Linear equation for text cryptography using letters' coordinates

Thamir A. Jarjis (University of Mosul)
Yahya Q. I. Al-Fadhili (University of Mosul)

Indonesian Journal of Electrical Engineering and Computer Science
Vol 24, No 1: October 2021

The linear encryption such as Caesar, mono-alphabetic are used to solve the encryption problem in different fields. This module usually encrypts any letter to exact and one corresponding letter. With advanced technologies in computers, these algorithms seem not to be high level secure. This paper proposed a secure encryption algorithm using modified linear encryption by considering the letters’ positions of the plaintext body. Two advantages the proposed algorithm has against traditional ones. First, the cryptography procedures are simple and secure. Secondly, it has higher security because of the non- ingrained nature of poly-alphabetic for substitution. Consequently, the plaintext body is considered as a 2-D matrix, such that, each letter has two coordinates, the ith and jth. These procedures depend on substituting the coordinates of the letter into a linear equation to provide a different substitution letter. The performance of these procedures showed better and robust results by applying the frequency analysis test for this proposed algorithm evaluating.