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Symmetric-key cryptography - Glossary | MDN 1/3 https://developer.mozilla.org/en-US/docs/Glossary/Symmetric-key_cryptography reference web, html, css, javascript, documentation 2026-05-05T05:46:25.478241+00:00 kb-cron

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  1. Glossary
  2. Symmetric-key cryptography

Symmetric-key cryptography

Symmetric-key cryptography is a term used for cryptographic algorithms that use the same key for encryption and for decryption. The key is usually called a "symmetric key" or a "secret key". This is usually contrasted with public-key cryptography, in which keys are generated in pairs and the transformation made by one key can only be reversed using the other key. Symmetric-key algorithms should be secure when used properly and are highly efficient, so they can be used to encrypt large amounts of data without having a negative effect on performance. Most symmetric-key algorithms currently in use are block ciphers: this means that they encrypt data one block at a time. The size of each block is fixed and determined by the algorithm: for example AES uses 16-byte blocks. Block ciphers are always used with a mode , which specifies how to securely encrypt messages that are longer than the block size. For example, AES is a cipher, while CTR, CBC, and GCM are all modes. Using an inappropriate mode, or using a mode incorrectly, can completely undermine the security provided by the underlying cipher.

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