Remailer Introduction ===================== There are several anonymous remailer services running on the Internet. These are programs that accept mail, strip off information that would identify the origin of the message, and forward the mail to the designated recipient. This simple scheme alone, however, is insecure if the anonymous remailer becomes compromised (or if the remailer was set up by an untrustworthy party in the first place). Whoever controls the remailer will have access to the identities of senders and recipients. One solution to this is to use _chains_ of remailers that send encrypted messages. For example, suppose Bill wishes to send a message to Louis using a chain of remailers A, B, and C. He writes the message (possibly encrypting it for Louis), then encrypts the result (including the fact that Louis is the recipient) using a public key supplied by remailer C. Then he encrypts this result using a public key supplied by remailer B. Then he encrypts this result using a public key supplied by A and sends the message to A. When A receives the message, it decrypts the message with its key to produce something encrypted for B, learns that the next remailer in the chain is B, strips off the information that the message came from Bill, and sends the message on to B. B then decrypts, learns that the next remailer in the chain is C, strips off the information that the message came from A, and sends the result to C. C then decrypts, learns that the destination is Louis, strips off the information that the message came from B, and sends the result to Louis. With this arrangement, only A knows that the original message came from Bill, and only C knows that the intended recipient is Louis. In general, the sender and recipient can both be known only to someone who has compromised all remailers in the chain. If Bill wishes, he can include an encrypted "response block" in his message to Louis, which defines a remailer chain that Louis can use to reply to Bill. Louis can use this chain without knowing who Bill is - only the last remailer in the chain need know the final recipient. Bill can also establish a _pseudonym_ for use in signing his anonymous messages. Mailcrypt includes facilities for sending messages via remailers, for defining chains of remailers, for generating response blocks, and for using pseudonyms.
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