predetermined code

详细解释:【经】 预先制订的编码

例句：

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