We have developed a prototype electronic notary system (CYNOS : CYber NOtary System). CYNOS proves facts by providing the evidence (notary token) of events and/or actions that could be used to solve disputes between entities. It is a signature- based system and uses various security techniques to enable the timely certification of entities and fair and highly reliable delivery. It also cooperates with our CA (CANP : Certification Authority for secure Network Platform) through the network. This paper describes CYNOS with regard to its service, functions, and mechanism. The ability of CYNOS to support the nonrepudiation service and some issues on system management are discussed. The additional requirements that are needed if the certification mechanism is to realize practical notarization functions are addressed.