ePortfolios and the learning artifacts they contain must be portable and accessible for the purpose of supporting life-long learning experiences. In this paper, we identify that ePortfolios must also maintain the credibility of the learning artifacts, especially assessment artifacts that are used as evidence by the learner for demonstrating a particular competency. These assessment artifacts are vulnerable to modification or alteration during transfer between distributed ePortfolio systems. As a result, we propose the use of certified assessment artifacts to detect these vulnerabilities. We also present a distributed architecture for a virtual learning environment that incorporates the sharing of certified assessment artifacts between a learning management system, and an ePortfolio system called dotFOLIO that we are currently developing.