telephone network security and the capn crunch whistle in the 1960s and early 1970s
TRANSCRIPT
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Telephone Network Securityand the “Cap’n Crunch” whistlein the 1960’s and early 1970’s
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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.
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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.
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Hierarchical Network
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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.
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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.
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Signaling Cont.
• In order to reduce the probability that a human voice will mimic switch signals, special tone pairs were used.
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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.
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Push Button Local Loop Signaling
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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)
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Interoffice Signaling
• A different signaling protocol is needed to prevent a user from sending signals to switches downstream.
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Interoffice Signaling
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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.
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A Blue Box Device
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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
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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)
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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.
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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.
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What about the Cap’n!?!