Date: Wed, 10 Dec 2003 17:02:56 -0800 From: Michael Sierchio <kudzu@tenebras.com> To: Brett Glass <brett@lariat.org> Cc: security@freebsd.org Subject: Re: s/key authentication for Apache on FreeBSD? Message-ID: <3FD7C240.4030005@tenebras.com> In-Reply-To: <6.0.0.22.2.20031210173916.04f57be8@localhost> References: <6.0.0.22.2.20031210115335.04c2fc50@localhost> <20031210093927.70c87960.amonk@gnutec.com> <6.0.0.22.2.20031210124332.04e94ac0@localhost> <16343.33321.632599.190251@oscar.buszard-welcher.com> <6.0.0.22.2.20031210173916.04f57be8@localhost>
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Brett Glass wrote: > The people in question have Palm Pilots. And, yes, in a pinch > slips of paper could be generated. The key thing is to be able > to get in from a public kiosk without the risk of compromised > passwords. The problem with S/key or OPIE authentication is that it is sadly subject to a MITM attack, and relies on blind trust in the server. The challenge is not a random challenge, it is unfortunately a sequence number and salt -- if I trick you into typing in the one-time password with a lower sequence number than the current one you are proper fucked. I can then generate all of the subsequent "one-time" passwords. If you have a half-authenticated SSL connection, and are conducting the exchange over it, then it should be fine.
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