[Cryptography] Random permutation model for encryption as a teaching tool?

Ralf Senderek crypto at senderek.ie
Mon Oct 15 13:39:15 EDT 2018

On Mon, 15 Oct 2018, Stephan Neuhaus wrote:

> page on block ciphers for example.
> However, the set of possible n-bit keys contains only 2^n elements, whereas 
> there are (2^b)! possible permutations of b-bit blocks, which is obviously 
> vastly more if b is of the same order as n. Furthermore, not all permutations 
> are good for block ciphers; e.g. those that have many fixed points (and most 
> random permutations will have at least one) are evidently not well suited.
> So the question is, is this a good model *for teaching*?

IMHO no. It is not necessary to teach the inner workings of AES but at the 
very least the fundamental idea of a Feistel cipher and the problem of
using short keys (ie. brute force attack on DES since 1999) would lay
a more serious foundation for the understanding of modern cryptography
than fiddling with permutations.


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