As the e-Commerce based on the XML technology is getting bigger, user authentication, integrity, non-repudiation and confidentiality has become important for security. Since the XML technology is widely used for exchanging information among the Internet e-business systems, the security of XML documents is essentially required and XML digital signature should be supported. To support the digital signature of XML documents, W3C proposed the XML-Signature specification as an international standard that describes five transform algorithms. In this paper, we design and implement a XML/PKI based digital tax invoice system. Our system supports the five transforming algorithms defined in the XML-Signature specification and exchanges digital tax invoices among enterprises securely. We design and implement the flexible and efficient system consists of reusable components using CBD(Component Based Development).