Abstract

In 1940 the US Army’s Signal Intelligence Service (SIS) cracked PURPLE, the Japanese diplomatic cipher. Shortly after that accomplishment, William Friedman, legendary cryptographer and civilian head of SIS, wrote his Preliminary Historical Report on the Solution of the “B” Machine. In it he introduced the mysterious “Identification of Homologs” and stated there that it had been a crucial technology to the success of cracking PURPLE. Despite that dramatic assessment, the concept simply disappeared, ignored by all subsequent authors of PURPLE histories and technical analyses. So what exactly is the Identification of Homologs and what role did it play in the cryptanalysis of PURPLE? That is the subject of this paper. We give a complete technical description, as well as historical information, some newly uncovered, about how SIS collected PURPLE “data”.

摘要

1940 年，美国陆军信号情报局 (SIS) 破解了日本外交密码 PURPLE。取得这一成就后不久，传奇密码学家兼 SIS 文职负责人威廉·弗里德曼 (William Friedman) 撰写了他的《关于“B”机解决方案的初步历史报告》。在其中，他介绍了神秘的“同系物鉴定”，并表示这是成功破解紫色的关键技术。尽管做出了如此戏剧性的评估，这个概念还是消失了，被紫色历史和技术分析的所有后续作者所忽视。那么同源物识别到底是什么？它在 PURPLE 密码分析中扮演了什么角色？这就是本文的主题。我们提供了关于 SIS 如何收集紫色“数据”的完整技术描述以及历史信息（一些新发现的信息）。