MODIFICATION OF THE CAESAR CIPHER USING PRIME NUMBERS TO ENHANCE SECURITY IN CRYPTOGRAPHY

Abstract

The Caesar Cipher is a classical cryptographic algorithm that applies a static character shift, resulting in a limited key space and vulnerability to brute-force and frequency analysis attacks; this limitation highlights a research gap in developing a simple yet more secure and efficient modification of the algorithm. This study aims to enhance the security of the Caesar Cipher by introducing a prime number based dynamic key mechanism, in which each plaintext character is encrypted using the i-th prime number according to its position, thereby increasing ciphertext variability and reducing repetitive patterns. The proposed method is evaluated using texts of varying lengths to examine encryption and decryption consistency, key space expansion, character diffusion, and computational efficiency. The security analysis focuses on resistance to brute-force and statistical frequency analysis attacks, while performance evaluation considers processing time and theoretical algorithmic complexity. The experimental results demonstrate that employing prime numbers as dynamic keys significantly enlarges the key space and improves resistance to classical cryptanalysis without introducing substantial computational overhead. Therefore, the proposed approach provides a more effective and secure solution compared to the conventional