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In cryptography, encryption is the process of transforming information (referred to as plaintext) using an algorithm (called cipher) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information (in cryptography, referred to as ciphertext). In many contexts, the word encryption also implicitly refers to the reverse process, decryption (e.g. “software for encryption” can typically also perform decryption), to make the encrypted information readable again (i.e. to make it unencrypted).

Encryption has long been used by militaries and governments to facilitate secret communication. Encryption is now used in protecting information within many kinds of civilian systems, such as computers, networks (e.g. the Internet e-commerce), mobile telephones, wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic teller machines. Encryption is also used in digital rights management to prevent unauthorized use or reproduction of copyrighted material and in software also to protect against reverse engineering (see also copy protection).

Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to protect the integrity and authenticity of a message; for example, verification of a message authentication code (MAC) or a digital signature. Standards and cryptographic software and hardware to perform encryption are widely available, but successfully using encryption to ensure security may be a challenging problem. A single slip-up in system design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See, e.g., traffic analysis, TEMPEST, or Trojan horse.

Main article: History of cryptography

Encryption has been used to protect communications since ancient times, but only organizations and individuals with extraordinary need for confidentiality had bothered to exert the effort required to implement it. Al-Kindi was a pioneer in cryptanalysis and cryptology. He gave the first known recorded explanation of cryptanalysis in A Manuscript on Deciphering Cryptographic Messages. Encryption, and successful attacks on it, played a vital role in World War II. Many of the encryption techniques developed then were closely-guarded secrets (Kahn). In the mid-1970s, with the introduction of the U.S. Data Encryption Standard and public key cryptography, strong encryption emerged from the preserve of secretive government agencies into the public domain.

• Helen Fouché Gaines, “Cryptanalysis”, 1939, Dover. ISBN 0-486-20097-3
• Ibrahim A. Al-Kadi, “The origins of cryptology: The Arab contributions”, Cryptologia, 16(2) (April 1992) pp. 97–126.
• Ibrahim A. Al-Kadi, “Cryptography and Data Security: Cryptographic Properties of Arabic”, proceedings of the Third Saudi Engineering Conference. Riyadh, Saudi Arabia: Nov 24-27, Vol 2:910-921., 1991.
• David Kahn, The Codebreakers - The Story of Secret Writing (ISBN 0-684-83130-9) (1967)
• Abraham Sinkov, Elementary Cryptanalysis: A Mathematical Approach, Mathematical Association of America, 1966. ISBN 0-88385-622-0

• Cryptography - term which encompasses encryption and other concepts used for hiding information
• Encryption software
• Cipher - algorithm used for encryption
• Key - special knowledge needed for successful decyption

Look up encryption in Wiktionary, the free dictionary.

• SecurityDocs Resource for encryption whitepapers
• Accumulative archive of various cryptography mailing lists. Includes Cryptography list at metzdowd and SecurityFocus Crypto list.