🚀 go-pugleaf

In article <ARI.HUTTUNEN.92Oct13203817@cardhu.cs.hut.fi> Ari.Huttunen@hut.fi (Ari Huttunen) writes:
>In article <wa6JsB7w165w@works.uucp> ferret@works.uucp (Dave Ferret) writes:
>
>! Just a sidenote to 'Hackers' words...
>
>!   There are also encryption algorithms that when used to encrypt the 
>! plaintext over and over and over, will yield the un-encrypted text. (Ie: 
>! Its a circular encryption -- Sorry, I don't know the correct term here)
>
>Any encryption scheme that has a fixed block length *must* do this. Think
>of a series of encryptions:
>	x_1 -> x_2 -> x_3 -> ... -> x_k -> ... -> x_n -> ...
>If 'n' is greater than the possible number of messages that can be encoded
>in the fixed length block, there must be some blocks in the chain that
>are the same (pigeonhole principle). Let x_k and x_n be the same blocks.
>Then by encrypting x_k (n-k)-times yields x_k.
>
>(n-k) might be quite large, though. ;-)

However there is nothing in your argument to say that (k,n) are not
dependent on the original block being encrypted.

for "circular", we want something more like:

there exists n such that

 n
E (x) = x   for all blocks x  

where E is the encryption function in question.

Mark
-- 
Mark Henderson, SoftQuad Inc, 108-10070 King George Hwy, Surrey, B.C. V3T 2W4
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