Patent ID: 6915423

Claim:
A method of providing a time stamping service for setting a client's system clock, comprising the steps of: a) requesting the time stamping service of a time stamp authority server (TSA) by a service requester based on combination of a time stamping request (TimeStampReq) service message set by a random number and a request message for setting the client's system clock; b) receiving the time stamping service request from said requester by said time stamp authority server (TSA), creating a message authentication code (MAC) based on combination of current time (genTime) information and the time stamping request (TimeStampReq) service message in response to the requesting, creating a response message by inserting a message certificate (Macinfo) structure including the message certificate (Macinfo) into a field of a time stamping response (TimeStampResp) message, and sending the response message; c) receiving the response message sent from said time stamp authority server by said requester, creating a message authentication code (MAC) by extracting the current time (genTime) information and the time stamping request (TimeStampReq) service message, which are included in the response message, and verifying the integrity of the response message by comparing the message authentication code (MAC) with another message authentication code (MAC) additionally included in the response message; d) downloading a certificate revocation list from a directory server by said requester, extracting the current time (genTime) information from the response message transmitted from the time stamp authority server (TSA), and verifying the validity of the certificate revocation list (CRL) by comparing the current time (genTime) information with time information set in the certificate revocation list (CRL); and e) downloading a certificate for an electronic signature of said time stamp authority server from said directory server by said requester, verifying validity of the time stamp response (TimeStampResp) service message, and, if the time stamp response (TimeStampResp) service message is valid, setting the client's system clock using the current time (genTime) information extracted from the response message.