Cipher Block Chaining (CBC)
What is Cipher Block Chaining (CBC)?
Cipher Block Chaining, or CBC, is a block cipher mode of operation in which each plaintext block is combined with the previous ciphertext block before encryption, so the blocks are linked together instead of being encrypted independently.
Examples
- A system uses AES in CBC mode to encrypt a file so that repeating patterns in the original data are harder to spot than they would be in simpler block-by-block encryption.
- A secure application uses CBC with a random initialization vector so the same message encrypted twice does not begin with the same ciphertext.
Discover 🔎
When people first learn about encryption, it is easy to imagine that a message is simply scrambled all at once. In reality, many encryption systems work in fixed-size blocks. That creates an important design question. If each block were encrypted in isolation, what would happen when the same data pattern appeared again and again? The answer is that patterns could leak through in ways defenders do not want.
Cipher Block Chaining was created to solve that problem by linking blocks together. Instead of treating each block as a separate island, CBC makes each block depend on what came before it. This gives the ciphertext a more connected and less predictable structure, which is why CBC became such an important part of practical cryptography for many years.
Summary 📝
Cipher Block Chaining is a mode of operation that links block cipher encryption steps together so each plaintext block depends on the previous ciphertext block. This helps reduce visible patterns and makes block encryption more suitable for real-world data. CBC is an important concept in cryptography because it shows how encryption strength depends not only on the algorithm, but also on how the algorithm is used.
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