Preimage Attack on MD4 Hash Function as a Problem of Parallel Sat-Based Cryptanalysis

In this paper we study the inversion problem of MD4 cryptographic hash function developed by R. Rivest in 1990. By MD4-k we denote a truncated variant of MD4 hash function in which k represents a number of steps used to calculate a hash value (the full version of MD4 function corresponds to MD4-48). H. Dobbertin has showed that MD4-32 hash function is not one-way, namely, it can be inverted for the given image of a random input. He suggested to add special conditions to the equations that describe the computation of concrete steps (chaining variables) of the considered hash function. These additional conditions allowed to solve the inversion problem of MD4-32 within a reasonable time by solving corresponding system of equations. The main result of the present paper is an automatic derivation of “Dobbertin’s conditions” using parallel SAT solving algorithms. We also managed to solve several inversion problems of functions of the kind MD4-k (for k from 31 up to 39 inclusive). Our method significantly outperforms previously existing approaches to solving these problems

Impact on the Higgs Production Cross Section and Decay Branching Fractions of Heavy Quarks and Leptons in a Fourth Generation Model

In a fourth generation model with heavy quarks, the production cross section of the Higgs boson in the gluon-gluon fusion process is significantly increased due to additional quark loops. In a similar way, the partial decay width of the decay channels $H\rightarrow gg, \gamma \gamma$ and $\gamma Z$ is modified. These changes and their impact on the Higgs search are discussed.Comment: 9 pages, 6 figures, minor changes with a few more references adde

OPUCEM: A Library with Error Checking Mechanism for Computing Oblique Parameters

After a brief review of the electroweak radiative corrections to gauge-boson self-energies, otherwise known as the direct and oblique corrections, a tool for calculation of the oblique parameters is presented. This tool, named OPUCEM, brings together formulas from multiple physics models and provides an error-checking machinery to improve reliability of numerical results. It also sets a novel example for an "open-formula" concept, which is an attempt to improve the reliability and reproducibility of computations in scientific publications by encouraging the authors to open-source their numerical calculation programs. Finally, we demonstrate the use of OPUCEM in two detailed case studies related to the fourth Standard Model family. The first is a generic fourth family study to find relations between the parameters compatible with the EW precision data and the second is the particular study of the Flavor Democracy predictions for both Dirac and Majorana-type neutrinos.Comment: 10 pages, 19 figures, section 3 and 4 reviewed, results unchanged, typo correction

S_3 Flavor Symmetry and Leptogenesis

We consider leptogenesis in a minimal S_3 extension of the standard model with an additional Z_2 symmetry in the leptonic sector. It is found that the CP phase appearing in the neutrino mixing is the same as that for the CP asymmetries responsible for leptogenesis. Because of the discrete S_3 x Z_2 flavor symmetries, the CP asymmetries are strongly suppressed. We therefore assume that the resonant enhancement of the CP asymmetries takes place to obtain a realistic size of baryon number asymmetry in theuniverse. Three degenerate right-handed neutrino masses of O(10) TeV are theoretically expected in this model.Comment: 25 pages, 3 figure