In the French Army archives three cryptograms encrypted by the M-209 were found. They date from 1944 and come from the 1st French Army. Since the security rules in the military require them...

Genuine French WWII M-209 cryptograms

“Breaking German Army Ciphers” is the title of a Cryptologia article from 2005, describing the lucky survival of several hundred authentic Enigma messages of World War II, and an account of a ciphertext-only cryptanalysis of a large number of these messages, leaving only a few (mostly short messages) unbroken. After reviewing the work done, and investigating the reasons for both lucky breaks and close misses, the modern ciphertext-only attack on Enigma messages is improved, especially on genuine ones with short lengths and/or many garbles. The difficulties of a proper measure for the candidate’s closeness to a plaintext are clarified. The influence on the decryption process of an empty plugboard and one with only a few correct plugs is examined. The method is extended by a partial exhaustion of the plugboard combined with an optimized hillclimbing strategy. The newly designed software succeeds in breaking formerly unbroken messages.

methods

Modern breaking of Enigma ciphertexts

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background

Cryptanalysis of the Hagelin cryptograph

The Hagelin M-209 portable encryption device was used by the U.S. Army in World War II and the Korean War, as well as by other armies and in embassy settings. In this article, a fully automated, computerized known-plaintext attack is presented. It is based on hillclimbing and a novel fitness function: the aggregate displacement error. Performance evaluation shows that this attack is able to recover key settings for messages as short as 50 characters. To validate these results, several publicly available challenge messages were solved with this method, including a message with only 40 letters.

Automated Known-Plaintext Cryptanalysis of Short Hagelin M-209 Messages

The Hagelin M-209 was a mechanical encryption device used by the U.S. Army during World War 2 (WWII) and the Korean War, as well as by other armies and diplomatic services. The Hagelin M-209 has be...

Genuine French WWII M-209 cryptograms

References

Modern breaking of Enigma ciphertexts

Cryptanalysis of the Hagelin cryptograph

Automated Known-Plaintext Cryptanalysis of Short Hagelin M-209 Messages

Ciphertext-only cryptanalysis of short Hagelin M-209 ciphertexts