A recursive solution for Turing’s H-M factor

Turing devised an electromechanical device, called a Bombe, to decipher German Enigma messages. His original design was considerably improved by the addition of Welchman’s diagonal board, allowing the use of much weaker menus and even menus without closures. Turing then made some extensive calculations to predict the performance of the improved Bombe. He provided a table, called the H-M factor, which allowed the expected number of stops to be predicted for menus containing a given number of letters and closures, but he gave no indication of how he constructed the table. This article is of technical interest and sheds some light on the H-M factor, including its variability with the tree-arrangement of the menu. It derives the H-M factor using a recursive technique for both the standard Bombe and the Jumbo Bombe, a later version incorporating the machine gun mechanism. These results may be of interest to those that code or run Bombe emulators.     

Rejewski’s equations: Solving for the entry permutation

In 1932, Marian Rejewski, who was a young mathematician working at the Polish Cipher Bureau, brilliantly recovered the internal wiring of the military Enigma. His initial efforts were unsuccessful because he assumed that the entry permutation was the same as in the commercial machine. Luckily he tried the identity permutation as an alternative and that proved to be correct. This note describes how Rejewski’s equations may be used to deduce the entry permutation without any guesswork, a technique that was later rediscovered by Alan Turing and by Lieutenant Andrew Gleason.     

CYPHER MACHINES MAINTENANCE AND RESTORATION SPANNING SIXTY YEARS

We describe the life and times of a servicing mechanic for cypher equipment for the Royal Air Force during World War II and an opportunity to serve again as a cypher machine restorer for Bletchley Park Museum.     

BETRAYAL AT PEARL HARBOR BOOK REVIEW

The Ultra background is given to some operations by U. S. Navy escort carriers against U-boats in 1943 and 1944.     

FROM THE ARCHIVES: U-BOAT HF WT SIGNALLING

A Royal Navy document on U-boat radio procedures in WWI is reproduced, with annotations.     

RASTERSCHLÜSSEL 44 – THE EPITOME OF HAND FIELD CIPHERS

The German hand cipher Rasterschlüssel 44, which replaced Double Playfair in August 1944, is described and an account is given of its use by the Wehrmacht and of its crypt analysis by the Allies.     

THE NSA PERSPECTIVE ON TELECOMMUNICATIONS PROTECTION IN THE NONGOVERNMENTAL SECTOR

This paper presents the travels of a cryptological Intelligence mission through Germany near the end of World War II to locate German Signal Intelligence information documents, and equipment.     

A SOLUTION OF THE HEBERN MESSAGES

This paper is the account of a computer-aided solution of the Hebern messages first solved by William F. Friedman in 1924.     

哈萨克族人名规范化译写软件设计

主要论述了哈萨克族人名汉字译写规范化软件的设计思路及实现方法。本软件是以“大用”维哈柯视窗forWin dows 98系统为操作平台 ,以VB和Access为软件开发工具设计的。它利用VB中的字符串处理函数和数据库连接技术及SQL语句数据查询技术 ,有效地处理了哈文词中每个字母因位置不同写法不同而引起的计算机编码也不同这一问题 ,从而实现了哈萨克族人名的计算机自动翻译功能。这套软件有助于哈萨克族人名汉字译写规范化 ,具有极高的应用价值