Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Fri, 16 May 2008 21:43:44 +0400
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Subject: Re: OpenSSH key blacklisting

On Fri, May 16, 2008 at 06:24:51PM +0100, Craig Edwards (Brain) wrote:
> I havent been following this debacle too closely as i dont have much to 
> do with debian, however, wouldnt such a system be vulnerable to false 
> positives if you are just going to hash partial fingerprints rather than 
> whole fingerprints?

Such a system would have a higher likelihood of false positives, yes.
However, it would not exactly be "vulnerable" to them - or at least, the
worst-case impact (depending on server settings) is a DoS for a given
user's ability to login.  With 48-bit partial fingerprints, there may be
like one such false positive in the entire world, or none.  If we go
down to 40 bits, it's less than one in a million of different keys.
(I am assuming a blacklist size of around 200,000 partial fingerprints.)

In fact, the Debian/Ubuntu patch already uses partial fingerprints based
on my earlier suggestion, but I was more conservative at the time, so I
suggested 80 bits.  Willy Tarreau has since convinced me that even as
low as 40 bits is reasonable.

Oh, and we are not "hashing" fingerprints, we're merely matching them.

Alexander

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.