Hi guys, my company is switching over to ssh and we have an old RS6000
that is running AIX 4.2 that we have to install ssh on. Is there a
package that I can download to install it like Sun has? I'm having
trouble with the info that I got and don't have any install
instructions. Any help would be great. Thanks guys!!

-----Original Message-----
From: Darren Tucker [mailto:[EMAIL PROTECTED] 
Sent: Friday, April 07, 2006 11:46 PM
To: Enrique Sanchez Vela
Cc: [email protected]
Subject: Re: prngd usage on OpenSsh4.3p2

Enrique Sanchez Vela wrote:
> I've been toying with openssh 4.3p2 for a while now on
> AIX 5.1 and I am trying to build it with prngd
> support, however, everytime I start sshd or issue an
> ssh command (whith prngd daemon not running) it just
> works fine.
> 
> I am building sshd with the following options, 
> 
> ./configure --with-ipaddr-display --with-md5-passwords
> --with-privsep-path=/var/empty
> --with-privsep-user=sshd --sysconfdir=/etc/ssh/
> --with-ssl-dir=/usr/local/ssl --prefix=/usr/local
> --with-prngd-port=708 --with-rand-helper=prngd
> 
> if anyone could explain the behaivor to me, I would
> appreciate.

--with-rand-helper doesn't take any arguments (other than yes/no).  What

you're doing there is always building ssh-rand-helper.

Normally, when you run configure, it checks if OpenSSL's RNG is 
"self-seeded".  For modern versions of OpenSSL, this basically means the

OpenSSL itself checks if there's a decent entropy source on your system 
such as /dev/random (which AIX 5.1 doesn't have) or prngd /egd (it 
actually only checks for the presence of a prngd/egd socket at a few 
default places).

At OpenSSH build time, if the RNG isn't self-seeded configure 
automatically builds "ssh-rand-helper", which is an external process 
that runs around collecting entropy from various sources, mashing them 
together and returning the result to whichever process ran it.  This is 
then used to seed OpenSSL's RNG, which is then supplies the randomness 
used for the ssh/sshd process.

Aat run time, the OpenSSH processes that need the RNG again check if 
OpenSSL's considers the RNG self-seeded.  OpenSSL checks again, and if 
it finds an entropy source it is used. If not, it tells OpenSSH that 
it's not self-seeded and OpenSSH runs ssh-rand-helper (if it was built) 
or fails with a "PRNG not seeded error" (if it wasn't).  You can see 
what it's doing by adding "-vvv" to an ssh command line.

Now in your case, you're always building ssh-rand-helper, so even if you

stop prngd, OpenSSH has a source of entropy.  If you remove the 
--with-rand-helper option from configure and rebuild OpenSSH then you 
will probably get the behaviour you expect.

The other thing to bear in mind is that some of these things are 
detected at build time *of both OpenSSL and OpenSSH* and some are also 
dependant on the versions in question.

ssh-random-helper also knows how to talk to prngd.  Before OpenSSH 
4.0p1, if configure found prngd at build time then ssh-rand-helper would

fail at run time if prngd wasn't running.  From 4.0p1, it will fall back

to collecting entropy from commands in this case (you will usually see 
an error from ssh in this case).

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
     Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.

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