svn commit: r239569 - head/etc/rc.d

[Dag-Erling Smørgrav]

David O'Brien <obrien at FreeBSD.org> writes:
> Dag-Erling Smørgrav <des at des.no> writes:
> > Is there a reason to choose sha256 over a weaker, faster hash?
> Using a weaker hash could reduce the amount of entropy in the
> output (due to collisions).
>
> The Yarrow paper makes this argument (but willing to potentially loose
> some entropy) in 5 'The Generic Yarrow Design an Yarrow-160'
>
>     The reason is if you take an 'm' bit random value and apply a hash
>     function that produces 'm' bits of output, the result has less than
>     'm' bits of entropy due to the collisions that occur.  This is a very
>     minor effect, and overall results in the loss of at most a few bits
>     of entropy.

I was thinking along the lines of feeding at least 2 * m into the hash
function, possibly much more.  Remember that we're talking about finding
an alternative to discarding large amounts of data.

DES
-- 
Dag-Erling Smørgrav - des at des.no