diff --git a/lib/jwcrypto.js b/lib/jwcrypto.js
index 3a2a6e9..c709a28 100644
--- a/lib/jwcrypto.js
+++ b/lib/jwcrypto.js
@@ -9,9 +9,13 @@
 var algs = require("./algs/index"),
     utils = require("./utils"),
     delay = utils.delay,
+    rng = require("./rng"),
     libs = require("../libs/minimal");
 
-var RNG = new libs.SecureRandom();
+var RNG = new rng.RNG();
+
+// start autoseeding now
+RNG.autoseed();
 
 function NoSuchAlgorithmException(message) {
   this.message = message;
@@ -137,9 +141,9 @@ exports.decrypt = function(encryptedPayload, encryptionAndMACKeys, cb) {
   
 };
 
-// rng
+// entropy here is a string that is expected to be relatively high entropy
 exports.addEntropy = function(entropy) {
-  // do something! FIXME XXX
+  RNG.addEntropy(entropy);
 };
 
 exports.assertion = require("./assertion");
diff --git a/lib/rng.js b/lib/rng.js
new file mode 100644
index 0000000..6dad8cd
--- /dev/null
+++ b/lib/rng.js
@@ -0,0 +1,80 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * abstract out RNG depending on client or server.
+ *
+ * auto-seeding has to be requested.
+ * (the seed is automatic, not the decision to auto-seed.)
+ *
+ * nextBytes takes a byteArray as input and populates it,
+ * because that's how the cool kids do it and so we will not bikeshed.
+ */
+
+var utils = require("./utils"),
+    delay = utils.delay,
+    libs = require("../libs/minimal"),
+    sjcl = libs.sjcl;
+
+// detect if we have native crypto support
+var crypto = null;
+try {
+  crypto = require("crypto");
+} catch(e) {}
+
+// proper boolean for whether we have native support
+var IS_NATIVE = !!crypto;
+
+function NativeRNG() {
+}
+
+NativeRNG.prototype = {
+  addEntropy: function(seed_in) {
+    // do nothing, natively we don't care
+  },
+  autoseed: function(cb) {
+    // yay, don't need to do anything
+    if (cb)
+      delay(cb)();
+  },
+  nextBytes: function(byteArray) {
+    var randomBytes = crypto.randomBytes(byteArray.length);
+    for (var i=0; i<byteArray.length; i++)
+      byteArray[i] = randomBytes[i];
+  }
+};
+
+function BrowserRNG() {
+}
+
+BrowserRNG.prototype = {
+  // WARNING: assumes that there's enough entropy in here to say it's 256
+  addEntropy: function(seed_in) {
+    sjcl.random.addEntropy(seed_in, 256);
+  },
+  autoseed: function(cb) {
+    // see if we have window.crypto.getRandomValues
+    if (window.crypto.getRandomValues) {
+      // then sjcl already seeded itself
+      if (cb)
+        delay(cb)();
+    } else {
+      sjcl.random.addEventListener('seeded', function(blarg) {
+        // no passing of arguments to the callback
+        if (cb)
+          cb();
+      });
+
+      // tell sjcl to start collecting some randomness      
+      sjcl.random.startCollectors();
+    }
+  },
+  nextBytes: function(byteArray) {
+    var randomBytes = sjcl.random.randomWords(byteArray.length);
+    for (var i=0; i<byteArray.length; i++)
+      byteArray[i] = randomBytes[i];
+  }
+};
+
+exports.RNG = IS_NATIVE ? NativeRNG : BrowserRNG;
\ No newline at end of file
diff --git a/libs/exports.js b/libs/exports.js
index fce470d..c9489e3 100644
--- a/libs/exports.js
+++ b/libs/exports.js
@@ -6,7 +6,6 @@
 
 exports.RSAKey = RSAKey;
 exports.BigInteger = BigInteger;
-exports.SecureRandom = SecureRandom;
 exports.sjcl = sjcl;
 exports.hex2b64 = hex2b64;
 exports.b64tohex = b64tohex;
diff --git a/libs/exports_minimal.js b/libs/exports_minimal.js
index a52af75..34681ba 100644
--- a/libs/exports_minimal.js
+++ b/libs/exports_minimal.js
@@ -5,7 +5,6 @@
 //
 
 exports.BigInteger = BigInteger;
-exports.SecureRandom = SecureRandom;
 exports.sjcl = sjcl;
 exports.hex2b64 = hex2b64;
 exports.b64tohex = b64tohex;
diff --git a/libs/minimal_package.txt b/libs/minimal_package.txt
index 7b7d760..6efdb95 100644
--- a/libs/minimal_package.txt
+++ b/libs/minimal_package.txt
@@ -6,6 +6,4 @@ external/base64.js
 external/jsbn-optimized.js
 external/jsbn2-optimized.js
 jsbn-patch.js
-external/prng4.js
-external/rng.js
 exports_minimal.js
diff --git a/test.html b/test.html
index 038ded2..ee3a2c6 100644
--- a/test.html
+++ b/test.html
@@ -9,9 +9,20 @@
     function runkeygen() {
       var jwcrypto = require("./lib/jwcrypto");
       var start = new Date();
+      jwcrypto.addEntropy("12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890");
       jwcrypto.generateKeypair({algorithm: "DS", keysize: 256}, function(err, kp) {
         var end = new Date();
-        alert(end-start);
+        alert(end-start + "ms");
+      });
+    }
+
+    function runrandom() {
+      var rng = require("./lib/rng");
+      var the_rng = new rng.RNG();
+      the_rng.autoseed(function() {
+        var bytes = new Array(20);
+        the_rng.nextBytes(bytes);
+        alert(bytes);
       });
     }
 
@@ -19,6 +30,7 @@
 </head>
 <body>
 <button onclick="runkeygen();">keygen-DS256</button>
+<button onclick="runrandom();">run-random</button>
 <!--
 <button onclick="runtests();">run tests</button>
 <button onclick="runperftests();">run perf tests</button>
diff --git a/test/jwcrypto-test.js b/test/jwcrypto-test.js
index 2ec6a07..bcbc74c 100644
--- a/test/jwcrypto-test.js
+++ b/test/jwcrypto-test.js
@@ -15,6 +15,18 @@ var suite = vows.describe('API tests');
 // disable vows (often flakey?) async error behavior
 suite.options.error = false;
 
+suite.addBatch({
+  "adding entropy": {
+    topic: function() {
+      jwcrypto.addEntropy("foobarbaz");
+      return null;
+    },
+    "works": function() {
+      assert.ok(true);
+    }
+  }
+});
+
 testUtils.addBatches(suite, function(alg, keysize) {
   var keypair;
   var obj = {foo: "bar"};
diff --git a/test/rng-test.js b/test/rng-test.js
new file mode 100644
index 0000000..10d09ea
--- /dev/null
+++ b/test/rng-test.js
@@ -0,0 +1,59 @@
+#!/usr/bin/env node
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const
+vows = require('vows'),
+assert = require('assert'),
+rng = require('../lib/rng');
+
+var suite = vows.describe('RNG tests');
+
+suite.addBatch({
+  "create rng": {
+    topic: function() {
+      return new rng.RNG();
+    },
+    "looks good": function(rng) {
+      assert.isObject(rng);
+      assert.isFunction(rng.addEntropy);
+      assert.isFunction(rng.autoseed);
+      assert.isFunction(rng.nextBytes);
+    },
+    "and when we seed": {
+      topic: function(rng) {
+        rng.addEntropy("foobar");
+        return null;
+      },
+      "all is well": function() {
+        assert.ok(true);
+      }
+    },
+    "and when we autoseed": {
+      topic: function(rng) {
+        rng.autoseed(this.callback);
+      },
+      "eventually returns": function() {
+        assert.ok(true);
+      },
+      "and when we get random bytes": {
+        topic: function(rng) {
+          var bytes = [0,0,0,0,0,0,0,0,0,0];
+          rng.nextBytes(bytes);
+          return bytes;
+        },
+        "contains stuff": function(bytes) {
+          assert.isArray(bytes);
+        },
+        "and that stuff is random'ish": function(bytes) {
+          // this test is unlikely to fail unless no randomness is getting out
+          assert.ok(!(bytes[0] == 0 && bytes[1] == 0 && bytes[2] == 0));
+        }
+      }
+    },
+  }
+});
+// run or export the suite.
+if (process.argv[1] === __filename) suite.run();
+else suite.export(module);