Verification failed despite correct proof and message

[torao]

Situation: To create a proof for a message using VRF prove() and when it's used the verify() with the same message, it could fail.

Caused by: a bug in passing the message from Go to C as a byte array. Specifically, it must pass an address of the array (so-called pointer or reference), but it was passed not array address but Go slice address as follows:

func Prove(privateKey *[SECRETKEYBYTES]byte, message []byte) (*[PROOFBYTES]byte, error) {
  ...
  messagePtr := (*C.uchar)(unsafe.Pointer(&message))
  if C.crypto_vrf_prove(proofPtr, privateKeyPtr, messagePtr, messageLen) != 0 {...}
}

The &message specifies not array address but slice address.

messagePrt := (*C.uchar)(unsafe.Pointer(&message[0]))
                         // or C.NULL if len(message) == 0

When proof() and verify() were using exactly the same instance of the message []byte slice, verification seemed to succeed because the contents pointed to by both addresses were equal. However, in case that the slices had the same data but different instances, it failed because the data pointed to by the slice addresses where different. This was essentially a memory access violation and could have caused a SIGSEGV.

Fixed: in PR #12 . This issue has been created to share the issue.