The art of creating and solving codes is used to encrypt messages globally allowing you to send top-secret messages, sensitive information, and day to day messages to your friends via WhatsApp.
Cryptanalysis involves breaking such codes. You’re probably imagining those movies with spies hacking into a “confidential database”. However, cryptanalysis originated long before the flashing of ones and zeros on a computer screen, and a hacker saying “I’m in”. In fact, the very first recording of cryptanalysis dates all the way back to the 9th century, in a book called Risalah fi Istikhraj al-Mu'amma (A Manuscript on Deciphering Cryptographic Messages), published by Arab Abu Yūsuf Yaʻqūb ibn ʼIsḥāq aṣ-Ṣabbāḥ al-Kindī (known as the father of Arab philosophy).
To fully understand the impact of his work it’s important to understand which cypher he cracked first. A simple substitution cypher is one where every letter of the alphabet is substituted for another. A classic example of this is the Caesar shift, where each letter is shifted a certain number of places down the alphabet e.g. A->C, and B->D, C->E, etc. Although the Caeser shift may be easy to crack, other substitutions (which aren’t limited to shifting and can be substituted with any other letter or character) prove to be a challenge. For years, this type of encryption was used to send messages. That is until Al-Kindi proposed the method on how to crack it, frequency analysis.
Frequency analysis is a method in which the most frequent and least frequent letters in an encrypted text is examined and compared to that of its plaintext counterpart. For example, the most common letter used in the English alphabet is E, followed by T, whereas the least common ones are J, Q and Z. Considering this knowledge, and comparing this to the most common letters that come up in an encrypted text, it becomes much easier to solve.
Of course, after this discovery, cryptologists merely had to find more cunning ways to encrypt codes that were harder to crack as cryptography is the ever-evolving art.
*The cool kid of the 9th Century*
If you found this an interesting read I highly recommend reading The Code Book, which gives an in-depth look into the evolution of cryptography!
Written by Zara Mansoor, a Year13 student