Random walk tests for pseudo-random number generators

It is well known that there are no perfectly good generators of random number sequences, implying the need of testing the randomness of the sequences produced by such generators. There are many tests for measuring the uniformity of random sequences, and here we propose a few new ones, designed by random walks. The experiments we have made show that our tests discover some discrepancies of random sequences passing many other tests

A Generalized Approach to Optimization of Relational Data Warehouses Using Hybrid Greedy and Genetic Algorithms

As far as we know, in the open scientific literature, there is no generalized framework for the optimization of relational data warehouses which includes view and index selection and vertical view fragmentation. In this paper we are offering such a framework. We propose a formalized multidimensional model, based on relational schemas, which provides complete vertical view fragmentation and presents an approach of the transformation of a fragmented snowflake schema to a defragmented star schema through the process of denormalization. We define the generalized system of relational data warehouses optimization by including vertical fragmentation of the implementation schema (F), indexes (I) and view selection (S) for materialization. We consider Genetic Algorithm as an optimization method and introduce the technique of "recessive bits" for handling the infeasible solutions that are obtained by a Genetic Algorithm. We also present two novel hybrid algorithms, i.e. they are combination of Greedy and Genetic Algorithms. Finally, we present our experimental results and show improvements of the performance and benefits of the generalized approach (SFI) and show that our novel algorithms significantly improve the efficiency of the optimization process for different input parameters

A Polynomial-Time Key-Recovery Attack on MQQ Cryptosystems

International audienceWe investigate the security of the family of MQQ public key cryptosystems using multivariate quadratic quasigroups (MQQ). These cryptosystems show especially good performance properties. In particular, the MQQ-SIG signature scheme is the fastest scheme in the ECRYPT benchmarking of cryptographic systems (eBACS). We show that both the signature scheme MQQ-SIG and the encryption scheme MQQ-ENC, although using different types of MQQs, share a common algebraic structure that introduces a weakness in both schemes. We use this weakness to mount a successful polynomial time key-recovery attack. Our key-recovery attack finds an equivalent key using the idea of so-called {\it good keys} that reveals the structure gradually. In the process we need to solve a MinRank problem that, because of the structure, can be solved in polynomial-time assuming some mild algebraic assumptions. We highlight that our theoretical results work in characteristic $2$ which is known to be the most difficult case to address in theory for MinRank attacks. Also, we emphasize that our attack works without any restriction on the number of polynomials removed from the public-key, that is, using the minus modifier. This was not the case for previous MinRank like-attacks against \MQ\ schemes. From a practical point of view, we are able to break an MQQ-SIG instance of $80$ bits security in less than $2$ days, and one of the more conservative MQQ-ENC instances of $128$ bits security in little bit over $9$ days. Altogether, our attack shows that it is very hard to design a secure public key scheme based on an easily invertible MQQ structure

MACEDONIA

Abstract. In this paper we propose a definition and construction of a new family of one-way candidate functions RN: Q N → Q N, where Q = {0, 1,..., s −1} is an alphabet with s elements. Special instances of these functions can have the additional property to be permutations (i.e. one-way permutations). These one-way functions have the property that for achieving the security level of 2 n computations in order to invert them, only n bits of input are needed. The construction is based on quasigroup string transformations. Since quasigroups in general do not have algebraic properties such as associativity, commutativity, neutral elements, inverting these functions seems to require exponentially many readings from the lookup table that defines them (a Latin Square) in order to check the satisfiability for the initial conditions, thus making them natural candidates for one-way functions. 3 Key words: one-way functions, one-way permutations, quasigroup string transformation

On the importance of the key separation principle for different modes of operation

The key separation principle for different modes of operation of the block ciphers is a cryptographic folklore wisdom that states: One should always use distinct keys for distinct algorithms and distinct modes of operation. If this principle is violated, then there are generic attacks that can recover the whole or a part of the encrypted messages. By the advent of software packages and libraries that offer some or all modes of operation of block ciphers, the violation of this principle is really possible in practice. We show that under the same key, OFB mode of operation is a special case of the CBC mode of operation, and that if CBC and CTR modes of operation are interchangeably used under the same secret key - then the security of the encryption process is seriously weakened. Moreover in the chosen plaintext attack scenario with interchanged use of CBC and OFB mode under the same key, we give a concrete list of openssl commands that can extract the complete plaintext without knowing the secret key