A personal computer (PC) system and methods for proving dates of digital data
files,
which are accessed, created, modified, received, or transmitted by the PC 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
means 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 PC, and is installed
locally relative to the PC.
