hmac ourselves

Author: calvinmetcalf

lib/sync.js

@@ -1,7 +1,47 @@
-var createHmac = require('create-hmac')
+var createHash = require('create-hash')
 var checkParameters = require('./precondition')
 var defaultEncoding = require('./default-encoding')
 var Buffer = require('safe-buffer').Buffer
+var ZEROS = Buffer.alloc(128)
+var sizes = {
+  md5: 16,
+  sha1: 20,
+  sha224: 28,
+  sha256: 32,
+  sha384: 48,
+  sha512: 64,
+  rmd160: 20,
+  ripemd160: 20
+}
+function computePad (alg, key) {
+  var blocksize = (alg === 'sha512' || alg === 'sha384') ? 128 : 64
+  if (key.length > blocksize) {
+    key = hash(alg, key)
+  } else if (key.length < blocksize) {
+    key = Buffer.concat([key, ZEROS], blocksize)
+  }
+  var ipad = Buffer.allocUnsafe(blocksize)
+  var opad = Buffer.alloc(blocksize + sizes[alg])
+
+  for (var i = 0; i < blocksize; i++) {
+    ipad[i] = key[i] ^ 0x36
+    opad[i] = key[i] ^ 0x5C
+  }
+  return {
+    ipad: ipad,
+    opad: opad,
+    alg: alg,
+    blocksize: blocksize
+  }
+}
+function hash (algo, buffer) {
+  return createHash(algo).update(buffer).digest()
+}
+function hmac (pad, data) {
+  var h = hash(pad.alg, Buffer.concat([pad.ipad, data]))
+  h.copy(pad.opad, pad.blocksize)
+  return hash(pad.alg, pad.opad)
+}
 module.exports = function (password, salt, iterations, keylen, digest) {
   if (!Buffer.isBuffer(password)) password = Buffer.from(password, defaultEncoding)
   if (!Buffer.isBuffer(salt)) salt = Buffer.from(salt, defaultEncoding)
@@ -10,6 +50,8 @@ module.exports = function (password, salt, iterations, keylen, digest) {
 
   digest = digest || 'sha1'
 
+  var pad = computePad(digest, password)
+
   var hLen
   var l = 1
   var DK = Buffer.allocUnsafe(keylen)
@@ -21,7 +63,7 @@ module.exports = function (password, salt, iterations, keylen, digest) {
 
   for (var i = 1; i <= l; i++) {
     block1.writeUInt32BE(i, salt.length)
-    var U = createHmac(digest, password).update(block1).digest()
+    var U = hmac(pad, block1)
 
     if (!hLen) {
       hLen = U.length
@@ -33,7 +75,7 @@ module.exports = function (password, salt, iterations, keylen, digest) {
     U.copy(T, 0, 0, hLen)
 
     for (var j = 1; j < iterations; j++) {
-      U = createHmac(digest, password).update(U).digest()
+      U = hmac(pad, U)
       for (var k = 0; k < hLen; k++) T[k] ^= U[k]
     }