For those of you who have had their fill of the last week’s posts on the Somerton Man, here’s a different cipher mystery that doesn’t get aired even 1% as much: the Feynman Ciphers.

The first Feynman Cipher (F1, 380 characters long) turned out to be based on a 5 x 76 transposition path cipher (the plaintext was “WHANTHATAPRILLEWITHHISSHOURESSOOTE”, i.e the start of Chaucer’s Canterbury Tales), but what is a little odd is that nobody seems to have yet made any inroads at all into the other two, though it is often remarked that transposition may well be involved. In that sense, they’re a bit like the d’Agapeyeff challenge cipher, which is also believed to be a multi-stage cipher including one or more transposition stages.

At 261 characters long, the second Feynman Cipher (F2) is a little shorter than F1: this length factorizes to 3 x 3 x 29, or 9 x 29, or 3 x 87. It also includes all 26 letters, which rules out a lot of tricky ciphers such as Playfair and Phillips.


Though normally very good at identifying cipher types, Cryptocrack doesn’t do particularly well in this: it suggests Phillips, FracMorse, Playfair and Beaufort as its top four tips, none of which seem hugely likely to me. What is interesting, though, is that if you transpose the ciphertext (say, using some of the seven transposed routes listed by James Lyons), Cryptocrack produces a quite different set of recommendations, suggesting instead Trifid (which it almost certainly isn’t), but more reasonably Running Key and occasionally Vigenere.

Personally, I don’t think it’s a Vig: so right now, my prediction is that it’ll turn out to be a funky path transposition combined with Running Key (combining this with Vigenere would surely be just a bit too sadistic). Perhaps this will be what James Lyons will say too, when he gets round to posting part 3 (his part 2 is here.

Finally: the third Feynman Cipher (F3) is short too: 231 characters, which factorizes to 3 x 7 x 11. Much as James Lyons notes, I currently expect more or less everything said about F2 to hold true for F3: so I epxect it’s probably a Running Key (or perhaps Vigenere, but I doubt it) combined with a funky path transposition.


What do you think?

4 thoughts on “A quick look at the Feynman Ciphers…

  1. Shurupag on August 27, 2014 at 6:06 am said:

    How do I make a picture appear beside my name when I post here?

  2. Sean Riddle on August 29, 2014 at 5:58 pm said:


  3. Sean: oops, my typo, now fixed, thanks! 🙂

  4. Thomas on July 4, 2015 at 4:01 pm said:

    I have invented a childish and simple transposition method some time ago. But this is too large a puzzle for me to try it with pencil and paper to see if this was perhaps encrypted just by my method. Maybe, somebody with a computer and C skills in a jiffy.

    As this margin is too narrow to contain the description of my method, I simply give an example of a short ciphertext and its plaintext. 🙂



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