A buddy of mine travels quite a bit for work. While on the road, he's constantly having to use wifi connections he comes across. Since wifi can be less than secure, I was wondering if the following would help keep his traffic (and passwords) safe-er.

I was considering setting up a linux box on his network that he could SSH into while on an outside wifi connection, then setup a tunnel so all his traffic would be encrypted.

Does this actually help, or would a bad wifi connection just allow a 'badguy' to grab his SSH key and nullify any benefit to the secure tunnel?

If this isn't a good idea, any other suggestions are welcome.

Yes, that would work as long as there is no man-in-the-middle attack. That means he has a public key in the known-hosts file of the mobile device, so that he can tell if traffic is intercepted.

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A far more effective strategy would be to use VPN, to create a "tunnel" to the remote system, through which all traffic would pass without any special awareness on the part of any application that wished to use the tunnel. Doesn't matter whether the transport is wireless or wired. "It could be carrier-pigeon," ahh, so to speak, and it would still be secure(d).

You should, of course, secure the VPN connection using individual, unique, password-protected cryptographic keys, issued by the host system. (Do not use "PSK == pre-shared-keys == mere passwords.")

The best form of cryptographic security is the most unobtrusive one. It should require no special awareness, and no special procedures, for its successful employment by any user or application that uses it. "It Just Works.™" ssh, on the other hand, does require special awareness and special procedures, without which communications that were supposed to be secure could be utterly and completely disclosed without the awareness of anyone ... "merely due to, say, the carelessness of the operator."

Always remember that the greatest threat to mechanized security is ... ... human realities. Uh huh. Computers may be mechanical, but we humans are not. "Wea culpa."