Secure messaging system with derived keys

A method for a sender at an organization to send a message to a recipient, wherein the organization has a gateway, a key generator, a server, and an intranet to which the sender, gateway, key generator, and server are connected and wherein the recipient is outside of the organization, wherein the recipient is a customer of the organization, and wherein the recipient has a recipient identity (ID), the method comprising:

• using the key generator to derive a symmetric key for encrypting the message from a master key using a hash message authentication code (HMAC) function whose inputs include the master key and the recipient ID;
• providing the derived symmetric key from the key generator to the gateway over the intranet;
• encrypting the message at the gateway using the derived symmetric key to produce an encrypted message;
• providing the encrypted message from the gateway to the recipient outside of the organization over the Internet;
• at the recipient, receiving the encrypted message;
• authenticating the recipient to the server and establishing a secure sockets layer (SSL) link between the server and the recipient;
• providing a derived symmetric key request to the server from the recipient, wherein the derived symmetric key request includes the recipient ID;
• using the server to obtain the derived symmetric key from the key generator over the intranet using the recipient ID and to provide the derived symmetric key obtained from the key generator to the recipient over the SSL link;
• and
• at the recipient, using the derived symmetric key provided by the server over the SSL link to decrypt the encrypted message.