Glossary of Security Terms: Cipher

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In cryptography, a cipher is an algorithm that can encode cleartext to make it unreadable, and to decode it back. Modern ciphers are designed to withstand attacks discovered by a cryptanalyst. Each algorithm is judged against known classes of attacks. Ciphers operate two ways, either as block cipher on successive blocks, or buffers, of data. They also are classified according to how their keys 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.