fix(sdk): Update ec-wrapped salt value (#464)

Author: dmihalcik-virtru

lib/tdf3/src/crypto/salt.ts

@@ -0,0 +1,11 @@
+const generateSalt = async () => {
+  const encoder = new TextEncoder();
+  const data = encoder.encode('TDF');
+
+  // Generate hash
+  const hashBuffer = await crypto.subtle.digest('SHA-256', data);
+
+  return new Uint8Array(hashBuffer);
+};
+
+export const ztdfSalt = generateSalt();

lib/tdf3/src/models/key-access.ts

@@ -5,6 +5,7 @@ import { pemPublicToCrypto } from '../../../src/nanotdf-crypto/pemPublicToCrypto
 import { cryptoPublicToPem } from '../../../src/utils.js';
 import { Binary } from '../binary.js';
 import * as cryptoService from '../crypto/index.js';
+import { ztdfSalt } from '../crypto/salt.js';
 import { Policy } from './policy.js';
 
 export type KeyAccessType = 'remote' | 'wrapped' | 'ec-wrapped';
@@ -44,7 +45,7 @@ export class ECWrapped {
       pemPublicToCrypto(this.publicKey),
     ]);
     const kek = await keyAgreement(ek.privateKey, clientPublicKey, {
-      hkdfSalt: new TextEncoder().encode('salt'),
+      hkdfSalt: await ztdfSalt,
       hkdfHash: 'SHA-256',
     });
     const iv = generateRandomNumber(12);

lib/tdf3/src/tdf.ts

@@ -54,6 +54,7 @@ import {
 import { unsigned } from './utils/buffer-crc32.js';
 import { ZipReader, ZipWriter, keyMerge, concatUint8 } from './utils/index.js';
 import { CentralDirectory } from './utils/zip-reader.js';
+import { ztdfSalt } from './crypto/salt.js';
 
 // TODO: input validation on manifest JSON
 const DEFAULT_SEGMENT_SIZE = 1024 * 1024;
@@ -707,7 +708,7 @@ async function unwrapKey({
       const serverEphemeralKey: CryptoKey = await pemPublicToCrypto(sessionPublicKey);
       const ekr = ephemeralEncryptionKeysRaw as CryptoKeyPair;
       const kek = await keyAgreement(ekr.privateKey, serverEphemeralKey, {
-        hkdfSalt: new TextEncoder().encode('salt'),
+        hkdfSalt: await ztdfSalt,
         hkdfHash: 'SHA-256',
       });
       const wrappedKeyAndNonce = base64.decodeArrayBuffer(entityWrappedKey);

lib/tests/server.ts

@@ -12,6 +12,7 @@ import { Binary } from '../tdf3/index.js';
 import { type KeyAccessObject } from '../tdf3/src/models/index.js';
 import { valueFor } from './web/policy/mock-attrs.js';
 import { AttributeAndValue } from '../src/policy/attributes.js';
+import { ztdfSalt } from '../tdf3/src/crypto/salt.js';
 
 const Mocks = getMocks();
 
@@ -185,7 +186,7 @@ const kas: RequestListener = async (req, res) => {
             ['deriveBits', 'deriveKey']
           );
           const kek = await keyAgreement(kasPrivateKey, ephemeralKey, {
-            hkdfSalt: new TextEncoder().encode('salt'),
+            hkdfSalt: await ztdfSalt,
             hkdfHash: 'SHA-256',
           });
           const iv = wk.slice(0, 12);
@@ -214,7 +215,7 @@ const kas: RequestListener = async (req, res) => {
           ['deriveBits', 'deriveKey']
         );
         const kek = await keyAgreement(sessionKeyPair.privateKey, clientPublicKey, {
-          hkdfSalt: new TextEncoder().encode('salt'),
+          hkdfSalt: await ztdfSalt,
           hkdfHash: 'SHA-256',
         });
         const iv = generateRandomNumber(12);