code: func DeriveKeyMySQL(key []byte, blockSize int) []byte {
  	rKey := make([]byte, blockSize)
  	rIdx := 0
  	for _, k := range key {
  		if rIdx == blockSize {
  			rIdx = 0
  		}
  		rKey[rIdx] ^= k
  		rIdx++
  	}
  	return rKey
  }
docs: // DeriveKeyMySQL derives the encryption key from a password in MySQL algorithm.
  // See https://security.stackexchange.com/questions/4863/mysql-aes-encrypt-key-length.