What is an X.509 certificate?

At eNotaryLog, when we notarize your document, we apply a seal using an X.509 digital certificate which is unique to each notary. An X.509 certificate is a standard defining the format of public-key certificates. When your document is sealed with an X.509 certificate we are ensuring that it is tamper-evident and any modification(s) after our notarization will be evident.

Further information on X.509 can be found on Wikipedia.