Techniques for Random Masking in Hardware

A new technique for Boolean random masking of the logic and operation in terms of nand logic gates is proposed and applied for masking the integer addition. The new technique can be used for masking arbitrary cryptographic functions and is more efficient than previously known techniques, recently applied to the Advanced Encryption Standard (AES). New techniques for the conversions from Boolean to arithmetic random masking and vice versa are also developed. They are hardware oriented and do not require additional random bits. Unlike the previous, software-oriented techniques showing a substantial difference in the complexity of the two conversions, they have a comparable complexity being about the same as that of one integer addition only. All the techniques proposed are in theory secure against the first-order differential power analysis on the logic gate level. They can be applied in hardware implementations of various cryptographic functions, including AES, (keyed) SHA-1, IDEA, and RC6     

Correlation attacks on up/down and stop/go cascades

A probabilistic analysis is conducted to determine conditional and unconditional correlation weaknesses of cascades of up/down clocked shift registers. Similar results are also obtained for cascades of stop/go clocked shift registers. It is theoretically explained how to use the derived properties for fast correlation attacks, whose objective is to recover the linear feedback shift-register initial states, and the conditions for their success are obtained. The analysis and computations conducted indicate that the attacks are feasible in the practical case of relatively short cascades composed of long shift registers     

Embedding probabilities for the Alternating Step Generator

The edit distance correlation attack on the well- known alternating step generator for stream cipher applications was proposed by Golic and Menicocci. The attack can be successful only if the probability of the zero edit distance, the so-called embedding probability, conditioned on a given segment of the output sequence, decreases with the segment length, and if the decrease is exponential, then the required segment length is linear in the total length of the two linear feedback shift registers involved. The exponential decrease for the maximal value of the embedding probability, regarded as a function of the output segment, was estimated experimentally by Golic and Menicocci. In this paper, by using the connection with the interleaving and decimation operations, the embedding probability is analyzed theoretically. Exponentially small upper bounds on the maximal embedding probability are thus derived. An exact expression for the minimal embedding probability is also determined     

Characterization of lactic acid bacteria isolated from Bukuljac, a homemade goat's milk cheese

The Bukuljac cheese is traditionally homemade cheese, produced from heat-treated goat's milk without the addition of any bacterial starter culture. The presence of lactic acid bacteria (LAB) in Bukuljac cheese has been analyzed by using a polyphasic approach including microbiological and molecular methods such as rep-PCR with (GTG)5 primer. Lactobacillus paracasei subsp. paracasei represents a dominant strain in the microflora of analyzed cheese. Out of 55 Gram-positive and catalase-negative isolates, 48 belonged to L. paracasei subsp. paracasei species. Besides lactobacilli, five Lactococcus lactis subsp. lactis and two Enterococcus faecalis were found. Results of PCR-denaturing gradient gel electrophoresis (DGGE) of DNA extracted directly from the fresh cheese revealed the presence of Leuconostoc mesenteroides. Only lactobacilli showed a high proteolytic activity and hydrolyzed alpha(s1)- and beta-caseins. They are also producers of diacetyl. In addition, 34 out of 55 isolates, all determined as lactobacilli, showed the ability of auto-aggregation. Among 55 isolates, 50 also exhibited antimicrobial activity.     

The transmission of fragmented chromosomes in Drosophila melanogaster

We investigated the fate of dicentric chromosomes in the mitotic divisions of Drosophila melanogaster. We constructed chromosomes that were not required for viability and that carried P elements with inverted repeats of the target sites (FRTs) for the FLP site-specific recombinase. FLP-mediated unequal sister-chromatid exchange between inverted FRTs produced dicentric chromosomes at a high rate. The fate of the dicentric chromosome was evaluated in the mitotic cells of the male germline. We found that dicentric chromosomes break in mitosis, and the broken fragments can be transmitted. Some of these chromosome fragments exhibit dominant semilethality. Nonlethal fragments were broken at many sites along the chromosome, but the semilethal fragments were all broken near the original site of sister-chromatid fusion, and retained P element sequences near their termini. We discuss the implications of the recovery and behavior of broken chromosomes for checkpoints that detect double-strand break damage and the functions of telomeres in Drosophila.     

Potential of lactic acid bacteria isolated from specific natural niches in food production and preservation

Autochthonous strains of lactic acid bacteria (LAB) have been isolated from traditionally homemade cheeses collected from specific ecological localities across Serbia and Montenegro. Genetic and biochemical analysis of this LAB revealed that they produce bacteriocins, proteinases and exopolysaccharides. LAB produces a variety of antimicrobial substances with potential importance for food fermentation and preservation. Apart from the metabolic end products, some strains also secrete antimicrobial substances known as bacteriocins. Among the natural isolates of LAB from homemade cheeses, bacteriocin producers were found in both lactococci and lactobacilli. Lactococcus lactis subsp. lactis BGMN1-5 was found to produce three narrow spectrum class II heat-stable bacteriocins. In addition to bacteriocin production, BGMN1-5 synthesized a cell envelope-associated proteinase (CEP) and shows an aggregation phenotype. Another isolate, L. lactis subsp. lactis BGSM1-19 produces low molecular mass (7 kDa) bacteriocin SM19 that showed antimicrobial activity against Staphylococcus aureus, Micrococcus flavus and partially against Salmonella paratyphi. Production of bacteriocin reaches a plateau after 8 h of BGSM1-19 growth. Bacteriocin SM19 retained activity within the wide pH range from 1 to 12 and after the treatment at 100 degrees C for 15 min. Among collection of lactobacilli, the isolate Lactobacillus paracasei subsp. paracasei BGSJ2-8 produces heat-stable bacteriocin SJ (approx. 5 kDa) polypeptide. It retained activity after treatment for 1 h at 100 degrees C, and in the pH range from 2 to 11. In addition to isolates from cheeses, bacteriocin-producing human oral lactobacilli were detected. Most of them showed antimicrobial activity against streptococci, staphylococci and micrococci, but not against Candida. Isolate BGHO1 that showed the highest antimicrobial activity was determined as L. paracasei. Interestingly, Lactobacillus helveticus BGRA43, which was isolated from the human intestine showed strong activity against Clostridium sporogenes, but it was not possible to detect any bacteriocin production in this isolate by using standard procedures. Further analysis of antimicrobial activity revealed that BGRA43 has a relatively broad spectrum. Lactobacilli resistant to nisin were also detected among natural isolates. They produce bacteriocins, which have no activity against nisin producing lactococci.     

Edit distances and probabilities for correlation attacks onclock-controlled combiners with memory

A theoretical framework for correlation attacks based on edit distances and edit probabilities on binary keystream generators consisting of clock-controlled shift registers combined by a function with memory is introduced. Recursive algorithms for efficient computation of the proposed many-to-one string edit distances and statistically optimal edit probabilities are derived for both constrained and unconstrained irregular clocking. The distances and probabilities are based on mutually correlated linear transforms of input and output sequences in the corresponding regularly clocked combiner with memory. Linear transforms can also incorporate linear models of clock-controlled shift registers. The complexity of the recursive algorithms is exponential in the memory size of the input linear transform which can be considerably smaller than the memory size of combining function. This is demonstrated for a special type of combiners with memory based on a time-varying memoryless function. In addition, a decimation method for reducing the memory size of the input linear transform is proposed. The design criteria with respect to the introduced correlation attacks are also discussed     

A method for convergence analysis of iterative probabilisticdecoding

A novel analytical approach to performance evaluation of soft-decoding algorithms for binary linear block codes based on probabilistic iterative error correction is presented. A convergence condition establishing the critical noise rate below which the expected bit-error probability tends to zero is theoretically derived. It explains the capability of iterative probabilistic decoding of binary linear block codes with sparse parity-check matrices to correct, with probability close to one, error patterns with the number of errors (far) beyond half the code minimum distance. Systematic experiments conducted on truncated simplex codes seem to agree well with the convergence condition. The method may also be interesting for the theoretical analysis of the so-called turbo codes     

Fast reconstruction of clock-control sequence

Two fast techniques for reconstructing the initial state of the clock-control shift register in the shrinking generator, one based on list decoding and the other on information set decoding, are investigated. Both start from computing the a posteriori probabilities for the clock-control bits from a known segment of the output sequence, under the assumption that the initial state of the clock-controlled shift register is already recovered