Patent ID: 7904725
Filing Date: 2011-03-08
Classification: G06Q,H04L

Abstract:
1. A method of verifying an electronic signature associated with and signing an electronic document, the method comprising: receiving the electronic signature, the electronic signature comprising a signature value generated by a signer, a plurality of timestamps, and a certificate chain, wherein the electronic document comprises content data, wherein the signature value comprises an encryption by the signer's private key of a digest of the content data, wherein each timestamp comprises an encryption by a timestamp authority's private key of both a time value and a digest of the signature value, the timestamp therefore including an encrypted time value encrypted by the timestamp authority's private key, and wherein the certificate chain comprises certificates, a certificate comprising an encryption, by a private key of a certificate authority, of identity information corresponding to the signer and of the signer's public key; determining that one or more certificates in the certificate chain are invalid; determining an earliest invalidity time of the one or more invalid certificates; verifying the timestamps associated with the electronic signature, the encrypted time value of each timestamp represents a time when the corresponding timestamp authority verified the electronic signature by: decrypting the digest of the content data using the signer's public key, computing a digest of the content data, and comparing the decrypted digest with the computed digest; accessing the time value of each of the timestamps to identify the earliest valid timestamp; and declaring the electronic signature as valid if the time value of the earliest valid timestamp is earlier than the earliest invalidity time value of the one or more invalid certificates.