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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...
Prior to the availability of decent true and pseduo random number generators, a large number of books were published that contain strings of random numbers -- simply because creating such data was hard to do. Most decent universities, probably every single land grant university surely, will have such books. I know we do here. They've been long forgotten, but are an excellent source of truly random data. No need to do all the futzing around, just pull some data from the books.
No sig is worth reading.
What about ciphersaber?
Actually one time pads where used a lot by the government (English, American, etc) a few years ago.
Typically you have a person sitting at a bingo roller thingy... who pulls out letters at random.
These random letters are then written down on a big peice of paper as a one time pad.
A copy of this is given to the person who needs to send data, and a copy is given to the reciever.
The person doing the encoding takes another peice of paper and every three lines writes the pad down. (Maybe the paper with the pad it self had two lines between each pad sequance... I dont remember hehehe)
On the second line is the message...
on the third line, you do a bit of addition mod(26) (Actually I believe they left out a few letters to make the msg easier to read...)
The person then writes their message under the pad sequence. So you might have something like this:
a=1, b=2, c=3...
(note, I am just hitting keys, replace with a real random sequance)
ahfxd adbgf ewefg hzqdf wrhwd wrghl
thisi sthem essag etobe sentx xxxxx
upoqm txjls jpxgp mtffk pwv........
so
a + t = 1 + 20 = 21 = u
h + h = 8 + 8 = 16 = p
etc etc
Urgh... my ride is here so I have to take off... but you get the idea. I might have mad a few mistakes in this post because I did the entire thing in a bit of a hurry.
A good (and really fun) book to read is Cryptonomicon. Its based in two timelines and during the story it talks a lot about cryptography. Quite a good book.
Anyways, sorry I could not finish the post. Good luck
Luke
One of the most popular pre-WWII ciphers was the Playfair Cipher. Very simple, just know the code word of the day.
Wheeeee