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Security Fundamentals & Crypto · Foundational

Advanced Encryption Standard (AES)

NIST-standard symmetric block cipher (Rijndael) with a 128-bit block and 128-, 192-, or 256-bit keys.

Definition

AES was selected by NIST in 2001 (FIPS 197) to replace DES. It uses a substitution-permutation network with 10, 12, or 14 rounds depending on key size. AES is the most widely used symmetric cipher, supported in hardware via AES-NI, and AES-256 is approved for Top Secret data.

Example

WPA3, BitLocker, TLS, and IPsec all commonly use AES.

Exam tip

AES block size is always 128 bits regardless of key size; AES-256 is considered quantum-resistant in practice.

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