[RC5] Time out and DES-II-2 challenge

Travis Siegel tsiegel at softcon.com
Thu Jul 2 18:27:06 EDT 1998

On Wed, 1 Jul 1998, Jason Untulis wrote:

> One other blocksize-related note to add to Eric's fine summary. Early in
> RC5-64, when the new blocksizes were added (original RC5-56 blocks were
> only 2^28 AFAIR), there were bugs in handling the 2^31 block size,
> presumably related to the fact that 2^31 is the maximum size of a 32 bit
> signed integer. (Not a difficult mistake for the coders to make...) Many, if
> not most people, who wanted bigger blocks chose the 2^30 size and probably
> left it there.

Actually, initially, you could select anything from 2^28 all the way
through 2^32 (2^32 is the max that can be held in an unsigned long int) As
a result, block reports were getting scrambled, as they checked 2^33 keys
actually.  That was the reason for trimming things back to a max of 2^31
(plus the extra key makes it 2^32 (max) and the overflow problems went

> The assertion made in Adam's 2.7100 announcement is that this 2^31 block
> handling has been fixed. Looking at the Readme I've seen no indication in
> the version history of this. You may want to test this out before DES-II-2
> starts...

As pointed out above, there never was a problem with 2^31 block sizes, so
there would be no reason to mention a fix in the readme files.  it was
only the very first client releases for rc5-64 that had the 2^32 block
size allowed to be chosen, so unless you've got one of those, you'd not
see any mention of that size of blocks.

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