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).

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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.

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