3,871 research outputs found
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 and 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
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