crypto: add a crypto.uuid() method

Ref: https://en.wikipedia.org/wiki/Universally_unique_identifier

Author: tlhunter

lib/crypto.js

@@ -139,6 +139,15 @@ function createVerify(algorithm, options) {
   return new Verify(algorithm, options);
 }
 
+function uuid() {
+  // Generate 32 random hexadecimal characters
+  const src = randomBytes(16).toString('hex');
+
+  // The 13th random hex character is discarded and replaced with '4'
+  return `${src.substr(0, 8)}-${src.substr(8, 4)}-4${src.substr(13, 3)}` +
+    `-${src.substr(16, 4)}-${src.substr(20, 32)}`;
+}
+
 module.exports = exports = {
   // Methods
   createCipheriv,
@@ -169,6 +178,7 @@ module.exports = exports = {
   scryptSync,
   setEngine,
   timingSafeEqual,
+  uuid,
   getFips: !fipsMode ? getFipsDisabled :
     fipsForced ? getFipsForced : getFipsCrypto,
   setFips: !fipsMode ? setFipsDisabled :

test/parallel/test-crypto-uuid.js

@@ -0,0 +1,17 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+const assert = require('assert');
+const crypto = require('crypto');
+
+const UUID_V4_REGEX =
+  /[a-f0-9]{8}-[a-f0-9]{4}-4[a-f0-9]{3}-[a-f0-9]{4}-[a-f0-9]{12}/;
+
+// Test crypto.randomBytes() implementation
+for (let i = 0; i < 100; i++) {
+  const uuid = crypto.uuid();
+  assert.ok(UUID_V4_REGEX.test(uuid));
+}