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… Continue reading Cipher Feedback (CFB) Mode
Month: November 2022
Cipher Block Chaining (CBC) Mode
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… Continue reading Cipher Block Chaining (CBC) Mode
Block Cipher Modes of Operation
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,… Continue reading Block Cipher Modes of Operation
Encryption Process
Here, we restrict to description of a typical round of AES encryption. Each round comprise of four sub-processes. The first round process is depicted below − Byte Substitution (SubBytes) The 16 input bytes are substituted by looking up a fixed table (S-box) given in design. The result is in a matrix of four rows and… Continue reading Encryption Process
Advanced Encryption Standard
The more popular and widely adopted symmetric encryption algorithm likely to be encountered nowadays is the Advanced Encryption Standard (AES). It is found at least six time faster than triple DES. A replacement for DES was needed as its key size was too small. With increasing computing power, it was considered vulnerable against exhaustive key… Continue reading Advanced Encryption Standard
Triple DES
The speed of exhaustive key searches against DES after 1990 began to cause discomfort amongst users of DES. However, users did not want to replace DES as it takes an enormous amount of time and money to change encryption algorithms that are widely adopted and embedded in large security architectures. The pragmatic approach was not… Continue reading Triple DES
Key Generation
The round-key generator creates sixteen 48-bit keys out of a 56-bit cipher key. The process of key generation is depicted in the following illustration − The logic for Parity drop, shifting, and Compression P-box is given in the DES description. DES Analysis The DES satisfies both the desired properties of block cipher. These two properties… Continue reading Key Generation
Round Function
The heart of this cipher is the DES function, f. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output.
Data Encryption Standard
The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST). DES is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8… Continue reading Data Encryption Standard
Feistel Block Cipher
Feistel Cipher is not a specific scheme of block cipher. It is a design model from which many different block ciphers are derived. DES is just one example of a Feistel Cipher. A cryptographic system based on Feistel cipher structure uses the same algorithm for both encryption and decryption. Encryption Process The encryption process uses… Continue reading Feistel Block Cipher