http://www.anagram.com/~jcrap/Volume_2/protect2.pdf
"Practical Secret Protection", Thomas Martin, Laurence O’Toole
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Alice wants to send a secret to Bob. Alice kills everyone on the planet except Bob, and sends the message in clear. It should be noted that although this method could potentially involve 2^32.5=6,000,000,000 operations this is significantly fewer than the 2⁵⁶ that are required to brute-force attack the simplest cipher known to man. Furthermore, these operations only need to be performed once ... ever, after which Alice and Bob can communicate in perfect secrecy as often as is required.