Manual Reference Pages - FORGERIES (7)
forgeries - how easy it is to forge mail
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,
(3) all intermediate machines are secure.
cryptography can automatically ensure the integrity and secrecy
of their mail messages, as long as
the sending and receiving machines are secure.
Like postal mail,
electronic mail can be created entirely at the whim of the sender.
Message-ID can all contain whatever information the sender wants.
For example, if you inject a message through
SMTP, you can simply type in a
qmail-inject lets you set up
MAILNAME environment variables
to produce your desired
From field on every message.
Like postal mail,
electronic mail is postmarked when it is sent.
Each machine that receives an electronic mail message
Received line to the top.
Received line contains quite a bit of information.
In conjunction with the machines 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
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.
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
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
Visit the GSP FreeBSD Man Page Interface.
Output converted with manServer 1.07.