WebAuthn Android Keystore attestation verification sample in NodeJS

verify.androidkey.webauthn.js

const crypto    = require('crypto');
const base64url = require('base64url');
const cbor      = require('cbor');
const asn1      = require('@lapo/asn1js');
const jsrsasign = require('jsrsasign');

/* Android Keystore Root is not published anywhere.
 * This certificate was extracted from one of the attestations
 * The last certificate in x5c must match this certificate
 * This needs to be checked to ensure that malicious party wont generate fake attestations
 */
let androidkeystoreroot = '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';

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

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

var 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 findOID = (asn1object, oid) => {
    if(!asn1object.sub)
        return

    for(let sub of asn1object.sub) {
        if(sub.typeName() !== 'OBJECT_IDENTIFIER' || sub.content() !== oid) {
            let result = findOID(sub, oid);

            if(result)
                return result

        } else {
            return asn1object
        }
    }
}

let asn1ObjectToJSON = (asn1object) => {
    let JASN1 = {
        'type': asn1object.typeName()
    }

    if(!asn1object.sub) {
        if(asn1object.typeName() === 'BIT_STRING' || asn1object.typeName() === 'OCTET_STRING')
            JASN1.data = asn1object.stream.enc.slice(asn1object.posContent(), asn1object.posEnd());
        else
            JASN1.data = asn1object.content();

        return JASN1
    }

    JASN1.data = [];
    for(let sub of asn1object.sub) {
        JASN1.data.push(asn1ObjectToJSON(sub));
    }

    return JASN1
}

let containsASN1Tag = (seq, tag) => {
    for(let member of seq)
        if(member.type === '[' + tag + ']')
            return true

    return false
}

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}
}

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

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

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

    return fields
}

var validateCertificatePath = (certificates) => {
    if((new Set(certificates)).size !== certificates.length)
        throw new Error('Failed to validate certificates path! Dublicate certificates detected!');

    for(let i = 0; i < certificates.length; i++) {
        let subjectPem  = certificates[i];
        let subjectCert = new jsrsasign.X509();
        subjectCert.readCertPEM(subjectPem);

        let issuerPem = '';
        if(i + 1 >= certificates.length)
            issuerPem = subjectPem;
        else
            issuerPem = certificates[i + 1];

        let issuerCert = new jsrsasign.X509();
        issuerCert.readCertPEM(issuerPem);

        if(subjectCert.getIssuerString() !== issuerCert.getSubjectString())
            throw new Error('Failed to validate certificate path! Issuers dont match!');

        let subjectCertStruct = jsrsasign.ASN1HEX.getTLVbyList(subjectCert.hex, 0, [0]);
        let algorithm         = subjectCert.getSignatureAlgorithmField();
        let signatureHex      = subjectCert.getSignatureValueHex()

        let Signature = new jsrsasign.crypto.Signature({alg: algorithm});
        Signature.init(issuerPem);
        Signature.updateHex(subjectCertStruct);

        if(!Signature.verify(signatureHex))
            throw new Error('Failed to validate certificate path!')
    }

    return true
}

let verifyAndroidKeyAttestation = (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));

/* ----- VERIFY SIGNATURE ----- */
    let signatureBaseBuffer = Buffer.concat([attestationStruct.authData, clientDataHashBuf]);

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

    let leafCert = base64ToPem(attestationStruct.attStmt.x5c[0].toString('base64'));

    signatureIsValid = crypto.createVerify('sha256')
        .update(signatureBaseBuffer)
        .verify(leafCert, signatureBuffer);

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

    let attestationRootCertificateBuffer = attestationStruct.attStmt.x5c[attestationStruct.attStmt.x5c.length - 1];
    if(attestationRootCertificateBuffer.toString('base64') !== androidkeystoreroot)
        throw new Error('Attestation root is not invalid!');

    let certPath = attestationStruct.attStmt.x5c.map((cert) => {
        cert = cert.toString('base64');

        let pemcert = '';
        for(let i = 0; i < cert.length; i += 64)
            pemcert += cert.slice(i, i + 64) + '\n';

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

    validateCertificatePath(certPath);
/* ----- VERIFY SIGNATURE ENDS ----- */

    let certASN1       = asn1.decode(attestationStruct.attStmt.x5c[0]);

/* ----- VERIFY PUBLIC KEY MATCHING ----- */
    let certJSON       = asn1ObjectToJSON(certASN1);
    let certTBS        = certJSON.data[0];
    let certPubKey     = certTBS.data[6];
    let certPubKeyBuff = certPubKey.data[1].data;

    /* CHECK PUBKEY */
    let coseKey = cbor.decodeAllSync(authDataStruct.COSEPublicKey)[0];

    /* ANSI ECC KEY is 0x04 with X and Y coefficients. But certs have it padded with 0x00 so for simplicity it easier to do it that way */
    let ansiKey = Buffer.concat([Buffer([0x00, 0x04]), coseKey.get(COSEKEYS.x), coseKey.get(COSEKEYS.y)])

    if(ansiKey.toString('hex') !== certPubKeyBuff.toString('hex'))
        throw new Error('Certificate public key does not match public key in authData')
/* ----- VERIFY PUBLIC KEY MATCHING ENDS ----- */

/* ----- VERIFY CERTIFICATE REQUIREMENTS ----- */
    let AttestationExtension     = findOID(certASN1, '1.3.6.1.4.1.11129.2.1.17');
    let AttestationExtensionJSON = asn1ObjectToJSON(AttestationExtension);

    let attestationChallenge     = AttestationExtensionJSON.data[1].data[0].data[4].data

    if(attestationChallenge.toString('hex') !== clientDataHashBuf.toString('hex'))
        throw new Error('Certificate attestation challenge is not set to the clientData hash!');

    let softwareEnforcedAuthz = AttestationExtensionJSON.data[1].data[0].data[6].data;
    let teeEnforcedAuthz      = AttestationExtensionJSON.data[1].data[0].data[7].data;

    if(containsASN1Tag(softwareEnforcedAuthz, 600) || containsASN1Tag(teeEnforcedAuthz, 600))
        throw new Error('TEE or Software autherisation list contains "allApplication" flag, which means that credential is not bound to the RP!');
/* ----- VERIFY CERTIFICATE REQUIREMENTS ENDS ----- */

    return true
}


let androidKeyWebAuthnSample = {
    "rawId": "AZD7huwZVx7aW1efRa6Uq3JTQNorj3qA9yrLINXEcgvCQYtWiSQa1eOIVrXfCmip6MzP8KaITOvRLjy3TUHO7_c",
    "id": "AZD7huwZVx7aW1efRa6Uq3JTQNorj3qA9yrLINXEcgvCQYtWiSQa1eOIVrXfCmip6MzP8KaITOvRLjy3TUHO7_c",
    "response": {
        "clientDataJSON": "eyJ0eXBlIjoid2ViYXV0aG4uY3JlYXRlIiwiY2hhbGxlbmdlIjoiVGY2NWJTNkQ1dGVtaDJCd3ZwdHFnQlBiMjVpWkRSeGp3QzVhbnM5MUlJSkRyY3JPcG5XVEs0TFZnRmplVVY0R0RNZTQ0dzhTSTVOc1pzc0lYVFV2RGciLCJvcmlnaW4iOiJodHRwczpcL1wvd2ViYXV0aG4ub3JnIiwiYW5kcm9pZFBhY2thZ2VOYW1lIjoiY29tLmFuZHJvaWQuY2hyb21lIn0",
        "attestationObject": "o2NmbXRrYW5kcm9pZC1rZXlnYXR0U3RtdKNjYWxnJmNzaWdYRjBEAiAsp6jPtimcSgc-fgIsVwgqRsZX6eU7KKbkVGWa0CRJlgIgH5yuf_laPyNy4PlS6e8ZHjs57iztxGiTqO7G91sdlWBjeDVjg1kCzjCCAsowggJwoAMCAQICAQEwCgYIKoZIzj0EAwIwgYgxCzAJBgNVBAYTAlVTMRMwEQYDVQQIDApDYWxpZm9ybmlhMRUwEwYDVQQKDAxHb29nbGUsIEluYy4xEDAOBgNVBAsMB0FuZHJvaWQxOzA5BgNVBAMMMkFuZHJvaWQgS2V5c3RvcmUgU29mdHdhcmUgQXR0ZXN0YXRpb24gSW50ZXJtZWRpYXRlMB4XDTE4MTIwMjA5MTAyNVoXDTI4MTIwMjA5MTAyNVowHzEdMBsGA1UEAwwUQW5kcm9pZCBLZXlzdG9yZSBLZXkwWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAAQ4SaIP3ibDSwCIORpYJ3g9_5OICxZUCIqt-vV6JZVJoXQ8S1JFzyaFz5EFQ2fNT6-5SE5wWTZRAR_A3M52IcaPo4IBMTCCAS0wCwYDVR0PBAQDAgeAMIH8BgorBgEEAdZ5AgERBIHtMIHqAgECCgEAAgEBCgEBBCAqQ4LXu9idi1vfF3LP7MoUOSSHuf1XHy63K9-X3gbUtgQAMIGCv4MQCAIGAWduLuFwv4MRCAIGAbDqja1wv4MSCAIGAbDqja1wv4U9CAIGAWduLt_ov4VFTgRMMEoxJDAiBB1jb20uZ29vZ2xlLmF0dGVzdGF0aW9uZXhhbXBsZQIBATEiBCBa0F7CIcj4OiJhJ97FV1AMPldLxgElqdwhywvkoAZglTAzoQUxAwIBAqIDAgEDowQCAgEApQUxAwIBBKoDAgEBv4N4AwIBF7-DeQMCAR6_hT4DAgEAMB8GA1UdIwQYMBaAFD_8rNYasTqegSC41SUcxWW7HpGpMAoGCCqGSM49BAMCA0gAMEUCIGd3OQiTgFX9Y07kE-qvwh2Kx6lEG9-Xr2ORT5s7AK_-AiEAucDIlFjCUo4rJfqIxNY93HXhvID7lNzGIolS0E-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-EJjWazLKpFMiYbMcK2QZpOCqXMmE_6sy_ghJ0whdJdKKv6luU1_ZtTgZRBmNbxTt6CjpnFYPts-Ea4QFKNmMGQwHQYDVR0OBBYEFD_8rNYasTqegSC41SUcxWW7HpGpMB8GA1UdIwQYMBaAFMit6XdMRcOjzw0WEOR5QzohWjDPMBIGA1UdEwEB_wQIMAYBAf8CAQAwDgYDVR0PAQH_BAQDAgKEMAoGCCqGSM49BAMCA0gAMEUCIEuKm3vugrzAM4euL8CJmLTdw42rJypFn2kMx8OS1A-OAiEA7toBXbb0MunUhDtiTJQE7zp8zL1e-yK75_65dz9ZP_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-xNal1qaC4P_39JDn13H0Qibb2xr_oWy8etxXfSVpyqt7AtVAFdPkMrKo7XTuxIdUGko2MwYTAdBgNVHQ4EFgQUyK3pd0xFw6PPDRYQ5HlDOiFaMM8wHwYDVR0jBBgwFoAUyK3pd0xFw6PPDRYQ5HlDOiFaMM8wDwYDVR0TAQH_BAUwAwEB_zAOBgNVHQ8BAf8EBAMCAoQwCgYIKoZIzj0EAwIDRwAwRAIgNSGj74s0Rh6c1WDzHViJIGrco2VB9g2ezooZjGZIYHsCIE0L81HZMHx9W9o1NB2oRxtjpYVlPK1PJKfnTa9BffG_aGF1dGhEYXRhWMWVaQiPHs7jIylUA129ENfK45EwWidRtVm7j9fLsim91EUAAAAAKPN9K5K4QcSwKoYM73zANABBAVUvAmX241vMKYd7ZBdmkNWaYcNYhoSZCJjFRGmROb6I4ygQUVmH6k9IMwcbZGeAQ4v4WMNphORudwje5h7ty9ClAQIDJiABIVggOEmiD94mw0sAiDkaWCd4Pf-TiAsWVAiKrfr1eiWVSaEiWCB0PEtSRc8mhc-RBUNnzU-vuUhOcFk2UQEfwNzOdiHGjw"
    },
    "type": "public-key"
}

verifyAndroidKeyAttestation(androidKeyWebAuthnSample)

Don't forget to install dependencies:

npm i @lapo/asn1js base64url cbor jsrsasign

@herrjemand I get the following error :

verify-android-key.js:55
'type': asn1object.typeName()
TypeError: Cannot read property 'typeName' of undefined
at asn1ObjectToJSON

Am I missing something?

androidkeystoreroot this is only for ECDSA... RSA is not that root cert.