Abstract-This study is mainly about the discrete logarithm problem in the ElGamal cryptosystem over the abelian group U(n) where n is one of the following forms p

We consider the Markoff–Rosenberger equation $$\begin{aligned} ax^2+by^2+cz^2=dxyz \end{aligned}$$ a x 2 + b y 2 + c z 2 = d x y z with $$(x,y,z)=(U_i,U_j,U_k)$$ ( x , y , z ) = ( U i , U j , U k ) , where $$U_i$$ U i denotes the i-th generalized Lucas number of first/second kind. We provide an upper bound for the minimum of the indices and we apply the result to completely resolve concrete equations, e.g. we determine solutions containing only balancing numbers and Jacobsthal numbers, respectively.

Cryptography is the science of using mathematics that's used to hide information or data that is being sent between participants in a way that prevents other people from reading it. The need of exchanging messages secretly promoted the creation of cryptosystems to enable receivers to interpret the exchanged information. In this study, a particular public key cryptosystem called Rabin Cryptosystem is presented considered with the help of Chinese Reminder Theorem. Since the decryption algorithm of the Rabin cryptosystem is based on computing square roots modulo n, where n = p.q where p and q are primes. This study suggests a modification of Rabin cryptosystem that can make the cryptosystem more immune against some attacks. This modification focuses on considering n = p.q.r where p, q and r are primes. This new modification of Rabin cryptosystem is called H-Rabin Cryptosystem. Also, some basic mathematical concepts are explained and it finally compares the H-Rabin Cryptosystem, RSA cryptosystem and Rabin cryptosystem in terms of security and efficiency. This H-Rabin cryptosystem is a public key cryptosystem where the private key is composed of three primes, p, q and r and a public key composed of n = p.q.r and it is based on the hardness of factoring. Therefore, this new modification can make the cryptosystem more immune against some future attacks.

In this paper, we find all the solutions (X, Y, Z) = (FI, FJ, FK), where FI, FJ, and FK represent nonzero Fibonacci numbers, satisfying a generalization of Markoff equation called the Jin-Schmidt equation: AX2 + BY2 + CZ2 = DXYZ + 1.

ITRU cryptosystem is a public key cryptosystem and one of the known variants of NTRU cryptosystem. Instead of working in a truncated polynomial ring, ITRU cryptosystem is based on the ring of integers. The authors claimed that ITRU has better features comparing to the classical NTRU, such as having a simple parameter selection algorithm, invertibility, and successful message decryption, and better security. In this paper, we present an attack technique against the ITRU cryptosystem, and it is mainly based on a simple frequency analysis on the letters of ciphertexts.