[Hardware] Notes... The case for an open client

david fleischer cilantro_il at yahoo.com
Wed Aug 18 13:18:09 EDT 2004


What is the point of having an error check if
re-checking the key-block will take the same amount of
work as the key processing itself?
is this going to be a sampled check only?
to have fail safe checking it would be necessary to
have a means of checking that every block was
processed correctly.

david

--- Elektron <elektron_rc5 at yahoo.ca> wrote:

> > A CRC could be used instead of a sum for the
> residual. The CRC 
> > polynomial X^32+1 would be easy enough to
> implement in both hardware 
> > and software and offers the same distributive
> properties as addition. 
> > It would be nice if everyone used the same
> residual function but it's 
> > not absolutely necessary. The residual is used for
> local testing and 
> > random verification.
> 
> XORing is probably better than adding (except
> there's no carrying, so 
> there's a greater chance that an error in one bit
> could be negated by a 
> second error in the same bit). A CRC would be
> possible, but perhaps too 
> slow, especially for software cores.
> 
> Most CPUs seem to be able to add and XOR at the same
> speed, though, so 
> I guess the decision lies with the hardware people.
> 
> - Purr
> 
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