You Probably Didn’t Know Al-Kindi’s Work On Deciphering Cryptographic Messages

Nearly 2000 years ago, Julius Caesar was busy invading neighboring countries to expand his Roman Empire. He needed a way to communicate his battle plans and tactics with his generals and soldiers without the enemy finding out. Thus, Caesar started to write his messages in code, and, as such, the Roman Geezer was invented. During the Second World War, male and female codebreakers of Bletchley Park were the behind-the-scenes heroes that helped their lands to victory by cracking the German Enigma cipher. The history behind ciphers and code-breaking always needed to be concealed, it’s origin not known. Until 1987, when a historian uncovered an ancient Arabic manuscript in the Sulaimaniyyah Ottoman Archive in Istanbul.

‘The Philosopher of the Arabs’ and his encrypted secrets

‘A Manuscript on Deciphering Cryptographic Messages’ proved how a 9th century polymath had been the father of cryptanalysis: Abu Yusuf Ya’qub ibn Ishaq Al-Kindi. His name is not unknown to history. Al-Kindi, known as the Philosopher of the Arabs (i.e. also referred to as Alkindus in Europe), was best known for his work ‘On First Philosophy’ for which he’s noted the bridge between Greek and Islamic philosophy, praised for his efforts to make Greek philosophical thought accessible to a Muslim audience.

Abu Yusuf Al-Kindi was born in the year 801 in the city of Kufah, in modern Iraq. He descended from the royal Kindah tribe who had wielded power and influence, but lost most of its prominence, though his family continued to hold high court positions. Al-Kindi began his education in Kufah, then moved to Baghdad to complete his studies. He quickly grasped the attention of Caliph Al-Ma’mun who, at the time, established Bayt- al-Hikma (i.e. House of Wisdom), a research institute and library collecting the greatest Greek and Persian philosophical and scientific works. With colleagues Al-Khawarizmi and the Banu Musa brothers, Al-Kindi responsibilities as calligrapher entailed translation of the works to Arabic in order to acquire knowledge of the previous civilizations. In some cases, the texts were encrypted, and here, Al-Kindi’s initial motivation for code-breaking arose with the desire to access encrypted secrets in his library’s texts.

Frequency analysis and the cryptogram solved

Al-Kindi’s invention was based on newly-developed mathematical techniques from the Arabs, but also on a deeper understanding of the structure of language and writing during that time. Simultaneously, linguists were hoping to gain a deeper insight in the structure of the Qur’an. Eventually, Al-Kindi’s technique of cryptography came to be known as ‘frequency analysis’ since he realized that letters from the alphabet appear in varying frequencies in written text. Thus, these variations in frequency could be analyzed and exploited to break ciphers. Hence, Al-Kindi advised code-breakers to count the frequencies of letters in an encrypted text and identify their true meaning according to the calculated frequencies:

“One way to solve an encrypted message, if we know its language, is to find a different plaintext of the same language long enough to fill one sheet or so, and then we count the occurrences of each letter. We call the most frequently occurring letter the ‘first’, the next most occurring letter the ‘second’, the following most occurring the ‘third’, and so on, until we account for all the different letters in the plaintext sample.

“Then we look at the cipher text we want to solve, and we also classify its symbols. We find the most occurring symbol and change it to the form of the ‘first’ letter of the plaintext sample, the next most common symbol is changed to the form of the ‘second’ letter, and so on, until we account for all symbols of the cryptogram we want to solve”

Now, it might seem as an obvious given, especially for mathematicians familiar with the science, but at the time, it was a radical breakthrough that destroyed the security of existing encryption systems. In the end, Al-Kindi’s findings pressured cryptographers to develop a new sense of secrecy for their messages.

Al-Kindi and the door to a digital world

When Caliph Al-Ma’mun died, he was succeeded by his brother. Al-Kindi was employed as tutor to his son. However, the rivalry between the scholars at Bayt Al-Hikma the House of Wisdom, and the orthodoxy of subsequent Caliphs, had an impact on Al-Kindi’s welfare and his scholarship. Al-Kindi was a prolific commentator rather than a translator, often raising relevant issues. During his life time, he remained known as a prominent Muslim philosopher, but now is credited a well-established mathematician and scientist. From his now-famous manuscript on cryptography, it became apparent that he was exploring earliest insights of statistics, and established a textual study of the Qur’an that the Arabic language has a characteristic letter frequency. Abu Yusuf Al-Kindi died in 873 in Baghdad, Iraq, leaving historians about 290 books on various subjects such as astronomy, medicine, mathematics, linguistics and music.

The development of cryptoanalysis fueled the desire to invent stronger ciphers and codes. Intellectuals raced each other through time in an attempt to establish the next unbreakable code. Clearly, cryptography remained an important science in our society and its digital culture since it ultimately paved the way for inventions we can’t imagine going without anymore: computers, the Internet and the digital world.

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