Mixminion

Mixminion uses the "mixed network" architecture (English Mix network ) to provide a very high degree of anonymity , as well as to prevent listening and other types of attacks when sending messages. The servers, called “mixers,” which run the volunteers, receive messages, decrypt them, split them into blocks, mix them and pass them to other “mixers”. Each email goes through several servers so that there is no single server connecting the sender of the message and its recipient. ^[2]

• Ability to receive and send anonymous electronic messages - users should be able to receive messages from anonymous senders and send messages to anonymous recipients using a standard SMTP mail client.
• Guaranteeing the integrity of the message - if the letter reaches, then only in its entirety.
• Ease of use - the protocol must use existing architectures without requiring any special hardware requirements.
• Advanced anonymity - the disclosure of one message does not entail the disclosure of others. ^{[3] [4]}

When sending anonymous messages, Mixminion splits it into sections of the same size, bringing the packets in the same form and choosing the path for sending through the mixed network for each packet. The program encrypts each packet with a public key for each server in its path, one after the other. When sending a packet, Mixminion sends it to the first “mix server” on the way. The first server decrypts the packet, reading which next server should receive the packet and forwards it. As a result, the packet arrives at the final “mix server”, which sends it to the selected recipient. Since no server knows more than one adjacent server, they cannot associate the recipient with the sender. ^[2]

Mixminion allows Alice to send messages to Bob in one of three ways:

1. Forward - only Alice remains anonymous.
2. Direct reply - only Bob remains anonymous.
3. Anonymized reply - Both Alice and Bob remain anonymous. ^[five]

Node

The basic structure of mixed networks. A mixed network consists of servers called nodes. Each node is associated with a public key. When the node receives an encrypted message, decryption takes place, the separation into packets of the same length of 28Kb, then the packets are mixed and sent further without information about the sender. ^[2]

Directory Servers

Servers that manage the list of public keys in nodes, as well as monitor the functioning of nodes and their workload. ^[6]

NYM Server

Servers that are used to send and receive letters without revealing an identity. ^[7]

SURBs (Single-Use Reply Blocks)

Mixminion supports the technology of “one-time response blocks” (Eng. “Single-Use Reply Blocks”, abbreviated “SURB”) to identify anonymous recipients . SURB encodes half the path to the destination, then each “mix server” in the queue “deploys” one layer in the path, and then encrypts the message for the destination recipient. When the message reaches the addressee, he can decrypt the message and read which SURB was used to send it, but the sender does not know which recipient received the anonymous message. ^[eight]

Tag Attack

A tag attack is characterized by modifying the message by changing part of it (for example, using the bitwise operation NOT) so that the message can later be identified by this distinguishing feature. ^[9]

Attack on weekend nodes

The output node has access to the decrypted message and may belong to an attacker who will listen to the node secretly from network users. ^[ten]

Denial of Service

An attacker can send a large number of messages in a certain direction, damaging nodes and disrupting the normal operation of the network. ^[7]

• Finding a simple way to prevent tag attacks. ^[eleven]
• Improving the algorithm for choosing the best delivery path for a large number of messages. ^[eleven]

• Anonymous Networks
• Remailer
• Bitmessage

• Mixminion: creating an anonymous third type remailer protocol
• Windows GUI Frontend for Mixminion
• Cipherpunk remailers

• George Danezis; Roger Dingledine; David Hopwood; Nick Mathewson Mixminion: Design of a Type III Anonymous Remailer Protocol . - 2002.
• George Danezis; Roger Dingledine; David Hopwood; Nick Mathewson Mixminion: Design of a Type III Anonymous Remailer Protocol . - 2003. Archived on March 12, 2017.