replace buffer hex string comparisons with cmp

In order to compare buffers, fullnode had been exclusively using node's
toString('hex') function and then doing a string comparison. This method is
subject to timing attacks for any cryptography-sensitive code. We replace all
such instances with the cmp.eq function which is constant-time.

Related issue: #23

lib/ach.js

@@ -12,6 +12,7 @@
  */
 var AESCBC = require('./aescbc');
 var Hash = require('./hash');
+var cmp = require('./cmp');
 
 var ACH = {};
 
@@ -29,7 +30,7 @@ ACH.decrypt = function(encbuf, cipherkeybuf) {
   var hmacbuf = encbuf.slice(0, 256 / 8);
   encbuf = encbuf.slice(256 / 8, encbuf.length);
   var hmacbuf2 = Hash.sha256hmac(encbuf, cipherkeybuf);
-  if (hmacbuf.toString('hex') !== hmacbuf2.toString('hex'))
+  if (!cmp.eq(hmacbuf, hmacbuf2))
     throw new Error('Message authentication failed - HMACs are not equivalent');
   return AESCBC.decrypt(encbuf, cipherkeybuf);
 };

lib/base58check.js

@@ -9,6 +9,7 @@
  */
 var base58 = require('./base58');
 var sha256sha256 = require('./hash').sha256sha256;
+var cmp = require('./cmp');
 
 var Base58Check = function Base58Check(obj) {
   if (!(this instanceof Base58Check))
@@ -44,7 +45,7 @@ Base58Check.decode = function(s) {
   var hash = sha256sha256(data);
   var hash4 = hash.slice(0, 4);
 
-  if (csum.toString('hex') !== hash4.toString('hex'))
+  if (!cmp.eq(csum, hash4))
     throw new Error("Checksum mismatch");
 
   return data;

lib/bsm.js

@@ -17,6 +17,7 @@ var BW = require('./bw');
 var Hash = require('./hash');
 var Address = require('./address');
 var Sig = require('./sig');
+var cmp = require('./cmp');
 
 var BSM = function BSM(obj) {
   if (!(this instanceof BSM))
@@ -94,7 +95,7 @@ BSM.prototype.verify = function() {
 
   var address = Address().fromPubkey(ecdsa.keypair.pubkey, undefined, this.sig.compressed);
   //TODO: what if livenet/testnet mismatch?
-  if (address.hashbuf.toString('hex') === this.address.hashbuf.toString('hex'))
+  if (cmp.eq(address.hashbuf, this.address.hashbuf))
     this.verified = true;
   else
     this.verified = false;

lib/cbc.js

@@ -10,6 +10,7 @@
  * http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher-block_chaining_.28CBC.29
  */
 var Random = require('./random');
+var cmp = require('./cmp');
 
 var CBC = {};
 
@@ -119,7 +120,7 @@ CBC.pkcs7unpad = function(paddedbuf, blocksize) {
   var padbuf = paddedbuf.slice(paddedbuf.length - padlength, paddedbuf.length);
   var padbuf2 = new Buffer(padlength);
   padbuf2.fill(padlength);
-  if (padbuf.toString('hex') !== padbuf2.toString('hex'))
+  if (!cmp.eq(padbuf, padbuf2))
     throw new Error('invalid padding');
   return paddedbuf.slice(0, paddedbuf.length - padlength);
 };

lib/expmt/ecies.js

@@ -4,6 +4,7 @@ var Point = require('../point');
 var Hash = require('../hash');
 var Pubkey = require('../pubkey');
 var Privkey = require('../privkey');
+var cmp = require('../cmp');
 
 // http://en.wikipedia.org/wiki/Integrated_Encryption_Scheme
 var ECIES = function ECIES() {
@@ -46,7 +47,7 @@ ECIES.decrypt = function(encbuf, toprivkey) {
   var c = encbuf.slice(33, encbuf.length - 32);
   var d = encbuf.slice(encbuf.length - 32, encbuf.length);
   var d2 = Hash.sha256hmac(c, kM);
-  if (d.toString('hex') !== d2.toString('hex'))
+  if (!cmp.eq(d, d2))
     throw new Error('Invalid checksum');
   var messagebuf = AESCBC.decrypt(c, kE);
   return messagebuf;

lib/expmt/stealth/key.js

@@ -4,6 +4,7 @@ var Pubkey = require('../../pubkey');
 var Point = require('../../point');
 var Hash = require('../../hash');
 var KDF = require('../../kdf');
+var cmp = require('../../cmp');
 
 var SKey = function SKey(payloadKeypair, scanKeypair) {
   if (!(this instanceof SKey))
@@ -79,7 +80,7 @@ SKey.prototype.isForMe = function(senderPubkey, myPossiblePubkeyhashbuf) {
   var pubkeybuf = pubkey.toDER(true);
   var pubkeyhash = Hash.sha256ripemd160(pubkeybuf);
 
-  if (pubkeyhash.toString('hex') === myPossiblePubkeyhashbuf.toString('hex'))
+  if (cmp.eq(pubkeyhash, myPossiblePubkeyhashbuf))
     return true;
   else
     return false;

lib/expmt/stealth/message.js

@@ -4,6 +4,7 @@ var ECIES = require('../ecies');
 var Keypair = require('../../keypair');
 var Address = require('../../address');
 var Pubkey = require('../../pubkey');
+var cmp = require('../../cmp');
 
 var SMessage = function SMessage(obj) {
   if (!(this instanceof SMessage))
@@ -75,7 +76,7 @@ SMessage.prototype.decrypt = function() {
 SMessage.prototype.isForMe = function() {
   var receivePubkey = this.toSKey.getReceivePubkey(this.fromKeypair.pubkey);
   var receiveAddress = Address().fromPubkey(receivePubkey);
-  if (receiveAddress.toString('hex') === this.receiveAddress.toString('hex'))
+  if (cmp.eq(receiveAddress.hashbuf, this.receiveAddress.hashbuf))
     return true;
   else
     return false;

lib/interp.js

@@ -18,6 +18,7 @@ var BR = require('./br');
 var BW = require('./bw');
 var Sig = require('./sig');
 var Pubkey = require('./pubkey');
+var cmp = require('./cmp');
 
 var Interp = function Interp(obj) {
   if (!(this instanceof Interp))
@@ -684,7 +685,7 @@ Interp.prototype.step = function() {
       }
       var buf1 = this.stack[this.stack.length - 2];
       var buf2 = this.stack[this.stack.length - 1];
-      var fEqual = buf1.toString('hex') === buf2.toString('hex');
+      var fEqual = cmp.eq(buf1, buf2);
       // Opcode.OP_NOTEQUAL is disabled because it would be too easy to say
       // something like n != 1 and have some wiseguy pass in 1 with extra
       // zero bytes after it (numerically, 0x01 == 0x0001 == 0x000001)

lib/script.js

@@ -17,6 +17,7 @@ var BR = require('./br');
 var BW = require('./bw');
 var BN = require('./bn');
 var Opcode = require('./opcode');
+var cmp = require('./cmp');
 
 var Script = function Script(buf) {
   if (!(this instanceof Script))
@@ -372,12 +373,10 @@ Script.prototype.isScripthashIn = function() {
  */
 Script.prototype.findAndDelete = function(script) {
   var buf = script.toBuffer();
-  var hex = buf.toString('hex');
   for (var i = 0; i < this.chunks.length; i++) {
     var script2 = Script({chunks: [this.chunks[i]]});
     var buf2 = script2.toBuffer();
-    var hex2 = buf2.toString('hex');
-    if (hex === hex2)
+    if (cmp.eq(buf, buf2))
       this.chunks.splice(i, 1);
   }
   return this;