[Cryptography] Exotic Operations in Primitive Construction

Dave Horsfall dave at horsfall.org
Thu Oct 1 02:49:00 EDT 2020

On Wed, 30 Sep 2020, Peter Gutmann wrote:

> If you're referring to an implementation in C, it's not even that any 
> more, any compiler from the last 15-20 years has a rotate recogniser and 
> will translate 'x << y | x >> ( wordsize - y )' into a single rotate 
> instruction.

Thank you :-)  I was trying to figure out how to do a rotation in C, but 
I'm a little rusty now; all I could think of was a single shift and test 
the sign bit etc.

Rotation of course is about as important in crypto as is XOR, or, for that 
matter, the famous NSA instruction ("population count") on the Cray 

-- Dave

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