Abstract: A method for proving the validity of a digital document digitally signed using a digital key that corresponds to a digital certificate in a chain of digital certificates issued by certification authorities within a hierarchy of certification authorities. At least one secure digital time stamp is applied to at least one record comprising the digital document, the digital signature, certificate chain data, and information relating to the revocation of certificates by certification authorities within the certificate chain. If, at some later time, one or more digital certificates either expire or are revoked, the timestamp serves as evidence of the integrity of the signed digital document.

Abstract: A method for proving the validity of a record digitally signed by a user having a digital certificate issued by a certification authority within a hierarchy of certification authorities. The user signs the record, and obtains the digital certificates and certificate revocation information for all the certification authorities in the chain of the hierarchy extending from the user to the root certification authority. A timestamp is applied to the record, the digital certificates and the certificate revocation information to establish a point in time in which all items were created, current and valid. If, at some later point, one or more of the digital certificates either expire or are revoked, the timestamp serves as evidence of the integrity of the signed record.

Abstract: A method and system for electronic messaging in which a sender of an electronic message receives a return receipt, without having to send the message contents to a third party. The sender contacts a server to obtain an encryption key to encrypt the message. The server returns an encryption key along with key retrieval information to the sender. The key retrieval information can be used to obtain from the server the decryption key corresponding to the returned encryption key. The sender encrypts the message using the encryption key and sends the message, along with the key retrieval information, to the recipient. The recipient sends the key retrieval information to the server to retrieve the corresponding decryption key. The recipient then decrypts the encrypted message received from the sender using the decryption key. When the recipient sends a request to obtain the decryption key, the server notifies the sender when the key has been successfully retrieved.