Encryption

In cryptography, encryption is the process of encoding information. This process converts the original representation of information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorised parties can decipher an encrypted text back to the plaintext and access the original information. Encryption does not prevent interference per se, but denies the intelligible content to a potential eavesdropper.

For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key, but a well-designed encryption scheme requires considerable computing resources and expertise. An authorised recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorised users.

Historically, various forms of cryptography have been used to aid encryption. Early encryption techniques were often used in military messaging. Since then, new techniques have emerged that have become common in all areas of modern computing. Modern encryption schemes use the concepts of public key and symmetric key. Modern encryption techniques provide security because modern computers are inefficient at decrypting encryption.

Ancient

One of the earliest forms of cryptography is symbol substitution, which was first found in the tomb of Khnumhotep II, who lived in 1900 BC in Egypt. Symbol substitution cryptography is 'non-standard', meaning that symbols require a cipher or key to be understood. This type of early cryptography was used throughout ancient Greece and Rome for military purposes. One of the most famous developments in military cryptography was Caesar's Cipher, which was a system in which a letter in a normal text is shifted down a fixed number of alphabet positions to obtain the encoded letter. A message encoded with this type of encryption could be decoded with the fixed number on Caesar's Cipher.

Around 800 AD, the Arab mathematician Al-Kindi developed the technique of frequency analysis - which was an attempt to systematically decipher Caesar's ciphers. This technique looked at the frequency of the letters in the encrypted message to determine the appropriate shift. This technique was rendered ineffective after the creation of Leone Alberti's polyalphabetic cipher in 1465, which incorporated several sets of languages. For frequency analysis to be useful, the person trying to decipher the message would have to know which language the sender had chosen.

19th-20th century

Around 1790, Thomas Jefferson theorised about a cipher to encode and decode messages in order to provide a more secure way of military correspondence. The cipher, known today as the Wheel Cipher or the Jefferson Disk, although never actually built, was theorised as a coil that could string together an English message of up to 36 characters. The message could be deciphered by connecting the mixed message to a receiver with an identical cipher.

A device similar to the Jefferson Disk, the M-94, was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in US military communications until 1942.

In World War II, the Axis powers used a more advanced version of the M-94 called the Enigma Machine. The Enigma machine was more complex because, unlike Jefferson's wheel and the M-94, each day the jumble of letters changed to a completely new combination. Each day's combination was known only to the Axis, so many thought that the only way to crack the code would be to try over 17,000 combinations in 24 hours. The Allies used computing power to severely limit the number of reasonable combinations they could check each day, leading to the breakdown of the Enigma machine.

The modern

Today, cryptography is used in the transfer of communications over the Internet for security and commerce. As computing power continues to increase, computer cryptography is constantly evolving to prevent attacks.