Sharif Digital Repository

In this thesis, first we will have a brief review on hash functions and related concepts.Then, we will descibe the hash function, Cubehash, which is one of the competitors in the competition held by NIST for selecting SHA-3 standard. Next, we will describe an attack based on linearization of differential paths in hash functions and apply this attack on Cubehash. At the end, we will discuss the results of this attack on Cubehash  

The crypto-processors are used for encryption and decryption of the sensitive and important information. A crypto-processor converts input plaintext to ciphertext by an input key using a particular cryptographic algorithm. It also converts ciphertext to plaintext by the same or another key. Cryptographic standards are divided in two types: symmetric key algorithms (private key) and asymmetric key algorithms (public key). Current processors generally support only one or a few number of cryptographic algorithms. The motivation of this project is design and implementation of a multi-standard crypto-processor which supports the most of symmetric and asymmetric cryptographic algorithms, such as... 

Collision attack is one of the usual attacks in cryptanalysis of hash functions. One method for applying this attack is linear approximation of equivalent compress function. Finding collisions for linearized compress function, having low Hamming weight, with a large probability could provide collisions for the main compress function. For this purpose, the problem of finding collision for used compress function is modeled by that of the linearized one, having low Hamming weight differences with a large probability. The problem of finding collisions with low Hamming weight differences is equivalent to the problem of finding codewords with low Hamming weights in linear binary code. Canteaut and... 

Correlation-intractability is a random-oracle-like property of hash functions, so one can expect that constructions that are secure in random-oracle-model, remain secure when implemented using a correlation-intractable hash function. This is true about Fiat-Shamir transform which is a method for eliminating interaction from public-coin interactive proofs. One can see that when this method is applied to a public-coin three-round honest-verifier zero-knowledge proof, using a correlation-intractable hash function that also satisfies some mild assumption, the result is a NIZK argument. This is the basis for the correlation-intractability framework for NIZK which recently has been used to... 

A hash function maps efficiently every finite length string to a fixed one. The output represents the entire content of the input, similar to digital fingerprint of input text. In order to be able to use a hash function in cryptography, it should be hard to find two distinct inputs with the same output (collision), because finding a collision in hash functions leads to malicious attacks on many security systems.We say a hash function is provably collision resistant, if finding a collision can be reduced to the known hard problems. Family of MD hash functions are one of the most famous applied hash functions which are considerably used in industrial applications. However, they are not... 

Nowadays, intelligent transportation systems have become possible and practical with the help of vehicular ad-hoc networks. This network is a subset of mobile ad-hoc networks introduced and studied separately due to its unique properties. With the help of vehicular ad-hoc networks, the level of road and drivers safety is increased and safety messages can be sent to road side units or other vehicles, so real-time is one of the main requirements of these networks. Other advantages of implementing such networks include providing entertainment and internet access services.On the other hand, these networks face various challenges, including routing data packets, preserving security requirements,... 

With the advent of the Internet of Things (IoT), e-health has become one of the main topics of research. Due to the sensitivity of patient information, patient privacy seems challenging. Nowadays, patient data is usually stored in the cloud in healthcare programs, making it difficult for users to have enough control over their data. The recent increment in announced cases of security and surveillance breaches compromising patients' privacy call into question the conventional model, in which third-parties gather and control immense amounts of patients' Healthcare data. In this work, we try to resolve the issues mentioned above by using blockchain technology. We propose a blockchain-based...