Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!ames!killer!mjbtn!raider!crc
From: crc@raider.MFEE.TN.US (Charles Cain)
Newsgroups: sci.electronics
Subject: Re: advice on descrambler
Summary: VCII techincalities
Message-ID: <120@raider.MFEE.TN.US>
Date: 27 Jun 89 05:13:07 GMT
References: <111377@sun.Eng.Sun.COM> <680@lopez.UUCP>
Reply-To: crc@raider.UUCP (Charles Cain)
Organization: RaiderNet Public Access, Murfreesboro, TN
Lines: 35
Distribution:na

The first method, gated sync, is a fairly old system. 90% of the satellite 
systems in use today use the MA/COM Videocipher II system, with the rest being 
a conglomerate of OAK ORION, SA B-MAC, and CBS Network uses VideoCipher I.

This being stated, VCII is probably the widest used in consumer applications. 
The system is quite secure as it uses the DES algorithm for encryption purposes
and DIGITAL AUDIO. Therefore, one could unscramble the video easily but the 
audio is a whole different matter.

The video is stripped of all H sync and V sync information and it is digitized
and transmitted with the 56 bit 'key' for descrambling. The audio is digitized 
also and is transmitted where the H Sync used to be. The color subcarrier is
also done this way. For purposes of transmission, a replacement H Sync pulse
is generated and  transmitted and this is the gated sync pulse. On dark scenes
it might lock up to an ordinary TV set but when a lightly colored scene comes 
up it will get scrambled up REAL good.

If someone is lucky enough to guess the 56 bit key, then he might think he has
the system beat. Not quite. There are 2 modes of operation, fixed key and 
individually addressable. Fixed key is used mostly during testing. When the
system is fully operational, IA is used. Each uplink site that is transmitting
scrambled material has a computer that transmits the next months key and the
address of those descramblers authorized to receive the program. The computer
is capable of authorizing or deauthorizing up to 2.5 million descramblers a day.

Hope this helps some.


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