Date: Mon, 9 Feb 2009 14:13:30 -0800 (PST) From: Lyndon Nerenberg <lyndon@orthanc.ca> To: Jason Stone <freebsd-security@dfmm.org> Cc: freebsd-security@freebsd.org, Daniel Roethlisberger <daniel@roe.ch> Subject: Re: OPIE considered insecure Message-ID: <alpine.BSF.2.00.0902091402040.61088@mm.orthanc.ca> In-Reply-To: <20090209134738.G15166@treehorn.dfmm.org> References: <200902090957.27318.mail@maxlor.com> <20090209170550.GA60223@hobbes.ustdmz.roe.ch> <alpine.BSF.2.00.0902091246280.61088@mm.orthanc.ca> <20090209134738.G15166@treehorn.dfmm.org>
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> Right, but that's not the problem they're trying to solve. They're trying to > solve the problem of logging in _from_ an untrusted machine, to a trusted > machine. Okay, I got it backawrds. > So, an alternative might be to carry around a USB key with a one-time private > key, different from your normal private keys, and have the public key > command-squashed on the server to remove itself from authorized_keys before > running the shell. That's what I do -- multiple throw-away keys on a USB stick, for emergencies. However if you're that paranoid you better be carrying around your own set of ssh binaries on that stick as well. > You could generate several, each with a different passphrase (assuming that > you could manage to remember that many passphrases and which keys they go > with), and get a similar effect to printing out a card with the next ten OPIE > passwords. It's not that hard to come up with a scheme that lets you map from an identifier tagged to the private key to the corresponding password (in your head). It's a pain at the start, but once you've used a given scheme for a while it becomes second nature. Akso, note that you can get similar behaviour using K5 with one-off instances of your principal (e.g. lyndon.a6d5mps@EXAMPLE.ORG). The advantage here is that there are no key files involved (but you still want to carry a trusted kinit binary with you). The downside is that most sites don't have K5/GSSAPI enabled. And of those that do, a significant percentage of the implementations still don't to dynamic realm discovery, therefore you need a pre-existing arrangement to map your realm to the appropriate KDCs. --lyndon Happiness is a good martini, a good meal, a good cigar, and a good woman ... or a bad woman, depending on how much happiness you can stand. -- George Burns
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