The Code Book summary

So, ciphers emerged early on, but they were rapidly countered by cryptanalysts, experts who devise strategies to crack codes. And of all those in the field, none were more skilled than the Arab cryptanalysts who, in 750 AD, invented an extremely effective cipher-breaking tool: frequency analysis, which is used to crack a monoalphabetic cipher.

Every written language uses certain letters and words more often than others, and frequency analysis is designed to identify these characters in a monoalphabetically encrypted message; knowing which letters are used the most is a major aid in deciphering a code.

Frequency analysis was challenging the security of the monoalphabetic cipher. In the sixteenth century, a Frenchman named Blaise de Vigenère developed a cryptographic technique that used 26 distinct cipher alphabets in a single message – in other words, a polyalphabetic cipher.

Vigenère’s cipher was first published in 1586 and called “Le Chiffre Indéchiffrable”, or the unbreakable cipher. It works like this:

Did you know that the US military had the idea of employing Native American Navajos as radio operators during World War II? The logic was that their language could never be deciphered as there was no written record of it. But this interesting bit of history isn’t the only time a little-known language joined forces with cryptography.

The Rosetta Stone, unearthed in 1798, bore the same message in three different languages: Greek, Demotic and in hieroglyphics that had never been seen before. The English linguistic prodigy Thomas Young jumped at the opportunity to decode the hieroglyphs.

The invention of radio and the increasing secrecy necessitated by the World Wars made finding secure methods of communication more important than ever. So, during World War I, the US military started working on a virtually unbreakable system called the one-time pad cipher.

This cipher, considered the “holy grail of cryptography,” is a variation on Vigenère’s system. It uses two identical books, one held by the sender and one by the receiver. Each page of the book contains a unique, randomly generated 24-letter codeword. After the sender uses the random code to deliver a message, each party then destroys the page that was used, meaning each code is only used once.

By 1926, the British were keeping close tabs on German communications and began intercepting some odd ciphers. This was the work of Enigma and it was baffling the Allied cryptanalysts. But, ironically enough, a method that the Germans had devised to increase their security would eventually expose Enigma’s weakness.

German communications relied on two keys to send their messages. All correspondence would use a daily key, but every message would start with a new key solely for decrypting that message. To prevent errors, the sender would repeat the message key twice – a simple three-letter phrase that gave instructions on how to set the scrambler discs.

Enigma and its eventual deciphering made one thing clear: computing was the future of cryptography. As computers were made commercially available, new forms of secure communication emerged. The expansion of commercial computers into the businesses world in the 1960s necessitated a new form of security for financial transactions and trade negotiations.

The result was IBM’s Lucifer, a system that translates written messages into binary code, breaks it into 64 blocks and then scrambles it 16 times according to a given key. By 1976, Lucifer was approved by the US National Security Administration (NSA) as the Data Encryption Standard, or DES.

Enigma changed the game of cryptography, and ever since its invention, the field has transformed from one based on language to one heavily influenced by mathematicians. In fact, physics may now hold the key to cryptography’s future, because cryptography has finally realized its ultimate goal of outpacing cryptanalysis.

How? Through the impenetrability of the DES and RSA ciphers.