WebAuthn Packed attestation verification sample in NodeJS

verify.packed.webauthn.js

const crypto    = require('crypto');
const base64url = require('base64url');
const cbor      = require('cbor');
const jsrsasign = require('jsrsasign');
const elliptic  = require('elliptic');
const NodeRSA   = require('node-rsa');

let COSEKEYS = {
    'kty' : 1,
    'alg' : 3,
    'crv' : -1,
    'x'   : -2,
    'y'   : -3,
    'n'   : -1,
    'e'   : -2
}

let COSEKTY = {
    'OKP': 1,
    'EC2': 2,
    'RSA': 3
}

let COSERSASCHEME = {
    '-3': 'pss-sha256',
    '-39': 'pss-sha512',
    '-38': 'pss-sha384',
    '-65535': 'pkcs1-sha1',
    '-257': 'pkcs1-sha256',
    '-258': 'pkcs1-sha384',
    '-259': 'pkcs1-sha512'
}

var COSECRV = {
    '1': 'p256',
    '2': 'p384',
    '3': 'p521'
}

var COSEALGHASH = {
    '-257': 'sha256',
    '-258': 'sha384',
    '-259': 'sha512',
    '-65535': 'sha1',
    '-39': 'sha512',
    '-38': 'sha384',
    '-37': 'sha256',
    '-260': 'sha256',
    '-261': 'sha512',
    '-7': 'sha256',
    '-36': 'sha512'
}

let hash = (alg, message) => {
    return crypto.createHash(alg).update(message).digest();
}

let base64ToPem = (b64cert) => {
    let pemcert = '';
    for(let i = 0; i < b64cert.length; i += 64)
        pemcert += b64cert.slice(i, i + 64) + '\n';

    return '-----BEGIN CERTIFICATE-----\n' + pemcert + '-----END CERTIFICATE-----';
}

var getCertificateInfo = (certificate) => {
    let subjectCert = new jsrsasign.X509();
    subjectCert.readCertPEM(certificate);

    let subjectString = subjectCert.getSubjectString();
    let subjectParts  = subjectString.slice(1).split('/');

    let subject = {};
    for(let field of subjectParts) {
        let kv = field.split('=');
        subject[kv[0]] = kv[1];
    }

    let version = subjectCert.version;
    let basicConstraintsCA = !!subjectCert.getExtBasicConstraints().cA;

    return {
        subject, version, basicConstraintsCA
    }
}

var parseAuthData = (buffer) => {
    let rpIdHash      = buffer.slice(0, 32);          buffer = buffer.slice(32);
    let flagsBuf      = buffer.slice(0, 1);           buffer = buffer.slice(1);
    let flagsInt      = flagsBuf[0];
    let flags = {
        up: !!(flagsInt & 0x01),
        uv: !!(flagsInt & 0x04),
        at: !!(flagsInt & 0x40),
        ed: !!(flagsInt & 0x80),
        flagsInt
    }

    let counterBuf    = buffer.slice(0, 4);           buffer = buffer.slice(4);
    let counter       = counterBuf.readUInt32BE(0);

    let aaguid        = undefined;
    let credID        = undefined;
    let COSEPublicKey = undefined;

    if(flags.at) {
        aaguid           = buffer.slice(0, 16);          buffer = buffer.slice(16);
        let credIDLenBuf = buffer.slice(0, 2);           buffer = buffer.slice(2);
        let credIDLen    = credIDLenBuf.readUInt16BE(0);
        credID           = buffer.slice(0, credIDLen);   buffer = buffer.slice(credIDLen);
        COSEPublicKey    = buffer;
    }

    return {rpIdHash, flagsBuf, flags, counter, counterBuf, aaguid, credID, COSEPublicKey}
}

let verifyPackedAttestation = (webAuthnResponse) => {
    let attestationBuffer = base64url.toBuffer(webAuthnResponse.response.attestationObject);
    let attestationStruct = cbor.decodeAllSync(attestationBuffer)[0];

    let authDataStruct = parseAuthData(attestationStruct.authData);

    let clientDataHashBuf   = hash('sha256', base64url.toBuffer(webAuthnResponse.response.clientDataJSON));
    let signatureBaseBuffer = Buffer.concat([attestationStruct.authData, clientDataHashBuf]);

    let signatureBuffer     = attestationStruct.attStmt.sig
    let signatureIsValid    = false;

    if(attestationStruct.attStmt.x5c) {
    /* ----- Verify FULL attestation ----- */
        let leafCert = base64ToPem(attestationStruct.attStmt.x5c[0].toString('base64'));
        let certInfo = getCertificateInfo(leafCert);

        if(certInfo.subject.OU !== 'Authenticator Attestation')
            throw new Error('Batch certificate OU MUST be set strictly to "Authenticator Attestation"!');

        if(!certInfo.subject.CN)
            throw new Error('Batch certificate CN MUST no be empty!');

        if(!certInfo.subject.O)
            throw new Error('Batch certificate CN MUST no be empty!');

        if(!certInfo.subject.C || certInfo.subject.C.length !== 2)
            throw new Error('Batch certificate C MUST be set to two character ISO 3166 code!');

        if(certInfo.basicConstraintsCA)
            throw new Error('Batch certificate basic constraints CA MUST be false!');

        if(certInfo.version !== 3)
            throw new Error('Batch certificate version MUST be 3(ASN1 2)!');

        signatureIsValid = crypto.createVerify('sha256')
            .update(signatureBaseBuffer)
            .verify(leafCert, signatureBuffer);
    /* ----- Verify FULL attestation ENDS ----- */
    } else if(attestationStruct.attStmt.ecdaaKeyId) {
        throw new Error('ECDAA IS NOT SUPPORTED YET!');
    } else {
    /* ----- Verify SURROGATE attestation ----- */
        let pubKeyCose = cbor.decodeAllSync(authDataStruct.COSEPublicKey)[0];
        let hashAlg    = COSEALGHASH[pubKeyCose.get(COSEKEYS.alg)];
        if(pubKeyCose.get(COSEKEYS.kty) === COSEKTY.EC2) {
            let x = pubKeyCose.get(COSEKEYS.x);
            let y = pubKeyCose.get(COSEKEYS.y);
            
            let ansiKey = Buffer.concat([Buffer.from([0x04]), x, y]);

            let signatureBaseHash = hash(hashAlg, signatureBaseBuffer);

            let ec  = new elliptic.ec(COSECRV[pubKeyCose.get(COSEKEYS.crv)]);
            let key = ec.keyFromPublic(ansiKey);

            signatureIsValid = key.verify(signatureBaseHash, signatureBuffer)
        } else if(pubKeyCose.get(COSEKEYS.kty) === COSEKTY.RSA) {
            let signingScheme = COSERSASCHEME[pubKeyCose.get(COSEKEYS.alg)];

            let key = new NodeRSA(undefined, { signingScheme });
            key.importKey({
                n: pubKeyCose.get(COSEKEYS.n),
                e: 65537,
            }, 'components-public');

            signatureIsValid = key.verify(signatureBaseBuffer, signatureBuffer)
        } else if(pubKeyCose.get(COSEKEYS.kty) === COSEKTY.OKP) {
            let x = pubKeyCose.get(COSEKEYS.x);
            let signatureBaseHash = hash(hashAlg, signatureBaseBuffer);

            let key = new elliptic.eddsa('ed25519');
            key.keyFromPublic(x)

            signatureIsValid = key.verify(signatureBaseHash, signatureBuffer)
        }
    /* ----- Verify SURROGATE attestation ENDS ----- */
    }

    if(!signatureIsValid)
        throw new Error('Failed to verify the signature!');

    return true
}



let packedFullAttestationWebAuthnSample = {
    "rawId": "wsLryOAxXMU54s2fCSWPzWjXHOBKPploN-UHftj4_rpIu6BZxNXppm82f7Y6iX9FEOKKeS5-N2TALeyzLnJfAA",
    "id": "wsLryOAxXMU54s2fCSWPzWjXHOBKPploN-UHftj4_rpIu6BZxNXppm82f7Y6iX9FEOKKeS5-N2TALeyzLnJfAA",
    "response": {
        "clientDataJSON": "eyJjaGFsbGVuZ2UiOiJZTVdFVGYtUDc5aU1iLUJxZFRreVNOUmVPdmE3bksyaVZDOWZpQzhpR3ZZeXB1bkVPQ1pHWjYtWTVPVjFydk1pRGdBaldmRmk2VUMwV3lLR3NqQS1nQSIsIm9yaWdpbiI6Imh0dHBzOi8vd2ViYXV0aG4ub3JnIiwidHlwZSI6IndlYmF1dGhuLmNyZWF0ZSJ9",
        "attestationObject": "o2NmbXRmcGFja2VkZ2F0dFN0bXSjY2FsZyZjc2lnWEcwRQIhAIzOihC6Ba80o5JnoYOJJ_EtEVmWQcAvxVCnsCFnVRQZAiAfeIddLPsPl1FeSX8B5xZANcQKGNoO7pb0TZPnuJdebGN4NWOBWQKzMIICrzCCAZegAwIBAgIESFs9tjANBgkqhkiG9w0BAQsFADAhMR8wHQYDVQQDDBZZdWJpY28gRklETyBQcmV2aWV3IENBMB4XDTE4MDQxMjEwNTcxMFoXDTE4MTIzMTEwNTcxMFowbzELMAkGA1UEBhMCU0UxEjAQBgNVBAoMCVl1YmljbyBBQjEiMCAGA1UECwwZQXV0aGVudGljYXRvciBBdHRlc3RhdGlvbjEoMCYGA1UEAwwfWXViaWNvIFUyRiBFRSBTZXJpYWwgMTIxMzkzOTEyNjBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABPss3TBDKMVySlDM5vYLrX0nqRtZ4eZvKXuJydQ9wrLHeIm08P-dAijLlG384BsZWJtngEqsl38oGJzNsyV0yiijbDBqMCIGCSsGAQQBgsQKAgQVMS4zLjYuMS40LjEuNDE0ODIuMS42MBMGCysGAQQBguUcAgEBBAQDAgQwMCEGCysGAQQBguUcAQEEBBIEEPigEfOMCk0VgAYXER-e3H0wDAYDVR0TAQH_BAIwADANBgkqhkiG9w0BAQsFAAOCAQEAMvPkvVjXQiuvSZmGCB8NqTvGqhxyEfkoU-vz63PaaTsG3jEzjl0C7PZ26VxCvqWPJdM3P3e7Kp18sj4RjEHUmkya2PPipOwBd3p0qMQSQ8MeziCPLQ9uvGGb4YShcvaprMv4c21b4piza-znHneNCmmq-ZS4Y23o-vYv085_BEwyLPcmPjSZ5qWysCq7rVvZ7OWwcU1zu5RhSZyUKl8dzK9lAzs5OdRH2fzEewsW2OkB_Ow_jBvAxqwLXXTHuwMFaRfpmBoZuQlcofSrnwJ8KA-K-e0dKTz2zC8EbZrWYrSpbrHKyqxeBT6DkUd8H4tgAd5lOr_yqrtVmIaRfq07NmhhdXRoRGF0YVjElWkIjx7O4yMpVANdvRDXyuORMFonUbVZu4_Xy7IpvdRBAAAAAPigEfOMCk0VgAYXER-e3H0AQMLC68jgMVzFOeLNnwklj81o1xzgSj6ZaDflB37Y-P66SLugWcTV6aZvNn-2Ool_RRDiinkufjdkwC3ssy5yXwClAQIDJiABIVggAYD1TSpf120DSVxen8ki56kF1bmT4EXO-P0JnSk5mMwiWCB3TlMZBRqPY6llzDcfHd-oW0EHdaFNgBdlGGFobpHKlw"
    }
}

let packedSurrogateAttestationWebAuthnSample = {
    "id": "H6X2BnnjgOzu_Oj87vpRnwMJeJYVzwM3wtY1lhAfQ14",
    "rawId": "H6X2BnnjgOzu_Oj87vpRnwMJeJYVzwM3wtY1lhAfQ14",
    "response": {
        "attestationObject": "o2NmbXRmcGFja2VkZ2F0dFN0bXSiY2FsZzn__mNzaWdZAQCPypMLXWqtCZ1sc5QdjhH-pAzm8-adpfbemd5zsym2krscwV0EeOdTrdUOdy3hWj5HuK9dIX_OpNro2jKrHfUj_0Kp-u87iqJ3MPzs-D9zXOqkbWqcY94Zh52wrPwhGfJ8BiQp5T4Q97E042hYQRDKmtv7N-BT6dywiuFHxfm1sDbUZ_yyEIN3jgttJzjp_wvk_RJmb78bLPTlym83Y0Ws73K6FFeiqFNqLA_8a4V0I088hs_IEPlj8PWxW0wnIUhI9IcRf0GEmUwTBpbNDGpIFGOudnl_C3YuXuzK3R6pv2r7m9-9cIIeeYXD9BhSMBQ0A8oxBbVF7j-0xXDNrXHZaGF1dGhEYXRhWQFnSZYN5YgOjGh0NBcPZHZgW4_krrmihjLHmVzzuoMdl2NBAAAAOKjVmSRjt0nqud40p1PeHgEAIB-l9gZ544Ds7vzo_O76UZ8DCXiWFc8DN8LWNZYQH0NepAEDAzn__iBZAQDAIqzybPPmgeL5OR6JKq9bWDiENJlN_LePQEnf1_sgOm4FJ9kBTbOTtWplfoMXg40A7meMppiRqP72A3tmILwZ5xKIyY7V8Y2t8X1ilYJol2nCKOpAEqGLTRJjF64GQxen0uFpi1tA6l6N-ZboPxjky4aidBdUP22YZuEPCO8-9ZTha8qwvTgZwMHhZ40TUPEJGGWOnHNlYmqnfFfk0P-UOZokI0rqtqqQGMwzV2RrH2kjKTZGfyskAQnrqf9PoJkye4KUjWkWnZzhkZbrDoLyTEX2oWvTTflnR5tAVMQch4UGgEHSZ00G5SFoc19nGx_UJcqezx5cLZsny-qQYDRjIUMBAAE",
        "clientDataJSON": "eyJvcmlnaW4iOiJodHRwOi8vbG9jYWxob3N0OjMwMDAiLCJjaGFsbGVuZ2UiOiJBWGtYV1hQUDNnTHg4T0xscGtKM2FSUmhGV250blNFTmdnbmpEcEJxbDFuZ0tvbDd4V3dldlVZdnJwQkRQM0xFdmRyMkVPU3RPRnBHR3huTXZYay1WdyIsInR5cGUiOiJ3ZWJhdXRobi5jcmVhdGUifQ"
    },
    "type": "public-key"
}

verifyPackedAttestation(packedFullAttestationWebAuthnSample)
verifyPackedAttestation(packedSurrogateAttestationWebAuthnSample)

Don't forget to install dependencies:

npm i base64url cbor jsrsasign node-rsa elliptic

thanks for this 👍

Thanks Yuriy. So useful! So happy I found your stuff. Many guides that walk devs through registering and authentication leave assertion and attestation only at a high level. You've curated, and authored, a wonderful set of resources. I wonder if the publishers of https://webauthn.guide/ for example might add a link to your stuff at the end of their guide.