Telephone Network Security

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20 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Telephone Network Security

and the “Cap’n Crunch” whistle

in the 1960’s and early 1970’s

Overview


The telephone network topology.


Telephone switch signaling protocols.


What is Phone Phreaking?


Hacking the telephone network of the 1960s
and 1970s.


What was done to fix the problem.

The Telephone Network of the
1960’s and early 1970s


Primary function of a telephone network is
to connect telephones together.


Not feasible to connect every user to every
other user directly.


A network is needed.


Hierarchical Network.

Hierarchical Network

Hierarchical Network


Lowest level


end users connected to local
exchange.


Next level up


local exchanges connected
to the primary trunk exchanges.


Next level up


the primary trunk exchanges
connected to the secondary trunk
exchanges.


Can extend to as many levels as needed.

Signaling


Signaling is the means by which routing
information is sent to switches.


Two main types of signaling.



Local
-
loop signaling



Interoffice signaling


Signals were sent on the same line that was
used to transmit voice.

Signaling Cont.


In order to reduce the probability that a
human voice will mimic switch signals,
special tone pairs were used.



Local
-
Loop Signaling


User picks up a telephone and “dials” a
number.


Two types


Rotary


Push Button


The switch at the local exchange routes the
number.

Push Button Local Loop
Signaling

Phone Phreaking

Phreaking


1. The art and science of cracking
the phone network (so as, for example, to
make free long
-
distance calls.)

2. By extension, security
-
cracking in any
other context (especially, but not
exclusively, on communication networks)

Interoffice Signaling


A different signaling protocol is needed to
prevent a user from sending signals to
switches downstream.


Interoffice Signaling

The Blue Box


Codes for interoffice signaling were
published in a Bell Labs journal article.


A box with 7 buttons could be built to route
a call anywhere in the world!


The first device confiscated by the phone
company was blue.


Steve Wozniak was in the Blue Box
business.

A Blue Box Device

How to make a free phone call

Phone


Local Exch.


Account.

System


Primary Exch.


Secondary Exch.

Primary Exch.


Local Exch.


Phone

1(800)555
-
5555

KP
-
187
-
ST

KP
-
07
-
ST

KP
-
095
-
ST

KP
-
252
-
0011
-
ST

Ring

Was the telephone system a
secure network?


The routing signals are sent over the same
lines that carry voice signals (in
-
band).


Cost must have been a factor.


Not only free calls


Bouncing calls between switches (untraceable)


Flooding the network (Denial of service)


How was it fixed?


By 1976 virtually all interoffice trunks were
converted to a new type of signaling


Common Channel Interoffice Signaling


Interoffice signals sent over separate lines.


Benefits of CCIS


Reduces call time set up.


Eliminates false customer simulated in
-
band
signaling.


Send data out of band, parallel to the voice
circuit.


What about the Cap’n!?!