diff --git a/browser.js b/browser.js
index e69de29..cbb26aa 100644
--- a/browser.js
+++ b/browser.js
@@ -0,0 +1,36 @@
+/**
+ * Browser eccrypto implementation.
+ */
+
+"use strict";
+
+require("es6-promise").polyfill();
+var EC = require("elliptic").ec;
+
+var ec = new EC("secp256k1");
+
+exports.getPublic = function(privateKey) {
+  // XXX(Kagami): `elliptic.utils.encode` returns array for every
+  // encoding except `hex`.
+  return new Buffer(ec.keyPair(privateKey).getPublic("arr"));
+};
+
+exports.sign = function(privateKey, msg) {
+  var key = ec.keyPair(privateKey);
+  var sig;
+  try {
+    sig = new Buffer(key.sign(msg).toDER());
+    return Promise.resolve(sig);
+  } catch(e) {
+    return Promise.reject();
+  }
+};
+
+exports.verify = function(publicKey, msg, sig) {
+  var key = ec.keyPair(null, publicKey);
+  if (key.verify(msg, sig)) {
+    return Promise.resolve();
+  } else {
+    return Promise.reject();
+  }
+};
diff --git a/index.js b/index.js
index a07ca4e..220141e 100644
--- a/index.js
+++ b/index.js
@@ -21,11 +21,8 @@ exports.getPublic = function(privateKey) {
  * Create an ECDSA signature.
  * @param {Buffer} privateKey A 32-byte private key
  * @param {Buffer} msg The message being signed
- * @return {Promise.<Buffer,number>} A promise that resolves with the
- * signature or rejects with error code:
- *
- *   - 0: invalid nonce
- *   - -1: invalid private key or message
+ * @return {Promise.<Buffer,undefined>} A promise that resolves with the
+ * signature or rejects on bad private key/message.
  */
 // FIXME(Kagami): What to do in case of invalid nonce?
 exports.sign = function(privateKey, msg) {
@@ -35,11 +32,11 @@ exports.sign = function(privateKey, msg) {
         if (code === 1) {
           resolve(sig);
         } else {
-          reject(code);
+          reject();
         }
       });
     } catch(e) {
-      reject(-1);
+      reject();
     }
   });
 };
@@ -49,12 +46,8 @@ exports.sign = function(privateKey, msg) {
  * @param {Buffer} publicKey The public key
  * @param {Buffer} msg The message being verified
  * @param {Buffer} sig The signature
- * @return {Promise.<null,number>} A promise that resolves on correct
- * signature and rejects on bad signature with error code:
- *
- *   - 0: incorrect signature
- *   - -1: invalid public key
- *   - -2: invalid signature
+ * @return {Promise} A promise that resolves on correct signature and
+ * rejects on bad signature/public key.
  */
 exports.verify = function(publicKey, msg, sig) {
   return new Promise(function(resolve, reject) {
@@ -62,7 +55,7 @@ exports.verify = function(publicKey, msg, sig) {
       if (code === 1) {
         resolve();
       } else {
-        reject(code);
+        reject();
       }
     });
   });
diff --git a/package.json b/package.json
index e33dd9e..4f17cd7 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,7 @@
   "main": "index.js",
   "browser": "browser.js",
   "scripts": {
-    "test": "mocha && jshint .",
+    "test": "mocha && xvfb-run -a karma start && jshint .",
     "m": "mocha",
     "k": "xvfb-run -a karma start",
     "kc": "xvfb-run -a karma start --browsers Chromium",
@@ -46,6 +46,7 @@
     "mocha": "*"
   },
   "dependencies": {
+    "elliptic": "^0.15.15",
     "es6-promise": "^2.0.1",
     "secp256k1": "~0.0.13"
   }
diff --git a/test.js b/test.js
index 6864784..188add7 100644
--- a/test.js
+++ b/test.js
@@ -8,6 +8,7 @@ var msg = Buffer("test");
 
 describe("Key", function() {
   it("should allow to convert private key to public", function() {
+    expect(Buffer.isBuffer(publicKey)).to.be.true;
     expect(publicKey.toString("hex")).to.equal("041b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f70beaf8f588b541507fed6a642c5ab42dfdf8120a7f639de5122d47a69a8e8d1");
   });
 });
@@ -16,6 +17,7 @@ describe("ECDSA", function() {
   it("should allow to sign and verify message", function() {
     return eccrypto.sign(privateKey, msg)
       .then(function(sig) {
+        expect(Buffer.isBuffer(sig)).to.be.true;
         return eccrypto.verify(publicKey, msg, sig);
       });
   });
@@ -23,16 +25,15 @@ describe("ECDSA", function() {
   it("shouldn't verify incorrect signature", function(done) {
     eccrypto.sign(privateKey, msg)
       .then(function(sig) {
+        expect(Buffer.isBuffer(sig)).to.be.true;
         return eccrypto.verify(publicKey, Buffer("other msg"), sig);
-      }).catch(function(code) {
-        expect(code).to.equal(0);
+      }).catch(function() {
         done();
       });
   });
 
   it("should reject promise on invalid key when signing", function(done) {
-    eccrypto.sign(Buffer("test"), msg).catch(function(code) {
-      expect(code).to.equal(-1);
+    eccrypto.sign(Buffer("test"), msg).catch(function() {
       done();
     });
   });
@@ -40,9 +41,9 @@ describe("ECDSA", function() {
   it("should reject promise on invalid key when verifying", function(done) {
     eccrypto.sign(privateKey, msg)
       .then(function(sig) {
+        expect(Buffer.isBuffer(sig)).to.be.true;
         return eccrypto.verify(Buffer("test"), msg, sig);
-      }).catch(function(code) {
-        expect(code).to.equal(-1);
+      }).catch(function() {
         done();
       });
   });
@@ -50,10 +51,10 @@ describe("ECDSA", function() {
   it("should reject promise on invalid sig when verifying", function(done) {
     eccrypto.sign(privateKey, msg)
       .then(function(sig) {
+        expect(Buffer.isBuffer(sig)).to.be.true;
         sig[0] ^= 1;
         return eccrypto.verify(publicKey, msg, sig);
-      }).catch(function(code) {
-        expect(code).to.equal(-2);
+      }).catch(function() {
         done();
       });
   });