Date: Sun, 6 Oct 1996 08:18:57 -0400
From firstname.lastname@example.org Sun Oct 6 08: 20:17 1996
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- AMERICA / EUROPE - WHERE ARE THE DIFFERENCES?
Bevin BODEN wrote:
> What are the differences between video cypher and videocrypt
Ok, I'll take a stab at this. VideoCipher II+ video is not really
'Ciphered', but rather only inverted with the horizontal and vertical
sync pulses ripped out and replaced with digital data. Also the color
burst is shifted in voltage so TV sets with robust sync circuits cannot
lock onto the color burst alone. It is the audio in VCII+ that is
really encrypted, using DES. The audio is digitized, DES encrypted,
then inserted into the horizontal and vertical sync intervals now made
available by the absence of the sync pulses. The DES encrypted audio is
VCII+ major strength. No one has really cracked DES, and all existing
VCII hacks are modifications to existing decoders to fool them into
believing the channel is subscribed to. There is/was a hack called the
MIP that was supposed to 'break' the II+ board, but it too was only
exploiting channels that went into 'free preview' mode. It fooled the
decoder into believing the channel was in perpetual free preview mode.
The last I had heard about the MIP is nearly a year old, and they were
trying to pull keys out of existing VCII+ boards. By doing that, they
could then decode the raw authorization datastream and get the current
monthly keys. By doing that VCII+ would be effectively compromised.
Each scrambled channel is encrypted under its own key, but those
individual channel keys are encrypted under the current monthly key.
Each modules keys seem to be protected by hardware mechanisms that are
hard to circumvent.
VideoCrypt is a cut-rotate video scrambling mechanism. Each video line
is divided into 256 points, and then the video line is 'left justified'
around a random point picked for each line. I believe the European
implementations of VideoCrypt are an analog system, while DSS used in
the US is digital, but mostly the same algorithm. I have no idea how
the audio is protected, if at all, with VideoCrypt. Compromising
VideoCrypt requires getting the random number generator seed value.
Under the DSS implementation I believe these seed values are encrypted
under a public key mechanism, where the 'smart cards' contain the
corresponding private key needed to decrypt seed values targeted for a
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