Patent ID: 6851049

Claim:
A method for facilitating secure transmission of an email message to anonymous recipients without divulging the identities of the anonymous recipients, comprising: identifying recipients of the email message, wherein the recipients can include known recipients, who can be identified by examining the email message, and anonymous recipients, who cannot be identified by examining the email message; generating a session key for the email message; encrypting a body of the email message with the session key; creating a recipient block for the email message that contains an entry for each recipient of the email message; wherein each entry in the recipient block contains the session key encrypted with a public key associated with the recipient to form an encrypted session key, so that only a corresponding private key held by the recipient can be used to decrypt the encrypted session key; wherein each entry additionally contains an identifier for the associated public key, but different than the associated public key, so that each recipient can determine whether the recipient possesses the corresponding private key that can decrypt the encrypted session key; wherein identifiers for public keys belonging to known recipients are statistically unique; wherein identifiers for public keys belonging to anonymous recipients are not statistically unique; and sending the email message to the recipients.