The method in which a message is divided into blocks and each block is encrypted separately is known as Electronic Codebook (ECB) mode. In ECB mode, the plaintext message is divided into fixed-size blocks, and each block is encrypted independently using the same key. This means that identical plaintext blocks will yield identical ciphertext blocks. Therefore, ECB is straightforward and simple to implement.
However, one of the key characteristics of ECB is that it does not provide good security for larger messages or systems where patterns in the plaintext may reveal information about the ciphertext. It lacks diffusion, meaning that an attacker can discern patterns by observing repeated blocks in the ciphertext, which could potentially lead to vulnerabilities in the encryption scheme. Despite its simplicity, ECB is generally not recommended for use in cryptographic protocols where the security of the message is critical.
Other modes, such as Cascade, Counter (CTR), and Output Feedback (OFB), employ different mechanisms for encrypting data, often combining blocks in ways that ensure enhanced security over simply encrypting each block independently as in ECB. These methods generally introduce features like feedback, chaining, or counter-based operations, which improve the diffusion and overall security of the encryption process.