fix(passkey-crypto): change deriveEnterpriseSalt output encoding from base64 to base64url

Retail's hmac.ts now returns base64url-encoded PRF salt. The SDK must
match this encoding so HMAC values are compatible and passkey
authentication does not silently fail.

WCN-410

TICKET: WCN-410

Author: derranW26

modules/passkey-crypto/package.json

@@ -35,7 +35,8 @@
   },
   "dependencies": {
     "@bitgo/public-types": "6.1.0",
-    "@bitgo/sdk-core": "^36.44.0"
+    "@bitgo/sdk-core": "^36.44.0",
+    "@bitgo/sjcl": "^1.1.0"
   },
   "devDependencies": {
     "@types/node": "^18.0.0"

modules/passkey-crypto/src/attachPasskeyToWallet.ts

@@ -37,8 +37,8 @@ export async function attachPasskeyToWallet(params: {
   const keychain = await wallet.getEncryptedUserKeychain();
   const keychainId = keychain.id;
 
-  // Derive enterprise-scoped salt
-  const enterpriseSalt = deriveEnterpriseSalt(device.prfSalt, enterpriseId);
+  // Derive enterprise-scoped salt (already base64url-encoded)
+  const prfSalt = deriveEnterpriseSalt(device.prfSalt, enterpriseId);
 
   // Decrypt private key with existing passphrase
   const privateKey = bitgo.decrypt({ password: existingPassphrase, input: keychain.encryptedPrv });
@@ -53,7 +53,7 @@ export async function attachPasskeyToWallet(params: {
     publicKey: {
       allowCredentials: [{ type: 'public-key', id: credentialIdBuffer }],
     } as PublicKeyCredentialRequestOptions,
-    evalByCredential: { [device.credentialId]: enterpriseSalt },
+    evalByCredential: { [device.credentialId]: prfSalt },
   });
 
   if (!authResult.prfResult) {
@@ -64,20 +64,12 @@ export async function attachPasskeyToWallet(params: {
   const prfPassword = derivePassword(authResult.prfResult);
   const encryptedPrv = bitgo.encrypt({ password: prfPassword, input: privateKey });
 
-  // Convert enterpriseSalt from hex to base64url (URL-safe, no padding)
-  // as required by the server's prfSalt validation.
-  const prfSaltBase64url = Buffer.from(enterpriseSalt, 'hex')
-    .toString('base64')
-    .replace(/\+/g, '-')
-    .replace(/\//g, '_')
-    .replace(/=+$/, '');
-
   // PUT webauthnInfo to keychain endpoint
   const updatedKeychain = await bitgo
     .put(bitgo.url(`/${coin}/key/${keychainId}`, 2))
     .send({
       webauthnInfo: {
-        prfSalt: prfSaltBase64url,
+        prfSalt,
         otpDeviceId: device.id,
         encryptedPrv,
       },

modules/passkey-crypto/src/deriveEnterpriseSalt.ts

@@ -1,4 +1,4 @@
-import { createHmac } from 'crypto';
+import * as sjcl from '@bitgo/sjcl';
 
 /**
  * Derives an enterprise-scoped PRF salt to prevent cross-enterprise key reuse.
@@ -8,9 +8,11 @@ import { createHmac } from 'crypto';
  *
  * @param baseSalt - Server-provided base64url-encoded PRF salt
  * @param enterpriseId - Enterprise identifier
- * @returns Hex-encoded HMAC-SHA256 digest
+ * @returns Base64url-encoded HMAC-SHA256 digest
  */
 export function deriveEnterpriseSalt(baseSalt: string, enterpriseId: string): string {
-  const keyBytes = Buffer.from(baseSalt.replace(/-/g, '+').replace(/_/g, '/'), 'base64');
-  return createHmac('sha256', keyBytes).update(enterpriseId).digest('hex');
+  const keyBits = sjcl.codec.base64url.toBits(baseSalt);
+  const dataBits = sjcl.codec.utf8String.toBits(enterpriseId);
+  const resultBits = new sjcl.misc.hmac(keyBits, sjcl.hash.sha256).mac(dataBits);
+  return sjcl.codec.base64url.fromBits(resultBits);
 }

modules/passkey-crypto/test/unit/deriveEnterpriseSalt.test.ts

@@ -5,7 +5,7 @@ import { deriveEnterpriseSalt } from '../../src';
 const REAL_FIXTURE = {
   basePrfSalt: 'ZqJ64M2dL65zn2-Jxd58SMN2ILc9QjbCFxUTGHd_LC8',
   enterpriseId: '69c2aea1a3d7bc07f7f775c0ca86b0ec',
-  expectedDerivedSalt: 'a226ac3aace4bb2b84cfff34e37fb7217620852bb72d5e0dfdad4c2c8473994f',
+  expectedDerivedSalt: 'oiasOqzkuyuEz_8043-3IXYghSu3LV4N_a1MLIRzmU8',
 };
 
 describe('deriveEnterpriseSalt', function () {
@@ -37,10 +37,10 @@ describe('deriveEnterpriseSalt', function () {
     assert.notStrictEqual(saltA, saltB);
   });
 
-  it('returns a non-empty hex string', function () {
+  it('returns a non-empty base64url string', function () {
     const result = deriveEnterpriseSalt(REAL_FIXTURE.basePrfSalt, REAL_FIXTURE.enterpriseId);
     assert.strictEqual(typeof result, 'string');
     assert.ok(result.length > 0);
-    assert.match(result, /^[0-9a-f]{64}$/);
+    assert.match(result, /^[A-Za-z0-9_-]+$/);
   });
 });