use hmac.Equal for consistent-time equality

README.md

@@ -89,8 +89,6 @@ If you'd like to help with any of the items below, send a pull-request!
 - Only supports [version
   3](https://github.com/RNCryptor/RNCryptor-Spec/blob/0625abe597e67af4a9a40f460a10bc069b7caf48/RNCryptor-Spec-v3.md)
   of the RNCryptor spec.
-- Lacks [consistent-time equality
-  checking](https://github.com/RNCryptor/RNCryptor-Spec/blob/0625abe597e67af4a9a40f460a10bc069b7caf48/RNCryptor-Spec-v3.md#consistent-time-equality-checking).
 - Only provides functions for password-based encryption, lacks function for [key-based
   encryption](https://github.com/RNCryptor/RNCryptor-Spec/blob/0625abe597e67af4a9a40f460a10bc069b7caf48/RNCryptor-Spec-v3.md#key-based-encryption-abstract-language).
 

rncryptor.go

@@ -34,7 +34,9 @@ func Decrypt(password string, data []byte) ([]byte, error) {
   testHmac.Write(msg)
   testHmacVal := testHmac.Sum(nil)
 
-  verified := bytes.Equal(testHmacVal, expectedHmac)
+  // its important to use hmac.Equal to not leak time
+  // information. See https://github.com/RNCryptor/RNCryptor-Spec
+  verified := hmac.Equal(testHmacVal, expectedHmac)
 
   if !verified {
     return nil, errors.New("Password may be incorrect, or the data has been corrupted. (HMAC could not be verified)")