forgeries(7)                                             Miscellaneous Information Manual                                             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 coopera-
       tive 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
       contain 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 conjunction with the machine's logs, it lets a competent system administra-
       tor 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
       possible 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  cooperat-
       ing 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)

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