# History of Information Security

Instructor: Rocco Arizzi

Rocco has a PhD. in Electrical Engineering, a graduate certificate in Cybersecurity, and has taught university Math, Physics, Engineering, and Computer Science.

Information security goes way back - all the way back to the Second World War and even classical times! Here, we'll travel through the history of information security from ancient methods of hiding communications to the famous Enigma machine and modern cryptography.

## From Antiquity to World War II

Information security as a science in and of itself is relatively new. However, the practice of securing information has been around as long as people have been needing to keep secrets. Some notable attempts in the ancient world to hide information were simply clever means of concealment. For instance, the ancient Greeks are thought to have tattooed messages on the scalps of slaves who subsequently grew out their hair to cover the message. The slaves were then sent to the intended recipient and would have their heads shaved to reveal the secret. Leonardo da Vinci is famous for writing backward in his notebooks using a mirror to make it difficult for others to know what he was writing.

### The Caesar Cipher

Several ancient cultures, including the Greeks, Romans and Hebrews, made use of simple substitution ciphers. These were mostly for diplomatic and military communication. Julius Caesar is historically credited with the most basic type of substitution cipher, which bears his name to this day. The Caesar cipher encodes a message by shifting the alphabet by a predetermined number of letters and substituting a new letter for each letter in the message.

In the example above, the alphabet was shifted over five letters, and the word STUDY became NOPYT. As you can see, this is a fairly easy code to break if you know how it was encrypted. You simply have to know how many letters the alphabet was shifted and you can decode the entire message. Even if you did not have the key, it could be determined quickly through trial and error. As a result, substitution ciphers had to become much more complicated over the centuries in order to be effective. For the Caesar cipher, the sender and receiver of the message had to have one shared piece of information, or 'key', which was a single digit indicating how far to shift the alphabet.

As ciphers became more complicated, often combining multiple substitution ciphers, the shared key between the sender and receiver also got longer. This made it difficult and time consuming for individuals to both encode and decode the messages.

### The Enigma Machine

Cryptography took a big leap with the invention of mechanical rotor machines in the early 20th century. The machines consisted of connected gears and rotors that could be set to a predetermined key and would automatically encrypt a message by combining multiple substitution ciphers in sequence. The most famous cryptographic rotor machine was the Enigma machine employed by the Germans during World War II. The cracking of Enigma messages by Allied code-breakers is thought to have been a major factor in the outcome of the war.

## The Computer Age

As the computer era revolutionized the processing, storage and sharing of information, the stakes went up for information security. The need to protect personal, financial and classified information resulted in the rapid development of mathematical and computational methods of protecting information. The first official standard of encryption, known as the Data Encryption Standard (DES) was published in 1975 and instituted in 1977.

### The Diffie-Hellman Key Exchange

One of the biggest problems in modern information security is that of the exchange of secret keys. The recipient of a message cannot decipher it without knowing the key that the sender used for encryption. This key must be kept secret, or else anyone could decipher the message. The problem is how to privately share the key. In 1976, American mathematicians Whitfield Diffie and Martin Hellman developed a method of asymmetric key exchange whereby both the sender and receiver exchange cryptographic keys. The keys are then combined mathematically in such a way that only someone with both keys can decipher the message.

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