TUCoPS :: Phreaking Voice Mail :: faxint.txt

Fax Machine Interception


This article is reprinted from Full Disclosure #23. Copyright (c) 1991 Full 
Disclosure. Permission granted by publisher to reprint when subscription 
information provided: Full Disclosure, Box 903-R, Libertyville, Illinois 
60048, Phone: (708) 395-6200, Fax: (708) 395-6022, BBS: (708) 395-3244, Toll 
free: (800) 786-6184. Subscriptions: $18 for 12 issues.

As with the introduction of all new communications technologies, there is a 
time lag between the availability of the technology and commercial 
development of interception devices. Accompanying the use of both are 
unanticipated risks and the potential for misuse and misunderstandings.

False Sense of Security

With the widespread proliferation of fax machines came increased use. In 
general, a document transferred has been given the same sort of validity as 
one sent or received by U.S. Mail. In general, such communications were 
originally secure. Now that interception equipment is available, the sense of 
security has become false.

For all practical purposes, fax is a remote photocopying machine. The process 
begins with the sending unit converting the image on the page into a 
digitized image (numbers in an electronic format) and transmitting it as a 
noise sounding signal over a phone line. The receiving fax converts the 
signal into dots and prints it.

Since the image is transmitted over standard phone lines, the communication 
is subject to interception. However, rather than tapping the line with a tape 
recorder or simply listening to the oral communications, an interception 
device that makes sense of the specialized signal is necessary. Sometimes 
this is done by recording the transmission and later converting the recording 
of the modem signal to a computer image, sometimes it is done 'on the fly' as 
the signal is being intercepted.

Simple Fax Intercepts

Why not just use a standard fax machine for interception? The signal 
sequences and handshaking at the time machines first connect complicates the 
possibility. During startup, the machines automatically select one of several 
built in protocols depending on line conditions. That is why on really noisy 
connections, the transmission of a page can take much longer. Directly 
connecting a 3rd fax machine to the line may confuse this process. Both the 
receiving unit and the intercepting machine would be sending signals about 
line conditions and protocol. However, if a 3rd fax machine did manage to get 
properly synchronized to the signal in use without interfering with the 
initial handshake, it would print an image identical to the one received by 
the intended recipient. We had mixed results when we tried this in our lab. 
Sometimes we managed to get all three machines synchronized. Using unmodified 
fax machines to attempt intercepts didn't provide sufficient reliability to 
be considered a viable approach. Indeed, continued attempts of this approach 
would likely put both sender and recipient(s) on notice that something was 
wrong as connections would be repeatedly lost.

This doesn't mean that it is really complicated to intercept faxes. The 
Philadelphia Inquirer reported in September 1990 that Japanese hackers have 
been stealing valuable information from corporations by using fax 
interception. The article claimed it could be done by anyone with a little 
knowledge of electronics. We agree, we have intercepted faxes in our lab. 
(See front cover for one such example.)

Doing It Right

The latest commercially available fax interception devices generally use fax 
boards in IBM PC or compatible computers. The actual hardware used for fax 
interception is often the same as used by normal computer-fax systems. The 
software is more sophisticated. Rather than attempting to synchronize with 
the sending unit by sending protocol information, it adjusts to whatever 
protocol the two main players have established and stores the signal 

After interception, the electronic information is stored in the computer and 
is available for review, to be printed, altered or discarded. Such equipment 
can be left unattended for long periods if necessary, or monitored for the 
instant use of information in cases where law enforcement is standing by 
waiting for some specific bit evidence.

Cellular Fax Interception

Cellular phone based fax machines provide ripe opportunity for `hacker' 
intercepts, since the signal is available via low cost police scanners. No 
physical connection to a common carrier network is necessary. There is 
absolutely no risk of being detected.

Commercial fax interception equipment gets more complicated, though. Since 
fax messages might be on the same phone lines as voice or other computer 
modem communications, some of the interception devices automatically route 
different types of communications to different interception devices. This 
provides the interceptor with a separate recordings of voice phone calls, 
faxes, and other computer communications.

Such fax interceptions are based upon the interceptor having a specific 
target. Distributing the sorts of information received for analysis isn't 
much different from an ordinary, now old fashioned, wiretap. 

Broadband Interception

Presorting of signals and voice communications as described above makes 
broadband scanning for fax messages easy. The interception of satellite or 
microwave links has become possibile. Cooperation by a common carrier with 
the government has happened in the past, and strikes a chord of dangerous 
reality today. But it really takes little by way of home fabricated equipment 
to monitor much of the satellite link traffic. Commercial equipment is also 
available. One commercial fax interception unit can decode up to 150 
simultaneous fax transmissions from a 6,000 phone line satellite link.

Such broadband interception can also be done on oral calls, however, the task 
of listening to all the conversations for the important ones is much, much 
greater compared to scanning faxes. First, faxes are usually much more direct 
and to the point than normal phone conversations (not so much about Sunday's 
game). Additionally, optical character recognition (OCR) process can be used 
to convert much of the text to standard computer data and then be 
mechanistically selected for closer scrutiny by an automated search of 
keywords of interest. Encryption of a fax could also be noted, perhaps 
triggering further attention.

The risks resulting from broadband interceptions are henious. Your fax could 
be intercepted not because you were a selected target of law enforcement, 
industrial spies or miscreant hackers, but because of the route your fax 
travelled through the common carrier networks. Broadband interceptions become 
a modern day version of general warrants. Satellite signals don't respect 
borders. Interception in nations with no privacy concerns for radio signals 
of what we, as users, understand to be Constitutionally protected 
communications has become a real threat. There are areas contained within our 
national frontiers where the United States Constitution does not apply. 
Foreign embassies present one such clearcut example. The status on Indian 
Reservations is not cleancut. 

Dangers of Fax

The February 13, 1990 issue of the American Bankers' Association publication 
``Bankers Weekly'' reported that ``In one incident, a bank suffered a $1.2 
million loss through fraudulent funds transfer requests which were 
accomplished using nothing more than business letterhead, tape and sissors.'' 
A fax machine made such simple tools effective. Inordinate reliance on 
technology permitted the loss to actually happen.

The journal continues that there is a need for legislation (changes to the 
Uniform Commercial Code) to put a stop to the problem. Unfortunately, 
legislative efforts alone cannot correct the problem. The first step, is an 
understanding of the technology.

Once the technology is understood, administrative procedures can be 
implemented by users of fax machines to protect themselves. That protection 
cannot be successful without understanding the limitations of the machinery. 
Taking any communications device for granted is a high risk path.

New Techniques For Fraud

The advent of fax technology has opened the door to new methods of fraud. 
Those intent on committing fraud have always devised methods of bypassing 
normal authentication systems in order to steal. As technology evolves, these 
methods also evolve. Protective measures must follow suit.

Faxes represent a multiple whammy. People who send faxes have some geographic 
distance between them. Because of past reliance on semi-automated 
communications, formal verification proceedures are bypassed, substituting 
the mysterious nature of modern communications. There was a time, even 
recently, that tellers at banks asked for positive identification even in the 
case of small cash transactions inside a bank. Yet today we witness orders 
for large sums being processed simply because ``it came by fax.'' This is 
truly a conspiracy of laxness and misinformation.

A written purchase order from a company is likely to have a particular form, 
and include a signature. One attempting to issue a fraudulent purchase order 
would need to forge both the form and the signature. Additionally, envelopes 
and possibly a postage meter imprint from the issuing company would also be 
needed. Elsewhere in this issue we reprint a letter from the Federal 
Communications Commission. The letterhead was, for reasons we have been 
unable to determine, typed instead of printed. Some of the recipients we've 
talked to have placed calls to verify the authenticity of the letter. As it 
turns out, the letter was authentic and official.

A purchase order sent by fax on the other hand, can be created by cutting, 
pasting and xeroxing together parts of other orders from the company. When 
received by fax, the fake would appear legitimate.

PC's & Fax: The Miscreants Gun

The advent of PC based fax boards exaggerates these problem. A fax that 
originates, is received by, or intercepted by a personal computer (PC) fax 
board really opens the door for miscreants.

A fax, when stored on a PC is easily modified using ordinary commercial 
software intended for preparation of graphics. An image of the fax can be 
brought up on the screen and parts of it altered or cut and pasted 
electronically. For example, a purchase order could have a shipping address 
altered. A signature could be removed from one document and placed on 
another. All such operations can be done on a computer screen in moments. 
Document changes that could take a professional forger hours to accomplish 
could be done in minutes by an amateur, even an underage one.

Bogus faxes can be created to be sent to another fax, or incoming faxes could 
be altered by an employee and printed as authentic. Detection is difficult to 
impossible, depending on verification techniques used at audit.

The difficulty of intercepting standard U.S. Mail or voice phone calls and 
altering the content by a third party is enormous compared to fax messages. 
Before a fax message is printed, it is just a series of electrical signals. 
Any alternations result in changes without a trace of the alteration.

The receipt of a fax is <B>not<D> a confirmation of its content, unless other 
corroborative authentication validates the information.

Someone with access to a phone closet can route incoming fax line to a PC. 
The fax can then be connected to a different phone line. All incoming faxes 
would be first received by the PC and the operator could alter, erase, or 
forward without change those faxes to the standard fax machine. A pre-review 
and alteration if desired scheme can be effected. The same can not easily be 
accomplished with normal voice phone calls, or the U.S. Mail.

With the advent of the Caller-ID services, this information should soon be 
incorporated into fax machines, so the true number of the caller will be 
placed on the fax. This will still do nothing to prevent transmission of 
bogus faxes over that phone line.

Protect Yourself

The best rule for protecting one's interests when using faxes is to use them 
only with other confirmation or as confirmation of other communications. They 
should never be used for final copies of contracts, purchase orders or other 
important documents that could have a significant impact if altered, or 
entirely fabricated.  Where would we be if our WW2 treaties terminating 
hostilities were faxed documents. Additionally, information that would not be 
given out over a standard phone conversation, subject to a wiretap, or other 
listeners (via a speakerphone, extension, etc), should not be sent by fax. 
There is no way to tell who may pick up a received fax and read it. In fact, 
it is more likely an unintended party will read a fax than pick up an 
extension phone and eavesdrop on a voice call (intentionally or not).

It should be kept in mind that any errant employees or others that could get 
access to the fax phone line(s) could intercept all faxes sent or received 
and make use of the fax images for whatever purpose they desired.

The intercepted faxes can be used to collect or create incriminating 
evidence, industrial espionage, or as the base of documents to be used in 
forgery. There's a whole new meaning to autograph collection.


Fax technology in its current form provides a useful service for business and 
others. However, the risks must be examined so the use doesn't go beyond that 
which is appropriate given its current functionality / risk ratio.

In conclusion, the convenience of a fax must be weighed against its risks and 
procedures implemented to authenticate incoming and outgoing faxes as well as 
what information is communicated by fax. As with all technologies, it must be 
understood so that it can be used for purposes that are appropriate for the 
needs of the technology and the user. A lack of understanding can leave the 
user exposed to unnecessary danger, liability and loss. When used with an 
understanding of the benefits as well as the pitfalls, a fax machine can 
greatly enhance productivity.

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