In cryptography, a round or round function is a basic transformation that is repeated (iterated) multiple times inside the algorithm. Splitting a large algorithmic function into rounds simplifies both implementation and cryptanalysis.
For example, encryption using an oversimplified three-round cipher can be written as , where C is the ciphertext and P is the plaintext. Typically, rounds are implemented using the same function, parameterized by the round constant and, for block ciphers, the round key from the key schedule. Parameterization is essential to reduce the self-similarity of the cipher, which could lead to slide attacks.
Increasing the number of rounds "almost always" protects against differential and linear cryptanalysis, as for these tools the effort grows exponentially with the number of rounds. However, increasing the number of rounds does not always make weak ciphers into strong ones, as some attacks do not depend on the number of rounds.
The idea of an iterative cipher using repeated application of simple non-commutating operations producing diffusion and confusion goes as far back as 1945, to the then-secret version of C. E. Shannon's work "Communication Theory of Secrecy Systems"; Shannon was inspired by mixing transformations used in the field of dynamical systems theory (cf. horseshoe map). Most of the modern ciphers use iterative design with number of rounds usually chosen between 8 and 32 (with 64 and even 80 used in cryptographic hashes).
For some Feistel-like cipher descriptions, notably the one of the RC5, a term "half-round" is used to define the transformation of part of the data (a distinguishing feature of the Feistel design). This operation corresponds to a full round in traditional descriptions of Feistel ciphers (like DES).
Inserting round-dependent constants into the encryption process breaks the symmetry between rounds and thus thwarts the most obvious slide attacks. The technique is a standard feature of most modern block ciphers.
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In cryptography, confusion and diffusion are two properties of the operation of a secure cipher identified by Claude Shannon in his 1945 classified report A Mathematical Theory of Cryptography. These properties, when present, work together to thwart the application of statistics and other methods of cryptanalysis. Confusion in a symmetric cipher is obscuring the local correlation between the input (plaintext) and output (ciphertext) by varying the application of the key to the data, while diffusion is hiding the plaintext statistics by spreading it over a larger area of ciphertext.
In cryptography, a block cipher is a deterministic algorithm that operates on fixed-length groups of bits, called blocks. Block ciphers are the elementary building blocks of many cryptographic protocols. They are ubiquitous in the storage and exchange of data, where such data is secured and authenticated via encryption. A block cipher uses blocks as an unvarying transformation. Even a secure block cipher is suitable for the encryption of only a single block of data at a time, using a fixed key.
Four recent trends have emerged in the evolution of authenticated encryption schemes: (1) Regarding simplicity, the adoption of public permutations as primitives allows for sparing a key schedule and the need for storing round keys; (2) using the sums of p ...
Springer2023
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In the last few years, the field of lightweight cryptography has seen an influx in the number of block ciphers and hash functions being proposed. In the past there have been numerous papers that have looked at circuit level implementation of block ciphers ...
Most of the cryptographic protocols that we use frequently on the internet are designed in a fashion that they are not necessarily suitable to run in constrained environments. Applications that run on limited-battery, with low computational power, or area ...