Hybrid Cryptosystem Combination Algorithm of Hill Cipher 3x3 and Elgamal to Secure Instant Messaging for Android

Abstract

Instant messaging is commonly used in communication, which made a high level of security as an essential part. To secure the huge amount of messages, one of the techniques used is hybrid cryptosystem. A Symmetric Hill Cipher 3x3 and ElGamal Asymmetric Algorithm combination will be used to perform the hybrid encryption scheme. Symmetric Hill Cipher with a square 3x3 key matrix for the encryption process and ElGamal Asymmetric for encrypt the key of Hill Cipher. The strength of Asymmetric ElGamal is the difficulty of calculating discrete logs in a large prime modulus. In this research, the running time is directly proportional to the length of text during the encryption and decryption process.