Bossnass

Given a sample of encoded text with word breaks already included. Assuming a letter for letter swap, how would I go about decoding it? I don't have a specific sample, I'm just wondering the procedure one would follow.

numist

there is an algorithm for how often a letter appears in common writing, so if you dont have an algorithm you could use pattern matching, which works best if you have a program (although I dont know where you could get one)

however, if you find a three letter word, most common three letter words are and & the, so replace the letters that are shared in other words, and see if anything makes sense, if not, try again.

It could take some time, but its the easiest kind of encryption to break.

If they are skipping letters or using some other sort of pattern with random junk in between, you are s-o-l unless you have some sort of key - algorithm.

good luck

numist

kel

http://deafandblind.com/word_frequency.htm

If your saying that the order has been preserved, and that it is simply a substitution encryption, you can write a program that counts the frequency of each symbol. The most frequent symbol is designated as one letter, the next most frequent is designated as another letter, and so on and so forth. Once the program gives you the tentative answer it should be legible. You can fine tune the substitution from there if it isn't already correct.

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Fearless_Hyena

If I understand you right these are called "cryptograms". Letter frequency and word frequency are key. E is the most common letter in the English language, so a good start would be to go thru the passage, count the occurrences of each letter and substitute E for the most common. "The" is one of the most common words, so if you see a lot of 3-letter words ending in E, then make that guess for T and H and see if it makes sense. Any common 3-letter combos that are NOT "the" are probably "and". And so on...if E was a bad guess, then try the 2nd, it's almost surely one of the top 3 top occurring letters in the sample. The most common letter that ends 3-letter combos the most often is almost surely E.

Neato

Newspapers often have Cryptoquips. Same thing, only you get one letter told to you. I like to do them when I get the paper.
Look for words with apostrophes in them. Other good words to look for are "that" and if it is a question sentance check if it starts with "when", "what" or "if". Also watch for double letters, they have less posiblities than other, lone letters.

Bossnass

I've recieved the samples I was supposed to decode, one for an algebra assignment and another for a little online initiation. Pure coincidence that they both fell on the same week.

One was a long numrical string which happened to divide evenly by 4, and then was easily cracked as base 8 logs.

The other took a little time, but was a pretty simple "one letter switiched for another". After I realized the letter was signed with the same # of characters in the # number of words of a name I knew, and thanks to the help here, I was able to decode it.

Thanks.

thingstodo

This spy stuff is cool. Now I've got to go try some of this out.

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grassygnoll

If anybody wants to read a nicely written book (for beginners) Simon Singh wrote a very good book on cryptography called The Code Book. It starts out with very simple cyphers and shows how they progressed to the amazing stuff we have today. Dude has a website but he pushes his books to much. His Links are really good tho...

www.simonsingh.com

The only other book by him that I read was Fermat's Last Theorem. It was better than I thought a book about a math problem could ever be... but it was still a book about a math problem.

shakran

I was just about to recommend Singh's book, grassygnoll! I'm reading it right now and it's excellent!