Recently, by the development of information technology, we can get various information from anywhere in real time. However, personal information is exposed to threats which may incur unwanted information leakage. Cryptography serves as a primary study to prevent this leakage. However, some theories of cryptography are based on complex mathematical theories which make many people confused. Therefore, in this paper, we develope a software which is helpful to understand RSA algorithm, which is widely used algorithm in digital signature to protect personal information.