Utility Software Design to Comprehend The Cryptography Cast-128 Method

Abstract

At present, data security techniques known as cryptography are influential and widely used. There are lots of cryptographic algorithms. The main problem faced by a student taking this course is they difficult to understand the procedures of a cryptographic algorithm due to its complexity and involves many calculations. CAST is a block ciphers belonging to the family of DES (Data Encryption System) that uses substitutions and permutations (known as Substitution Permutation Network or SPN) in key calculations and encryption and decryption processes. The CAST algorithm has two versions, namely CAST-128 and CAST-256 where both are distinguished by the length of the used key. The maximum Key length allowed in CAST is 128 bits or 16 characters. In addition CAST-128 allows key sizes to vary from 40 bits to 128 bits with the addition of 8-bits. While the length of plain text that can be encrypted and decrypted is 64 bits (8 characters) and supports all types of plain text. This study describes the procedures of CAST-128, the design of encryption procedures from CAST-128, calculations from the Key Schedule using Substitution Boxes (S-Boxes), how the CAST-128 encryption and decryption algorithms work, the results of the implementation of the CAST-128 algorithm created a program that also functions as a learning program to understand the CAST- 128 algorithm with the process of key formation, CAST-128 algorithm encryption and decryption.