorGetInfo.algorithms.map((_alg) => _alg.alg);
if (getInfoAlgs.indexOf(attestationStatementAlg) < 0) {
throw new Error(
`Attestation statement alg ${attestationStatementAlg} did not match one of ${getInfoAlgs}`,
);
}
}
// Prepare to check the certificate chain
const authenticatorCerts = x5c.map(convertCertBufferToPEM);
const statementRootCerts = attestationRootCertificates.map(
convertCertBufferToPEM,
);
/**
* If an authenticator returns exactly one certificate in its x5c, and that cert is found in the
* metadata statement then the authenticator is "self-referencing". In this case we forego
* certificate chain validation.
*/
let authenticatorIsSelfReferencing = false;
if (
authenticatorCerts.length === 1 &&
statementRootCerts.indexOf(authenticatorCerts[0]) >= 0
) {
authenticatorIsSelfReferencing = true;
}
if (!authenticatorIsSelfReferencing) {
try {
await validateCertificatePath(authenticatorCerts, statementRootCerts);
} catch (err) {
const _err = err as Error;
throw new Error(
`Could not validate certificate path with any metadata root certificates: ${_err.message}`,
);
}
}
return true;
}
type COSEInfo = {
kty: COSEKTY;
alg: COSEALG;
crv?: COSECRV;
};
/**
* Convert ALG_SIGN values to COSE info
*
* Values pulled from `ALG_KEY_COSE` definitions in the FIDO Registry of Predefined Values
*
* https://fidoalliance.org/specs/common-specs/fido-registry-v2.2-ps-20220523.html#authentication-algorithms
*/
export const algSignToCOSEInfoMap: { [key in AlgSign]: COSEInfo } = {
secp256r1_ecdsa_sha256_raw: { kty: 2, alg: -7, crv: 1 },
secp256r1_ecdsa_sha256_der: { kty: 2, alg: -7, crv: 1 },
rsassa_pss_sha256_raw: { kty: 3, alg: -37 },
rsassa_pss_sha256_der: { kty: 3, alg: -37 },
secp256k1_ecdsa_sha256_raw: { kty: 2, alg: -47, crv: 8 },
secp256k1_ecdsa_sha256_der: { kty: 2, alg: -47, crv: 8 },
rsassa_pss_sha384_raw: { kty: 3, alg: -38 },
rsassa_pkcsv15_sha256_raw: { kty: 3, alg: -257 },
rsassa_pkcsv15_sha384_raw: { kty: 3, alg: -258 },
rsassa_pkcsv15_sha512_raw: { kty: 3, alg: -259 },
rsassa_pkcsv15_sha1_raw: { kty: 3, alg: -65535 },
secp384r1_ecdsa_sha384_raw: { kty: 2, alg: -35, crv: 2 },
secp512r1_ecdsa_sha256_raw: { kty: 2, alg: -36, crv: 3 },
ed25519_eddsa_sha512_raw: { kty: 1, alg: -8, crv: 6 },
};
/**
* A helper to format COSEInfo a little nicer than we can achieve with JSON.stringify()
*
* Input: `{ "kty": 3, "alg": -257 }`
*
* Output: `"{ kty: 3, alg: -257 }"`
*/
function stringifyCOSEInfo(info: COSEInfo): string {
const { kty, alg, crv } = info;
let toReturn = '';
if (kty !== COSEKTY.RSA) {
toReturn = `{ kty: ${kty}, alg: ${alg}, crv: ${crv} }`;
} else {
toReturn = `{ kty: ${kty}, alg: ${alg} }`;
}
return toReturn;
}
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