cvs commit: src/sys/modules/random Makefile src/sys/dev/random randomdev.h randomdev_soft.c randomdev_soft.h yar

Richard Coleman richardcoleman at
Mon Apr 12 05:07:29 PDT 2004

David Malone wrote:
> On Sun, Apr 11, 2004 at 08:46:43AM +0100, Mark Murray wrote:
>>Yarrow is unsuitable for this purpose; it is a great generator when
>>you have a low-entropy environment and you need to protect against
>>attackers having potential knowledge of the inputs.
> I still think it would be nice if our random infrastructure had a
> block-until-accumulated-'enough'-randomness mode, like the old
> /dev/random had, to avoid some future attack based on Yarrow's fixed
> size state. I don't think it will be a realistic attack any time
> soon, but it might be nice for baco-hat types. In the case where
> high-quality, fast hardware based generators are available, this
> seems to be a more realistic option though.
> I'm happy enough to live without this, since we thrashed this out
> before, but if you're looking at options, you might keep it at the
> back of your mind.
> 	David.

I think the old /dev/random caused more problems than it solved.  Most 
apps just used /dev/urandom to avoid all the end-user questions about 
the blocking.

And the beauty of the Yarrow PRNG is that as long as you have enough 
initial entropy to get started, you can pull as many bytes as you want 
and still remain cryptographically strong (within some very high limit 
of like 2^120 bytes before the next re-keying).

Richard Coleman
richardcoleman at

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