Cipher Block Chaining (CBC)
Security+ 🏆 • Cryptography 🔒
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Difficulty: premium
Definition
Cipher Block Chaining is a block-cipher mode that links blocks together: each plaintext block is XORed with the previous ciphertext block before encryption. A fresh, unpredictable IV starts the chain so identical plaintext blocks encrypt differently.
Examples
- File encryption with AES-CBC where each file uses a new 16-byte random IV stored alongside the ciphertext, plus a separate HMAC to detect tampering.
- Older TLS 1.0/1.2 suites using AES-CBC to protect records (many environments now prefer AEAD modes instead).
Discover 🔎
CBC turns a block cipher like AES into a scheme that hides patterns. Instead of encrypting each block independently, it mixes every plaintext block with the previous ciphertext block so repeats don’t show through. One unpredictable initialization vector (IV) kicks off the first block so two identical messages won’t start with the same ciphertext.
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