Incryptography, acipher is an algorithm that canencryptplaintext to make it unreadable, and todecrypt the encoded data back to plaintext again.

Ciphers were common long before the information age (e.g.,substitution ciphers,transposition ciphers, andpermutation ciphers), but none of them were cryptographically secure except for theone-time pad.

In the modern age, ciphers have evolved dramatically.AES,RSA andBlowfish are examples of ciphers that are integral part of contemporary encryption standards and systems.

Modern ciphers are designed to withstand attacks discovered throughcryptanalysis. There is no guarantee that all attack methods have been discovered, so each algorithm isrecommended for different purposes based on known classes of attacks.

Ciphers operate either asblock ciphers on successive blocks (or buffers) of data, or asstream ciphers on a continuous data flow (often of sound or video).

Ciphers are also classified according to how theirkeys are handled:

• symmetric key algorithms use the same key to encode and decode a message. The key also must be sent securely if the message is to stay confidential.
• asymmetric key algorithms use one key for encryption and the other for decryption.

See also

• Web Crypto API
• SubtleCrypto supported algorithms
• Related glossary terms:
  • Block cipher mode of operation
  • Ciphertext
  • Cipher suite
  • Cryptanalysis
  • Cryptography
  • Decryption
  • Encryption
  • Key
  • Plaintext
  • Public-key cryptography
  • Symmetric-key cryptography
• Cipher on Wikipedia