PRNG

lib/crypto-platform.browser.js

@@ -1,6 +1,5 @@
 /**
  * Browser Bitmessage crypto implementation.
- *
  * Documentation: <http://www.w3.org/TR/WebCryptoAPI/>
  * Browsers support: <http://caniuse.com/#feat=cryptography>
  * Blink implementation details: <https://sites.google.com/a/chromium.org/dev/blink/webcrypto>
@@ -34,3 +33,9 @@ exports.ripemd160 = function(buf) {
   // so use module.
   return Promise.resolve(ripemd160(buf));
 };
+
+exports.randomBytes = function(size) {
+  var arr = new Uint8Array(size);
+  window.crypto.getRandomValues(arr);
+  return new Buffer(arr);
+};

lib/crypto-platform.js

@@ -25,3 +25,12 @@ exports.ripemd160 = function(buf) {
   hash.update(buf);
   return Promise.resolve(hash.digest());
 };
+
+/**
+ * Generate cryptographically strong pseudo-random data.
+ * @param {number} size - Number of bytes
+ * @return {Buffer} Buffer with random data.
+ */
+exports.randomBytes = function(size) {
+  return crypto.randomBytes(size);
+};

lib/crypto.js

@@ -7,6 +7,7 @@
 "use strict";
 
 var cryptoPlatform = require("./crypto-platform");
+
 Object.keys(cryptoPlatform).forEach(function(key) {
   exports[key] = cryptoPlatform[key];
 });

test.js

@@ -56,6 +56,29 @@ describe("Crypto", function() {
       expect(res.toString("hex")).to.equal("5e52fee47e6b070565f74372468cdc699de89107");
     });
   });
+
+  it("should implement cryptographically secure PRNG", function() {
+    var size = 100;
+    var rnd = bmcrypto.randomBytes(size);
+    expect(Buffer.isBuffer(rnd)).to.be.true;
+    expect(rnd.length).to.equal(size);
+    // Very simple statistical test.
+    var bytes = {};
+    var sum = 0;
+    var value;
+    for (var i = 0; i < size; i++) {
+      value = rnd[i];
+      sum += value;
+      if (!bytes[value]) {
+        bytes[value] = 0;
+      }
+      bytes[value]++;
+      expect(bytes[value]).to.be.below(5);
+    }
+    // Ideal sum = (255 / 2) * size = 12750
+    expect(sum).to.be.above(10000);
+    expect(sum).to.be.below(15000);
+  });
 });
 
 describe("Address", function() {