add support for signing/verifying messages

This adds a new Message class with static methods for signing and verifying a
message the same way as bitcoind. (In a nutshell, messages a prepended with
"Bitcoin Signed Message:" before being hashed and signed).

There is one important piece missing ... verifying a signature with an address,
and not a public key. I have not yet implemented this because the cryptography
interface of bitcore does not allow me to derive the public key from a
signature. This will need to be added before verifying from an address is
possible.

bitcore.js

@@ -48,6 +48,7 @@ requireWhenAccessed('RpcClient', './lib/RpcClient');
 requireWhenAccessed('Wallet', './lib/Wallet');
 requireWhenAccessed('WalletKey', './lib/WalletKey');
 requireWhenAccessed('PeerManager', './lib/PeerManager');
+requireWhenAccessed('Message', './lib/Message');
 module.exports.Buffer = Buffer;
 
 if (typeof process.versions === 'undefined') {

lib/Message.js

@@ -0,0 +1,42 @@
+'use strict';
+var imports = require('soop').imports();
+var coinUtil = imports.coinUtil || require('../util');
+var Key = imports.Key || require('./Key');
+
+var Message = function() {
+};
+
+Message.sign = function(str, key) {
+  var hash = Message.magicHash(str);
+  var sig = key.signSync(hash);
+  return sig;
+};
+
+Message.verifyWithPubKey = function(pubkey, message, sig) {
+  var hash = Message.magicHash(message);
+  var key = new Key();
+  if (pubkey.length == 65)
+    key.compressed = false;
+  key.public = pubkey;
+
+  return key.verifySignatureSync(hash, sig);
+};
+
+//TODO: Message.verify ... with address, not pubkey
+
+Message.magicBytes = new Buffer('Bitcoin Signed Message:\n');
+
+Message.magicHash = function(str) {
+  var magicBytes = Message.magicBytes;
+  var prefix1 = coinUtil.varIntBuf(magicBytes.length);
+  var message = new Buffer(str);
+  var prefix2 = coinUtil.varIntBuf(message.length);
+
+  var buf = Buffer.concat([prefix1, magicBytes, prefix2, message]);
+
+  var hash = coinUtil.twoSha256(buf);
+
+  return hash;
+};
+
+module.exports = require('soop')(Message);

test/test.Message.js

@@ -0,0 +1,57 @@
+'use strict';
+
+var chai = chai || require('chai');
+var should = chai.should();
+var bitcore = bitcore || require('../bitcore');
+var Message = bitcore.Message;
+var coinUtil = bitcore.util;
+
+describe('Message', function() {
+  describe('sign', function() {
+    it('should return a signature', function() {
+      var key = bitcore.Key.generateSync();
+      var sig = Message.sign('my message', key);
+      sig.length.should.be.greaterThan(0);
+    });
+  });
+
+  describe('verifyWithPubKey', function() {
+    it('should verify a signed message', function() {
+      var message = 'my message';
+      var key = bitcore.Key.generateSync();
+      var sig = Message.sign(message, key);
+      Message.verifyWithPubKey(key.public, message, sig).should.equal(true);
+    });
+  });
+
+  describe('magicBytes', function() {
+    it('should be "Bitcoin Signed Message:\\n"', function() {
+      Message.magicBytes.toString().should.equal('Bitcoin Signed Message:\n');
+    });
+  });
+
+  describe('magicHash', function() {
+    it('should hash the message with the magic bytes', function() {
+      var str = 'my message';
+      var magicBytes = Message.magicBytes;
+      var prefix1 = coinUtil.varIntBuf(magicBytes.length);
+      var message = new Buffer(str);
+      var prefix2 = coinUtil.varIntBuf(message.length);
+
+      var buf = Buffer.concat([prefix1, magicBytes, prefix2, message]);
+
+      var hash = coinUtil.twoSha256(buf);
+
+      var hash2 = Message.magicHash(str);
+
+      hash.toString().should.equal(hash2.toString());
+    });
+
+    it('should hash this message the same way as bitcoinjs-lib', function() {
+      var hashHex = '74eacdc6c04724869380907bf4aab561a1494a4a800fba266b29b8158c2c4cec';
+
+      var str = 'this is a test message';
+      hashHex.should.equal(Message.magicHash(str).toString('hex'));
+    });
+  });
+});