[Hardware] Notes... The case for an open client
elektron_rc5 at yahoo.ca
Mon Aug 16 15:01:52 EDT 2004
> Prior to the start of RC5-72, there was some internal discussion about
> ignoring the mangling requirements and simply incrementing natively,
> but it
> was decided to instead stay with standard RC5 mangling that had been
> done in
> RC5-56 and RC5-64 rather than introduce any possible problems. There
> been timings done of the performance difference gained by removing the
> mangle/unmangle operations, and it turned out to be relatively trivial
> than a few percent in keyrate, I think). Although speed improvements
> and there are always good, picking the safety of past implementation
This way, we can keep the first few S-boxes dependant on L and L
(I think). The 1/256 of the time that it overflows will always be a
problem, then be too much (though you could increment key.mid by 0x100
and check for an overflow, which would save you the 1/65536 and 1/16M
chance that other bytes overflow).
> In any case, changing the incrementing of the "high" bits much above
> would not really be possible without (effectively) discarding all of
> work that had already been done.
Of course, since this is (currently) done by proxies, it's not the
biggest deal in the world (and 1/2^32 of the time is quite small).
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