Cryptograms

Cracking the code can be hard but is fun...

How a Cryptogram is Created

A cryptogram is a puzzle where a sentence in the language of choice - for these purposes, English, is turned into a code that you need to solve. Most cryptograms contain several sentences to give you a fair chance of using several techniques to work out the code, rather than just guess as you would with a code of just a few words.

An extract of a cryptogram might look like the following:
ci xv cnv xvyc hir najv ci xvac cnv xvyc

It appears as gobbledygook, and indeed the origin of these puzzles was not for academic exercise but to communicate and send important and sensitive messages from one person to another, and the encryption ensured that, if good enough, even if the message was intercepted the information would not be of use to the potential enemy.

Creating a Cryptogram

When creating a crpytogram, the standard format is to substitute each letter of the alphabet for another letter, or a symbol. Thus there may be a substitution of A --> S and D --> T and so on.

Of course symbols may be used instead of letters of the alphabet, but no matter - the technique is the same. The shorter the message, generally the harder it is to decrypt as there is less to apply some clever techniques to and therefore you generally end up guessing. However communicating important messages in a few words is often impractical, and so it was not uncommon to see several pages of code: enough for most skilled code breakers to eventually decipher the message.

Making a Cipher Harder

The specific cryptogram discussed above is a substitution cipher cryptogram. Strictly speaking, a code speaks to substition at the level of words or phrases, whilst the cipher deals with the lower level, letter-by-letter substitution.

A cipher can be made harder to decode with several methods. Firstly, you can mis-spell the words on purpose which makes it much harder for those looking for certain patterns (discussed further down) to crack the code. So you could turn the words: "this is crucial" to "tiz eezs crewshul" - much harder to read, but still intelligible once deciphered and read out aloud.

In addition to wanton mis-spelling, you can also use what are called void characters - these are extra characters added to the alphabet that are to be ignored. The person who receives the message skips them, but the person who is cracking the code can be very confused by these characters and it can make the cipher a lot harder to decode.

Sometimes people also mix in some codewords as well, thus '@' might mean 'the secret castle'. Again these can make the code harder to crack, though once it is cracked the codewords meaning can usually be guessed from the context of the message.

Also, other characters can be added with special functions: for instance to mean a double letter, or to ignore the preceeding letter. It can become as sophisticated as you like; the longer the set of rules of course the harder it can be to remember and the more mistakes may come in, but there is a trade off with security.

Solving a Cryptogram

There are several techniques and methods that can be used.

The first approach is the simple guess: manually plugging through different combinations. This is slow and is not practically going to solve a cipher, you would need a very fast computer to use this technique!

The most common method to use is called frequency analysis. Here you look at how many times each letter occurs in the cipher and then compare to the average frequency with which letters occur in the language of choice. We know that 'e' is the most commonly occurring letter in english so the letter that occurs the most in the cipher alphabet may well be 'e' as well.

There are tables available showing the frequencies, so you can compare across. Clearly the more cipher text you have the more likely it is to conform to the average distribution; hence with very small cryptograms frequency analysis is very hard to apply.

You can also use distribution of letters in the cipher relative to each other letter to try to work out for instance which are vowels and which are consonants. The vowels will normally be seen before and after most other letters, whilst consonants will show up as more choosy as to which other letters they will 'bind' with: many consonant - consonant combinations are very rare, for instance.

In order to understand if there is a one to one substitution going on, then it is a good idea to count the number of distinct characters in the cipher : if there are more than 26 then clearly other characters are being used: these may be voids, codes or characters with special meaning.

Another tip is, if the message has spaces in, to look for one letter words. If they are there, you should have already identified where the 'a' or 'i' are in the cipher, as these are the only one letter words in english. Similarly you can often find words like 'the', 'to' and so on with a similar method. The letter that occurs most commonly before the 'e' is often 'h', so again this can often be used to discover a letter.

Each time you solve another letter in the cipher, write it out again with the known letters and you can then often guess from context and part-words what the others are.

As for that snippet of a cryptogram at the top, it reads: "to be the best you have to beat the best". Did you manage to decipher it?

Cryptograms

Author: Dan

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Last Updated: Sep 21st 2006

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