Modes of Operation

Modes of operation in cryptography are techniques used to securely process blocks of data, typically when encrypting or decrypting data that is larger than the block size of the underlying cryptographic algorithm. These modes define how the encryption or decryption process is applied to multiple blocks of data, ensuring confidentiality, integrity, and authenticity.

Common modes of operation include:

1. Electronic Codebook (ECB): Each block of plaintext is independently encrypted into a corresponding block of ciphertext. Identical plaintext blocks result in the same ciphertext blocks, making it vulnerable to pattern analysis.
2. Cipher Block Chaining (CBC): Each plaintext block is XORed with the previous ciphertext block before encryption, adding randomness and preventing pattern repetition. Initialization Vector (IV) is required for the first block.
3. Cipher Feedback (CFB): Each ciphertext block becomes part of the feedback loop, generating a keystream that is XORed with the plaintext to produce the ciphertext.
4. Output Feedback (OFB): Similar to CFB, but the keystream is generated independently from the ciphertext blocks, avoiding error propagation.
5. Counter (CTR): Each block is encrypted with a unique counter value, turning the block cipher into a stream cipher. This mode is parallelizable and widely used in modern cryptography.