Symmetric-key algorithm

A cryptographic algorithm that uses the same secret key, or easily related keys, for encryption and decryption. Its security depends on keeping the key secret.

Block cipher: A symmetric-key cipher that transforms fixed-size blocks of data under a secret key. Block ciphers are a major design family for symmetric encryption.
Secret key: Information kept confidential because possession grants access to a cryptographic operation. The same protected secret, or a closely related key, enables both sides of symmetric cryptography.
Advanced Encryption Standard: A widely used block cipher standardized by NIST, with 128-bit blocks and 128-, 192-, or 256-bit keys. AES is the dominant standardized symmetric block cipher in many applications.
Asymmetric-key cryptography: Cryptography based on a public key and a mathematically related private key. Unlike symmetric algorithms, it does not require both parties to possess the same secret beforehand.
Data Encryption Standard: A 1970s block cipher standardized in the United States and later superseded by AES. DES shaped practical symmetric encryption before its short key became vulnerable to exhaustive search.
Stream cipher: A symmetric-key cipher that combines plaintext with a generated stream of pseudorandom bits. Stream ciphers encrypt data incrementally rather than in fixed-size blocks.
Plaintext: Data in its original, unencrypted form. Symmetric encryption transforms plaintext into ciphertext and permits its recovery.
ChaCha20: A stream cipher designed by Daniel J. Bernstein and standardized for modern network security. ChaCha20 provides a fast alternative to AES, especially where hardware acceleration is unavailable.
Public-key encryption: Encryption in which a public key encrypts data that only its corresponding private key can decrypt. It avoids distributing a shared encryption key, but is generally less efficient for bulk data.
Lucifer (cipher): A block cipher developed at IBM that contributed to the design of the Data Encryption Standard. Lucifer provides a direct design ancestor of a landmark standardized symmetric cipher.

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