[RC5] Hello / kernel optimization

Art Pannek mrrelaxed at foxinternet.net
Wed Jul 11 08:37:31 EDT 2001

Kyle Markley wrote:

> Hello,
> I just subscribed to the list, so my apologies if this is any breach of
> etiquitte.
> I have heard that the RC5 kernel for Pentium 4 is, well, slow.  I consider
> myself pretty handy with an assembler so I'd like to write a new kernel.  My
> problem is that I don't know much about RC5.
> What's the quickest way to ramp up on what the RC5 algorithm actually does, at a
> high level of abstraction?  In lieu of not finding any "How to Understand RC5"
> documentation, I've looked at the existing kernel sources and I don't find them
> transparent.  I figure the experts are here, so this is the right place to ask.
> My particular concerns are:
>   - What are the operations to be performed for each data element?  (i.e. what
> do the rounds do and how do they break down?)
>   - Are there any interactions between data elements that make parallelization
> tricky?  (Is this what the "mangle-increment" stuff is all about?)
> Thanks!
> ---
> Kyle Markley

Here is a link to the RFC that describes the RC5 algorithm.


And here is a link to the current RC5 challenge.


Contest identifier: RC5-32/12/8

There is also a crypto FAQ on the main page. http://www.rsa.com

The "rounds" refers to expansion of the "key" in a one way algorithm.

The "expanded key" is used in the two way "block cypher" algorithm to encrypt or


Art Pannek

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