Mixmaster remailer

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A Mixmaster remailer (also type II remailer ) is an anonymizing Internet service that accepts and forwards e-mails ( remailer ). Before the message is forwarded, all information that suggests the origin and the sender is removed.

The Mixmaster software for servers only processes encrypted e-mail in a very specific format. In contrast to the use of the older Cypherpunk protocol, the sender is dependent on specialized Mixmaster software for clients in order to generate such e-mail.

Origin and development

Mixmaster was created according to the suggestions of Lance Cottrell and was supposed to eliminate the weaknesses of the Cypherpunk remailer. David Chaum developed the underlying Mix-Net-Protocol itself in 1981. Today's Mixmaster message format has been in use on the Internet since 1995.

Mixmaster software can be installed on different operating systems. Individual client solutions were created exclusively for Windows or Unix derivatives (including Linux); also those who support Cypherpunk in addition to Mixmaster.

method

Before a message is forwarded by the remailer, the so-called message header is modified and the sender-related information is removed. The final recipient of an email treated in this way receives the remailer's only sender information.

Techniques that subsequently increased the security level of the Cypherpunk remailers are part of the Mixmaster protocol from the start. The Mixmaster client already ensures that every message sent has the same size. For this purpose, oversized e-mails are divided into smaller ones of approx. 20  Ki B, smaller ones brought to this size by adding random data.

For Mixmaster, the chaining of remailers and encryption using public-key procedures are an integral part of the protocol. Individual message packages that may This may arise from the forced division, can be delivered via different (also different lengths) remailer chains, the last link of which must be one and the same remailer. Only the last remailer is able to compose such a message.

Mixmasters can be combined with Cypherpunk remailers and then, if necessary, automatically reformatting a conventional Cypherpunk message into Mixmaster format (remix) and forwarding it to other Mixmaster remailers.

Other special features

  • The Mixmaster server maintains a message pool in which all incoming messages are first collected. The size of the pool is adjustable.
  • Messages are sent from the message pool in random order.
  • If there is insufficient data traffic within a period of time, Mixmaster itself generates messages without meaningful content, which are forwarded via remailers, but ultimately destroyed.
  • Copies of the same email can be sent via different chains. Mixmasters maintain a message cache on the basis of which the last remailer destroys the duplicates after the first successful delivery; the end recipient only receives each email once.

Attacks against the Mixmaster remailer

Mixmasters are resistant to almost all known attacks. So far, only one theoretical approach is known:

An attacker withholds the message whose recipient he wants to find out. Then he sends his own messages to the Mixmaster. He does this until the Mixmaster's message pool is filled with his messages. Then he sends off the withheld message. All messages that go through the Mixmaster are either sent to the attacker or to a third address. The third address is that of the recipient of the withheld message.

See also

literature

Web links

Remailer programs