crypto: Implement HKDF for Node.js < 15.0.0

src/node/utils/crypto.js

@@ -0,0 +1,43 @@
+'use strict';
+
+const {Buffer} = require('buffer');
+const crypto = require('crypto');
+const util = require('util');
+
+// TODO: Delete this once support for Node.js < 15.0.0 is dropped.
+const hkdfFallback = async (digest, ikm, salt, info, keylen) => {
+  // https://datatracker.ietf.org/doc/html/rfc5869#section-2.2
+  const prkHmac = crypto.createHmac(digest, salt);
+  prkHmac.update(ikm);
+  const prk = prkHmac.digest();
+
+  // https://datatracker.ietf.org/doc/html/rfc5869#section-2.3
+  let len = 0;
+  const t = [Buffer.alloc(0)];
+  while (len < keylen) {
+    const hmac = crypto.createHmac(digest, prk);
+    hmac.update(t[t.length - 1]);
+    hmac.update(info);
+    hmac.update(Buffer.from([t.length % 256]));
+    const tn = hmac.digest();
+    t.push(tn);
+    len += tn.length;
+  }
+  const buf = Buffer.concat(t);
+  return (buf.byteOffset === 0 && buf.buffer.byteLength === keylen
+    ? buf : Uint8Array.prototype.slice.call(buf, 0, keylen)).buffer;
+};
+
+/**
+ * Promisified version of Node.js's crypto.hkdf.
+ */
+exports.hkdf = crypto.hkdf ? util.promisify(crypto.hkdf) : hkdfFallback;
+
+/**
+ * Promisified version of Node.js's crypto.randomBytes
+ */
+exports.randomBytes = util.promisify(crypto.randomBytes);
+
+exports.exportedForTesting = {
+  hkdfFallback,
+};