[Cryptography] Unicity distance of Playfair

[Charles Jackson]

On Mon, Mar 28, 2016 at 1:38 PM, mok-kong shen <mok-kong.shen at t-online.de>
wrote:

> To make my argument clear: Compare the general case of poly-alphabetical
> substitution (with a 26*26 matrix where the coulmns are fairly random
> permutations of the alphabet) and the special case (namely Vigenere,
> with a 26*26 matrix where the first column is the alphabet as such and
> each successive column is a rotation by one place of the preceeding
> column). Evidently the number of possible keys of the two cases are
> exactly the same.
>

​I am confused here.  If each row of the matrix is a distinct permutation
of the alphabet, then  I think there are (26!)^26 possible keys.  For the
Vigenere there (26!) keys.  Big difference.

-- 

Chuck
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