Add HKDF fallback for Node 14, where SubtleCrypto is not available

src/crypto/hkdf.js

@@ -9,13 +9,53 @@ import util from '../util';
 
 const webCrypto = util.getWebCrypto();
 const nodeCrypto = util.getNodeCrypto();
+const nodeSubtleCrypto = nodeCrypto && nodeCrypto.webcrypto && nodeCrypto.webcrypto.subtle;
 
-export default async function HKDF(hashAlgo, key, salt, info, length) {
+export default async function HKDF(hashAlgo, inputKey, salt, info, outLen) {
   const hash = enums.read(enums.webHash, hashAlgo);
   if (!hash) throw new Error('Hash algo not supported with HKDF');
 
-  const crypto = webCrypto || nodeCrypto.webcrypto.subtle;
-  const importedKey = await crypto.importKey('raw', key, 'HKDF', false, ['deriveBits']);
-  const bits = await crypto.deriveBits({ name: 'HKDF', hash, salt, info }, importedKey, length * 8);
+  if (webCrypto || nodeSubtleCrypto) {
+    const crypto = webCrypto || nodeSubtleCrypto;
+    const importedKey = await crypto.importKey('raw', inputKey, 'HKDF', false, ['deriveBits']);
+    const bits = await crypto.deriveBits({ name: 'HKDF', hash, salt, info }, importedKey, outLen * 8);
     return new Uint8Array(bits);
+  }
+
+  if (nodeCrypto) {
+    const hashAlgoName = enums.read(enums.hash, hashAlgo);
+    // Node-only HKDF implementation based on https://www.rfc-editor.org/rfc/rfc5869
+
+    const computeHMAC = (hmacKey, hmacMessage) => nodeCrypto.createHmac(hashAlgoName, hmacKey).update(hmacMessage).digest();
+    // Step 1: Extract
+    // PRK = HMAC-Hash(salt, IKM)
+    const pseudoRandomKey = computeHMAC(salt, inputKey);
+
+    const hashLen = pseudoRandomKey.length;
+
+    // Step 2: Expand
+    // HKDF-Expand(PRK, info, L) -> OKM
+    const n = Math.ceil(outLen / hashLen);
+    const outputKeyingMaterial = new Uint8Array(n * hashLen);
+
+    // HMAC input buffer updated at each iteration
+    const roundInput = new Uint8Array(hashLen + info.length + 1);
+    // T_i and last byte are updated at each iteration, but `info` remains constant
+    roundInput.set(info, hashLen);
+
+    for (let i = 0; i < n; i++) {
+      // T(0) = empty string (zero length)
+      // T(i) = HMAC-Hash(PRK, T(i-1) | info | i)
+      roundInput[roundInput.length - 1] = i + 1;
+      // t = T(i+1)
+      const t = computeHMAC(pseudoRandomKey, i > 0 ? roundInput : roundInput.subarray(hashLen));
+      roundInput.set(t, 0);
+
+      outputKeyingMaterial.set(t, i * hashLen);
+    }
+
+    return outputKeyingMaterial.subarray(0, outLen);
+  }
+
+  throw new Error('No HKDF implementation available');
 }

src/crypto/public_key/elliptic/ecdh_x.js

@@ -20,7 +20,7 @@ const HKDF_INFO = {
 /**
  * Generate ECDH key for Montgomery curves
  * @param {module:enums.publicKey} algo - Algorithm identifier
- * @returns Promise<{ A, k }>
+ * @returns {Promise<{ A: Uint8Array, k: Uint8Array }>}
  */
 export async function generate(algo) {
   switch (algo) {

src/crypto/public_key/elliptic/eddsa.js

@@ -33,7 +33,7 @@ nacl.hash = bytes => new Uint8Array(sha512().update(bytes).digest());
 /**
  * Generate (non-legacy) EdDSA key
  * @param {module:enums.publicKey} algo - Algorithm identifier
- * @returns Promise<{ A, seed }>
+ * @returns {Promise<{ A: Uint8Array, seed: Uint8Array }>}
  */
 export async function generate(algo) {
   switch (algo) {
@@ -56,8 +56,7 @@ export async function generate(algo) {
  * @param {Uint8Array} privateKey - Private key used to sign the message
  * @param {Uint8Array} hashed - The hashed message
  * @returns {Promise<{
- *   r: Uint8Array,
- *   s: Uint8Array
+ *   RS: Uint8Array
  * }>} Signature of the message
  * @async
  */

test/crypto/hkdf.js

@@ -0,0 +1,47 @@
+const { expect } = require('chai');
+
+const computeHKDF = require('../../src/crypto/hkdf');
+const enums = require('../../src/enums');
+const util = require('../../src/util');
+
+// WebCrypto implements HKDF natively, no need to test it
+const maybeDescribe = util.getNodeCrypto() ? describe : describe;
+
+module.exports = () => maybeDescribe('HKDF test vectors', function() {
+  // Vectors from https://www.rfc-editor.org/rfc/rfc5869#appendix-A
+  it('Test Case 1', async function() {
+    const inputKey = util.hexToUint8Array('0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b');
+    const salt = util.hexToUint8Array('000102030405060708090a0b0c');
+    const info = util.hexToUint8Array('f0f1f2f3f4f5f6f7f8f9');
+    const outLen = 42;
+
+    const actual = await computeHKDF(enums.hash.sha256, inputKey, salt, info, outLen);
+    const expected = util.hexToUint8Array('3cb25f25faacd57a90434f64d0362f2a2d2d0a90cf1a5a4c5db02d56ecc4c5bf34007208d5b887185865');
+
+    expect(actual).to.deep.equal(expected);
+  });
+
+  it('Test Case 2', async function() {
+    const inputKey = util.hexToUint8Array('000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f');
+    const salt = util.hexToUint8Array('606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeaf');
+    const info = util.hexToUint8Array('b0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff');
+    const outLen = 82;
+
+    const actual = await computeHKDF(enums.hash.sha256, inputKey, salt, info, outLen);
+    const expected = util.hexToUint8Array('b11e398dc80327a1c8e7f78c596a49344f012eda2d4efad8a050cc4c19afa97c59045a99cac7827271cb41c65e590e09da3275600c2f09b8367793a9aca3db71cc30c58179ec3e87c14c01d5c1f3434f1d87');
+
+    expect(actual).to.deep.equal(expected);
+  });
+
+  it('Test Case 3', async function() {
+    const inputKey = util.hexToUint8Array('0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b');
+    const salt = new Uint8Array();
+    const info = new Uint8Array();
+    const outLen = 42;
+
+    const actual = await computeHKDF(enums.hash.sha256, inputKey, salt, info, outLen);
+    const expected = util.hexToUint8Array('8da4e775a563c18f715f802a063c5a31b8a11f5c5ee1879ec3454e5f3c738d2d9d201395faa4b61a96c8');
+
+    expect(actual).to.deep.equal(expected);
+  });
+});

test/crypto/index.js

@@ -6,6 +6,7 @@ module.exports = () => describe('Crypto', function () {
   require('./ecdh')();
   require('./pkcs5')();
   require('./aes_kw')();
+  require('./hkdf')();
   require('./gcm')();
   require('./eax')();
   require('./ocb')();