What is patented about the ProofMark technology?

The ProofMark technology is protected under US Patent #6,381,696. The patent describes a system whereby irrefutable public key digital signature time-stamps are created and used. It is based upon the concept of transient time-interval-related secret cryptographic keys, which are used to digitally sign submitted data during specific time intervals, and then are permanently destroyed. The public-key correlate for each time interval is saved for future authentication of the content and time of creation of time-stamped data. The validity of the public keys is ensured through the certification of each time interval's public key using the previous time interval's secret key, immediately before that secret key is destroyed.