forgeries(7)      Device and Network Interfaces      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  com-
     pletely 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  inter-
     mediate 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 Mes-
     sage-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 administrator 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, many incompetent system administra-
     tors 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 back-
     wards.   Unfortunately,   some   traces   are   stymied   by



SunOS 5.5                 Last change:                          1






forgeries(7)      Device and Network Interfaces      forgeries(7)



     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 cryp-
     tography 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)



































SunOS 5.5                 Last change:                          2