Mixmaster Remailer - Revision history

David: /* Anonymous Proxies */

2006-02-22T08:11:55Z

Anonymous Proxies

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	The trivial solution is to send Alice's requests through an anonymizing proxy. The proxy would remove all information that might link the data to the sender and forward the message to Bob. A website where such a service is offered is [http://www.anonymizer.com www.anonymizer.com]. Using a proxy ensures that Bob does not know Alice's identity. The concept is easy to understand and it obviously works for the mentionned purpose.		The trivial solution is to send Alice's requests through an anonymizing proxy. The proxy would remove all information that might link the data to the sender and forward the message to Bob. A website where such a service is offered is [http://www.anonymizer.com www.anonymizer.com]. Using a proxy ensures that Bob does not know Alice's identity. The concept is easy to understand and it obviously works for the mentionned purpose.

	[[Image:anonymizer_com.jpg]]		::[[Image:anonymizer_com.jpg]]

	Can Alice be sure that the proxy operator does not spy on her? Unfortunately, she cannot. But the approach of the central proxy is based on the assumption that the proxy operator can be trusted. If you cannot trust the proxy operator you will need more sophisticated concepts to keep your privacy.		Can Alice be sure that the proxy operator does not spy on her? Unfortunately, she cannot. But the approach of the central proxy is based on the assumption that the proxy operator can be trusted. If you cannot trust the proxy operator you will need more sophisticated concepts to keep your privacy.
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	How can Alice take advantage of that? Assume she has a choice of three proxies X1, X2 and X3. Why not use proxy X1 to connect to proxy X2, and use that connection to connect to proxy X3? If done right, it would mean that only proxy X1 knows Alice and only proxy X3 knows Bob. In addition to that, the operator of proxy X2 would be needed to be able to link both connections to each other since X1 and X3 do not know each other.		How can Alice take advantage of that? Assume she has a choice of three proxies X1, X2 and X3. Why not use proxy X1 to connect to proxy X2, and use that connection to connect to proxy X3? If done right, it would mean that only proxy X1 knows Alice and only proxy X3 knows Bob. In addition to that, the operator of proxy X2 would be needed to be able to link both connections to each other since X1 and X3 do not know each other.

	[[Image:jurisdictional_arbitrage.png]]		::[[Image:jurisdictional_arbitrage.png]]

	=== Jurisdictional Arbitrage ===		=== Jurisdictional Arbitrage ===

David: /* Terminology */

2006-02-22T08:11:46Z

Terminology

← Older revision		Revision as of 08:11, 22 February 2006
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	==== Terminology ====		==== Terminology ====
	[[Image:tor_network_intro.jpg]]		::[[Image:tor_network_intro.jpg]]

	The basic building block of the Tor network are the '''OR'''s, the onion routers. The chain of ORs that connects Alice and Bob are called a '''circuit'''. Alice runs a special client software, the '''OP''' (onion proxy), that provides the SOCKS proxy for her applications. The directory servers are used to keep track of the ORs. That is necessary, because anyone can operate an OR and join the network. Obviously, the Tor network contains more than just three ORs and one directory server.		The basic building block of the Tor network are the '''OR'''s, the onion routers. The chain of ORs that connects Alice and Bob are called a '''circuit'''. Alice runs a special client software, the '''OP''' (onion proxy), that provides the SOCKS proxy for her applications. The directory servers are used to keep track of the ORs. That is necessary, because anyone can operate an OR and join the network. Obviously, the Tor network contains more than just three ORs and one directory server.

David: /* Routing */

2006-02-22T08:11:37Z

Routing

← Older revision		Revision as of 08:11, 22 February 2006
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	That way the cell never contains the entire routing information, let alone final destination. Additionally, once the connection is closed the ORs forget about the circIDs for that connection. That makes it impossible to backtrace (zurückverfolgen) the connection once it is closed.		That way the cell never contains the entire routing information, let alone final destination. Additionally, once the connection is closed the ORs forget about the circIDs for that connection. That makes it impossible to backtrace (zurückverfolgen) the connection once it is closed.

	[[Image:Tor_circID.jpg]]		::[[Image:Tor_circID.jpg]]

	==== Using the Circuit ====		==== Using the Circuit ====

David: /* Using the Circuit */

2006-02-22T08:11:29Z

Using the Circuit

← Older revision		Revision as of 08:11, 22 February 2006
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	When Alice wants to send a cell over her circuit, she first encrypts it with the secret key that she shares with the last OR in the circuit, Xn. She takes the result and encrypts it for Xn-1, continuing until she encrypts the cell for the first OR in her circuit. The resulting cell looks like this:		When Alice wants to send a cell over her circuit, she first encrypts it with the secret key that she shares with the last OR in the circuit, Xn. She takes the result and encrypts it for Xn-1, continuing until she encrypts the cell for the first OR in her circuit. The resulting cell looks like this:

	[[Image:onion1.png]]		::[[Image:onion1.png]]

	The onion-like structure of the message is what gave onion routing its name. As the cell passes through the circuit, each OR removes one layer of encryption. Only the last OR gets to see the final message, all the previous one just saw some encrypted message. But why not just encrypt it for X3? That way X1 and X2 would not have to perform the computionally expensive decryption. The reason is that by constantly mangling the packet it gets harder to trace because they always look different when they leave an OR.		The onion-like structure of the message is what gave onion routing its name. As the cell passes through the circuit, each OR removes one layer of encryption. Only the last OR gets to see the final message, all the previous one just saw some encrypted message. But why not just encrypt it for X3? That way X1 and X2 would not have to perform the computionally expensive decryption. The reason is that by constantly mangling the packet it gets harder to trace because they always look different when they leave an OR.
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	[[Image:onion2.png]]		::[[Image:onion2.png]]

	The reason for the encryption at each hop is the same as above. Alice can remove all the encryption layers from the message since she knows all the keys.		The reason for the encryption at each hop is the same as above. Alice can remove all the encryption layers from the message since she knows all the keys.

David: /* Reply Messages & Single-Use-Reply-Blocks */

2006-02-22T08:11:12Z

Reply Messages & Single-Use-Reply-Blocks

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	* Anonymized Reply		* Anonymized Reply

	[[Image:reply.jpg]]		::[[Image:reply.jpg]]

David: /* Überblick */

2006-02-22T08:11:03Z

Überblick

← Older revision		Revision as of 08:11, 22 February 2006
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	* Ununterscheidbarkeit zwischen Forward- und Replymessages		* Ununterscheidbarkeit zwischen Forward- und Replymessages

	[[Image:struktursmall.jpg]]		::[[Image:struktursmall.jpg]]

	=== Directory Server ===		=== Directory Server ===

David: /* Mixmaster Remailer */

2006-02-22T08:05:36Z

Mixmaster Remailer

← Older revision		Revision as of 08:05, 22 February 2006
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	Es ist auch möglich '''Kopien einer Nachricht''' über verschiedene Remailer Ketten zu versenden. Der letzte Remailer zerstört nach erfolgreicher Zustellung einer Kopie das Duplikat. Das Duplikat wird anhand einer Nachrichten-ID erkannt.		Es ist auch möglich '''Kopien einer Nachricht''' über verschiedene Remailer Ketten zu versenden. Der letzte Remailer zerstört nach erfolgreicher Zustellung einer Kopie das Duplikat. Das Duplikat wird anhand einer Nachrichten-ID erkannt.

	Remailer merken sich die '''ID''''s verarbeiteter Packete in einem '''Cache'''. Dadurch ~~wirdden~~ '''Replay Attacken''' begegnet (siehe auch Schwächen von Mixmaster).		Remailer merken sich die '''ID''''s verarbeiteter Packete in einem '''Cache'''. Dadurch wird '''Replay Attacken''' begegnet (siehe auch Schwächen von Mixmaster).
	Ursprünglich existierte der Ansatz, die Packete mit '''Zeitstempeln''' zu versehen, um '''Replay Attacken''' verhindern zu können. Allerdings entstand damit das Problem, dass bei zu kurz in der Zukunft liegenden Zeitstempeln der Timeout-Zeitpunkt überschritten wird, noch bevor das Packet an seinem Zielort ankommt. Bei zu lange in der Zukunft liegenden Zeitstempeln werden im Netzwerk Packete, die kurz vor dem Ablauf ihres Timeouts stehen selten. Nun kann ein Angreifer folgenden Angriff fahren: er hält das Packet, deren Weg durch das Netzwerk er nachvollziehen möchte, eine Zeit lang fest und schickt es anschliessend weiter auf die Reise. Wenn später im Netzwerk ein Packet auftaucht, deren Zeitstempel kurz vor dem Timeout ist, ist die Wahrscheinlichkeit gross, dass es sich um das zu verfolgende Packet handelt.		Ursprünglich existierte der Ansatz, die Packete mit '''Zeitstempeln''' zu versehen, um '''Replay Attacken''' verhindern zu können. Allerdings entstand damit das Problem, dass bei zu kurz in der Zukunft liegenden Zeitstempeln der Timeout-Zeitpunkt überschritten wird, noch bevor das Packet an seinem Zielort ankommt. Bei zu lange in der Zukunft liegenden Zeitstempeln werden im Netzwerk Packete, die kurz vor dem Ablauf ihres Timeouts stehen selten. Nun kann ein Angreifer folgenden Angriff fahren: er hält das Packet, deren Weg durch das Netzwerk er nachvollziehen möchte, eine Zeit lang fest und schickt es anschliessend weiter auf die Reise. Wenn später im Netzwerk ein Packet auftaucht, deren Zeitstempel kurz vor dem Timeout ist, ist die Wahrscheinlichkeit gross, dass es sich um das zu verfolgende Packet handelt.

David: /* Überblick */

2006-02-22T08:00:22Z

Überblick

← Older revision		Revision as of 08:00, 22 February 2006
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	=== Überblick ===		=== Überblick ===
	Mixminion stellt eine Erweiterung vom Mixmaster dar, gewährt dabei Abwärtskompatibilität. Sie werden auch als Typ3-Remailer bezeichnet.		Mixminion stellt eine Erweiterung vom Mixmaster dar, gewährt dabei Abwärtskompatibilität. Sie werden auch als Typ3-Remailer bezeichnet.
	Mixnetze können gemischt aus Mixmaster- sowie Mixminionservern bestehen. Beim Typwechsel muss das Paket ~~gegeben~~ geremixed werden.		Mixnetze können gemischt aus Mixmaster- sowie Mixminionservern bestehen. Beim Typwechsel muss das Paket gegebenenfalls geremixed werden.

	Unterschiede zu Mixmaster		Unterschiede zu Mixmaster

David: /* General */

2006-02-22T07:56:20Z

General

← Older revision		Revision as of 07:56, 22 February 2006
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	Mixmaster, Mixminion and Tor are tools to achieve anonymity or pseudonymity, but exactly what does that mean? Anonymity means that you can do something without enabling other peoples to get hold of your identity. The roles in the scenario are fixed. It is always '''A'''lice that wants to communicate with '''B'''ob. Usually Alice is a human and Bob is either a computer (e.g. webserver) or human as well. Eve is trying to '''e'''a'''ve'''sdrop (belauschen) on them. To be more precise, Eve wants to find out that Alice and Bob are communicating with each other.		Mixmaster, Mixminion and Tor are tools to achieve anonymity or pseudonymity, but exactly what does that mean? Anonymity means that you can do something without enabling other peoples to get hold of your identity. The roles in the scenario are fixed. It is always '''A'''lice that wants to communicate with '''B'''ob. Usually Alice is human and Bob is either a computer (e.g. webserver) or human as well. Eve is trying to '''e'''a'''ve'''sdrop (belauschen) on them. To be more precise, Eve wants to find out that Alice and Bob are communicating with each other.

David: /* General */

2006-02-22T07:54:59Z

General

← Older revision		Revision as of 07:54, 22 February 2006
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	Mixmaster, Mixminion and Tor are tools to achieve anonymity or pseudonymity, but exactly what does that mean? Anonymity means that you can do something without other ~~people~~ ~~knowing~~ ~~that~~ ~~who~~ ~~you~~ ~~are~~. The roles in the scenario are fixed. It is always '''A'''lice that wants to communicate with '''B'''ob. Usually Alice is a human and Bob is either a computer (e.g. webserver) or human as well. Eve is trying to '''e'''a'''ve'''sdrop (belauschen) on them. To be more precise, Eve wants to find out that Alice and Bob are communicating with each other.		Mixmaster, Mixminion and Tor are tools to achieve anonymity or pseudonymity, but exactly what does that mean? Anonymity means that you can do something without enabling other peoples to get hold of your identity. The roles in the scenario are fixed. It is always '''A'''lice that wants to communicate with '''B'''ob. Usually Alice is a human and Bob is either a computer (e.g. webserver) or human as well. Eve is trying to '''e'''a'''ve'''sdrop (belauschen) on them. To be more precise, Eve wants to find out that Alice and Bob are communicating with each other.