L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura.com/~loki/remailer/remailer-essay.html.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....random order, thus hiding the correspondence between incoming and outgoing messages. Perhaps the most intuitive way of measuring the anonymity of a message M in a mix system is to just count the number of messages M has been mixed with while passing through the system. However, as pointed out in [Cot94] and [GT96] this is not enough as all the other messages could, for instance, come from a single known sender. Indeed, the attacker may mount the so called n 1 attack based on this observation by sending n 1 of their own messages to each of the mixes on M s path. In this case, the receiver of M ....

....have very strong anonymity set properties. We take the scenario in which the anonymity set of a message passing through a mix includes (at least) the senders of all the messages which have ever passed through that mix. This turns out to be the case for the pool mix introduced by Cottrell in [Cot94]. This mix always stores a pool of n messages (see Figure 1) When incoming N messages have accumulated in its bu er, it picks n randomly out of the n N it has, and stores them, forwarding the other ones in the usual fashion. Thus, there is always a small probability of any message which has ever ....

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L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura. com/~loki/remailer/remailer-essay.html.

....then researchers and developers have described many mix variations, e.g. Jak99,GT96,KEB98] These have di erent aims and approaches, yet we still fail to understand the performance and anonymity tradeo s between them. In fact, some of the mixes used in well known elded systems such as Mixmaster [Cot94,MC00] are mentioned only brie y or not at all in the literature. We aim to start closing this gap by enumerating and exploring a variety of mix architectures. In particular, we consider the extent to which the mixes are vulnerable to active attacks such as the n 1 attack. More speci cally, an ....

....consider the extent to which the mixes are vulnerable to active attacks such as the n 1 attack. More speci cally, an attacker targeting a speci c message going into a mix can manipulate the batch of messages entering that mix so the only message unknown to him in the batch is the target message [Cot94,GT96]. This manipulation may involve delaying or dropping most or all other incoming messages (a trickle attack) or ooding the batch with attacker messages (a ooding attack) We call these attacks or combinations of them blending attacks. We provide a rigorous analysis and comparison of several ....

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L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura.com/~loki/remailer/remailer-essay.html.

....privacy is a great concern for users of electronic commerce. Numerous protocols have emerged for protecting the anonymity of individuals. These protocols have been in the areas of protecting general Internet communications [23] commercial transactions [25] web based communications [21, 1] email [9, 18], and electronic cash [28] However, Work by this author supported by ONR. y Work by this author was also performed at AT T Research. 814 P. Syverson and S. Stubblebine, Group Principals and the Formalization of Anonymity. in FM 99 Formal Methods, Vol. I, Springer Verlag LNCS 1708, ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/~ loki/remailer/remailer-essay.html

....a great concern for users of electronic commerce. Numerous protocols have emerged for protecting the anonymity of individuals. These protocols have been in the areas of protecting general Internet communications [SGR97] commercial transactions [SSG97] web based communications [RR97, Ano] email [Cot, GT96], and electronic cash [Way96] However, little work has been done on formally representing or analyzing privacy in such protocols. In this paper, we provide an epistemic language and logic and use it to reason about anonymity protocols and anonymity services. We also describe an associated model ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/ loki/remailer /remailer-essay.html

....is less remote if the last COR is also compromised and we assume that the data sent over it is not end to end encrypted for the responder. We will return to this discussion below. 10 7 Related Work Basic comparison of Onion Routing to broadly related anonymity mechanisms, such as remailers [11, 5] and ISDN Mixes [14] can be found in [16] Also mentioned there are such complementary connection based mechanisms as LPWA [7] and the Anonymizer [1] These are both very effective at anonymizing the data stream in different ways, but they both pass all traffic directly from the initiator via a ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/eloki/remailer/remailer-essay.html

....sender s address with some alias, permitting replies. These sorts of remailers store sensitive state: the mapping between the alias and the true return address. Also, mail forwarded through a chain of remailers may be tracked because it appears the same to each remailer. Mix based remailers like [4, 8] use mixes to provide anonymous e mail services. Essentially, the mail message is carried in the innermost layer of an onion like data structure. Another onion like structure, used for a return address, can be contained in the message. This makes the return path self contained, and the remailer ....

L. Cottrell. "Mixmaster and Remailer Attacks", http://obscura.obscura.com/ e loki/remailer/remailer-essay.html

....Data may also be passed through a privacy filter before being sent over an anonymous connection. This removes identifying information from the data stream, to make communication anonymous too. Although onion routing may be used for anonymous communication, it differs from anonymous remailers [20, 9] in two ways: Communication is real time and bidirectional, and the anonymous connections are application independent. Onion routing s anonymous connections can support anonymous mail as well as other applications. For example, onion routing may be used for anonymous Web browsing. A user may wish ....

....sender s address with some alias, permitting replies. These sorts of remailers store sensitive state: the mapping between the alias and the true return address. Also, mail forwarded through a chain of remailers may be tracked because it appears the same to each remailer. Mix based remailers like [20, 9] use mixes to provide anonymous e mail services. Essentially, the mail message is carried in the innermost layer of the onion 6 data structure. Another onion type structure, used for a return address, can be contained in the message. This makes the return path self contained, and the remailer ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/~loki/remailer/remailer-essay.html

....submission, the bidder can reveal the key. We will indicate SBC to a given message M using a secret S by hMiS : To prevent the auctioneer from identifying the bidder s address prior to release of the SBC secret, bids should be submitted through an anonymizing mechanism, e.g. Mixmaster remailers [3] or onion routing [11] The owner of an item up for auction has a vested interest in the auctioneer continuing to accept new (potentially higher) bids until the auction is over. In order for him to be able to test that this is happening, we allow him to submit test bids. These can be explicitly ....

L. Cottrell. "Mixmaster and Remailer Attacks", http://obscura.obscura.com/~loki/remailer/remailer-essay.html. Note: Mixmaster remailers are based on the original mix design of Chaum [2].

....share the same code base, each differs in minor ways; some allow posting to newsgroups but others do not, some do not accept pgp encrypted messages; some even use different formats. Their lack of a unified interface significantly complicates their use and hinders their acceptance. The Mixmaster [7] remailer written by Lance Cottrell of UCSD is a significant step forward because it represents the first true mix. However, it is reported that Mixmaster relies on legacy cypherpunk remailers to provide message forwarding services 3 . Most importantly, Mixmaster lacks return paths. 1.3 Overview ....

....is the last. However, all others, i.e. intermediate hops, should not know the number of preceding hops nor the number of following ones. Chaum [2] presents a general solution where data is divided into a fixed number of fixed size blocks. This is the solution implemented in the Mixmaster package [7]. 10 As well as the method itself: The Anonymous E mail Conversation Page 24 of IBM Here we present another approach that is simpler and more storage efficient. The basic idea is to ensure that some padding (encrypted or not) always follows information carrying data. An example should ....

L. Cottrell, "Mixmaster and Remailer Attacks," by WWW at http://obscura.com/~loki/remailer-essay.html.

....from his her bank directly to the store s bank during a purchase. There are several services currently operating whose offer range from simple anonymous e mail to sophisticated mixmaster remailers to anonymizers for web browsing. See for example [PW85, GT96] for research papers on this subject and [C96] for an account on the Mixmaster Remailer. Such services focus on anonymity, but either do not provide consistency or do not provide modular security and protection from dossiers. Furthermore, remailers often use table based translation and thus do not fulfill the property of no private user ....

L. Cottrell, Mixmaster and Remailer Attacks. http://obsucra.com/~loki/remailer/remaileressay. html.

....sender s address with some alias, permitting replies. These sorts of remailers store sensitive state: the mapping between the alias and the true return address. Also, mail forwarded through a chain of remailers may be tracked because it appears the same to each remailer. Mix based remailers like [4, 10] use mixes to provide anonymous e mail services. Essentially, the mail message is carried in the innermost layer of the onion data structure. Another onion type structure, used for a return address, can be contained in the message. This makes the return path self contained, and the remailer ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/eloki/remailer/remailer-essay.html

....random alias. In case of asynchronous communication, we assume the existence of an anonymizing relay service. One example is the anonymous remailer (AR) an anonymizing relay for electronic mail. There are at least a dozen Internet ARs offering varying degrees of anonymity and inter operability [11, 6, 13]. Anonymizers for synchronous communication are not yet widely used 2 The only currently available tool is the WWW Anonymizer [19] which provides (weakly) anonymous Web access. It is a single site service which implies a central point of trust as well as a central point of failure. This is far ....

L. Cottrell, "Mixmaster and Remailer Attacks," http://obscura.com/~loki/remailer-essay.html.

....OS did not support multiprogramming, so nodes in the experiment were either purely Mix forwarders or specialized application endpoints. The system supported one way anonymous messages, not bidirectional streams. 2. 5 The Mixmaster and Babel Remailers The Mixmaster for email by Lance Cottrell 1 [Cot] is probably the most perfectly suited implementation of Mix technology to date. It includes facets of the Mix design such as replay detection, uniform sizing, buffering, and reordering, all of which contribute to the untraceability of messages. The technology is almost as easy to deploy as ....

Lance Cottrell. Mixmaster and remailer attacks. See http://obscura.com/ ¸loki/remailer-essay.html.

....depending upon one s environment and threat model, several solutions exist. For e mail, anonymous remailers can be used to forward mail through a service that promises not to reveal the sender s identity to the recipient. User s worried about traffic analysis can use Babel [12] or other Mixmaster [8] based remailers which forward messages through a series of Chaum mixes [4] Each mix can identify only the previous and next mix, and never (both) the sender and recipient. For Web browsing, the Anonymizer [1] provides a degree of protection. Web connections made through the Anonymizer are ....

L. Cottrell, "Mixmaster and Remailer Attacks", http://obscura.obscura.com/eloki/remailer/remailer-essay.html

....UK, May, 1996. piece of information that he retrieves is publicly known, it may be possible for an outside observer to determine his sensitive interests by studying the patterns in his requests. Onion Routing makes it very difficult to match his HTTP requests to his site. Anonymous re mailers [5, 6] attempt to limit the feasibility of traffic analysis by providing an anonymous store and forward architecture. To prevent replay attacks, re mailers keep a log of sent messages. These two characteristics make the anonymous re mailer approach unsuitable for HTTP applications, as HTTP requests ....

....remarks. 2 Background Chaum [1] defines a layered object that routes data through intermediate nodes, called mixes. These intermediate nodes may reorder, delay, and pad traffic to complicate traffic analysis. Some work has been done using mixes in ATM networks [3] Anonymous Remailers like [5, 6] use mixes to provide anonymous e mail services and also to invent an address through which mail can be forwarded back to the original sender. Remailers work in a store and forward manner at the mail application layer, by stripping off headers at each mix, and forwarding the mail message to the ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/e loki/remailer/remailer-essay.html

....would appear elsewhere. Cypherpunk remailers are widely available; see [33] Figure 4.3 shows the traffic flow in a Cypherpunk remailer chain, and Figure 4.2 shows a recent snapshot of well known remailer status. 4. 3 The Mixmaster and Babel Remailers The Mixmaster for email by Cottrell 1 [21] is probably the most perfectly suited implementation of Mix technology to date. It includes facets of the Mix design such as replay detection, uniform sizing, batching, and reordering, all of which contribute to the untraceability of messages. The technology is almost as easy to deploy as ....

Lance Cottrell. Mixmaster and remailer attacks. See http://obscura.com/¸loki/ remailer-essay.html.

....via a trusted intermediary from his her bank to the store s bank during a purchase. There are several services currently operating that offer capabilities ranging from simple anonymous e mail to sophisticated mixmaster remailers. See for example [PW85, GT96] for research papers on this subject and [C96] for an account on the Mixmaster Remailer. Such services focus on providing anonymity in e mail exchanges, but either do not provide the consistency property or do not provide the modular security protection from dossiers properties we require of Janus. Furthermore, remailers often use ....

L. Cottrell, Mixmaster and remailer attacks. http://obsucra.com/ loki/ remailer/remailer-essay.html.

....Data may also be passed through a privacy filter before being sent over an anonymous connection. This removes identifying information from the data stream, to make communication anonymous too. Although onion routing may be used for anonymous communication, it differs from anonymous remailers [7, 16] in two ways: Communication is real time and bidirectional, and the anonymous connections are application independent. Onion routing s anonymous 1 Preliminary versions of portions of this paper have appeared in [28, 14, 24] connections can support anonymous mail as well as other applications. ....

....sender s address with some alias, permitting replies. These sorts of remailers store sensitive state: the mapping between the alias and the true return address. Also, mail forwarded through a chain of remailers may be tracked because it appears the same to each remailer. Mix based remailers like [7, 16] use mixes to provide anonymous e mail services. Essentially, the mail message is carried in the innermost layer of the onion data structure. Another onion type structure, used for a return address, can be contained in the message. This makes the return path self contained, and the remailer ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/~loki/remailer /remailer-essay.html

....for sockets in a wide variety of unmodified Internet applications by means of proxies. The proxies may also remove identifying information from the data stream, to make communication anonymous too. Although onion routing may be used for anonymous communication, it differs from anonymous remailers [7, 11] in two ways: Communication is realtime and bidirectional, and the anonymous connections are application independent. Onion routing s anonymous connections can support anonymous mail as well as other applications. For example, onion routing may be used for anonymous Web browsing. A user may wish ....

....Connections and Onion Routing to appear 1997 IEEE Symposium on Security and Privacy termediate nodes may reorder, delay, and pad traffic to complicate traffic analysis. Our onion routers are based on mixes. Some work has been done using mixes in ATM networks [5] Anonymous Remailers like [7, 11] use mixes to provide anonymous e mail services. Some invent an address through which mail can be forwarded back to the original sender. Remailers work in a store and forward manner at the mail application layer, by stripping off headers at each mix and forwarding the mail message to the next mix. ....

L. Cottrell. Mixmaster and Remailer Attacks, http://obscura.obscura.com/~loki/remailer /remailer-essay.html

....they share the same code base, each differs in minor ways; some allow posting to newsgroups while others do not, some do not accept pgp encrypted messages; some even use different formats. Their lack of a unified modus operandi complicates their use and hinders their acceptance. The Mixmaster [7] remailer written by L. Cottrell is a significant step forward as it constitutes the first true mix. 2.2 Overview of desired properties We begin the technical discussion by enumerating the desired properties of anonymous mail. 1. Anyone able to send email should be able to do so anonymously. 2. ....

....it is the last. However, all others, i.e. intermediate hops, should not know the number of preceding hops nor the number of following ones. Chaum [2] presents a general solution where data is divided into a fixed number of fixed size blocks. This is the solution implemented in the Mixmaster package[7]. Here we present another approach that is simpler and more storage efficient. The basic idea is to ensure that some padding (encrypted or not) always follows information carrying data. An example should make the point clear. Let string C of length Omega be composed of M bytes of data followed by ....

L. Cottrell, "Mixmaster and Remailer Attacks," http://obscura.com/~loki/remailer-essay.html.

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L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura.com/~loki/remailer/remailer-essay.html.

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L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura.com/~loki/remailer/remailer-essay.html.

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L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura.com/~loki/remailer/remailer-essay.html.

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L. Cottrell. Mixmaster and remailer attacks, 1994. http://www.obscura.com/~loki/remailer/remailer-essay.html.

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L. Cottrell. Mixmaster and Remailer Attacks. http://www.obscura.com/ loki/remaileressay. html

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L. Cottrell, "Mixmaster and Remailer Attacks," http://obscura.com/~loki/remailer-essay.html.

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