Process of disguising information as “ciphertext,” or data that will be unintelligible to an unauthorized person. Decryption is the process of converting ciphertext back into its original format, sometimes called plaintext (see cryptography). Computers encrypt data by applying an algorithm to a block of data. A personal key known only to the message's transmitter and intended receiver is used to control the encryption. Well-designed keys are almost impregnable. A key 16 characters long selected at random from 256 ASCII characters could take far longer than the 15-billion-year age of the universe to decode, assuming the perpetrator attempted 100 million different key combinations per second. Symmetric encryption requires the same key for both encryption and decryption. Asymmetric encryption, or public-key cryptography, requires a pair of keys, one for encryption and one for decryption.
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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.
The terms "encrypt" and "decrypt" are discouraged in international documents, since they tend to be mistranslated to "inter" (bury) and "disinter".