[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Redundancy in XOR encryption
> >
> > Compress P to get perfect compression (ie. 0 redundancy)
> > Encrypt F (the compressed text) using a repeated key XOR
> >
> > of course this is all rather theoretical as there is no such thing as
> > perfect compression, but I just thought it might be interesting to
> > see if this is indeed strong, superficially it appears so to me...
> >
>
> Paul:
> I think that if the cryptanalyst knows that F has zero redundancy
> that he can run searches from 0 to n bits for the key and have
> the computer flag solutions that have zero redundancy.
I never though of that.
> I also think that a perfectly compressed file would have a relative
> entropy value close to one also, hence the computer could flag possibles
> that have both characteristics.
yeah, these two are reasonably unlikely to occur together (only a
reasoned guess, anyone got any comments on this?)
so we really have a weakish system.
> Hence, instead of searching for plaintext by counting coincidences,
> we are searching the decrypts for solutions that have zero redundancy
> and a relative entropy value close to one. How many solutions will
> have both these qualities? I don't know. But if the compression method
> is known, brute force will be tried, and only having to try to
> decompress (read) data that has the resultant characteristics
> of compressed information will speed things up by quite a bit.
Yeah, this is still a form of brute force but I was thinking of this
in terms of a smallish (sub 200 bit) key, so brute force against
solutions with 0 entropy is a realistic possibility.
anyone else got a faster way to attack this highly theoretical,
will-never-be-implemented, type system??
I`d imagine there is some sort of way to measure the entropy "mixed
in" by the XOR thus giving a foothold in the key, but I can`t think
of anything right now, anyone got any ideas?
Datacomms Technologies web authoring and data security
Paul Bradley, [email protected]
Http://www.fatmans.demon.co.uk/crypt/
"Don`t forget to mount a scratch monkey"
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: 2.6.3ia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=CMZA
-----END PGP PUBLIC KEY BLOCK-----