Patent ID: 7444516

Claim:
A method of producing certifications of digital files, the method comprising: from time-to-time, while a tamper-resistant certification device is in an on-line mode, receiving a certified time stamp at the tamper-resistant certification device from a remote source remotely located with respect to the tamper-resistant certification device, wherein the tamper-resistant certification receives at a time of receipt a last certified time stamp; in response to receiving the certified time stamp, providing a time stamp receipt to the remote source from the tamper-resistant certification device; and from time-to-time, while the tamper-resistant certification device is in an off-line mode, receiving a digital file for certification at the tamper-resistant certification device, the digital file from a local source locally located with respect to the tamper-resistant certification device; determining a temporal offset from the time of receipt of the last certified time stamp received at the tamper-resistant certification device; and producing a certified digital file at the tamper-resistant certification device, the certified digital file comprising the contents of the digital file, the stamp receipt, and an indication of the determined temporal offset from the time of receipt of the last certified time stamp.