Predicting Outcomes of ElimLin Attack on Lightweight Block Cipher Simon

There are two major families in cryptanalytic attacks on symmetric ciphers: statistical attacks and algebraic attacks. In this position paper we argue that algebraic cryptanalysis has not yet been developed properly due to the weakness of the theory which has substantial difficulty to prove most basic results on the number of linearly independent equations in algebraic attacks. Consequently most authors present a restricted range of attacks which are shown experimentally to work with their computer but refrain from claiming results which would work on a larger computer but have not yet been tested. For example in recent 2015 work of Raddum we discover that (experimentally) ElimLin attack breaks up to 16 rounds of Simon block cipher however it is hard to know what happens for 17 rounds. In this paper we argue that one CAN predict and model the behavior of such attacks and evaluate complexity of the attacks which we cannot yet execute. To the best of our knowledge this has never been done before

Two philosophies for solving non-linear equations in algebraic cryptanalysis

Algebraic Cryptanalysis [45] is concerned with solving of particular systems of multivariate non-linear equations which occur in cryptanalysis. Many different methods for solving such problems have been proposed in cryptanalytic literature: XL and XSL method, Gröbner bases, SAT solvers, as well as many other. In this paper we survey these methods and point out that the main working principle in all of them is essentially the same. One quantity grows faster than another quantity which leads to a “phase transition” and the problem becomes efficiently solvable. We illustrate this with examples from both symmetric and asymmetric cryptanalysis. In this paper we point out that there exists a second (more) general way of formulating algebraic attacks through dedicated coding techniques which involve redundancy with addition of new variables. This opens numerous new possibilities for the attackers and leads to interesting optimization problems where the existence of interesting equations may be somewhat deliberately engineered by the attacker

High Saturation Complete Graph Approach for EC Point Decomposition and ECDL Problem

One of the key questions in contemporary applied cryptography is whether there exist an efficient algorithm for solving the discrete logarithm problem in elliptic curves. The primary approach for this problem is to try to solve a certain system of polynomial equations. Current attempts try to solve them directly with existing software tools which does not work well due to their very loosely connected topology and illusory reliance on degree falls. A deeper reflection on what makes systems of algebraic equations efficiently solvable is missing. In this paper we propose a new approach for solving this type of polynomial systems which is radically different than current approaches. We carefully engineer systems of equations with excessively dense topology obtained from a complete clique/biclique graphs and hypergraphs and unique special characteristics. We construct a sequence of systems of equations with a parameter K and argue that asymptotically when K grows the system of equations achieves a high level of saturation with lim_{K\to\infty} F/T = 1 which allows to reduce the regularity degree and makes that polynomial equations over finite fields may become efficiently solvable

On the Existence of Non-Linear Invariants and Algebraic Polynomial Constructive Approach to Backdoors in Block Ciphers

In this paper we study cryptanalysis with non-linear polynomials cf. Eurocrypt’95 (adapted to Feistel ciphers at Crypto 2004). Previously researchers had serious difficulties in making such attacks work. Even though this is less general than a general space partitioning attack (FSE’97), a polynomial algebraic approach has enormous advantages. Properties are more intelligible and algebraic computational methods can be applied in order to discover or construct the suitable properties. In this paper we show how round invariants can be found for more or less any block cipher, by solving a certain surprisingly simple single algebraic equation (or two). Then if our equation has solutions, which is far from being obvious, it will guarantee that some polynomial invariant will work for an arbitrarily large number of encryption rounds. This paper is a proof of concept showing that it IS possible, for at least one specific quite complex real-life cipher to construct in a systematic way, a non-linear component and a variety of non-linear polynomial invariants holding with probability 1 for any number of rounds and any key/IV. Thus we are able to weaken a block cipher in a permanent and pervasive way. An example of a layered attack with two stages is also shown. Moreover we show that sometimes our equation reduces to zero, and this leads to yet stronger invariants, which work for any Boolean function including the original historical one used in 1970-1990