Expending Technique Cryptography for Plaintext Messages by Modifying Playfair Cipher Algorithm with Matrix 5 x 19

Abstract

Cryptography or message hiding techniques can be a solution to avoid cybercrime. One of the techniques is Playfair Cipher that is a cryptographic algorithm. It can hide messages by forming a message key in the form of a 5x5 square-shaped key matrix to accommodate 25 capital letter characters by removing the letter and replacing it with the letter I and making plaintext messages into letter pairs (bigram) to do the encryption process with some rules and provisions in this algorithm. So that a ciphertext is formed which has the same character length as the plaintext. The Playfair Cipher algorithm mechanism is the weakness of Playfair Cipher, which is the limitation in accommodating characters. Eliminate the letter J that causes ambiguity and the length of the plaintext character and the same ciphertext so that it is easy to solve with the frequency of occurrence of the bigram. Modifying Playfair cipher algorithm by extending into 5x19 key matrix with ninety-five characters to hold any types of characters (capital letters, small, numbers, symbols) solving the ambiguity. The expansion techniques will form different ciphertext results with its plaintext to overcome the weakness of Playfair cipher. The aim of this research was to produce a Playfair cipher modification algorithm that could cover the weakness of Playfair cipher and result in differences in character length on plaintext and ciphertext implementation results from Playfair cipher modification.