Three-Pass Protocol Scheme for Securing Image Files Using the Hill Cipher 3x3 Algorithm

There will be a fatal risk when the submitted file is stolen or altered by someone else during the file submission process. To maintain the security of sending files from sender to recipient, it is necessary to secure files. The science of maintaining the security of messages is called cryptography. The authors were interested in examining the Three Pass Protocol scheme in this study because it eliminated the necessity for sender and receiver to exchange keys during the operation of the Hill Cipher 3x3 algorithm. The Hill Cipher algorithm was chosen because the key has an inverse and matrix-shaped value. Then the key used must be checked whether it has a GCD (Greatest Common Divisor) grade 1 or not and will be shaped like matrix. System implementation using the Java programming language using Android Studio software. System testing is done by encrypting and decrypting files. System testing results illustrate that the process encryption and decryption by the sender is faster than the recipient, so the encryption and decryption time needed directly proportional; the larger the pixel size of the image on the image file used, the longer it takes.