Harvard University, Kennedy School of Government
Harvard Information Infrastructure Project

Symposium on the Global Information Infrastructure:
Information, Policy & International Infrastructure
Cambridge, MA, January 28-30, 1996

Risk-Free Access Into The
Global Information Infrastructure
Via Anonymous Re-Mailers

by Paul A. Strassmann, US Military Academy, West Point; and Senior Advisor, SAIC
and William Marlow, Senior Vice President, Science Applications International Corporation (SAIC)

Quoted portions are excerpted from Raph Levien's Remailer List.

The Context

By far the greatest threat to the commercial, economic and political viability of the Global Information Infrastructure will come from information terrorists. Information terrorism has ceased to be an amateur effort and has migrated into the hands of well organized, highly trained expert professionals. Information terrorist attacks can be expected to become a decisive element of any combined threat to the economic and social integrity of the international community. Nations whose life-line becomes increasingly dependent on information networks should realize that there is no sanctuary from information-based assaults. Commercial organizations, especially in telecommunications, finance, transportation and power generation offer choice targets to massive disruption.

Information terrorism, as a particularly virulent form of information warfare, is a unique phenomenon in the history of warfare and crime. For the last two hundred years the theory of warfare has been guided by "force-exchange" equations in which the outcome was determined by the rate of attrition of each opposing force. In information attacks these equations do not apply because the attacker remains hidden and cannot be retaliated against.

Since biblical times, crimes have been deterred by the prospects of punishment. For that, the criminal had to be apprehended. Yet information crimes have the unique characteristic that apprehension is impossible, since even identification of the criminal is not feasible. Information crimes can be committed easily without leaving any telltale evidence such as fingerprints, traces of poison or bullets.

Changes Introduced By Anonymous Re-Mailers

The introduction of Anonymous Re-mailers into the Internet has altered the capacity to balance attack and counter-attack, or crime and punishment. The widespread use and easy access to acquiring the capacity to launch anonymous messages and software has so far not received adequate attention from a policy and legal standpoint. This topic is sufficiently technical that it has been largely avoided by experts who have so far concentrated on debating social, legal, political and economic consequences of the Global Information Infrastructure. Yet, unless there is a thorough understanding of the technologies that make the Anonymous Re-mailers sources of a pathological danger, there is little hope that effective preventive measures and safeguards can be put in place.

In many respects, the avoidance of technical discussions about some of the pathological aspects of the Internet remind me of the state of medical diagnosis prior to the recognition that bacteriology, prophylactics and inoculation can be only applied following the acceptance of rigorous, analytic and experimental disciplines.

Our Agenda

The purpose of this paper is to bring to the attention of policy-makers some of the relevant facts about Anonymous Re-mailers. All of the material quoted here comes from public sources which are easily accessible to anyone. The wide-spread current uses of Anonymous Re-mailers should be sufficient warning that this topic cannot be considered any more as something hidden, confidential or inappropriate for public discussion.

We find many similarities in the initial denials to the threats from AIDS by the medical and public health establishment. We are dismayed by the avoidance of a candid assessment by public officials about the vulnerability of the Global Information Infrastructure to destructive information epidemics. The purpose of this paper is to increase the awareness of potentially deadly risks that may inhibit the potential gains from the creation of a global information community.

What Is A Re-Mailer?

A re-mailer allows anyone to post messages to newsgroups or to individuals while remaining anonymous. The identity of the sender is hidden from the recipient and remains practically untraceable.

An anonymous re-mailer is a program that runs on a computer somewhere on the Internet. When you send mail to the re-mailer address, the re-mailer takes your name and your address off of the mail message and forwards it to its next destination. The recipient gets mail that has no evidence of where it originally came from, at least not in the headers. You might give away your secret identity in the body of the message, but that would be the sender's own fault.

Anonymous re-mailers can be "chained" so that a message is passed on from one anonymous re-mailer to another, in two or more separate anonymous "hops" as a way of making physical tracing or monitoring increasingly difficult.

One of the most prominent anonymous re-mailers is <anon.penet.fi> is in Finland. It is frequently used by the Russian (ex-KGB) criminal element. <Anon.penet.fi> assigns a numeric identification to each address from which it receives mail. Internet recipients can reply to that secret number. <anon.penet.fi> will also assign to them another anonymous number, and then forward the reply. This creates a double-blind situation where two people could have an ongoing exchange and never know who the other person was. This method of communication is favorite for engaging services of cybercriminals and for authorizing payment for their acts through a third party.

<Anon.penet.fi> can be also used to post a message to Usenet as well. The message can be read by thousands of people, and anyone can send an anonymous reply to the secret Finnish identity. The readers of this paper can easily avail themselves of these services without any special training. Detailed instructions for the use of a remailer service are usually included in the "help" software posted in the remailer's files. For example:

To get an anonymous re-mailer address follow the following instruction. First, you should send mail to: <help@anon.penet.fi>. You'll get back a nice help file automatically. Next, send mail to <ping@anon.penet.fi>. This will allocate your number--from now on you'll be something like <anXXXXXX@anon.penet.fi>, where XXXXXX is your number. Once you have received your anonymous address you can use it like your normal e-mail address.

These capabilities are not trivial, but a source of an exhaustive body of software and communications know-how which can be learned best by consulting one of the many tutorials about this topic, such as<ftp.csua.berkeley.edu: /pub/cypherpunks/re-mailer/hal's.remailer.gz>:

Cyberpunk re-mailers allow a person to send mail with no trace of identity. To use a re-mailer simply do the following:

  • Add the header Request-Remailing-To: and sending to one of the addresses listed below. These headers must be typed in exactly. Mail without these headers is either rejected or delivered to the re-mailer administrators.
  • If you cannot add the required headers, place two colons (::) on the very first line of your message, then on the next line type Request-Remailing-To: and the address you want to send anonymously to.
  • Skip a line, and then begin the message. By using this method you can send the message through more than one re-mailer which will certainly ensure that it will be anonymous.
  • Many re-mailers only allow one recipient per message. A number of standard Cyberpunk Re-mailers are available.
There is a wealth of easily accessible step-by-step instructional material available on the Internet how to use re-mailers and how to evade countermeasures or possibility of detection from any source. Re-mailer operators are in frequent contact with each other and exhibit many of the fraternal habits that previously were shared between amateur radio operators. Some of the most interesting sources of information are:

André Bacard's anonymous re-mailer FAQ is an excellent nontechnical introduction.

For a different take on Net anonymity, see L.Detweiler's home page.


  • Private Idaho is an anonymous re-mailer utility for Windows, supporting PGP, the cypherpunks re-mailers, and Mixmaster, and the <alpha.c2.org> alias server. It too automatically configures itself based on this re-mailer list.
  • <ChainMail> is a re-mailer chaining utility for Mac users, by Jonathan Rochkind. To use it, you need Eudora, MacPGP, and applescript, in addition to a number of applescript scripting additions.
  • <Privtool> is a PGP-aware mailer that also supports Mixmaster.
  • The Community ConneXion has put the Web-premail gateway on its SSL server. That means that you can send anonymous email from the Web without exposing your message in the clear on the connection between your Web browser and the gateway.
  • Sameer Parekh's NEXUS Berkeley / Community ConneXion has a web page set up for sending anonymous mail from your Web client.
  • Michael Hobbs has set up Web gateway to premail. Now you can send anonymous email directly from your Web browser. Don't use this for extremely sensitive stuff, though, because it isn't quite as secure as running premail yourself (in particular, the connection between your Web browser and the gateway is not encrypted).
  • A good source for re-mailer information is the Anonymity, re-mailers, and your privacy page compiled by "Galactus". This is also the best place to look for information about anon.penet.fi.
  • Matt Ghio's re-mailer list is available by fingering re-mailer.help.all@chaos.taylored.com. This file also has all the public keys for PGP-friendly re-mailers. Matt also has a pinging service similar to this one, available by fingering re-mailer-list@chaos.taylored.com.
  • Chaos is having problems getting recognized on the Net. Try re-mailer.help.all@ and see if that works any better. Newer information can be gotten by sending mail to mg5n+re-mailers@andrew.cmu.edu.
  • Help for the Alpha alias server (also available in a plain email version. This is the best way to create an alias for anonymous replies to mail. Not only is it the most cryptographically secure, but you get to pick the alias nickname of your choice. The email addresses are of the form <alias@alpha.c2.org>. Highly recommended.
  • Usura's home page has a bunch of re-mailer related stuff on it, including a help page on chaining re-mailers.
  • The Armadillo re-mailer now has its own Web page.
  • Crown re-mailer help and statistics.
  • Ecafe re-mailer has its own Web page, including quickie info about how to use the re-mailer without encryption or any other extras.
Other resources
  • You want to send secure mail to someone, but don't know their key. Where are you going to get it? Try the keyserver at MIT.
  • Vince Cate's Cryptorebel and Cypherpunk page has pointers to lots of cypherpunk resources.
  • John Perry's jpunix page has info on his MX service for hidden re-mailers, as well as cool links for Mixmaster and other stuff.
  • Lance Cottrell's home page, which has his Chain script, the Mixmaster re-mailer client (including Sun binaries!) as well as other cypberpunk related topics.
  • Vince Gambino's re-mailer page has a good collection of re-mailer help files.

Where Do You Find Re-Mailers?

Computers that offer remailing capabilities are operated by individuals or organizations as a public service, almost always at no charge because it costs so little to set one up. They are available globally. We offer a partial list of re-mailers:

$remailer{"extropia"} = "<remail@extropia.wimsey.com> cpunk pgp special";
$remailer{"portal"} = "<hfinney@shell.portal.com> cpunk pgp hash";
$remailer{"alumni"} = "<hal@alumni.caltech.edu> cpunk pgp hash";
$remailer{"bsu-cs"} = "<nowhere@bsu-cs.bsu.edu> cpunk hash ksub";
$remailer{"c2"} = "<remail@c2.org> eric pgp hash reord";
$remailer{"penet"} = "<anon@anon.penet.fi> penet post";
$remailer{"ideath"} = "<remailer@ideath.goldenbear.com> cpunk hash ksub reord";
$remailer{"hacktic"} = "<remailer@utopia.hacktic.nl> cpunk mix pgp hash latent cut post ek";
$remailer{"flame"} = "<remailer@flame.alias.net> cpunk mix pgp. hash latent cut post ek reord";
$remailer{"rahul"} = "<homer@rahul.net> cpunk pgp hash filter";
$remailer{"mix"} = "<mixmaster@remail.obscura.com> cpunk mix pgp hash latent cut ek ksub reord ?";
$remailer{"syrinx"} = "<syrinx@c2.org> cpunk pgp hash cut reord mix post";
$remailer{"ford"} = "<remailer@bi-node.zerberus.de> cpunk pgp hash ksub";
$remailer{"hroller"} = "<hroller@c2.org> cpunk pgp hash latent ek";
$remailer{"vishnu"} = "<mixmaster@vishnu.alias.net> cpunk mix pgp. hash latent cut ek ksub reord";
$remailer{"robo"} = "<robo@c2.org> cpunk hash mix";
$remailer{"replay"} = "<remailer@replay.com> cpunk mix pgp hash latent cut post ek";
$remailer{"spook"} = "<remailer@valhalla.phoenix.net> cpunk mix pgp hash latent cut ek reord";
$remailer{"rmadillo"} = "<remailer@armadillo.com> mix cpunk pgp hash latent cut";
$remailer{"ecafe"} = "<cpunk@remail.ecafe.org> cpunk mix";
$remailer{"wmono"} = "<wmono@valhalla.phoenix.net> cpunk mix pgp. hash latent cut ek";
$remailer{"shinobi"} = "<remailer@shinobi.alias.net> cpunk mix hash latent cut ek reorder";
$remailer{"amnesia"} = "<amnesia@chardos.connix.com> cpunk mix pgp hash latent cut ek ksub";
$remailer{"gondolin"} = "<mix@remail.gondolin.org> cpunk mix pgp hash latent cut ek reord";
$remailer{'alpha'} = '<alias@alpha.c2.org> alpha pgp';
$remailer{'gondonym'} = '<alias@nym.gondolin.org> alpha pgp';
Much of the knowledge about the characteristics of these re-mailers is available from <remailer-list@kiwi.cs.berkeley.edu>

Role Of Encryption

For added protection, users of Anonymous Re-mailers tend to encrypt their messages just in case one of the remailing links are compromised. PGP (Pretty Good Privacy) encryption is favored because it is freely available and easy to use. A typical digital signature would look like this:
    Version: 2.6.2

    -----END PGP SIGNATURE-----

For responses the sender will choose a passphrase. This phrase will be used to encrypt messages sent back to you. The encryption will be single-key encryption, not PGP's normal public-private key encryption. The reason for this is that public key encryption is usually not necessary in such cases. Single-key encryption does not require a database (such as in the widely used <anon.penet.fi> database for mapping aliases onto addresses), thus increasing the security of communications among anonymous users.

When a recipient responds to the e-mail, his response will be encrypted with the sender's pass-phrase. The sender can read the response by saving it to a file and using PGP on it. PGP will ask for the passphrase, enter the sender's reply, which will make it possible for the recipient to see the response to the e-mail. This feature allows both parties to be securely encrypted, protecting privacy and anonymity in both directions.

How Reliable Are The Re-Mailers?

The knowledge about the characteristics, reliability and trustworthiness of re-mailers is widely distributed through various bulletin boards. These are consulted by persons deeply immersed in Internet-related developments. There is an agile and very active global community that keeps track of the average latency time, uptime of frequently used re-mailers. They post their findings, which in many cases is superior to what a commercial customer is likely to find out about their own data center performance, or about the service quality offered by Compuserve, America-On-Line of Prodigy. Here is an excerpt from such a bulletin:
hacktic  remailer@utopia.hacktic.nl       **** *******     7:10  99.85%
c2       remail@c2.org                    -.-++ ++-.-+  2:10:42  99.83%
rmadillo remailer@armadillo.com           +++++ ++++++    37:03  99.69%
flame    remailer@flame.alias.net         ** * *******    14:55  99.64%
mix      mixmaster@remail.obscura.com     _ _-__...-++ 17:40:48  99.21%
amnesia  amnesia@chardos.connix.com        -+ +--+---   2:04:43  99.20%
ecafe    cpunk@remail.ecafe.org           ## ##-## #--  1:26:54  99.06%
extropia remail@extropia.wimsey.com       .- -.----_.  13:48:11  99.04%
replay   remailer@replay.com               + +** *****     5:36  98.84%
shinobi  remailer@shinobi.alias.net       -- -- - - +     54:43  98.78%
spook    remailer@valhalla.phoenix.net    *  ***** - *    35:07  98.36%
vishnu   mixmaster@vishnu.alias.net       **      #-*#     7:44  98.20%
bsu-cs   nowhere@bsu-cs.bsu.edu              #  # ##.#    28:07  97.78%
gondolin mix@remail.gondolin.org           - --_.----   9:45:55  97.62%
wmono    wmono@valhalla.phoenix.net          **  *   *    12:23  97.57%
hroller  hroller@c2.org                   #*+### -.. #  1:37:24  96.71%
ford     remailer@bi-node.zerberus.de     ._...--._.   21:21:22  95.83%
portal   hfinney@shell.portal.com         ########*#      27:36  95.55%
alumni   hal@alumni.caltech.edu           #     # *  +    25:47  95.29%
penet    anon@anon.penet.fi                  . -- --   13:55:20  87.78%
rahul    homer@rahul.net                  +* *+**+*  #     4:34  93.71%
robo     robo@c2.org                       #-##            5:59  27.86%
History key 
  # response in less than 5 minutes. 
  * response in less than 1 hour. 
  + response in less than 4 hours. 
  - response in less than 24 hours. 
  . response in less than 2 days. 

Specialization Of Services

The operators of various re-mailers are specialized in that they cater to select communities of Internet dwellers. They offer unique services to customers who are seeking different degrees of anonymity. Cognoscenti in the field can readily identify remailers who offer meets diffferent tastes and preferences. Here is an example of remailer characterizations:

<cpunk> A major class of remailers. Supports Request-Remailing-To: field.
<eric> A variant of the cpunk style. Uses Anon-Send-To: instead.
<penet> The third class of remailers (at least for right now). Uses X-Anon-To: in the header.
<pgp> Remailer supports encryption with PGP. A period after the keyword means that the short name, rather than the full email address, should be used as the encryption key ID.
<hash> Supports ## pasting, so anything can be put into the headers of outgoing messages.
<ksub> Re-mailer always kills subject header, even in non-pgp mode.
<nsub> Re-mailer always preserves subject header, even in pgp mode.
<latent> Supports Matt Ghio's Latent-Time: option.
<cut> Supports Matt Ghio's Cutmarks: option.
<post> Post to Usenet using Post-To: or Anon-Post-To: header.
<ek> Encrypt responses in reply blocks using Encrypt-Key: header.
<special> Accepts only pgp encrypted messages.
<mix> Can accept messages in Mixmaster format.
<reord> Claims to foil traffic analysis by reordering messages.
<mon> Re-mailer has been known to monitor contents of private email.
<filter> Re-mailer has been known to filter messages based on content. If not listed in conjunction with <mon>, then only messages destined for public
<alpha> Supports nyms according to the protocol used by alpha.c2.org. This list will be featuring reliability and latency measurements soon for these nymservers.
A fascinating example of specialization is a re-mailer service advertising the capacity to defeat "traffic analysis" used by intelligence agencies. All mail to each destination is first sent through <remail@sitename> which is a standard "cypherpunk" re-mailer with PGP with a few added features. The outgoing mail is not forwarded immediately upon receipt. Outgoing messages are stored in a pool until five minutes after each hour, when all messages in the pool are re-transmitted in a random order, ignoring the order in which they came in. Each message from the re-mailer is sent through a random path of other re-mailers in the re-mailernet. This usually involves between five to 20 "hops" from one re-mailer to another. In each case care is taken for at least one of the "hops" to be in a country with especially relaxed laws concerning electronic messages. Such measures would greatly complicate any tracing that may be contemplated by a law-enforcement agency.

Why Re-Mailers?

E-mail is as fast and casual as a voice phone call, but can be stored and retrieved with infinitely greater efficiency than paper letters or taped conversations. An e-mail message can be re-broadcast the world over, by anyone who comes across a copy of the transmission. Parts of any message can be extracted, edited and easily modified. Meanwhile, the e-mail address of the originator remains a label of its origin. If the storage of that message is not protected - and it rarely is - it can be accessed by anyone who takes the trouble to rummage through any of the many archived computer records that may have received such message. A casual e-mail exchange, with an identifying address, can be then used to compromise the originator. As e-mail traffic takes over an ever increasing share of personal communications, inspection of e-mail traffic can yield more comprehensive evidence than just about any wire-tapping efforts. E-mail-tapping is less expensive, more thorough and less forgiving than any other means for monitoring personal communications. Without protection of privacy, browsing through e-mail archives would become the preferred way for gathering evidence in law enforcement cases. It would also be used as the favorite means for collecting incriminating statements by lawyers engaged in civil litigation.

In casual e-mail exchanges it is easy to make an error. When the message is archived it could be used to haunt a person for decades afterwards. A message intended for a particular individual may be passed on to hundreds or even thousands of others. Unless its origin is anonymous, all e-mail can be traced through identifying addresses that preserve the name of the originator - as well as the names of those who forwarded it - wherever the message traversed. Unless a message is handled anonymously, a trace is left about everyone who received it or passed it on. It would be like a letter that not only identifies the name and address of its author, but also fingerprints of anyone who ever touched it.

It is one of the fundamental strengths of the Internet that it offers an almost universal capacity for free expression of ideas. A person's opinions can be sent anywhere in the world in a matter of minutes, with the originator's name displayed at the top. Is it consistent with the rights to individual privacy and freedom of expression to have one's name clearly associated with a message than may be easily disseminated to unintended recipients?

The issues here are the rights to the freedom of speech and to the rights to personal privacy. Having the right to free speech may work well in the case of verbal expression, but it may cease to have its intended purpose in face of retaliation that may take place decades later. In a system that theoretically can have infinitely large memory and indefinitely long remembrance, the freedom of expression and become abused and perverted by a government that does not respect individual rights.

With the widespread acceptance of Internet-mediated communications it was recognized that the simplest way of securing privacy is through anonymity. That's how anonymous re-mailers came into being. Given the technical characteristics of Internet, there is nothing to prevent anyone to set up a private (or public) anonymous remailing service. Any attempt to prohibit or regulate the use of anonymous re-mailers is technically unfeasible. In a democratic society it becomes politically unacceptable to suppress remailers as potential sources of criminal acts. Such absolute prohibitions would never pass through a legislative process in a free society.


Anonymous re-mailers are here to stay. Like in the case of many virulent diseases, there is very little a free society can do to prohibit travel or exposure to sources of infection. The best one can do is to start treating the pathologies inherent in the Internet in the same way as we have learned to deal with infectious epidemics. That calls for constructing new institutions and processes that are analogues to inoculation, immunization, prophylactics, clean water supply, sewers, hygiene, early detection of outbreaks of diseases, quarantine, the offices of health examiners, the Center of Disease Control and the World Health Organization.

The introduction of most of these restrictive means, imposed mostly by government, were often opposed by those who saw in public health injunctions infringement of individual rights. In due course an informed electorate found it expedient to accept most of the sanitary measures for disease control a bargain that was well worth it.

The history of public health teaches us that suppression of any disease must be preceded by a thorough understanding of its behavior, its method of transmission and how it creates its own ecology. As in the case of smallpox, yellow fever, flu epidemics, AIDS or malaria, it will take disasters before the public may accept that some forms of restrictions on the electronic freedom of speech and privacy may be worthwhile.

It was the purpose of this paper to explain the characteristics of anonymous remailers as one of the potential sources of infectious threats to the well-being of our information-based civilization. We trust that this will be seen as a useful contribution to an already raging debate of how to find a balance between the desirable and the dangerous.

Paul@Strassmann.com and William_Marlow@cpqm.saic.com will be pleased to respond to identifiable commentators on the points of view expressed herein.