Monday, 8 March 2010

Guest Post: Cool Concepts - Cryptanalysis!

Taken from Friday Nasiha - (subscribe and get a weekly Friday Nasiha email in your inbox!)

Communicating top secret information is a precarious and risky process, so to avoid vital statistics falling into the wrong hands, messages are scrambled, masked and coded so only those with the right information or tools can read them. This process is known as cryptography; the scrambling of a message is known as encryption and the de-scrambling is decryption. For anyone other than the intended recipient, the message is meaningless, unless that person uses cryptanalysis to break the code.

The real cryptanalysis milestone was passed by al-Kindi, who revolutionized the area when he wrote A Manuscript on Deciphering Cryptographic Messages. Part of this included a description of the method of frequency analysis, which means he noticed that if a normal letter is replaced with a different letter or symbol, the new letter will take on all the characteristics of the original one. So if all a's that appeared became t's, and all th's were replaced with g's, they would still have the features of the letter(s) they replaced. A word like athlete would become tglete! Even though the letters change, what cannot be disguised are certain characteristics a letter has, like its frequency of occurance.

If we look at the English language the letter e is the most common letter, accounting for thirteen percent of all letters. So, if e is replaced by symbol #, # would become the most common symbol, accounting for 13% of the 'new' symbols. A cryptanalyst can then work out that the # actually represents e.

From studying the Arabic text of the Quran closely, al-Kindi noticed the characteristic letter frequency, and laid cryptography's foundations which led many cryptographers from European Renaissance states to devise sever scheme to defeat it.

"The birth of cryptanalysis required a society which has reached a high standard of development in three disciplines, namely linguistics, statistics and mathematics. These conditions became available at the time of al-Kindi who had command of these three disciplines and more." - Dr. Simon Sing, The Code Book, 1999

Compiled From:"1001 Inventions:
Muslim Heritage in Our World
" - Salim T S Al-Hassani, pp. 268, 269

No comments:

Post a Comment