def block_is_left_aligned?(ciphertext,redundant_test_blocks)
      total_blocks = ciphertext.length / block_size
      uniq_blocks  = CryptBuffer(ciphertext).chunks_of(block_size).map(&:bytes).uniq.length

      (total_blocks - uniq_blocks ) == (redundant_test_blocks -1) 
    end
def block_is_left_aligned?(ciphertext,redundant_test_blocks)
      total_blocks = ciphertext.length / block_size
      uniq_blocks  = CryptBuffer(ciphertext).chunks_of(block_size).map(&:bytes).uniq.length

      (total_blocks - uniq_blocks ) == (redundant_test_blocks -1) 
    end
Check whether we need to pad any oracle prefix.
 For example: if the oracle prepends 7 bytes to all messages
 we have to add block_size - 7 bytes to "left-align" our messages