Dictionary of Computers - cryptography

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Science of creating and reading codes, for example, those produced by the German Enigma machine used in World War II, those used in the secure transmission of credit card details over the Internet, and those used to ensure the privacy of e-mail messages. Unencoded text (known as plaintext) is converted to an unreadable form (known as cyphertext) by the process of encryption. The recipient must then decrypt the message before it can be read. The breaking of such codes is known as cryptanalysis. No encryption method is completely unbreakable, but cryptanalysis of a strongly encrypted message can be so time-consuming and complex as to be almost impossible.

The growth of the Internet and online commerce has brought an increasing demand for good cryptography. Most Internet cryptography systems involve the use of digital ‘keys’ to encrypt and decrypt messages. In symmetric-key cryptography, both sender and recipient use the same key. An example of this is the Data Encryption Standard (DES), used by the US government. In public-key cryptography, each party has both a freely-available public key (used by anyone to encrypt messages) and a private key (used to decrypt received messages). The program Pretty Good Privacy (PGP) is a popular and effective (and free for non-commercial use) implementation of public-key cryptography. Encrypted messages may be further protected by concealing them within large graphics, audio, or video files – a technique known as steganography.

Many governments consider strong cryptography a threat to national security, as it makes ‘wiretapping’ (monitoring private messages) practically impossible. In the USA, strong encryption software is classified as a weapon under the International Traffic in Arms Regulations and its export is illegal. In addition, the Clipper chip system, introduced in 1994, and used to provide encyption in devices such as mobile phones, requires that the keys required to decrypt messages are made available to law enforcement officials.

In 2000, the UK government passed a Regulation of Investigatory Powers Act, under which holders of data encryption keys could be forced to hand these over to the police or security services.

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