Public key crypto by hand

[Robert J. Hansen]

> "solitaire" is done with cards, it was used by two men in jail,
> both characters in Neal Stephenson's "Cryptonomicon" ...
> imo a novel worth reading ... Bruce Schneier invented
> the game at Stephenson's request AFAIK.

Solitaire has some serious problems, and is not a public-key  
algorithm.  The original poster specifically requested public-key  
algorithms, not conventional crypto which can be done by hand.