Re: Where's Waldo? (challenge)

[sam stover <sam.stover () gmail com>]

der Mouse wrote:
> >     You and a friend play "Where's Waldo?". You solve the puzzle before
> >     your friend, and you want to prove to your friend you solved the
> >     puzzle, without giving him any hints. How do you do this?"
>
> I don't think I do.  I don't think this is possible without introducing
> third parties, or a rather severely nontraditional form of "Where's
> Waldo?".  Everything I can think of can be spoofed, such as with an
> auxiliary picture of Waldo....

I'm with you - my first thought was escrow.

But how much do you trust your friend?  You could always encrypt a file
(with any/all pertinent details) w/ his public key, send it to him, and
he could open it when he is "ready" to see if you knew the answer.

Conversely, you could send him the same file, encrypted with *your* key,
and wait until he's ready to see if you knew, then you un-encrypt it for
him.  This would most easily be accomplished if you were face to face
(i.e. he brings the file over to your house on his USB key, and watches
you decrypt it).

<shrug>

Both methods above are really forms of escrow - it's just that your
competitor/friend is the recipient, and uses encryption if you don't
trust him to not peek.



-- 
S.f.Stover
http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x15FFC42A
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