PC Magazine - September 16, 2003
You may know anonymous remailers from their somewhat shady association with spam, terrorists, child porn rings, and so on. But remailers - tools that let you send e-mail and post to newsgroups without revealing your identity - have practical and legitimate applications. For instance, they can be useful when you need to blow the whistle on corrupt practices in your workplace, discuss ideas in a politically oppressed country, or participate in a self-help group.
If you just want to hide your identity from casual observers, a Web e-mail from a Yahoo! address or an AOL screen name will work fine. But this technique won't stop anyone from figuring out who you are. Your message header reveals your IP address - the server through which you connect to the Internet. Using that IP address, a dedicated investigator can obtain your name, address, and phone number. Also, these messages aren't encrypted and can be read as they leave your computer.
Anonymous remailers hide your IP address by removing header information. In its simplest form, a remailer server acts as an intermediary. You send your message to the remailer, the remailer strips off the header, and then forwards your message to its destination. The receiver sees the remailer's IP address rather than yours.
This strategy was used by anon.penet.fi, a widely used anonymous remailer that operated out of Finland from 1993 to 1996. The problems encountered by anon.penet.fi demonstrate the weakness in this approach. The Finnish police forced the owner, Johan "Julf" Helsingius, to reveal the identities of individuals accused of copyright violation and other crimes. (Helsingius finally closed down the service because of massive abuse by spammers.)
Servers such as these are termed pseudonymous remailers, because their anonymity depends on the willingness and ability of the server administrator to keep the identities of its users confidential. Another now-defunct pseudonymous server, at alpha.c2.org, offered security-enhancing features, such as support for encryption, chained remailing, and reply blocks (a technique that lets people respond to you without learning your identity).
Truly anonymous remailers don't offer any way to reply to the sender. There are two main types: Cypherpunk (Type I) and Mixmaster (Type II). These are harder to use than pseudonymous remailers, but they're more secure. You need to learn how to use PGP encryption, build the message, and set up the chain of remailers through which your message is transmitted. Cypherpunk messages can be created in Notepad, but Mixmaster messages require special software.
Cypherpunk uses nested encrypted messages to route your message through several remailer servers before it reaches its destination. At each stop, a layer de-scribing the next destination is decrypted and removed before forwarding. Because the messages shrink with each hop, they can be tracked on the Internet using traffic analysis techniques. Mixmaster closes this security gap by rotating the encrypted headers from top to bottom as they are used, so all messages are the same size. Another technique to confuse traffic analysis is inserting a random lag time before messages are forwarded.
Web-based anonymous e-mail services are far more user-friendly but less secure. Hushmail, recently reviewed in PC Magazine, offers free and paid versions. Anonymizer.com's Total Net Shield product provides anonymous e-mail, surfing, and instant messaging. W3-Anonymous Remailer is another free, easy-to-use service.