<![CDATA[The rapid growth of digital technology has raised concerns about the security of textual data transmitted and stored electronically. Classical cryptography offers various approaches to address these concerns, including the Hill Cipher, which utilizes linear algebra principles for encryption. This study enhances the Hill Cipher by incorporating a permutation method and applying it to 97 selected ASCII characters, excluding the space character to ensure consistency. The system employs key matrices of sizes 3×3, 4×4, and 5×5, and the performance is evaluated through ciphertext entropy analysis. Experimental results demonstrate that the proposed method produces ciphertext distributions approaching uniformity, with entropy values close to the ideal level the proposed scheme yields ciphertext distributions close to uniform; representative entropy reaches ≈6.55 bits versus the ideal log₂(97) ≈ 6.60 bits, indicating limited leakage to frequency analysis. This uniformity reduces vulnerability to frequency analysis and improves overall message confidentiality. While larger key matrices increase computational complexity, they also contribute to greater encryption strength by producing more complex ciphertext. These findings highlight the effectiveness of combining Hill and Permutation Ciphers to strengthen the security of text data in digital communication.]]>
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