What is XSL attack?
In [[cryptography]], the '''XSL attack''' is a method of [[cryptanalysis]] for [[block cipher]]s. The attack was first published in 2002 by [[research]]ers [[Nicolas Courtois]] and [[Josef Pieprzyk]]. It was claimed that it may break the [[Advanced Encryption Standard]] (AES) [[cipher]] faster than a [[brute force attack]]. [[Advanced Encryption Standard|AES]] is already widely used in commerce and government for the transmission of secret and [[classified information]]. Finding a technique that can decrease the amount of time it takes to break the [[Ciphertext|secret message]] without having the [[Key (cryptography)|key]] could cause wide damage. In 2004 it was shown by one of the [[Cryptanalysis|cryptanalysts]], that the algorithm does not perform as described in its published paper. In addition, the method requires long effort. Unless shortened, the technique does not reduce the effort to break AES in comparison to a [[brute force attack]]. Therefore, it does not affect the real-world security of [[block cipher]]s in the near future. However, the attack has caused some experts to insert complexities in the algebraic simplicity of the current AES. The XSL attack relies on first analyzing the ''internal [[design]]'' of a cipher then deriving a system of [[quadratic polynomial|quadratic]] [[simultaneous equation]]s. These systems of [[equation]]s are typically very large, for example 8000 equations with 1600 [[variable]]s for the 128-[[bit]] AES. Several methods for solving such systems are known. In the XSL attack, a specialized algorithm, termed '''XSL''' ('''eXtended Sparse Linearization'''), is then applied to solve these equations and [[Computation|compute]] the [[key (cryptography)|key]]. The attack is well-known and famous for requiring only a handful of [[Known-plaintext attack|known plaintexts]] to perform. Previous methods of [[cryptanalysis]], such as [[Linear cryptanalysis|linear]] and [[differential cryptanalysis]], often require unrealistically large numbers of known or [[Chosen-plaintext at