Abstract: Improved computer-implemented methods for evidencing the existence of a digital document, anonymously evidencing the existence of a digital document, database management for systems for evidencing the existence of a digital document, and verifying the data integrity of a digital document provide increased reliability, security and enhance trust from users and third parties.

Abstract: A computer-implemented method for evidencing the existence of a digital document has the steps of obtaining one or a plurality of time stamp(s) of the digital document, obtaining one or a plurality of cryptographic hash(es) of the digital document, generating one or a plurality of evidence key(s) based on the time stamp(s) and the cryptographic hash(es), and storing the evidence key(s) to provide one or a plurality of stored evidence key(s). A computer system for evidencing the existence of a digital document is also provided. A computer-implemented tag chain system is also described.