AES
The Advanced Encryption Standard (AES) is the symmetric block cipher NIST standardized in 2001, supporting 128/192/256-bit keys, and is the de facto standard of modern encryption.
Purpose
It replaced DES, whose keys were too short, with a secure, efficient symmetric cipher well suited to hardware acceleration.
Mechanism
It applies several rounds of transformations to a 128-bit block: SubBytes (S-box substitution), ShiftRows, MixColumns, and AddRoundKey (XOR with the round key). The key length determines the round count (10/12/14 rounds), and the key schedule derives the round keys.
Use cases
- TLS data encryption
- File and disk encryption (LUKS, FileVault)
- VPN tunnels (IPsec/IKE)
- Database field encryption
Examples
- Input
key=256bit, data="hello"Outputciphertext in 16-byte blocksRequires a mode of operation and an IV
Common errors
- Using ECB mode makes identical plaintext blocks produce identical ciphertext blocks
- Use GCM, or CBC with a random IV
Related terms
DES
The Data Encryption Standard (DES) is the symmetric block cipher standardized in 1977, using a 56-bit key and 64-bit blocks; it is obsolete due to its short key. GLOSSARY
3DES (Triple DES)
Triple DES (3DES) strengthens DES by encrypting each data block three times with 56-bit keys in an encrypt-decrypt-encrypt (EDE) sequence, yielding 168 bits of key material, and served as the transitional cipher between DES and AES. GLOSSARY
Block Cipher
A block cipher is a symmetric cipher that encrypts and decrypts fixed-length blocks (e.g., 128 bits) and requires a mode of operation to handle arbitrary-length data. GLOSSARY
Mode of Operation
A mode of operation is a scheme that lets a block cipher handle arbitrary-length data, defining how multiple plaintext blocks are chained during encryption; common ones include ECB, CBC, CTR, and GCM. GLOSSARY
GCM (Galois/Counter Mode)
GCM is an AEAD mode that combines CTR encryption with GHASH authentication, providing confidentiality and integrity at once, and is the preferred mode of TLS 1.2/1.3. GLOSSARY