Sounds interesting. Has anybody used this, and are there any comments?


Tools like ssh and lsh are great for allowing secure remote access to your system. They offer essentially full, flexible remote control of a machine, in an ecrypted and authenticated manner. But they are complex pieces of software; there's no way to do what they do without being complex. And with complexity comes bugs. Tools like ssh and lsh, and VPNs like CIPE, PPTP, and more have all had serious flaws that would allow an attacker to get full control over your system.

If you leave such programs running all the time, you take the risk that someone is going to use an exploit on you before you have a chance to apply a patch. For some purposes, this is an acceptable - even necessary - tradeoff, but it would be nice to enable them only when actually needed, to minimize the risk. And for other purposes, ssh et. al. are overkill. Perhaps you only really need to remotely initiate a limited set of operations. In this case, you don't need a shell prompt, just a way to securely kick off scripts from elsewhere.

Enter 'Ostiary'. It is designed to allow you to run a fixed set of commands remotely, without giving everyone else access to the same commands. It is designed to do exactly and only what is necessary for this, and no more. The only argument given to the command is the IP address of the client, and only if the authentication is successful. The following are the key design goals:

* "First, do no harm." It should not be possible to use the Ostiary system itself to damage the host it's running on. In particular, it's willing to accept false negatives (denying access to legitimate users) in order to prevent false positives (allowing access to invalid users). * Insofar as possible, eliminate any possibility of bugs causing undesired operations. Buffer overflows, timing attacks, etc. should be impossible for an external attacker to execute. There's no point in installing security software if it makes you less secure. * Be extremely modest in memory and CPU requirements. I want to be able to fire off commands on my webserver (running on a Mac SE/30, a 16MHz 68030 machine) from my Palm Pilot (a 16MHz 68000 machine). Things like ssh already take 30 seconds or more to start up - I can't afford anything too fancy. * Keep things simple. I'm no crypto expert; I know I'm not capable of coming up with an ssh replacement. So I need to keep things so utterly simple that I can be sure I'm not missing anything important.

((Udhay Shankar N)) ((udhay @ ((

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