There are many different ways of encrypting information that exist. Some of the simplest types of cipher, have been described in this page. I have created a few executable (windows 95 onwards) which help the process of deciphering information. As you may have guessed, this page is still under heavy development, although not active development at the moment - as soon as I have worked on it, it will be updated! However, all information up is accurate - if you discover any inaccuracies in the software / text / dead-links then email me please!
My team has even got recognition by the local paper! Click here to see the article, posted in the Argus,17/1/04, page3
This is where a cipher-text alphabet is used instead of the standard A-Z. e.g.:
ORIGINAL : A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
CIPHER-TEXT: K E Y W O R D F G H I J L M N P Q S T U V X Z A B C
As you can see in the example above, each letter takes on another letter. The above uses the keyword 'KEYWORD', but any keyword can be used. The only limitations to a keyword is that if there are any repeating letters, the repeats must be removed. Once the keyword has been entered, the rest of the alphabet must be filled in behind it.
Examples of straight substitution ciphers are: Keyword, Ceaser, Affine shift.
Straight substitution ciphers are very weak as far as ciphers go, as it is
quite easy to crack using frequency analysis (see below). However, if
they are combined with an encryption method such as anagram / transposition
cipher, they are then made quite difficult (when decrypting, you won't get
the original cipher-text straight out, therefore making it seem a little
confusing at first.
VDKK CNMD ENQ CDBQXOSHMF SGHR EHQRS BHOGDQ. HSR MNS SGZS GZQC QDZKKX HR HS?!
traditional way of solving this cipher (by paper) would be with a wheel, but
in this modern age of computers, I have made this application, where you
enter the cipher, and enter the rotation amount (unfortunately it only
accepts positive rotation values… rot -1 = rot 25). You can download this
This type of cipher is one of the most hardest to encrypt by hand, but as with all straight substitution ciphers, it can be cracked easily with frequency analysis.
How they work: Each letter is assigned a number (A=1 à Z=26). Then to encrypt it, you choose a multiplier and adder values (take x as the letter to encrypt) C = (Mx + a ) % 26
For those who don't understand % (same as MOD), this is where you divide by the number, and the remainder is the result returned - this returns a number that can be put back in the alphabet again.
However, you cannot encrypt for all multiplier values, as they can return the same letter for different letters put in. (e.g. 0, all even #s, 13...) Download link below:
Common single letters
If the structure of the cipher has been kept, then it is quite likely, that a single letter on its own, will be either an A or an I (assuming standard english).
Deciphering is a very new concept to me, but having background knowledge in programming, creating the software was easy. This year at college I joined the cipher club, which involves different techniques for creating ciphers etc. Although the Southampton cipher challenge is over now, I shall still try to create a few more pieces of software, although the last two ciphers will require some quite complex array handling skills, as they use the ADFGVX cipher, being two stage.
http://www.cipher.maths.soton.ac.uk - Cipher Challenge, run by Southampton university
http://www.simonsingh.net - Simon Singh's website
If you have any comments / criticisms etc that you would like to tell me about on this subject, then please email me ASAP (!!)
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Last updated 29 June 2004