How can I tell when a message was originated?
I can attach a ``digital time-stamp'' to my message. First, I would have my computer calculate my digital signature and attach it to the original message. Next, I would have it calculate a message digest of the message plus the signature. Next, I would send the message digest (presumably over the Internet) to an external, trusted digital time-stamping service (DTS). (Bellcore has created a subsidiary to provide such a service.) The DTS would return a digital time-stamp consisting of:
The ``message'' that the DTS signs would be the combination of my
message digest (the digital fingerprint of my original message) and the
time-stamp. When my computer received the time-stamp from DTS it would
attach it to my message, add my digital signature and send you the
When you received my message, your computer would verify the time-stamp using the public key of the DTS, and it would verify my signature using my public key.