Patent ID: 7266698

Claim:
A time stamp verification method comprising: hashing, at a client terminal, a portion of a document that is to be protected by a time stamp so as to create a first hash value; communicating the first hash value to a time stamp server; encrypting, at the time stamp server, the received first hash value, a time value, and the time stamp server's identification using two different keys to generate first and second signatures; communicating the first and second signatures, the time value, and the time stamp server's identification to the client terminal; combining the received first and second signatures, time value, and time stamp server's identification with the first hash value generated by the client terminal to create a time stamp and storing the time stamp with the document; and verifying the time stamp stored with the document by: hashing the portion of the document that is protected by the time stamp to create a second hash value, comparing the second hash value to the first hash value stored within the time stamp to produce a first comparison result; decrypting the first signature within the time stamp to regenerate the first hash value, time value, and time stamp server's identification, comparing the regenerated first hash value, time value, and time stamp server's identification to the first hash value, time value, and time stamp server's identification stored within the time stamp to generate a second comparison result, and producing an indication that the time stamp for the document is authentic if the first and second comparison results both indicate matches.