twofish keysize

[Malte Gell]

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Am Mittwoch, 21. April 2004 11:05 schrieb Werner Koch:
> On Tue, 20 Apr 2004 15:02:45 +0200, Per Tunedal Casual said:

> > BTW I've been told it isn't wise to encrypt files larger than a few
> > MB using a block size of 64 bits. What's the limit for the block
> > size 128

> Not a few MB but several GB: Due to the birthday paradoxon you will
> notice on average identical blocks after 2^32 blocks (32 GB).  This
> yields patterns which help in cryptanalysis.  It is also the reason
> why ssh re-negotiates a new key after 1 gig.

Isn't this issue one of the reasons why OpenPGP compresses data before 
encrypting it? If a large cleartext chunk contains much redundant data, 
compression may reduce it and helps to reduce such patterns.  So 
encrypting with "only" a 64 bit block size shouldn't be a problem. Is 
this correct?

Malte

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