The following networks are discussed on this page.
- Morphmix / Tarzan
- Mixminion / Mixmaster
- MUTE / AntsP2P
Tor / Onion Routing
Tor and Onion Routing are both anonymizing proxy networks, allowing people to tunnel out through their low latency mix network. The two primary differences between Tor / Onion-Routing and I2P are again related to differences in the threat model and the out-proxy design (though Tor supports hidden services as well). In addition, Tor takes the directory-based approach – providing a centralized point to manage the overall ‘view’ of the network, as well as gather and report statistics, as opposed to I2P’s distributed network database and peer selection.
The I2P/Tor outproxy functionality does have a few substantial weaknesses against certain attackers – once the communication leaves the mixnet, global passive adversaries can more easily mount traffic analysis. In addition, the outproxies have access to the cleartext of the data transferred in both directions, and outproxies are prone to abuse, along with all of the other security issues we’ve come to know and love with normal Internet traffic.
However, many people don’t need to worry about those situations, as they are outside their threat model. It is, also, outside I2P’s (formal) functional scope (if people want to build outproxy functionality on top of an anonymous communication layer, they can). In fact, some I2P users currently take advantage of Tor to outproxy.
Comparison of Tor and I2P Terminology
While Tor and I2P are similar in many ways, much of the terminology is different.
|Client||Router or Client|
|Directory Server||Floodfill Router|
|Entry Guards||Fast Peers|
|Hidden Service||Eepsite or Destination|
|Hidden Service Descriptor||LeaseSet|
|Introduction point||Inbound Gateway|
|Onion Proxy||I2PTunnel Client (more or less)|
|Rendezvous Point||somewhat like Inbound Gateway + Outbound Endpoint|
Benefits of Tor over I2P
- Much bigger user base; much more visibility in the academic and hacker communities; benefits from formal studies of anonymity, resistance, and performance; has a non-anonymous, visible, university-based leader
- Has already solved some scaling issues I2P has yet to address
- Has significant funding
- Has more developers, including several that are funded
- More resistant to state-level blocking due to TLS transport layer and bridges (I2P has proposals for “full restricted routes” but these are not yet implemented)
- Big enough that it has had to adapt to blocking and DOS attempts
- Designed and optimized for exit traffic, with a large number of exit nodes
- Better documentation, has formal papers and specifications, better website, many more translations
- More efficient with memory usage
- Tor client nodes have very low bandwidth overhead
- Centralized control reduces the complexity at each node and can efficiently address Sybil attacks
- A core of high capacity nodes provides higher throughput and lower latency
- C, not Java (ewww)
Benefits of I2P over Tor
- Designed and optimized for hidden services, which are much faster than in Tor
- Fully distributed and self organizing
- Peers are selected by continuously profiling and ranking performance, rather than trusting claimed capacity
- Floodfill peers (“directory servers”) are varying and untrusted, rather than hardcoded
- Small enough that it hasn’t been blocked or DOSed much, or at all
- Peer-to-peer friendly
- Packet switched instead of circuit switched
- implicit transparent load balancing of messages across multiple peers, rather than a single path
- resilience vs. failures by running multiple tunnels in parallel, plus rotating tunnels
- scale each client’s connections at O(1) instead of O(N) (Alice has e.g. 2 inbound tunnels that are used by all of the peers Alice is talking with, rather than a circuit for each)
- Unidirectional tunnels instead of bidirectional circuits, doubling the number of nodes a peer has to compromise to get the same information.
- Protection against detecting client activity, even when an attacker is participating in the tunnel, as tunnels are used for more than simply passing end to end messages (e.g. netDb, tunnel management, tunnel testing)
- Tunnels in I2P are short lived, decreasing the number of samples that an attacker can use to mount an active attack with, unlike circuits in Tor, which are typically long lived.
- I2P APIs are designed specifically for anonymity and security, while SOCKS is designed for functionality.
- Essentially all peers participate in routing for others
- The bandwidth overhead of being a full peer is low, while in Tor, while client nodes don’t require much bandwidth, they don’t fully participate in the mixnet.
- Integrated automatic update mechanism
- Both TCP and UDP transports
- Java, not C (ewww)
Other potential benefits of I2P but not yet implemented
…and may never be implemented, so don’t count on them!
- Defense vs. message count analysis by garlic wrapping multiple messages
- Defense vs. long term intersection by adding delays at various hops (where the delays are not discernible by other hops)
- Various mixing strategies at the tunnel level (e.g. create a tunnel that will handle 500 messages / minute, where the endpoint will inject dummy messages if there are insufficient messages, etc)
Freenet is a fully distributed, peer to peer anonymous publishing network, offering secure ways to store data, as well as some approaches attempting to address the loads of a flash flood. While Freenet is designed as a distributed data store, people have built applications on top of it to do more generic anonymous communication, such as static websites and message boards.
Compared to I2P, Freenet offers some substantial benefits – it is a distributed data store, while I2P is not, allowing people to retrieve the content published by others even when the publisher is no longer online. In addition, it should be able to distribute popular data fairly efficiently. I2P itself does not and will not provide this functionality. On the other hand, there is overlap for users who simply want to communicate with each other anonymously through websites, message boards, file sharing programs, etc. There have also been some attempts to develop a distributed data store to run on top of I2P, (most recently a port of Tahoe-LAFS) but nothing is yet ready for general use.
However, even ignoring any implementations issues, there are some concerns about Freenet’s algorithms from both a scalability and anonymity perspective, owing largely to Freenet’s heuristic driven routing. The interactions of various techniques certainly may successfully deter various attacks, and perhaps some aspects of the routing algorithms will provide the hoped for scalability. Unfortunately, not much analysis of the algorithms involved has resulted in positive results, but there is still hope. At the very least, Freenet does provide substantial anonymity against an attacker who does not have the resources necessary to analyze it further.
Morphmix / Tarzan
Morphmix and Tarzan are both fully distributed, peer to peer networks of anonymizing proxies, allowing people to tunnel out through the low latency mix network. Morphmix includes some very interesting collusion detection algorithms and Sybil defenses, while Tarzan makes use of the scarcity of IP addresses to accomplish the same. The two primary differences between these systems and I2P are related to I2P’s threat model and their out-proxy design (as opposed to providing both sender and receiver anonymity). There is source code available to both systems, but we are not aware of their use outside of academic environments.
Mixminion / Mixmaster
Mixminion and Mixmaster are networks to support anonymous email against a very powerful adversary. High-latency messaging applications running on top of I2P (for example Syndie or I2PBote) may perhaps prove adequate to meet the threat model of those adversaries, while running in parallel along side the needs of low latency users, to provide a significantly larger anonymity set. High-latency support within the I2P router itself may or may not be added in a distant future release. It is too early to say if I2P will meet the needs of users requiring extreme protection for email.
As with Tor and Onion Routing, both Mixminion and Mixmaster take the directory based approach as well.
JAP (Java Anonymous Proxy) is a network of mix cascades for anonymizing web requests, and as such it has a few centralized nodes (participants in the cascade) that blend and mix requests from clients through the sequence of nodes (the cascade) before proxying out onto the web. The scope, threat model, and security is substantially different from I2P, but for those who don’t require significant anonymity but still are not satisfied with an Anonymizer-like service, JAP is worth reviewing. One caution to note is that anyone under the jurisdiction of the German courts may want to take care, as the German Federal Bureau of Criminal Investigation (FBCI) has successfully mounted an attack on the network. Even though the method of this attack was later found to be illegal in the German courts, the fact that the data was successfully collected is the concern. Courts change their minds based upon circumstance, and this is evidence that if a government body or intelligence agency wanted to, they could gather the data, even if it may be found inadmissible in some courts later)
MUTE / AntsP2P
Both of these systems work through the same basic antnet routing, providing some degree of anonymity based on the threat model of providing plausible deniability against a simple non-colluding adversary. With the antnet routing, they first either do a random walk or a broadcast search to find some peer with the data or identity desired, and then use a feedback algorithm to optimize that found path. This works well for applications that merely want to know what other people around them have to offer – “How are y’all doing” vs. “Hey Alice, how are you” – you basically get a local cluster of nodes that can share files with and maintain some degree of anonymity (though you don’t have much control over who is in that group of peers).
However, the algorithm does not scale well at all – if the application wants to speak with a particular peer it ends up doing a broadcast search or random walk (though if they are lucky enough for that to succeed, the antnet routing should optimize that found connection). This means that while these networks can work great at small scales, they are not suitable for large networks where someone wants to get in touch with another specific peer. That does not mean that there is no value in these systems, just that their applicability is limited to situations where their particular issues can be addressed.
This was a closed-source network targeted at Iranian users. Tor did a good writeup on what to look for in a circumvention tool. Suffice it to say that being closed source and publicly targeting a specific country are not good ideas. I2P is, of course, open source. However, that source, and our technical documentation, need much more review.
Paid VPN Services
Only your Cable company knows for sure…