Biblio
In cloud computing application scenarios involving computationally weak clients, the natural need for applied cryptography solutions requires the delegation of the most expensive cryptography algorithms to a computationally stronger cloud server. Group exponentiation is an important operation used in many public-key cryptosystems and, more generally, cryptographic protocols. Solving the problem of delegating group exponentiation in the case of a single, possibly malicious, server, was left open since early papers in the area. Only recently, we have solved this problem for a large class of cyclic groups, including those commonly used in cryptosystems proved secure under the intractability of the discrete logarithm problem. In this paper we solve this problem for an important class of non-cyclic groups, which includes RSA groups when the modulus is the product of two safe primes, a common setting in applications using RSA-based cryptosystems. We show a delegation protocol for fixed-exponent exponentiation in such groups, satisfying natural correctness, security, privacy and efficiency requirements, where security holds with exponentially small probability. In our protocol, with very limited offline computation and server computation, a client can delegate an exponentiation to an exponent of the same length as a group element by only performing two exponentiations to an exponent of much shorter length (i.e., the length of a statistical parameter). We obtain our protocol by a non-trivial adaptation to the RSA group of our previous protocol for cyclic groups.
The keys generated by (symmetric or asymmetric) have been still compromised by attackers. Cryptography algorithms need extra efforts to enhance the security of keys that are transferring between parities. Also, using cryptography algorithms increase time consumption and overhead cost through communication. Encryption is very important issue for protecting information from stealing. Unfortunately encryption can achieve confidentiality not integrity. Covert channel allows two parties to indirectly send information, where the main drawbacks of covert channel are detectability and the security of pre-agreement knowledge. In this paper, i merge between encryption, authentication and convert channel to achieve un-detectability covert channel. This channel guarantee integrity and confidentiality of covert data and sending data dynamically. I propose and implement un-detectability a covert channel using AES (Advanced Encryption Standard) algorithm and HMAC (Hashed Message Authentication Code). Where this channel is un-detectability with integrity and confidentiality agreement process between the sender and the receiver. Instead of sending fake key directly through channel, encryption and HMAC function used to hide fake key. After that investigations techniques for improving un-detectability of channel is proposed.
Educational software systems have an increasingly significant presence in engineering sciences. They aim to improve students' attitudes and knowledge acquisition typically through visual representation and simulation of complex algorithms and mechanisms or hardware systems that are often not available to the educational institutions. This paper presents a novel software system for CryptOgraphic ALgorithm visuAl representation (COALA), which was developed to support a Data Security course at the School of Electrical Engineering, University of Belgrade. The system allows users to follow the execution of several complex algorithms (DES, AES, RSA, and Diffie-Hellman) on real world examples in a step by step detailed view with the possibility of forward and backward navigation. Benefits of the COALA system for students are observed through the increase of the percentage of students who passed the exam and the average grade on the exams during one school year.