[Hardware] RC5 with FPGAs

[Olivier Meyer]

What about the partial matches: how would one do that in an FPGA?

On 9/7/06, david fleischer <cilantro_il at yahoo.com> wrote:
>
> That's interesting.
> How does byte-reversed increment work?
>
> You suggest doing 6 rounds instead of 3. This to avoid
> the penalty of storing the array until the key is
> tested. But the RC5 algorithm is separated into
> stages. You need all the data for the last step, so
> you need at least to have gone through 2 rounds when
> starting to encrypt the words.
> How does the pyramid work?
>
> David
>
> --- Dan Oetting <dan_oetting at qwest.net> wrote:
>
> >
> > On Sep 6, 2006, at 12:07 PM, david fleischer wrote:
> >
> > > By the way, I'm not sure pipelining will bring you
> > > great benefits in an FPGA. A back of the laptop
> > > calculation tells me that you'll need
> > approximately
> > > 1Kbit of memory per key. This may mean that most
> > of
> > > the archirecture will be shoveling data back and
> > forth
> > > to the core.
> >
> > You don't have to store the data. You can recompute
> > it. Instead of 3
> > rounds with intermediate data stored between rounds
> > you implement 6
> > rounds in a pyramid so the correct data is provided
> > to each stage as
> > it's needed..
> >
> > > I also have a question, can someone help me figure
> > out
> > > the code in the source ANSI cores? I cannot
> > understand
> > > how the key increment is done. (that is to say, I
> > see
> > > what the code is doing, but I cannot figure out
> > why
> > > this does any good.)
> >
> > What the code is doing is incrementing the key in
> > byte reversed
> > order. Why this is done is because the calculations
> > in the first 2
> > 1/2 iterations of the first round then become
> > constants so the loop
> > can run a few keys per second faster. It won't help
> > your hardware
> > unless your design is fully pipelined so you can
> > consolidate the
> > first few sets of gates in each pipe. But you still
> > need to implement
> > the byte reversed increment to be compatible with
> > the d.net project.
> >
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Olivier V. Meyer
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