[Cryptography] Unicity distance of Playfair

[mok-kong shen]

Am 19.03.2016 um 18:41 schrieb Max Kington:
>
> On 19 Mar 2016 2:08 pm, "mok-kong shen" <mok-kong.shen at t-online.de
> <mailto:mok-kong.shen at t-online.de>> wrote:
>  >
>  >
>  > Given the classical scheme Playfair, say, for 5*5 matrices, I am
>  > interested to determine its unicity-distance. How should one proceed
>  > to properly do that? Thanks in advance.
>
> http://practicalcryptography.com/cryptanalysis/text-characterisation/statistics/
> was a good reference when I was asked the same question on my masters.
>
> There are lots of academics on this list. Perhaps you even know some of
> them..

Playfair works with a pair of characters at each processing step.
Thus intuitively I have expected that the unicity-distance would
be an even number and not an odd number 27 in the table there.

Anyway, I should appreciate it very much, if someone could privide
me a terse recipe, listing which computations are to be done in order
to obtain the unicity-distance of Playfair. (I am attempting to
determine whether a certain suggested variant of Playfair provide
performance advantages or not and suppose that the unicity-distance
could be a useful measure for that purpose.)

M. K. Shen