[RC5] When RC5 will be finished...

Markus Landgren ei1lama at chl.chalmers.se
Thu Nov 1 18:49:33 EST 2001

The 72 bit contest has 256 times as many keys, but it will take even more
than 256 times the cpu time to exhaust the 72-bit keyspace. If I remember
the discussions from 1997 correctly this is because 64 bits fit right into
two 32-bit registers, and 72 bits don't. The transition from 56 to 64 was
quick and painless because there was room for another eight bits. A RC5-72
client will require a greater rewrite of the code, and the keyrates will
drop. This is all from a four year old memory and I don't think I really
understood the more technical details even then, so someone please correct
me if I am wrong.

When RC5-64 is over I'll probably go to GIMPS or ECCp-109 or something.

At 14:13 2001-11-01 -0000, someone wrote:
>Hi All,
>Regarding RC72, am I right in thinking it is 256 times stronger than RC64.
>If so, then if computers keep to Moores Law, doubling their power every 18
>months, in 12 years, our computers will be 256 times as fast as they are now
>(Software implemented Rotate instructions not withstanding).
>I don't think many people will be interested in setting their computers off
>on a 12 year (Min) mission just to crack a code.
>Cheers, Adrian

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