Well, I would say : - practical (using a manageable amount of paper, and/or common items like a chess board, playing cards or dominoes...) - fast enough (encr

Well, I would say : - practical (using a manageable amount of paper, and/or common items like a chess board, playing cards or dominoes...) - fast enough (encrypt say at least one word per minute, pretty sure manual RC4 doesn't qualify here) - secure against an adversary using computing ressources - provides a way to easily store a strong key, a shuffled deck is pretty good at this