1 files changed, 155 insertions, 0 deletions
diff --git a/packages/server/src/attestation/verifications/verifyAndroidSafetyNet.ts b/packages/server/src/attestation/verifications/verifyAndroidSafetyNet.ts
new file mode 100644
index 0000000..6f5365a
--- /dev/null
+++ b/packages/server/src/attestation/verifications/verifyAndroidSafetyNet.ts
@@ -0,0 +1,155 @@
+import base64url from 'base64url';
+import {
+  AttestationObject,
+  VerifiedAttestation,
+  SafetyNetJWTHeader,
+  SafetyNetJWTPayload,
+  SafetyNetJWTSignature,
+} from "@webauthntine/typescript-types";
+
+import toHash from "@helpers/toHash";
+import verifySignature from '@helpers/verifySignature';
+import convertCOSEtoPKCS from '@helpers/convertCOSEtoPKCS';
+import getCertificateInfo from '@helpers/getCertificateInfo';
+
+import parseAttestationAuthData from '../parseAttestationAuthData';
+
+
+/**
+ * Verify an attestation response with fmt 'android-safetynet'
+ */
+export default function verifyAttestationAndroidSafetyNet(
+  attestationObject: AttestationObject,
+  base64ClientDataJSON: string,
+): VerifiedAttestation {
+  const { attStmt, authData, fmt } = attestationObject;
+
+  if (!attStmt.response) {
+    throw new Error('No response was included in attStmt by authenticator (SafetyNet)');
+  }
+
+  // Prepare to verify a JWT
+  const jwt = attStmt.response.toString('utf8');
+  const jwtParts = jwt.split('.');
+
+  const HEADER: SafetyNetJWTHeader = JSON.parse(base64url.decode(jwtParts[0]));
+  const PAYLOAD: SafetyNetJWTPayload = JSON.parse(base64url.decode(jwtParts[1]));
+  const SIGNATURE: SafetyNetJWTSignature = jwtParts[2];
+
+  /**
+   * START Verify PAYLOAD
+   */
+  const { nonce, ctsProfileMatch } = PAYLOAD;
+  const clientDataHash = toHash(base64url.toBuffer(base64ClientDataJSON));
+
+  const nonceBase = Buffer.concat([
+    authData,
+    clientDataHash,
+  ]);
+  const nonceBuffer = toHash(nonceBase);
+  const expectedNonce = nonceBuffer.toString('base64');
+
+  if (nonce !== expectedNonce) {
+    throw new Error('Could not verify payload nonce (SafetyNet)');
+  }
+
+  if (!ctsProfileMatch) {
+    throw new Error('Could not verify device integrity (SafetyNet)');
+  }
+  /**
+   * END Verify PAYLOAD
+   */
+
+  /**
+   * START Verify Header
+   */
+  // Generate an array of certs constituting a full certificate chain
+  const fullpathCert = HEADER.x5c.concat([GlobalSignRootCAR2]).map((cert) => {
+    let pem = '';
+    // Take a string of characters and chop them up into 64-char lines (just like a PEM cert)
+    for (let i = 0; i < cert.length; i += 64) {
+      pem += `${cert.slice(i, i + 64)}\n`;
+    }
+
+    return `-----BEGIN CERTIFICATE-----\n${pem}-----END CERTIFICATE-----`;
+  });
+
+  const certificate = fullpathCert[0];
+
+  const commonCertInfo = getCertificateInfo(certificate);
+
+  const { subject } = commonCertInfo;
+
+  // TODO: Find out where this CN string is specified and if it might change
+  if (subject.CN !== 'attest.android.com') {
+    throw new Error('Certificate common name was not "attest.android.com" (SafetyNet)');
+  }
+
+  // TODO: Re-investigate this if we decide to "use MDS or Metadata Statements"
+  // validateCertificatePath(fullpathCert);
+  /**
+   * END Verify Header
+   */
+
+  /**
+   * START Verify Signature
+   */
+  const signatureBaseBuffer = Buffer.from(`${jwtParts[0]}.${jwtParts[1]}`);
+  const signatureBuffer = base64url.toBuffer(SIGNATURE);
+
+  const toReturn: VerifiedAttestation = {
+    verified: verifySignature(signatureBuffer, signatureBaseBuffer, certificate),
+    userVerified: false,
+  };
+  /**
+   * END Verify Signature
+   */
+
+
+  if (toReturn.verified) {
+    const authDataStruct = parseAttestationAuthData(authData);
+    const { counter, credentialID, COSEPublicKey, flags } = authDataStruct;
+
+    toReturn.userVerified = flags.uv;
+
+    if (!COSEPublicKey) {
+      throw new Error('No public key was provided by authenticator (SafetyNet)');
+    }
+
+    if (!credentialID) {
+      throw new Error('No credential ID was provided by authenticator (SafetyNet)');
+    }
+
+    const publicKey = convertCOSEtoPKCS(COSEPublicKey);
+
+    toReturn.authenticatorInfo = {
+      fmt,
+      counter,
+      base64PublicKey: base64url.encode(publicKey),
+      base64CredentialID: base64url.encode(credentialID),
+    };
+  }
+
+  return toReturn;
+}
+
+/**
+ * This "GS Root R2" root certificate was downloaded from https://pki.goog/gsr2/GSR2.crt
+ * on 08/10/2019 and then run through `base64url.encode()` to get this representation.
+ *
+ * The certificate is valid until Dec 15, 2021
+ */
+const GlobalSignRootCAR2 = 'MIIDujCCAqKgAwIBAgILBAAAAAABD4Ym5g0wDQYJKoZIhvcNAQEFBQAwTDEgMB4GA1UEC' +
+  'xMXR2xvYmFsU2lnbiBSb290IENBIC0gUjIxEzARBgNVBAoTCkdsb2JhbFNpZ24xEzARBgNVBAMTCkdsb2JhbFNpZ24wHhc' +
+  'NMDYxMjE1MDgwMDAwWhcNMjExMjE1MDgwMDAwWjBMMSAwHgYDVQQLExdHbG9iYWxTaWduIFJvb3QgQ0EgLSBSMjETMBEGA' +
+  '1UEChMKR2xvYmFsU2lnbjETMBEGA1UEAxMKR2xvYmFsU2lnbjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAKb' +
+  'PJA6-Lm8omUVCxKs-IVSbC9N_hHD6ErPLv4dfxn-G07IwXNb9rfF73OX4YJYJkhD10FPe-3t-c4isUoh7SqbKSaZeqKeMW' +
+  'hG8eoLrvozps6yWJQeXSpkqBy-0Hne_ig-1AnwblrjFuTosvNYSuetZfeLQBoZfXklqtTleiDTsvHgMCJiEbKjNS7SgfQx' +
+  '5TfC4LcshytVsW33hoCmEofnTlEnLJGKRILzdC9XZzPnqJworc5HGnRusyMvo4KD0L5CLTfuwNhv2GXqF4G3yYROIXJ_gk' +
+  'wpRl4pazq-r1feqCapgvdzZX99yqWATXgAByUr6P6TqBwMhAo6CygPCm48CAwEAAaOBnDCBmTAOBgNVHQ8BAf8EBAMCAQY' +
+  'wDwYDVR0TAQH_BAUwAwEB_zAdBgNVHQ4EFgQUm-IHV2ccHsBqBt5ZtJot39wZhi4wNgYDVR0fBC8wLTAroCmgJ4YlaHR0c' +
+  'DovL2NybC5nbG9iYWxzaWduLm5ldC9yb290LXIyLmNybDAfBgNVHSMEGDAWgBSb4gdXZxwewGoG3lm0mi3f3BmGLjANBgk' +
+  'qhkiG9w0BAQUFAAOCAQEAmYFThxxol4aR7OBKuEQLq4GsJ0_WwbgcQ3izDJr86iw8bmEbTUsp9Z8FHSbBuOmDAGJFtqkIk' +
+  '7mpM0sYmsL4h4hO291xNBrBVNpGP-DTKqttVCL1OmLNIG-6KYnX3ZHu01yiPqFbQfXf5WRDLenVOavSot-3i9DAgBkcRcA' +
+  'tjOj4LaR0VknFBbVPFd5uRHg5h6h-u_N5GJG79G-dwfCMNYxdAfvDbbnvRG15RjF-Cv6pgsH_76tuIMRQyV-dTZsXjAzlA' +
+  'cmgQWpzU_qlULRuJQ_7TBj0_VLZjmmx6BEP3ojY-x1J96relc8geMJgEtslQIxq_H5COEBkEveegeGTLg';