Thursday, August 11, 2016


In the German Wikipedia entry on dr Werner Weber there is a mistake.

During WWII Weber worked at OKW/Chi (Oberkommando der Wehrmacht/Chiffrier Abteilung – Codebreaking department of the Supreme Command of the Armed Forces) and he solved important Japanese diplomatic cipher systems.

The first major system solved was the transposed code J-19 FUJI, used in the period 1941-43. Although some TICOM reports state that he was unable to solve the successor to FUJI this is not correct.

The next main system was also a transposed code (Japanese designation TOKI) and it was solved in the period 1943-45 by OKW/Chi and by the Pers Z agency (decryption department of the German Foreign Ministry).

Why did some Germans say in postwar interrogations that they could not solve it? I don’t know.

Why did the Allied interrogators believe them? I don’t know.

Just clearing things up… 

Friday, August 5, 2016

Typex security measures

In The British Typex cipher machine i added information from report FO 850/171 (mentioned in the book ‘Alan Turing: The Enigma’):

Countermeasures against cribbing

As an ENIGMA type device (with a reflector) Typex was also vulnerable to the plaintext-ciphertext attacks used by the Allied codebreakers against the German plugboard Enigma. In order to hinder such attacks several measures were employed, such as burying the address in the middle of the text, cyclic encipherment for short messages and insertion of random letters in the text.

For example report FO 850/171 ‘Preparation of telegrams: use of code words: cypher machines and traffic: teleprinter services: en clair messages. Code 651 file 1 (to paper 4968)’ (25) says:

‘When encyphering on the Typex machine, the encyphered version of a letter can never be the letter itself. This sometimes makes it possible to assign with absolute accuracy even a small number of words known or estimated to be in a message to the actual letters of the cypher version by which they are represented. To obviate this danger operators must from time to time press a key not demanded by the text of the message; the additional letters resulting will make the accurate fitting to the cypher version of a piece of clear text quite impossible. Such an insertion should be made on average once in every 10 words while the body of the message is being encyphered; it should be made on average once in every three words during the encypherment of the codress, the prefatory details and the beginnings and endings, whichever of the methods of encypherment in paragraph 25 is being followed; it should also be made on average once in every three words throughout very short messages when they have to be encyphered separately in Typex (see paragraph 27). The insertion should be made within words and not between them.’

Monday, August 1, 2016

The US military attaché double transposition cipher

Apart from the standard cryptosystems (Military Intelligence Code, War Department Confidential Code. M-138-A strip cipher) US attaches also had an emergency double transposition cipher. According to the instructions for this system, found in the files of Pers Z (decryption department of the German Foreign Ministry) (2):

Use of cipher. To enable M/As to exchange safely secret or confidential messages with other attaches or with assistants or agents acting under their direction, the double transposition cipher is prescribed.

Keys. The keys will be determined by the M/A. They will consist of short phrases consisting of from five to twenty letters. They will be changed at frequent intervals.

However the same numerical sequence was used for both cages, which means that this system would have been vulnerable to cryptanalysis.