Mindblown: a blog about philosophy.
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Counter (CTR) Mode
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…
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Output Feedback (OFB) Mode
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…
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Cipher Feedback (CFB) Mode
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…
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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…
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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,…
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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…
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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…
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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…
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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…
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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.
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