Cable Scrambling News
by The Mad Phone-man

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CABLE COMPANIES RESPONSIBLE FOR THEFT OF SERVICE

A 1986 Showtime/The Movie Channel study that showed the cable industry itself
responsible for half the theft of service (1.4 Billion/year), in the country
may have understated the extent of the problem, according to panelists at a 
recent NCTA convention session on cable piracy.
 
Jerimy Stern, ex director of the OCST (Office of Cable TV Theft) which is a
joint venture funded by the NCTA and the MPAA (Motion picture Assc. of America)
stated that many cases of unauthorized reception occur through error or 
omission on the part of the cable companies and not through any willful,
malicious or criminal intent on the part of the viewer.
 
Loosely managed "Hot Disconnects" programs are the primary problem. The "Hot"
cable is left in the home to simplify reconnection when the new resident moves 
in. One panelist described a "tap verification" audit he did of 18,000 homes, in
which they found 332 basic and 1w=2 unauthorized hookups. After identifying
a pirate, a "sales specialist" was sent out to sign him up. They found 23%
were willing, making the program highly profitable.

Cable companies are now following this lead and are setting up their own 
"tap audit" programs.
 
The OCST has also become active in the prosecuting of dealers of pirate 
decoders (currently a highly profitable business) using third party resources
of the FBI and Customs Service. Customs is trying to cut the flow of off shore
decoders (Taiwan) being imported. Civil suits are being used sparingly
because of their high cost, the possibility of receiving nothing in return
and the possibility of countersuits for false prosecution. When a suit is won
the PR people are quick to publicize it thru the media.







The SSAVI Cable Scrambling System           
by Mad Phone-man

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Short of the D.E.S. based Video Cypher system, one of the most sophisticated
and versatile video/audio scrambling systems is the S.S.A.V.I. system. The 
acronym is the "Suppressed Sync Active Video Inversion". Zenith has exploited
this system for years and later enhanced versions, known as Z-Tac and A-Tac
have SSAVI at their roots.

SSAVI was successfully marketed to numerous over-the-air subscription services,
most of which are defunct now. In the wake of these services, however are 
thousands of SSAVI decoder units being sold by a variety of companies and
individuals for use on CATV systems.
 
There is an inherent problem in this re-marketing of STV units in that the
Zenith tuner has been stripped of its VHF  capability. The STV services were
UHF systems. The STV SSAVI units, therefore, had no need for VHF tuning 
capabilities.

There are, on the other hand, SSAVI units whose initial purpose was CATV based
and which do have VHF tuning capability. The average consumer, however is hard
pressed to know just what he might receive when ordering a SSAVI unit. 
companies employ a variety of techniques to modify the STV (UHF) units for VHF
reception. There are also numerous revisions of the SSAVI units, all from
Zenith, that date back to the pre-VLSI era. Most units which the author has
dealt with do employ VLSI technology and therefore are minus an entire PCB
which earlier models had mounted in their top shells and accommodated discreet
circuitry, later replaced by a single VLSI device (GATEARRAY).
 
The old discreet versions are the most versatile in terms of modifying, but
least available in numbers. Schematic diagrams for the discreet SSAVI devices
are available from Shojiki Electronics, (716) 284-2163 
This article, therefore will deal with the SSAVI units at a more superficial
level. There are 4-modes of operation obtained from 3 variables available to
the SSAVI operator. These variables are:
 
       1) Normal/ Suppressed sync
       2) Normal/ Inverted video
       3) Normal/ Suppressed audio
 
The 4 video modes of operation thus yield:
       1) Normal video/ Normal sync
       2) Normal video/ suppressed sync
       3) Inverted video/ Normal sync
       4) Inverted video/ suppressed sync
 
The first of these modes is "clear" transmission or "non-scrambled". The 
remaining three are designed to foil reception by standard TV receivers. In the
case of mode 2, thw sync pulses are offset from their normal "Blacker-than
black" position such that the front and back porch of the sync pedestal are at
+80 IRE units. This action prevents the sync-separator in a standard TV from
stripping off the sync pulses. The result is that horizontal sync is lost and
the picture tends to "tear" or roll horizontally. In addition, the AGC circuitry
is confused and tends to DC clamp the blackest portion of the video to the
sync level.
 
The level used in maximum security is mode 4. In this mode, the video is 
inverted between each horizontal sync pulse from line 25 to line 260 of the
active scan lines. The sync pulses are suppressed as described earlier, but
NOT inverted. This is a clever technique to foil pirate decoders. This is 
because if one simply inverts the composite video, one also inverts the sync
pedestal, thus inverting the chroma burst on the sync back porch. Thus the 
video chroma (color) will be incorrect. The successful decoder must, therefore
invert the video ONLY between horizontal sync pulses, and provide an offset
pulse gated to shift the sync pulses back to their normal level.
 
To further complicate matters, modes 1-4 may be switched between at random,
under command of the head end, to foil simple static decoders which cannot 
automatically track these mode switches.
 
Audio in the SSAVI system may also be displaced, preventing reception on a
standard TV receiver. It, when desired can be shifted, SCA style, to a
subcarrier. One can see that the SSAVI system provides a fairly high degree
of security.
 
The availability of SSAVI units and their employment by unauthorized persons
caused some initial grief for CATV operators. To render the SSAVI units non-
usable, Zenith changed the video inversion key employed by the CATV-SSAVI units
to differ from the STV SSAVI units.
 
The SSAVI units key on the binary level transmitted during the second half of
line 20 during the vertical blanking interval. When this level is high, the 
coming frame is to be inverted. When this level is low, the coming frame is
to be normal (non-inverted).
 
SSAVI cable systems, therefore, employ a couple of techniques to foil STV units
which are keying on line 20. One technique involves maintaining the video in the
inverted state, but transmitting a "bogus" line 20 key to cause the STV SSAVI
units to switch states at a random, frequent rate. This results in "flashing".
The picture switches between normal and inverted at a high rate producing an
annoying FLASH syndrome.
 
Another technique used by CATV-SSAVI systems is to transmit the bogus line 20
signal as described, but to transmit the key on line 21 which then allows the
video to become dynamically switched from normal to inverted once again.
 
Shojiki sells a manual on a circuit called Z-trap. This circuit foils the first 
of these techniques by returning control of the line 20 key to the user. The
circuit provides the user with a switch which selects between high and low for
insertion during line 20. The circuit stops the flashing.

The more state-of-the-art systems like Z-tac use a still different inversion 
key. The sync suppression technique is never-the-less, identical to the SSAVI
system.

It is an easy mater enough to use a STV-SSAVI unit for CATV reception. One
need only to employ a "block converter" ahead of the SSAVI unit. The STV-SSAVI
units can be tuned through the upper 2/3 of the UHF spectrum by means of a
multi-turn pot inside the unit. The block converter will up-convert CATV
frequencies into this same band of freqs. The block converters are available 
from Radio Shack and the likes.
 
The limitation in the block converter technique is that hyper-band and a large
portion of the super-band signals fall above UHF channel 83 and above the 
SSAVI's tuning range. For systems where all premium channels are in the 
mid-band, however, this technique works well.
 
If one has need of access to super/hyper band channels a converter-to-block
converter to SSAVI hook-up works equally well with an important caveat. The
converter must NOT re-modulate the video. Converters which provide mute/volume
control capability are therefore not acceptable. The reason for this follows.
The hook-up then, looks like this:
 
 
 
CATV-> Converter -->ch 3 --> Block conv --> ch 34-36 -->SSVI -->ch 3 --> TV
         down        out       up           tunable
 
The SSAVI decoder relies on a 504khz synchronizing signal derived from the 
carrier itself. Therefore, down converters which re-modulate destroy this 
reference and cause the SSAVI to malfunction. Simple heterodyning down-
converters allow the SSAVI unit access to the actual carrier of the 
transmitted video.

To circumvent all these frequency conversions, many resellers install small
VHF tuners into the SSAVI units. Depending on the quality of the tuner, the
reception may be better or worse than the multi-conversion system.
 
SSAVI units may also be modified to "skew" their internal timing so as to key
off of line 21 so as to be compatible with systems whose real inversion key 
resides on line 21 as described earlier. The older discreet IC SSAVI units lend
themselves to this most readily. The VLSI equipped units, never the less can 
also be modified to be one scan line shifted, by interruption of the 504khz
reference for 32 cycles.







CABLE TV SCRAMBLING TECHNIQUES       by The Mad Phone-man
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There are 4 major methods of pay-channel security and each has different
consequences for cable ready receivers. The 4 systems are jamming, trapping
out-of-band scrambling and in-band scrambling.
 
Jamming:
   A jamming signal is placed between the picture carrier and the aural
carrier of the secured channels. The cable operator supplies a filter for
each customer for each paid channel. This type of security is easily defeated
by homemade notch filters.
 
Trapping:
   In these systems frequency filters are installed in line with the cable
drops on telephone poles. The traps are removed for customers paying for the
premium channels. Cable-ready TV's work fine in these systems. 
 
Scrambling - The gated Sync Methods:
   Scrambling in the cable TV business still generally means pulsed sync 
suppression. In its simplest form, amplitude of the picture carrier is reduced
by 6 dB during the horizontal blanking intervals and sometimes during the
vertical blanking intervals. The resulting video signal has sync tips between
the black and white levels. Sync separators in the set cannot operate properly
with this signal, nor can AGC and color circuits, so the picture is scrambled.
The decoder compensates by attenuating the signal during the time in which
the transmitted signal was not attenuated. In order to accomplish this, the 
logic controlled gain switch must get timing information. In-band systems
transmit pulses as amplitude modulation of aural carrier or a separate carrier
in out of band systems.
 
Out of band scrambling:
     The usual setup is that the decoder is connected directly to the cable
ahead of the channel converter. Decoding is done at the pay channel frequency.
The decoder is likely to be in a separate box, added to an old system to 
provide pay channels. The box consists of a simple receiver (90-120mhz) for the
out-of-band data carrier and a broad band 6 dB gain switch. There is provision
for several scrambled channels, each which has a different data carrier.
This system is directly compatible with cable ready receivers. Without the
cable converter, the decoder is connected to the TV. Tuning and remote features
of the TV are preserved with the only inconvenience being the need to operate the
switch on the decoder when changing to and from any scrambled channel. Out-of- 
band systems tend to last until the operators using them rebuild to provide for 
a large increase in the number of channels.
 
In Band Scrambling:
    In this system any number of the available channels can be scrambled. 
Because the data carrier for each scrambled channel is its own aural carrier, 
only one data receiver, at the aural carrier frequency (eg. ch 3) is required.
The decoder detects the presence or absence of data automatically switching 
itself in or out. The converter-decoder box can be hardwired to decode just the
channels ordered, using a prom like device. Alternatively, the transmitted
channels can be "tagged" by time division multiplexing binary tag (program
identification)  data with the sync data on the aural carrier. The decoder 
boxes can be wired for "tiers" (groups of programs the cable operator sells
together) rather than fixed channels, giving the operator more flexibility.
The decoder boxes can be "addressable". These boxes have a separate out of band
data channel for data from the head end. Each box has a serial number burned
into its logic or otherwise available to its logic circuitry, and its channel
or tier authorization stored in volatile ram. A computer at the headend 
periodically addresses all decoders in the system individually and loads each
with the channel or tier capacity ordered by the customer. The need for house
calls is reduced, PPV (Pay per view) is possible, and missing boxes cam be 
turned off, rendering them useless for premium channel viewing. Some but not
all of these features can be programmed into out-of-band systems.
 
Aside form their ability to generate sync pulses, thus foiling the scrambling
system, cable ready TV's have presented another difficult problem for in-band
systems. Because the decoder operates at the converted channel, a channel 
converter is required ahead of it. Whether the TV receiver is cable-ready or
not, it operates only at the converted channel, wasting the tuning and remote
control features.

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