Encryption by Hand?

Arachn1d writes "A question for all those slashdot math-geeks out there: What's the simplest, but most secure encryption algorithm you can devise or provide a link to that can be carried out with nothing but a pen, some paper and a calculator? Bonus points for any public-key cryptography solutions!" Bruce Schneier developed an encryption algorithm designed to be performed with a deck of cards, but it's rather slow to do for fun. Well, you did say "a calculator", and if we assume a programmable calculator your options probably expand quite a bit...

Comments

Use a code book!

[MarkusQ]

1) Use a code book. Something with a concordence is good, though if you have the book in flat text you can easily make a concordence. Then you could write "fungal:17" to mean "staple" if "staple" (the word you intended) occured N words after (for some pre-agreed N) the seventeenth occurance of "fungal". There are a number of cute ways you could encode seventeen, and it's relatively easy to make N vary as well. Since this is "security through obscurity" you might as well have fun with it.

2) If you are going to be hand writing the messages as well, you may want to use out of band information (letter shapes, mispellings (with & without crossing out, etc.), line breaks, etc.) to either carry information or make it appear that you have hidden information & thus confuse the issue.

3) Split the message (e.g. every third word, etc.) in interesting ways.

4) Play Simon-says; send messages that say things you might have said, but that your recipient knows to ignore because they lack some feature.

Etc., etc. The list is pretty long, and success mostly depends on doing Odd Things the Bad Guys don't expect, and avoiding the Dumb Things that they will see right through.

Weren't you ever twelve?

-- MarkusQ