Journal of Digital Information Management Yunsheng Zhong 11 6 2013 http://dline.info/fpaper/jdim/v11i6/6.pdf With the popularity of the Internet, people can purchase and sell goods and services online just staying at home, and this trend is becoming increasingly apparent. The Internet, as a global computer network, has to provide the following five services: security, data integrity, authentication, usability, and reliable information. In case of lack of safety measures, Internet trading risk is very high. Digital certificates can provide proof of identity in Internet transactions, so that we can greatly reduce transaction risk. This paper describes an approach based on the X.509 standard for digital certificates, using the C language generate public key algorithm RSA, enabling digital certificate generation and signature verification process, the identity of certification users can be verified.