code: def encrypt(message, modN, e, blockSize):
      
      numList = string2numList(message)
      numBlocks = numList2blocks(numList, blockSize)  # only one block
      message = numBlocks[0]
      # return [modExp(blocks, e, modN) for blocks in numBlocks]
      return modExp(message, e, modN)
docs: given a string message, public keys and blockSize, encrypt using
      RSA algorithms.