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, storage devices (e.g. USB flash drives), 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.

One of the earliest public key encryption applications was called Pretty Good Privacy (PGP), according to Paul Rubens. It was written in 1991 by Phil Zimmermann and was bought by Network Associates in 1997 and is now called PGP Corporation.

There are a number of reasons why an encryption product may not be suitable in all cases. First e-mail must be digitally signed at the point it was created to provide non-repudiation for some legal purposes, otherwise the sender could argue that it was tampered with after it left their computer but before it was encrypted at a gateway according to Paul. An encryption product may also not be practical when mobile users need to send e-mail from outside the corporate network.

See also

• Cryptography
• Cold boot attack
• Encryption software

• Cipher
• Key
• Famous ciphertexts

Portal: Crypto key.svg

• Disk encryption
• Secure USB drive
• Secure Network Communications

References

• Helen Fouché Gaines, “Cryptanalysis”, 1939, Dover. ISBN 0-486-20097-3
• 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