A secure content distribution system is prototyped based on run-time partial reconfigurability of an FPGA. The system provides a robust content protection scheme for online content download services. The key idea is to divide the security module in a user terminal into Content-Specific Circuit (CSC) and Terminal Build-in Circuit (TBC) and to dynamically reconfigure CSC. CSC is customized for each content and transferred from a server in the form of encrypted configuration data. TBC is a uniquely identifiable processing unit that is combined with particular CSC to decrypt and decode contents. A content is properly decrypted and played by the security module only if its CSC is interlocked with the authorized TBC. To realize this CSC-TBC interlock authentication mechanism, partial reconfigurability of the FPGA is essential. This paper discusses the robustness and feasibility of the content distribution system through a proof-ofconcept demonstration.