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Hackers Underworld 2: Forbidden Knowledge
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BIOC.7
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1994-07-17
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******BIOC Agent 003's course in*******
* *
* ========================== *
* =BASIC TELECOMMUNICATIONS= *
* ========================== *
* Part VII *
***************************************
Preface:
After most neophyte phreaks overcome
their fascination with Metro codes and
WATS extenders, they will usually seek
to explore other avenues in the vast
phone network. Often they will come
across references such as "simply dial
KP + 2130801050 + ST for the Alliance
teleconferencing system in LA."
Numbers such as the one above were
intended to be used with a blue box;
this article will explain the
fundamental principles of the fine art
of blue boxing.
Genesis:
--------
In the beginning, all long distance
calls were connected manually by
operators who passed on the called
number verbally to other operators in
series. This is because pulse (aka
rotary) digits are created by causing
breaks in the DC current (see Basic
Telcom V). Since long distance calls
require routing through various
switching equipment and AC voice
amplifiers, pulse dialing cannot be
used to send the destination number to
the end local office (CO).
Eventually, the demand for faster and
more efficient long distance (LD)
service caused Bell to make a
multi-billion dollar decision. They
had to create a signaling system that
could be used on the LD Network.
Basically, they had two options:
[1] To send all the signaling and
supervisory information (ie, ON & OFF
HOOK) over separate data links. This
type of signaling is referred to as
out-of-band signaling.
-or-
[2] To send all the signaling
information along with the conversation
using tones to represent digits. This
type of signaling is referred to as
in-band signaling.
Being the cheap bastard that they
naturally are, Bell chose the latter
(and cheaper) method -- IN-BAND
signaling. They eventually regretted
this, though (heh, heh)...
IN-BAND SIGNALING PRINCIPLES:
-----------------------------
When a subscriber dials a telephone
number, whether in rotary or touch-tone
(aka DTMF), the equipment in the CO
interprets the digits and looks for a
convenient trunk line to send the call
on its way. In the case of a local
call, it will probably be sent via an
inter-office trunk; otherwise, it will
be sent to a toll office (class 4 or
higher -- see Telcom IV) to be
processed.
When trunks are not being used there is
a 2600 Hz tone on the line; thus, to
find a free trunk, the CO equipment
simply checks for the presence of 2600
Hz. If it doesn't find a free trunk the
customer will receive a re-order signal
(120 IPM busy signal) or the "all
circuits are busy..." message. If it
does find a free trunk it "seizes" it
-- removing the 2600 Hz. It then sends
the called number or a special routing
code to the other end or toll office.
The tones it uses to send this
information are called multi-frequency
(MF) tones. An MF tone consists of two
tones from a set of six master tones
which are combined to produce 12
separate tones. You can sometimes hear
these tones in the background when you
make a call but they are usually
filtered out so your delicate ears
cannot hear them. These are NOT the
same as touch-tones.
To notify the equipment at the far end
of the trunk that it is about to
receive routing information, the
originating end first sends a Key Pulse
(KP) tone. At the end of sending the
digits, the originating end then sends
a STart (ST) tone. Thus to call
914-359-1517, the equipment would send
KP + 9143591517 + ST in MF tones. When
the customer hangs up, 2600 Hz is once
again sent to signify a disconnect to
the distant end.
History:
--------
In the November 1960 issue of The Bell
System Technical Journal, an article
entitled "Signaling Systems for
Control of Telephone Switching" was
published. This journal, which was
sent to most university libraries,
happened to contain the actual MF tones
used in signaling. They appeared as
follows:
Digit Tones
----- -----
1 700 + 900 Hz
2 700 + 1100 Hz
3 900 + 1100 Hz
4 700 + 1300 Hz
5 900 + 1300 Hz
6 1100 + 1300 Hz
7 700 + 1500 Hz
8 900 + 1500 Hz
9 1100 + 1500 Hz
0 1300 + 1500 Hz
KP 1100 + 1700 Hz
ST 1500 + 1700 Hz
11 (*) 700 + 1700 Hz
12 (*) 900 + 1700 Hz
KP2 (*) 1300 + 1700 Hz
(*) Used only on CCITT SYSTEM 5 for
special international calling.
Bell caught wind of blue boxing in 1961
when it caught a Washington state
college student using one. They
originally found out about blue boxes
through police raids and informants.
In 1964, Bell Labs came up with
scanning equipment, which recorded all
suspicious calls, to detect blue box
usage. These units were installed in
CO's where major toll fraud existed.
AT&T Security would then listen to the
tapes to see if any toll fraud was
actually committed. Over 200
convictions resulted from the project.
Surprisingly enough, blue boxing is not
solely limited to the electronics
enthusiast; AT&T has caught
businessmen, film stars, doctors,
lawyers, college students, high school
students and even a millionaire
financier (Bernard Cornfeld) using the
device. AT&T also said that nearly
half of those that they catch are
businessmen.
Of course, phone phreaks have achieved
an almost cult status. They have also
had their fair share of media. In
October 1971, Esquire published the
infamous "Secrets of the Little Blue
Box" article which featured phreaks
such as Captain Crunch, who took his
name from the cereal which one gave
away whistles that produced a perfect
2600 Hz pitch; Joe Engressia, the blind
phreak; and Mark Bernay, one of the
nation's first and oldest phreaks.
Others such as Apple computer
co-founders Steve Wozniak & Steve Jobs
have also had blue box backgrounds.
1971 also saw the publication of the
first issue of YIPL, the phone phreak
newsletter, (now TAP) under the
editorship of supreme yippie Abbie
Hoffman.
Usage:
------
To use a blue box, one would usually
make a free call to any 800 number or
distant directory assistance (NPA-555-
1212). This, of course, is legitimate.
When the call is answered, one would
then swiftly press the button that
would send 2600 Hz down the line. This
has the effect of making the distant CO
equipment think that the call was
terminated and it leaves the trunk
hanging. Now, the user has about 10
seconds to enter in the telephone
number he wished to dial -- in MF, that
is. The CO equipment merely assumes
that this came from another office and
it will happily process the call.
Since there are no records (except on
toll fraud detection devices!) of these
MF tones, the user is not billed for
the call. When the user hangs up, the
CO equipment simply records that he
hung up on a free call.
DETECTION:
----------
Bell has had 20 years to work on
detection devices; therefore, in this
day and age, they are rather well
refined. Basically, the detection
device will look for the presence of
2600 Hz where it does not belong. It
then records the calling number and all
activity after the 2600 Hz. If you
happen to be at a fortress fone,
though, and you make the call short,
your chances of getting caught are
significantly reduced (see Telcom VI).
Incidentally, there have been rumors of
certain test numbers (see Telcom II)
that hook directly into trunks thus
avoiding the need for 2600 Hz and
detection!
Another way that Bell catches boxers is
to examine the CAMA (Centralized
Automatic Message Accounting) tapes.
When you make a call, your number, the
called number, and time of day are all
recorded. The same thing happens when
you hang up. This tape is then
processed for billing pu