forgeries(7)                                                      forgeries(7)

NAME

       forgeries - how easy it is to forge mail

SUMMARY

       An  electronic mail message can easily be forged.  Almost everything in
       it, including the return address, is completely under  the  control  of
       the sender.

       An  electronic mail message can be manually traced to its origin if (1)
       all system administrators of intermediate machines are both cooperative
       and  competent, (2) the sender did not break low-level TCP/IP security,
       and (3) all intermediate machines are secure.

       Users of  cryptography  can  automatically  ensure  the  integrity  and
       secrecy  of  their  mail messages, as long as the sending and receiving
       machines are secure.

FORGERIES

       Like postal mail, electronic mail can be created entirely at  the  whim
       of  the sender.  From, Sender, Return-Path, and Message-ID can all con-
       tain whatever information the sender wants.

       For example, if you inject a message through sendmail  or  qmail-inject
       or  SMTP,  you  can simply type in a From field.  In fact, qmail-inject
       lets you set up MAILUSER, MAILHOST, and MAILNAME environment  variables
       to produce your desired From field on every message.

TRACING FORGERIES

       Like  postal mail, electronic mail is postmarked when it is sent.  Each
       machine that receives an electronic mail message adds a  Received  line
       to the top.

       A  modern  Received  line contains quite a bit of information.  In con-
       junction with the machine's logs, it lets a competent  system  adminis-
       trator  determine  where the machine received the message from, as long
       as the sender did not break low-level TCP/IP security  or  security  on
       that machine.

       Large  multi-user machines often come with inadequate logging software.
       Fortunately, a system administrator can  easily  obtain  a  copy  of  a
       931/1413/Ident/TAP server, such as pidentd.  Unfortunately, some system
       administrators fail to do this, and are thus unable to figure out which
       local user was responsible for generating a message.

       If all intermediate system administrators are competent, and the sender
       did not break machine security or low-level TCP/IP security, it is pos-
       sible  to  trace  a  message backwards.  Unfortunately, some traces are
       stymied by intermediate system administrators who are uncooperative  or
       untrustworthy.

CRYPTOGRAPHY

       The sender of a mail message may place his message into a cryptographic
       envelope stamped with his seal.  Strong  cryptography  guarantees  that
       any two messages with the same seal were sent by the same cryptographic
       entity: perhaps a single person, perhaps a group of cooperating people,
       but in any case somebody who knows a secret originally held only by the
       creator of the seal.  The seal is called a public key.

       Unfortunately, the creator of the seal is often an insecure machine, or
       an  untrustworthy  central  agency, but most of the time seals are kept
       secure.

       One popular cryptographic program is pgp.

SEE ALSO

       pgp(1), identd(8), qmail-header(8)

                                                                  forgeries(7)