The current study aims to examine a general overview of the application of hash functions in cryptography and study the relationships between cryptographic hash functions and uses of the digital signature. Functions of the cryptographic hash are an important tool applied in several sections of data security, and application of hash function is common and used for various purposes such as File Integrity Verification, Key Derivation, Time stamping, Password Hashing, Rootkit Detection and Digital Signature. Digital Signature is a code that is linked electronically with the document including the sender's identity. Therefore, the digital signature is of high value in verifying digital messages or documents. Cryptographic hash functions do not present without mathematics. The success of computer science is attributed to mathematics; in other words, it is because of mathematical science, that computer science was understood and could be explained to all. The study aims to teach the reader hash functions and its applications such as digital signature and to show in details some hash functions and their designing.

To estimate the prevalence rate of bovine brucellosis in Khartoum State of Sudan and to compare the different serological tests, 636 stratified random samples of milk from farms and markets in the state were collected. Individual milk and blood samples were also collected from farms which showed positive reaction to the bulk milk ring test. All these samples were tested for Brucella antibodies using the milk ring test (MRT), Rose Bengal plate test (RBPT) and indirect ELISA test on milk and serum. The prevalence of Brucella antibodies was higher in milk compared with serum samples. In Enzyme-linked Immuno Sorbent Assay (ELISA) test using milk samples, it was 34.7%, followed by Milk Ring Test 32.5%, while the prevalence when using the serum was 27% with the Rose Bengal Plate Test and 24.4% when using serum-ELISA. The sensitivity and specificity of MRT were 85 and 95% and for RBPT were 92 and 94%, respectively. There were association between the MRT and milk-ELISA (p < 0.01) and between RBPT and serum-ELISA (p < 0.05). The percentage agreement among MRT and milk-ELISA was 83% Kappa (p < 0.01), while the percentage agreement between RBPT and serum-ELISA was 86% Kappa (p < 0.01). When comparing the sensitivity, specificity and percentage agreement between milk-ELISA and serum-ELISA for the same cows, sensitivity for milk-ELISA was 92.8% and the specificity was 98.8%. The percentage agreement between milk-ELISA and serum-ELISA was 79% Kappa (p < 0.01). Milk-ELISA will provide an easy and significant contribution to detect brucellosis compared to other serological tests.

A cross-sectional Seroprevalence study using Multistage-sampling techniques, was conducted from the period between February 2019 to June 2020 at two livestock export quarantine stations and Livestock markets located in Bossaso, Somalia, to determine the Seroprevalence and associated risk factor of ruminant’s brucellosis. A total of 1068 sera samples were screened for Brucella antibodies using the Rose Bengal plate test, all-positive Serum samples and 80% negative samples with RBPT from sheep and goats and 50% negative sample from cattle were further tested using iELISA. The overall Seroprevalence rate of brucellosis in the current study was 1% and 1.84% using RBPT and i-ELISA respectively in Goats while 9.5% and 9% were positive in cattle using RBPT and i-ELISA respectively but there were no positive samples for sheep by both test of (RBPT) and (i-ELISA). The most significant Associated risk factors were species, castration and other risk factors such as age and Sex can affect status of brucellosis but their contribution are statistically insignificant.

This study was carried to assess the risk associate with E. coli in marine fish in Port Sudan, Red Sea State, Sudan, through the production chain covering five stages. The stages were fish market, fish scaling, restaurant before cooking, and restaurant after cooking, and cooking and cooling for 24 h. A total of 50 fish samples were randomly selected from marine fish chain, in Port Sudan, Red Sea State, during the period from September to December 2018 to estimate the E. coli count using the TBX medium. In this study, the mean count of E. coli in the five stages of the fish chain was 257 +0.6 cfu. In fish market the mean was 247 +0.6 cfu, 758 +0.6 cfu in fish scaling stage, 283+0.6 cfu in restaurants before cooking, and 0.0 cfu after cooking and cooling for 24 hours after cooking. The chi-square test showed significant association between the load of E. coli among the fish chain and the most important potential risk factors (p-value ≤ 0.05), such as boxes cleaning (p-value= 0.000), hygienic practices (p-value= 0.002), waste disposal (p-value= 0.001), personal hygiene (p-value= 0.001), storage (p-value= 0.000) and general cleaning (p-value 0.002). The results of the frequencies of risk factors and their distribution in fish chain showed that 38% do not clean the boxes, 64% do not practice proper hygiene measures, 72% perform improper waste disposal, 72% had poor personal hygiene, 42% do not apply proper storage system, and 46% perform improper cleaning. All that will lead to medium overall risk estimation. Qualitative risk assessment for the E. coli in fish chain pathway was found to be high in the fish market and the exposure assessment in restaurant was found to be very low, so that the overall risk estimation for contamination with E. coli among the fish chain in Port Sudan was found to be Medium (The risky event is likely to occur more than once in the next three years).