# Re: Weakness of Feistel ciphers

Kim G. S. Øyhus <kim@xxxxxxxxxxx> wrote:
In article <7xmzeh5s5z.fsf@xxxxxxxxxxxxxxxxxxx>,
Paul Rubin <http://phr.cx@xxxxxxxxxxxxxx> wrote:
You could also look at the Hasty Pudding Cipher, one of the AES
submissions.

I need a cipher modula a Mersenne prime, prime products, or similar.

Suppose your modulus satisfies 2^(l-1) < n < 2^l. First you select
an l-bit block cipher (HPC may be a good candiate). To encrypt, you
iterate your block cipher repeatedly until the result is below n.
If your block cipher is any good at all, this will work.

This is the HPC trick. You could already have looked it up.

--
Kristian Gjøsteen
.

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