Secure bulk messaging mechanism in which, roughly described, a sender first
encrypts a message once. The message can be decrypted with a message decryption
key. These can be symmetric or asymmetric keys. For each recipient, the sender
then encrypts the message decryption key with the recipient's public key. The sender
then sends the encrypted message and the encrypted message decryption keys to a
store-and-forward server. Subsequently, one or more recipients connect to the server
and retrieve the encrypted message and the message encryption key that has been
encrypted with the recipient's public key. Alternatively, the server can forward
these items to each individual recipient. The recipient then decrypts the encrypted
message decryption key with the recipient's private key, resulting in an un-encrypted
message decryption key. The recipient then decrypts the message using the un-encrypted
message decryption key.
