密码一种密码系统，其中固定长度的明文里的单元，通常为字母，被任意倒置或按事先确定的符号系统替换

A cryptographic system in which units of plain text of regular length, usually letters, are arbitrarily transposed or substituted according to a predetermined code.

多倍长度多倍字长运算

{计} multi-length arithmetic