Secure token-based document server

A secure document server for operating on a network and receiving from a holder of a document token a request for a copy of a document identified by the document token, the document token including issuer content and a signature from an issuer and holder content and a signature from the holder, said secure document server comprising:

• means for locating in the issuer content a document identifier, a hint to a public key of the issuer, and a public key of the holder;
• the document identifier specifying where the document is stored on the network;
• means for identifying, in a key list on the secure document server, the public key of the issuer using the hint to the public key of the issuer;
• means for authenticating the issuer content of the document identifier with the public key of the issuer;
• means for locating in the holder content of the document a time stamp;
• the time stamp identifying when the holder of the document token requested the copy of the document;
• means for authenticating the holder content of the document identifier with the public key of the holder;
• means for authenticating the time stamp by verifying that the time stamp is within a predetermined window of time;
• and
• means for issuing, to the holder of the document identifier, a copy of the document identified by the document identifier when the issuer content and the holder content are positively authenticated by said authenticating means;
• said issuing means providing secure access to the document without prior knowledge of the public key of the holder.

A secure document mail system operating on a network, comprising:

• a sender mail client for sending an email message with a document attachment;
• the sender mail client including an encoder for substituting in the email message a document token for the document attachment;
• a recipient mail client for receiving the email message and the document token from a mail server;
• the recipient mail client including a decoder;
• a secure document server for receiving from the recipient mail client a request for a copy of a document identified by the document token in the email message;
• the document token including issuer content and a signature generated by the encoder of the sender mail client, and holder content and a signature generated by the decoder of the recipient mail client;
• wherein the secure document server further comprises:
• means for locating in the issuer content a document identifier, a hint to a public key of the issuer, and a public key of the holder;
• the document identifier specifying where the document is stored on the network;
• means for identifying, in a key list on the secure document server, the public key of the issuer using the hint to the public key of the issuer;
• means for authenticating the issuer content of the document identifier with the public key of the issuer;
• means for locating in the holder content of the document a time stamp;
• the time stamp identifying when the holder of the document token requested the copy of the document;
• means for authenticating the holder content of the document identifier with the public key of the holder;
• means for authenticating the time stamp by verifying that the time stamp is within a predetermined window of time;
• and
• means for issuing, to the recipient mail client, a copy of the document attachment identified by the document identifier when the issuer content and the holder content are positively authenticated by said authenticating means;
• said issuing means providing secure access to the document attachment without prior knowledge of the public key of the holder.