installDummyCryptoPolyfill.js

function installDummyCryptoPolyfill() {
  var global = (function(global) {
    return global;
  })(new Function('return this;')());

  try {
    global.crypto.getRandomValues(new Uint8Array(1));
    return;
  }
  catch (e) {
    console.warn("Installing dummy crypto RNG. This is not secure!");
    global.crypto = {
      _bytesGenerated: 0,
      _bytesMax: 4 + 64,
      _getRandomByte: function() {
        if (this._bytesGenerated >= this._bytesMax) {
          throw new Error("This RNG can only generate " + this._bytesMax + " bytes");
        }
        this._bytesGenerated += 1;
        return 0x00;
      },
      getRandomValues: function(arrayBufferView) {
        var newBytes = [];
        for (var i = 0; i < arrayBufferView.byteLength; ++i) {
            newBytes.push(this._getRandomByte());
        }
        new Uint8Array(arrayBufferView.buffer, arrayBufferView.byteOffset, arrayBufferView.byteLength).set(newBytes);
      },
    };
  }
}
installDummyCryptoPolyfill();