Block cipher
A block cipher is a keyed symmetric cryptographic algorithm that transforms fixed-size blocks of data into ciphertext.
Software Security for Developers
A block cipher is an encryption algorithm that divides data into fixed-size blocks and transforms each block using a secret key.
- How it is used
- Uses fixed-size encryption as the foundation for protecting data, while modes handle messages longer than one block.
- How deep it goes
- Explains block sizing, padding, modes, ECB leakage, IVs, and authenticated encryption, but stops short of mathematical internals.
- Examples
- Uses a 1,605-byte message and repeated HTTP response blocks to demonstrate padding, block processing, and ECB pattern leakage.
- What you can do after
- Configure AES-GCM with secure IVs and authentication tags, while rejecting ECB for practical encryption tasks.
Read how Software Security for Developers explains block cipher →
Real-World Cryptography
A block cipher is a keyed symmetric cipher that encrypts fixed-size blocks of data.
- How it is used
- Explains the fixed-block primitive underlying AES within authenticated encryption.
- How deep it goes
- Defines the interface and permutation model, then sketches AES rounds but defers exact subfunction mechanics.
- Examples
- Uses AES-128-bit blocks, a 4-by-4 byte state, repeated rounds, and the four named AES round functions.
- What you can do after
- Evaluate how AES maps blocks, reverses encryption, and transforms state through keyed rounds.
Hacking Cryptography
A block cipher is a keyed cryptographic algorithm that transforms fixed-size blocks of data.
- How it is used
- Frames symmetric encryption around fixed-size processing, mode selection, padding, and implementation security.
- How deep it goes
- Explains confusion, diffusion, padding, modes, cipher choices, and attack mechanisms, stopping short of cipher internals.
- Examples
- Uses DES, 3DES, AES, PKCS#7 padding, ECB, CBC, padding oracles, and the BEAST attack.
- What you can do after
- Evaluate block cipher choices and diagnose failures involving padding, modes, and reused CBC initialization vectors.
Related concepts
- AESincludes · AES is a standardized symmetric block cipher that encrypts and decrypts data in 128-bit blocks using 128-, 192-, or 256-bit keys.
- Davies–Meyer methodused by · The Davies–Meyer method is a compression-function construction that combines a block-cipher operation with a chaining value.
- message authentication codeused by · A message authentication code is a keyed cryptographic value generated from a message to verify its integrity and authenticity.
- stream ciphercontrasts with · A stream cipher is an encryption algorithm that combines plaintext sequentially with a generated keystream, typically using XOR.
- paddinguses · Padding is the addition of extra space, values, or data around or within a structure to satisfy size, alignment, layout, or processing requirements.
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