Hybrid Cryptosystem Algoritma Twofish dan Multi-Power RSA pada Pesan Email

Abstract

Email is a critical communication medium that is vulnerable to privacy and security data breaches. Sensitive information exchange requires a more secure communication medium than conventional email service providers, with additional security layers to prevent data leakage. This research develops a hybrid cryptographic system that combines Twofish symmetric encryption for message content and Multi-Power RSA asymmetric encryption for key management to strengthen email communication security. The research methodology integrates client-side cryptographic processing through C-to-WebAssembly conversion within a React and FastAPI web application framework, utilizing OAuth 2.0 authentication and Gmail API integration. Performance testing reveals that pure cryptographic operations (Twofish encryption: 50-100 ms, Multi-Power RSA key encryption: 1-13 ms) contribute only 6-12% of total processing time, while API communication overhead reaches 80-95%. Message encryption demonstrates linear complexity Θ(n) with Twofish processing 1 KB in 50 ms scaling to 40 KB in 100 ms, while Multi-Power RSA key operations exhibit Θ(n²) complexity scaling from 1 ms to 13 ms for the same data range. The decryption process achieves 30-37 ms for messages up to 40 KB with automatic key rotation support through historical keypair management. The hybrid cryptographic system successfully provides end-to-end encryption for email messages up to 8,000 words (~40 KB) with complete message integrity preservation, demonstrating effective balance between security enhancement and computational efficiency through the synergy of symmetric and asymmetric cryptographic algorithms.