Text Data Security through Double Encryption: Implementation of Unimodular Hill Cipher and Advanced Encryption Standard

Data security is a critical concern in the digital era, requiring robust encryption methods to protect sensitive information. This study presents a hybrid encryption system combining Unimodular Hill Cipher (UHC) and Advanced Encryption Standard (AES), implemented in Python, to enhance security. The encryption process involves two layers: the plaintext is first encrypted using UHC with an unimodular key matrix and then re-encrypted using AES in the Electronic Codebook (ECB) mode. The system’s performance was evaluated through time analysis, entropy measurement, and correlation analysis. Results showed an average encryption time of 10–300 ms, with a corresponding decryption time of 12–301 ms for text files up to 16 KB. The entropy values of ciphertexts reached an average of 7.98, indicating a high level of randomness, while the correlation between plaintext and ciphertext was as low as 0.18, confirming effective data obfuscation. Despite its strengths, the ECB mode’s vulnerability to repetitive data patterns and the challenges in generating truly random UHC keys highlight areas for further improvement. Future research should explore more secure AES modes, such as Cipher Block Chaining (CBC), and enhance key generation methods for UHC. This study demonstrates the potential of hybrid encryption systems to achieve high security and efficiency, making them suitable for safeguarding sensitive text data. The implementation is publicly available for further development and testing.