Block Cipher Modes of Operation for Confidentiality

This chapter addresses the standard approaches to use block ciphers to encrypt and decrypt plaintexts, while considering plaintexts of a size longer than that of a single block. In the Electronic Codebook (ECB) mode, the encryption and decryption operations are applied independently to each block. ECB mode is the simplest mode of operation. In the Cipher Block Chaining mode, the encryption and decryption processes combine successive blocks. OFB, CTR, and Cipher Feedback (CFB) modes of operation function like stream ciphers. Therefore, all of them use the same function to encrypt and decrypt. CTR mode is similar to OFB mode with the exception that a counter is used instead of an initialization vector. Like OFB, CFB mode operates as a stream cipher and makes use of an initialization vector and the same algorithm for encryption and decryption. The standard algorithm to protect data on storage devices is the XTS‐AES mode of operation.