Radio frequency certificates of authenticity (RFCOAs) are presented. In one implementation, a scattering agent is attached to an object to provide a reproducible radio frequency (RF) fingerprint that can be used to authenticate a tag or a seal for the object. In one implementation, the RF fingerprint is measured and digitized, combined with information associated with the object to which the RFCOA is attached, and stored in a radio frequency identification (RFID) system associated with the RFCOA. A scanner receives the fingerprint and the information and authenticates the information by comparing the fingerprint against a new fingerprint obtained from the object.