Mixmaster remailer
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
- Remailer , Cypherpunk Remailer , Nym Remailer , Mixminion
- Anonymity on the Internet , anonymizer
- Gate , I2P
literature
- E-Mail Security , Bruce Schneier ( ISBN 0-471-05318-X )
- Computer Privacy Handbook , Andre Bacard ( ISBN 1-56609-171-3 )
- Jens Kubieziel (2012): Anonymous on the net: How you protect yourself and your data, 3rd edition, Munich: Open Source Press. ( ISBN 978-3-941841-67-3 )
Web links
- Mixmaster homepage
- Anonymous sending of emails and Usenet postings
- Internet Draft: Mixmaster Protocol Version 2, Ulf Möller 2003
Remailer programs
- Mixmaster (English) The basic program for MS-DOS , Linux or Windows .
- QuickSilver (English) A comfortable remailer program for Mixmaster. After the installation you can use the update function to download and install the Mixmaster program. Quicksilver instructions in German.
- Jack B. Nymble (JBN) (English) An older remailer program for Mixmaster and Cypherpunk remailers . This program requires a separate installation of Mixmaster .
- OmniMix (English) proxy server for the selective anonymization of standard newsreaders and mail clients from Usenet articles or emails with the help of the Mixmaster and Cypherpunk remailer network including interaction with Nym servers . The portable system integrates Tor and GnuPG . Using complete encryption, d. H. including the header information (whole message encryption), according to the OpenPGP standard, the transmission of non-anonymized messages can also be automatically protected from being viewed.