Block Encryption Cipher Modes

Block cipher modes define how block ciphers like AES process data larger than a single block (typically 128 bits). Each mode has different security and performance characteristics.

Here’s a brief summary of common block cipher modes:

1. ECB (Electronic Codebook)

• Each block is encrypted independently.
• Simple but insecure: identical plaintext blocks produce identical ciphertext blocks.
• Not recommended for real-world use.

2. CBC (Cipher Block Chaining)

• Each block is XORed with the previous ciphertext block before encryption.
• Requires an IV (Initialization Vector) for the first block.
• Better security than ECB.
• Sensitive to bit-flipping and padding oracle attacks if not handled properly.

3. CTR (Counter Mode)

• Turns a block cipher into a stream cipher.
• Encrypts a counter value for each block and XORs it with the plaintext.
• Does not require padding.
• Must never reuse the same key and counter pair.

4. CFB (Cipher Feedback Mode)

• Encrypts previous ciphertext (or IV) and XORs with plaintext.
• Acts like a stream cipher.
• Good for streaming data.

5. OFB (Output Feedback Mode)

• Similar to CFB, but feeds the output of encryption (not the ciphertext) back in.
• Produces a keystream independent of plaintext.
• Errors in transmission do not propagate.
• Reusing IVs is dangerous.

6. GCM (Galois/Counter Mode)

• Based on CTR mode, but adds authentication (AEAD) using a Galois field hash.
• Encrypts and authenticates simultaneously.
• Fast and widely used in TLS and modern protocols.
• Nonce reuse compromises security.

7. XTS (XEX-based Tweaked CodeBook mode with ciphertext stealing)

• Designed for disk encryption.
• Encrypts blocks with a tweak (usually the block’s index).
• Protects against block swapping attacks.
• Not suitable for general-purpose encryption (e.g., messages).

Summary Table