I've played a lot with VIC and enjoy its complexity and effectiveness as a field cipher. However, RC4 has caught my attention lately and I've read there is a RC4-52 variant that can be done by hand.

Can anybody describe the rc4-52 algorithm? Is it with a deck of cards and just a swap of the values, or must they still be added somehow?


You can do RC4 using a 52-entry table, instead of a 256-entry table. All you do is change the modulo-256 arithmetic in RC4 to use modulo-52 arithmetic. There are no special changes needed, and no need to describe a special algorithm. If you want to see a description of how to perform it manually using a deck of cards, you can find that here: http://www.mail-archive.com/cryptography@wasabisystems.com/msg00065.html See also https://groups.google.com/forum/?fromgroups#!topic/sci.crypt/dw3FaK4lf2M

Related: If you've read Neal Stephenson's Cryptonomicon, you may have seen a reference to an encryption algorithm that can also be carried out with a deck of cards. The cipher is called Solitaire. It was invented by Bruce Schneier and was apparently inspired by RC4. However, it has cryptanalytic weaknesses. (If you haven't read Cryptonomicon, and you like science fiction, check it out: you're in for a treat!)

Keep in mind this is entirely theoretical. Performing RC4-52 with a deck of cards will be extremely slow and tedious in practice. And while I don't know of anyone who has seriously studied its security, there are reasons to doubt whether it will be secure against a serious attack. While it's fun to contemplate, I would not recommend that anyone use this to protect real secrets.

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