oss-sec mailing list archives

Re: OpenSSH key blacklisting


From: Nathanael Hoyle <nhoyle () hoyletech com>
Date: Wed, 04 Jun 2008 14:49:47 -0400

The Fungi wrote:
On Wed, Jun 04, 2008 at 11:14:12AM -0400, Nathanael Hoyle wrote:
[...]
However, the reason debian got into the mess they did in the first
place with this was specifically because they were trying to
remove responsibility from the can't-be-bothered users for
configuration. At one point, nearly all ssh key generation systems
required the user the type keys 'at random' on the keyboard,
and/or to move the mouse to generate an entropy pool for a seed
value for key generation. Because debian performs key-generation
on first boot in most cases, that early in the startup there might
not be sufficient entropy in the network traffic for utility. I
guess they found that users were either incapable of or
disinclined to participate in the key generation process.
[...]

Not to be argumentative, but have you installed OpenBSD lately
(effectively the reference platform for OpenSSH development)? For
years, its base install has run sshd by default, generated host keys
at first boot, and not prompted at the console for human interaction
to augment entropy for this process. I find it hard to blame this
*particular* behavior on Debian (unless you're suggesting that they
strong-armed OpenSSH upstream to integrate these changes on their
behalf?).

It's been about two years since I have installed OpenBSD.  I do not know
what entropy pool source OpenBSD uses for initial key generation.  It
was my understanding that the recently disclosed/discussed issue
involved a Debian-specific (and their downstreams, like Ubuntu) decision
to utilize the PID of the keygen process to seed the key generation,
severely limiting the effective keyspace.  If I completely misunderstood
this, my apologies to Debian.  It was not so much that I was saying that
eliminating user interaction was a bad thing (as I think most users
can't be bothered to set up a secure system), but that requiring user
interaction to set up validation may be a poor choice (as in the case of
requiring them to set key authority/revocation servers as the other
poster suggested).

-Nathanael


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