Re: Double transposition cryptanalysis

From: Stewart Strait (sstrait1_at_san.rr.com)
Date: 08/15/05

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    Date: Mon, 15 Aug 2005 08:42:03 GMT

    Rob Sullivan <cogito.ergo.cogito@gmail.com> wrote:
    > I've written a program to break double transposition ciphers based on
    > FairPlay, a Playfair cipher cracker. The original program used shotgun
    > hill-climbing, so all I really had to do was modify the
    > Playfair-specific parts.
    > The source code is below - I'd be interested in any comments or
    > suggestions.
    >
    > Thanks,
    > Rob
    ...
    1. How well has your code worked so far?

    2. It would save time if you could give a URL for the file
       trigrams_npf.txt used by your code.

    3. If anyone wants double incomplete columnar transposition
       test/challenge examples, perhaps you might be interested in:

       http://www.speakeasy.org/~straits/straits08.clb
       http://www.speakeasy.org/~straits/straits09.clb

       There are 10 examples in the 08 file and 20 in the 09 file.
       The plaintext should be fairly normal English, but text may
       begin and/or end in the middle of a word. The two transpositions
       in a given example have the same key. The plaintext length is
       always 907 letters, which is likely to make these examples easier
       than is typical for this system.

       stos08: 13<=key length<=22 [10 examples]
       stos09: 10<=key length<=15 [20 examples]

       Plaintext is not original.--

    Stewart Strait

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