EGD requirement a show stopper for me

[Damien Miller]

On Fri, 28 Jan 2000, Ben Lindstrom wrote:

> I've not looked at the source for where random number generation is
> needed, but where in the SSH process are they need.

Some randomness is needed for RSA key generation. The RSA key
generation routines in OpenSSL source from its own RAND_* routines.

OpenSSL with use /dev/random if it is present or will <looks at
OpenSSL sources> use some easily predictable (uid, pid, time) data to
seed its own hash pool.

Ouch. IMO this is woefully insufficient, and I will be explicitly
seeding the OpenSSL pool from our random number source.

OpenSSH also needs a reasonable amount on entropy to feed an ARC4
PRNG. The PRNG is periodically re-keyed with fresh entropy (256 bits
at a time IIRC).

The output of the PRNG is used for session keys, random pad bytes,
check digits, temp file names, rresvport port numbers and anything
else that needs remotely unpredictable numbers.

The problem is that there is no nice portable way to get high-quality 
random numbers. EGD does the job, at the cost of running a large PERL
daemon. (currently one for each user).

I have a patch which will enable users to run only one EGD per machine
and have it serve entropy over a localhost TCP socket. This is still
less than optimal, and I don't think that EGD has been designed for
this. For instance, it may be possible for one user to drain EGD's
entropy pool so it either blocks (DoS) or produces degraded data.

There are several options to pursue here:

1. Revive the random code from ssh 1.2.16.
2. Port the Linux or BSD kernel random driver to userspace
3. Port Yarrow[1]
4. Fix EGD
5. Roll our own

I think that if we are going to change the random source, then we
should use something that has been subjected to review. This precludes
1, 5 and (to a lesser extent) 4. Porting Yarrow is to me the most
attractive option, as it has been the subject of a formal design but
this may take some time.

-d

[1] http://www.counterpane.com/yarrow.html

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| "Bombay is 250ms from New York in the new world order" - Alan Cox
| Damien Miller - http://www.mindrot.org/
| Email: djm at mindrot.org (home) -or- djm at ibs.com.au (work)