# Re: C code of PEARL1, a block encryption algorithm emphasising simplicity

"Tom St Denis" <tom@xxxxxxx> wrote in message
news:4304b8f1-b407-4f79-88e4-

Well if it's a block cipher typically your plaintext can be longer
than a block? It was my vague understanding that he just gens a new
matrix for each block.

So if he encrypts a stream of identity blocks you get consecutive
blocks of PRNG data. If the PRNG is linear then you can break the
system.

If the matrix M is 4-by-4 then encrypting a stream over alphabet
{I1,I2,I3,I4} where (I1,I2,I3,I4) = I is the identity matrix, recovers
1/4 of M.

If the PRNG is secure [e.g. non-linear and non-correlated and large
enough search space] then why are you doing any of this nonsense
matrix work?

It is our view (yours and mine) that a PRNG is either secure or not. But
in Mok Kong Shen's view there are semi-secure (or 25%-secure,
20%-secure, 10%-secure etc) PRNGs that if 2N (or 4N, 5N, 10N etc) key
stream blocks is used to encrypt N plaintext blocks, it could be 100%
secure.

Regards,

Tran Ngoc Duong.

.

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