Modifikasi Ciphertext Base64 pada Algoritma Vigenere Cipher untuk Keamanan Teks Berbasis Plat Nomor Kendaraan Indonesia

Abstract

Cryptography is a technique used to maintain data confidentiality. One of the most widely used classical cryptographic algorithms is the Vigenere Cipher, which overcomes the weaknesses of the Caesar Cipher but still has security vulnerabilities against brute-force attacks and Kasiski analysis. To improve security and produce ciphertext that is easier to recognize, this study modifies the Vigenere Cipher ciphertext to produce output in the form of Indonesian vehicle license plates. The modification process is carried out by encrypting the plaintext using the Vigenere Cipher, then converting the encrypted ciphertext into a license plate format consisting of a region code, registration number, and serial code. In addition, modifications were also applied to the algorithm key. While the standard Vigenere Cipher uses the same key for encryption and decryption, this study uses two different keys, namely the encryption key and the decryption key generated from the encryption process. The test results show that the modified ciphertext has a greater length than the ciphertext before modification because it undergoes remapping in the form of a license plate. Security testing using TPK showed a significant decrease in value, from a range of 0.33–0.36 before modification to 0.07–0.17 after modification. This decrease indicates that the relationship between plaintext and ciphertext is lower, so that ciphertext modification based on Indonesian vehicle license plates can improve encryption security compared to the Vigenere Cipher before modification.