Category: 3. Block Cipher Modes of Operation

It can be considered as a counter-based version of CFB mode without the feedback. In this mode, both the sender and receiver need to access to a reliable counter, which computes a new shared value each time a ciphertext block is exchanged. This shared counter is not necessarily a secret value, but challenge is that…

It involves feeding the successive output blocks from the underlying block cipher back to it. These feedback blocks provide string of bits to feed the encryption algorithm which act as the key-stream generator as in case of CFB mode. The key stream generated is XOR-ed with the plaintext blocks. The OFB mode requires an IV…

In this mode, each ciphertext block gets ‘fed back’ into the encryption process in order to encrypt the next plaintext block. Operation The operation of CFB mode is depicted in the following illustration. For example, in the present system, a message block has a size ‘s’ bits where 1 < s < n. The CFB…

CBC mode of operation provides message dependence for generating ciphertext and makes the system non-deterministic. Operation The operation of CBC mode is depicted in the following illustration. The steps are as follows − Analysis of CBC Mode In CBC mode, the current plaintext block is added to the previous ciphertext block, and then the result…

In this chapter, we will discuss the different modes of operation of a block cipher. These are procedural rules for a generic block cipher. Interestingly, the different modes result in different properties being achieved which add to the security of the underlying block cipher. A block cipher processes the data blocks of fixed size. Usually,…