# Re: Use of simple schemes

*From*: Maaartin <grajcar1@xxxxxxxxx>*Date*: Thu, 12 Nov 2009 14:03:29 -0800 (PST)

On Nov 12, 10:01 pm, Mok-Kong Shen <mok-kong.s...@xxxxxxxxxxx> wrote:

Another scheme that is also (theoretically) very simple but faírly

expensive in computing is, I suppose, Hill's scheme employing matrices.

Now the Hill cipher is said to be weak in textbooks because, if the

matrix is n*n and one has n^2 units of corresponding plain and cipher

text, then the matrix can be found and the whole thing broken. But one

could afford to use a good sufficiently fast PRNG to dynamically

generate as many matrices as needed, using even any one n*n matrix for

much less than n^2 units of plaintext, when the computing cost is low

and the speed is acceptable. This way, Hill's scheme would be

practically applicable (eventually as a component of a larger scheme)

in my humble view.

But having a fast perfectly secure PRNG you could simply xor it's

output with the plaintext. Using an unsecure PRNG makes the Hill's

scheme vulnarable again. And again, you need an expensive analysis of

the cipher what is just what you wanted to avoid.

.

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