One embodiment of the present invention provides a system for sending an encrypted
message through a distribution list exploder in order to forward the encrypted
message to recipients on a distribution list. The system operates by encrypting
the message at a sender using a message key to form an encrypted message. The system
also encrypts the message key with a group public key to form an encrypted message
key. The group public key is associated with a group private key to form a public
key-private key pair associated with a group of valid recipients for the message.
Next, the system sends the encrypted message and the encrypted message key to the
distribution list exploder, and the distribution list exploder forwards the encrypted
message to a plurality of recipients specified in the distribution list. After
receiving the encrypted message and the encrypted message key, the recipient decrypts
the encrypted message key to restore the message key. Next, the recipient decrypts
the encrypted message using the message key to restore the message. In a variation
on the above embodiment, the recipient decrypts the encrypted message key by sending
the encrypted message key from the recipient to a group server, which holds the
group private key. The group server decrypts the encrypted message key using the
group private key to restore the message key, and returns the message key to the
recipient in a secure manner.
