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Brandon Enright wrote:
> Finally, one thing that hasn't been addressed in this patch is that on
> *nix, Nmap first tries "arandom" and then "urandom" before trying
> "random". If a box doesn't offer [au]random but does offer random Nmap
> will block -- /dev/random doesn't provide randomness as fast as Nmap
> uses it. The use of /dev/random should be dropped in favor of falling
> back on rand() or in the future, OpenSSL.
>
Per your suggestion of OpenSSL, this is a 4.20ALPHA4 CHANGELOG entry:
o Nmap no longer gets random numbers from OpenSSL when it is available
because that turned out to be slower than Nmap's other methods
(e.g. /dev/urandom on Linux, /dev/arandom on OpenBSD, etc.). Thanks
to Marek Majkowski for reporting the problem.
WRT to the /dev/random hanging, I see what you mean! I edited
nbase_rnd.c and Nmap immediately hangs and strace confirms it's from a
read(/dev/random).
But what are the odds of you mentioning this hanging so soon after this
(bit hostile) email[1] which mentions the exact behavior Nmap exhibits
when I only use /dev/random? Apparently his Linux box doesn't have
urandom (or it's a very strange coincidence since I've never had Nmap
just hang immediately for any other reason..)
Given the options of /dev/random, rand() and OpenSSL, it looks like
rand() may be the answer since random hangs and OpenSSL was slow.
Good find.
> Brandon
>
Thanks,
Kris Katterjohn
[1] http://seclists.org/nmap-dev/2008/q2/0182.html
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Received on May 01 2008
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