A system and methods for proving dates of digital data files, which are accessed,
created, modified, received, or transmitted by a computer includes a trusted time
source in a tamperproof environment, a first subsystem for saving the file at a
moment in time, a second subsystem for retrieving from the trusted time source
a date and a time corresponding to the moment in time, a third subsystem for appending
the date and the time retrieved from the trusted time source to the saved file,
a fourth subsystem for signing the saved file with the date and the time retrieved
from the trusted time source appended thereto, a fifth subsystem for hashing the
signed file to produce a digest, a sixth subsystem for signing the digest with
a key to produce a certificate, a seventh subsystem for appending the certificate
to the saved file, and an eighth subsystem for saving the file with the certificate
appended thereto. The trusted time source is a real time clock, which is not resettable,
is independent of any system clock of the computer, and is installed locally relative
to the computer.
