Internet X.509 PKI - Time Stamp Protocols
- The PKIX document describes a Time Stamp Authority (TSA) and a Temporal Data Authority (TDA), and the protocols to be used to communicate with them.
- http://www.ietf.org/internet-drafts/draft-ietf-pkix-time-stamp-15.txt

Trusted third-party time authority
- DigiStamp provides digital time stamps for e-commerce and intellectual property witnessing.
- http://www.digistamp.com