[rc5] RC64 keyspace

Steve Trottier STROTTIER at novell.com
Tue Oct 28 18:09:44 EST 1997

There goes their $1000. So much for resupplying the caffeinated beverages!

>>> Joseph Fisk <joe at rm405n-a.roberts.fit.edu> 10/28 7:24 PM >>>
Each block is 2^28 keys.  There are total 2^64 keys.  That means there are
2^36 blocks, or 68,719,476,740 blocks.  If two bits are used per block,
you'll need 137438953500 bits, which is 17,179MB.  I think you
accidentally calculated the size of the array needed to keep track of each
individual key!

>         In any event, I'd expect that the Bovine crew is going to need 
>      about 256-times as much storage for this information as was used in 
>      RC5-56.

That sounds right to me, too.  In 56-bit RC5 there were 2^28 blocks.  With
two bits per block you would need 536,870,912 bits, or 67.1MB.

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