another feature RNGs could provide

[Ben Laurie]

Jack Lloyd wrote:
> On Mon, Dec 12, 2005 at 12:20:26AM -0600, Travis H. wrote:
>> 2) While CTR mode with a random key is sufficient for creating a
>> permutation of N-bit blocks for a fixed N, is there a general-purpose
>> way to create a N-bit permutation, where N is a variable?  How about
>> picking a cryptographically strong permutation on N elements, where N
>> is not necessarily a power of 2?
> 
> Use can use the Bear or Lion constructions to form 2^{arbitrary} bit block
> ciphers quite easily.

Good ciphers aren't permutations, though, are they? Because if they
were, they'd be groups, and that would be bad.

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