analysis and implementation of LRW

[Allen]

David Wagner wrote:

[snip]

> Another possible interpretation of (2) is that if you use LRW to encrypt
> close to 2^64 blocks of plaintext, and if you are using a 128-bit block
> cipher, then you have a significant chance of a birthday collision,

Am I doing the math correctly that 2^64 blocks of 128 bits is 
2^32 bytes or about 4 gigs of data? Or am I looking at this the 
wrong way?

If 4 gigs is right, would it then be records to look for to break 
the code via birthday attacks would be things like seismic data, 
which tend to be very large. Feed a known file in and look at the 
output and use that to find the key for the unknown files?

As you can tell, my interests are often the vectors, not the 
exact details of how to achieve the crack. Currently I'm dealing 
with very large - though not as large as 4 gig - x-ray, MRI, and 
similar files that have to be protected for the lifespan of the 
person, which could be 70+ years after the medical record is 
created. Think of the MRI of a kid to scan for some condition 
that may be genetic in origin and has to be monitored and 
compared with more recent results their whole life.

Thanks,

Allen

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