def encode(text)
      # 计算需要填充的位数
      amount_to_pad = BLOCK_SIZE - (text.length % BLOCK_SIZE)
      amount_to_pad = BLOCK_SIZE if amount_to_pad == 0
      # 获得补位所用的字符
      pad_chr = amount_to_pad.chr
      "#{text}#{pad_chr * amount_to_pad}"
    end
def encode(text)
      # 计算需要填充的位数
      amount_to_pad = BLOCK_SIZE - (text.length % BLOCK_SIZE)
      amount_to_pad = BLOCK_SIZE if amount_to_pad == 0
      # 获得补位所用的字符
      pad_chr = amount_to_pad.chr
      "#{text}#{pad_chr * amount_to_pad}"
    end
对需要加密的明文进行填充补位
 返回补齐明文字符串