Anonymous Remailer - Types of Remailer

Types of Remailer

There are several strategies that affect the anonymity of the handled e-mail. In general, different classes of anonymous remailers differ with regard to the choices their designers/operators have made. These choices can be influenced by the legal ramifications of operating specific types of remailers.

It must be understood that every data packet traveling on the Internet contains the node addresses (as raw IP bit strings) of both the sending and intended recipient nodes, and so no data packet can ever actually be anonymous at this level. However, if the IP source address is false, there will be no easy way to trace the originating node (and so the originating entity for the packet). In addition, all standards-based e-mail messages contain defined fields in their headers in which the source and transmitting entities (and Internet nodes as well) are required to be included. However, since most users of e-mail do not have very much technical expertise, the full headers are usually suppressed by mail reading software. Thus, many users have never seen one.

Some remailers change both types of address in messages they forward, and the list of forwarding nodes in e-mail messages as well, as the message passes through; in effect, they substitute 'fake source addresses' for the originals. The 'IP source address' for that packet may become that of the remailer server itself, and within an e-mail message (which is usually several packets), a nominal 'user' on that server. Some remailers forward their anonymized e-mail to still other remailers, and only after several such hops is the e-mail actually delivered to the intended address.

There are, more or less, four types of remailers:

• Pseudonymous remailers

A Pseudonymous remailer simply takes away the e-mail address of the sender, gives a pseudonym to the sender, and sends the message to the intended recipient (that can be answered via that remailer).

• Cypherpunk remailers, also called type I

A Cypherpunk remailer sends the message to the recipient stripping away the sender address on it. One can not answer a message sent via a Cypherpunk remailer. The message sent to the remailer can usually be encrypted, and the remailer will decrypt it and send it to the recipient address hidden inside the encrypted message. In addition, it is possible to chain two or three remailers, so that each remailer can't know who is sending a message to whom. Cypherpunk remailers do not keep logs of transactions.

• Mixmaster remailers, also called type II

Mixmaster remailers require the use of a computer program to write messages. Such programs are not supplied as a standard part of most operating systems or mail management systems.

• Mixminion remailers, also called type III

A Mixminion remailer attempts to address the following challenges in Mixmaster remailers: replies, forward anonymity, replay prevention and key rotation, exit policies, integrated directory servers and dummy traffic. They are currently available for the Linux and Windows platforms. Some implementations are open source.