Instant Messaging Security Using Affine Cipher and RSA CRT Algorithm

The rapid growth of instant messaging platforms has exposed critical security vulnerabilities, including data interception, unauthorized access, and privacy breaches. This research develops a secure instant messaging framework using a hybrid cryptographic model that integrates the Affine Cipher for message encryption with RSA enhanced by the Chinese Remainder Theorem (RSA CRT) for secure key exchange. The Affine Cipher operates over ASCII characters 32-126 with a modulus of 95. Experimental validation demonstrates that RSA CRT encrypts Affine keys in an average of 0.003076 seconds and decrypts them in 0.0044 seconds. Message encryption time using Affine Cipher increases linearly with message length, while maintaining efficient performance for typical instant messages. The RSA CRT implementation significantly reduces computational overhead compared to standard RSA through the use of smaller exponents and modular operations. Testing showed minimal variation in execution times, with encryption ranging from 0.00187 to 0.0043 seconds and decryption from 0.003 to 0.007 seconds. Based on the running time analysis and the functionality evaluation, the integrated approach successfully demonstrates that the hybrid cryptographic model achieves optimal balance between robust security measures and practical operational efficiency, making it highly suitable for real-time messaging applications where both security and performance are critical requirements.