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Symmetric Encryption Algorithms: Understanding Block and Stream Ciphers

A deep dive into symmetric encryption algorithms, including block ciphers like AES and DES, stream ciphers, and their applications in modern cryptography.

January 15, 2026 1 min read By Scott Weeden cryptographysymmetric-encryptionaesdesencryption-algorithms

Symmetric Encryption Algorithms: Understanding Block and Stream Ciphers

Symmetric schemes use one shared key for both directions. Block ciphers (AES in particular) transform fixed-size blocks under a key; modes (CBC, CTR, GCM, …) define how multiple blocks are chained and how IVs/nonces participate. Authenticated encryption (preferably AEAD such as AES-GCM or ChaCha20-Poly1305) provides both confidentiality and integrity by default.

Older ciphers (DES, 3DES) appear only in legacy systems; plan migrations. Stream ciphers (or counter-based modes) suit streaming I/O when nonces are managed carefully. For every deployment, answer: how are keys rotated, how are nonces unique, and what happens on verification failure?

Course posts on AES internals, malleability, and one-time-pad limits connect back to the definitions sketched here—use this entry as the index for “which mode for which threat model.”