[RC5] RC5 question

Daniel Quintiliani coredump0 at mercurylink.net
Fri Oct 3 18:48:47 EDT 2003

On Fri, 3 Oct 2003 18:10:33 -0300, Décio Luiz Gazzoni Filho 
<decio at revistapcs.com.br> wrote:

> The problem is not export restrictions or anything (they've been lifted, 
> as far as I know); it's just the sheer amount of work that has to be 
> done. A book of mine states that since the inception of the computer 
> through the year 2000, there have been approximately a mole (6e23) of 
> computer operations performed on all computers on Earth. In comparison, 
> there are 3.4e38 RC5-128 keys to check. Even taking into account that 
> only 50% of keyspace is expected to be checked on average, that's 1.7e38 
> keys, or 1.7e40 cycles. Dividing out 1.7e38 by 6e23, you get a number 
> which is on the order of magnitude of a million times the age of the 
> universe.

Still, it's more fun than the RC5-72 since it's more relevant. According to 
the stats today the keyspace of RC5-72 will reach 100% in 462,417 days. 
Divided by 365.25 is about 1266 years. (Half that is about 633 years.) So 
both of these are not very good as contests but are fun "to work towards" 
as a game.


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