Thursday, November 29, 2018


In the The American M-209 cipher machine I’ve added the following under ‘Additional information’:

M-209 vs Enigma:

Regarding the cryptologic strength of the M-209 machine versus the plugboard Enigma, the expert on classical cipher systems George Lasry (15) has stated:

One comment about the security of the M-209. The claim that the Enigma is more secure than the M- 209 is disputable.

1) The best modern ciphertext-only algorithm for Enigma (Ostward and Weierud, 2017) requires no more than 30 letters. My new algorithm for M-209 requires at least 450 letters (Reeds, Morris, and Ritchie needed 1500). So the M-209 is much better protected against ciphertext-only attacks.

2) The Turing Bombe – the best known-plaintext attack against the Enigma needed no more than 15-20 known plaintext letters. The best known-plaintext attacks against the M-209 require at least 50 known plaintext letters.

3) The Unicity Distance for Enigma is about 28, it is 50 for the M-209.

4) The only aspect in which Enigma is more secure than M-209 is about messages in depth (same key). To break Enigma, you needed a few tens of messages in depth. For M-209, two messages in depth are enough. But with good key management discipline, this weakness can be addressed.

Bottom line – if no two messages are sent in depth (full, or partial depth), then the M-209 is much more secure than Enigma’.

I also added Lasry’s M-209 articles in the notes:

Friday, November 9, 2018

Interesting articles

1). From ‘Journal of Intelligence History’: ‘From improvisation to permanence: American perspectives on the U.S. signals intelligence relationship with Britain, 1940–1950’.

However I have to disagree with the following statement:

One of Friedman’s reasons for visiting TICOM was to confirm that the Germans had been unable to break any Allied high-grade encryption systems during the war. That spring, senior Army officers had asked why he was so confident that these systems remained invulnerable. Friedman responded that captured German documents contained no suggestion any major Allied systems had been broken, only the less sophisticated M-209 device and even then only when Allied code clerks made mistakes. ‘The overwhelming evidence’ Friedman concluded, ‘is that they are far behind us and have no appreciation of solution techniques we now regard as commonplace.’ For him, the Germans’ inability to penetrate Allied cryptographic systems reflected their ‘supreme confidence’ in Enigma. What Friedman learned from the TICOM effort confirmed his view that British and American successes in cryptanalysis and cryptography far exceeded those of the Germans’.

Regarding Typex it says that model 22 (with movement of all 5 rotors and two plugboards) was introduced in 1950 and not during WWII as claimed by some sites:

In 1946, the British authorities decided to further modify Typex to increase its cryptographic strength. The rotors and turnover mechanism were redesigned so that all rotors would turn as a message was encrypted and the machine was fitted with a pluggable ‘crossover’ at the entry and exit to the wiring maze. This new version of Typex was ready for service in September 1950 and it was predicted that it would provide adequate cipher security for another 10 years.

Wednesday, November 7, 2018

Resurrection of the Hayashi case

Recently I stated that I had given up on trying to locate an NSA report called ‘Interrogation of mr Hayashi’.

However after looking at the finding aid to NSA transfer group TR-0457-2016-0017 I saw that there is a file titled ‘INTERROGATION HAYASHI, TOKURO, 26 APRIL 1950 (S-058,590)’.

It is reasonable to assume that this is the file I was looking for so NARA’s FOIA office has reopened the case.

Let’s hope that it will be declassified soon.