fix implementation, with additional tests

README.md

@@ -1,3 +1,23 @@
-The HKDF Key Derivation Function
+# node-hkdf
+
+The HMAC-based Key Derivation Function for node.js.
 
 spec: https://tools.ietf.org/html/rfc5869
+
+## install
+
+    npm install hkdf
+
+## use
+
+    const HKDF = require('hkdf');
+
+    var hkdf = new HKDF('sha256', 'salt123', 'initialKeyingMaterial');
+    hkdf.derive('info', 42, function(key) {
+      // key is a Buffer, that can be serialized however one desires
+      console.log(key.toString('hex'));
+    });
+
+## license
+
+Apache License 2.0

lib/hkdf.js

@@ -9,8 +9,7 @@ var crypto = require("crypto");
 function zeros(length) {
   var buf = new Buffer(length);
 
-  // XXX is this the character zero, or the byte 0.
-  buf.fill("0");
+  buf.fill(0);
 
   return buf.toString();
 }
@@ -33,20 +32,28 @@ function HKDF(hashAlg, salt, ikm) {
 
 HKDF.prototype = {
   derive: function(info, size, cb) {
-    var prev = "";
-    var output = new Buffer(size);
+    var prev = new Buffer(0);
+    var output;
+    var buffers = [];
     var num_blocks = Math.ceil(size / this.hashLength);
+    info = new Buffer(info);
 
     for (var i=0; i<num_blocks; i++) {
       var hmac = crypto.createHmac(this.hashAlg, this.prk);
-      var input = prev + info + (0x01 * (i+1));
+      // XXX is there a more optimal way to build up buffers?
+      var input = Buffer.concat([
+        prev,
+        info,
+        new Buffer(String.fromCharCode(i + 1))
+      ]);
       hmac.update(input);
       prev = hmac.digest();
-      output.write(prev, this.hashLength * i, this.hashLength, 'binary');
+      buffers.push(prev);
     }
+    output = Buffer.concat(buffers, size);
 
     process.nextTick(function() {cb(output);});
   }
 };
 
-module.exports = HKDF;
+module.exports = HKDF;

package.json

@@ -1,7 +1,6 @@
 {
   "name"         : "node-hkdf",
   "version"      : "0.0.1",
-  "private"      : true,
   "description"  : "HKDF key derivation function",
   "main"         : "index",
   "repository" : {

test/all-test.js

@@ -18,14 +18,30 @@ suite.addBatch({
     "derives keys of the right length": function(err, key) {
       assert.equal(key.length, 42);
     }
+  },
+  "an hkdf with no salt" : {
+    topic: function() {
+      var self = this;
+      var hkdf = new HKDF('sha256', null, 'initialKeyingMaterial');
+      hkdf.derive('info', 42, function(key) {
+        // key is a Buffer, that can be serialized however one desires
+        self.callback(null, key);
+      });
+    },
+    "derives keys of the right length": function(err, key) {
+      // expected value generated using:
+      // https://github.com/warner/id-keywrapping-demo/blob/master/hkdf.py
+      assert.equal(key.toString('hex'), "5ff4745de6729d5a523337170ab6e12f202c81611bb8cb80e4b44675a16371cadd8e62eebc777b08bf83");
+    }
   }
 });
 
+// test vectors from RFC5869
 suite.addBatch({
   "test vector": {
     topic: function() {
       var self = this;
-      
+
       var ikm = new Buffer("0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b", 'hex');
       var salt = new Buffer("000102030405060708090a0b0c", 'hex');
       var info = new Buffer("f0f1f2f3f4f5f6f7f8f9", 'hex');
@@ -39,7 +55,25 @@ suite.addBatch({
     "works": function(err, output) {
       assert.equal(output.toString('hex'), "3cb25f25faacd57a90434f64d0362f2a2d2d0a90cf1a5a4c5db02d56ecc4c5bf34007208d5b887185865");
     }
+  },
+  "test another vector": {
+    topic: function() {
+      var self = this;
+
+      var ikm = new Buffer("0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b", 'hex');
+      var salt = new Buffer(0); // empty
+      var info = ''; // empty
+
+      var hkdf = new HKDF('sha256', salt, ikm);
+      hkdf.derive(info, 42, function(key) {
+        // key is a Buffer, that can be serialized however one desires
+        self.callback(null, key);
+      });
+    },
+    "works": function(err, output) {
+      assert.equal(output.toString('hex'), "8da4e775a563c18f715f802a063c5a31b8a11f5c5ee1879ec3454e5f3c738d2d9d201395faa4b61a96c8");
+    }
   }
 })
 
-suite.export(module);
+suite.export(module);