一、引言在以前的文章里,Mellen和Green-Wood讨论了多表密码,尤其是M94转轮密码机。他们考虑了下列三种情况的破译: ①字母表已知,密钥已知, ②字母表未知,密钥已知, ③字母表未知,密钥未知。本文将考虑第四种情况: ④宇母表已知,密钥未知。我们将考虑两种情形,即可用大量报文的长报文情况和只有极小量报文(可能 I. INTRODUCTION In previous articles, Mellen and Green-Wood discussed multi-table ciphers, especially the M94 cipher. They considered the following three cases of deciphering: ① the alphabet is known, the key is known, ② the alphabet is unknown, the key is known, ③ the alphabet is unknown, and the key is unknown. This article will consider the fourth case: (4) The UMI is known and the key is unknown. We will consider two cases, namely, the case of a long packet that can use a large number of packets and the case of a very small amount of packets