This work focused on securing data transfer in an unsecured network between the client and the sever. Here, Computer Aided Software Engineering (CASE) and Object-Oriented Software Engineering (OOSE) methodological approaches were used in the design and development of the digital signature with RSA algorithm system. Java programming and Hypertext Preprocessor scripting languages were used in the development of the algorithms, while Hypertext Markup Language was used in the system deployment in NetBeans integrated development environment. The system modelling exploits the Entity-Relationship (E-R) model in establishing the objects relationships. MySQL and SQLite were deployed in creation of the database connection and objects through programming for easy querying of the database. Encryption and decryption test was carried out to verify the functionality of the proposed model using public and private keys. Result showed that the developed model successfully encrypted and decrypted credit card details sent across the network without error.