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   Trust On First Use. It's a key-exchange method where you trust the
   first time you grab a key, and use that, instead of a cert-authority or
   anything like that. It's used for SSH iirc, though I could be wrong.
   The idea behind it is that unless the MITM performs a MITM the first
   time and every time thereafter, you'll at least notice the attack, and
   likely prevent it.
   I was going to provide a Wikipedia link, but I couldn't seem to find
   one, other than this one hidden in a user page.
   [1]https://en.wikipedia.org/wiki/User:Dotdotike/Trust_Upon_First_Use
   On 07/26/2013 09:06 AM, tz wrote:
   > Sorry for being slow, but what is TOFUing?
   >
   > On Fri, Jul 26, 2013 at 8:27 AM, Andy Isaacson <[2]adi@hexapodia.org
   [3]<mailto:adi@hexapodia.org>> wrote:
   >
   >
   >     I've run my primary browser with no trusted CAs, manually TOFUing
   >     certificates for sites, for months on end.  It's slightly easier
   than
   >     "view source" to use control-shift-K (in Firefox) and reload the
   page,
   >
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References

   1. https://en.wikipedia.org/wiki/User:Dotdotike/Trust_Upon_First_Use
   2. mailto:adi@hexapodia.org
   3. mailto:adi@hexapodia.org
   4. http://www.enigmail.net/