Cryptic but handy--VCR codes...
 How do VCRPlus+® codes work? Can
we decipher and predict them? (John, Albuquerque, NM
)
You want me locked up, eh? Gemstar guards
their code like the Smithsonian defends the
Hope diamond. Not that I blame them, after
all, it's their intellectual property and a
treasure.
The VCRPlus+® codes are why you don't
need your kids to program your VCR any
more. Take the number printed next to a show in the local TV listing; enter it into your
VCR remote control. Presto! You've programmed your VCR to record the show
automatically. A much needed breakthrough.
A couple of dauntless programmers (Curt Welch and Ken Sherriff), however, have cracked
Gemstar's cipher for codes up to six digits. Only Gemstar understands the full 8-digit
code.
Gemstar designed a code which deliberately obscures patterns. The rules change within
the system, Curt says but basically the cipher uses the following devices: scramble digits,
assume constants, lookup values in tables, and generate final results with equations. I've
posted a simple example below to illustrate the details.
An outfit (G&G Inc) that trains folks in the programming language, Java, has concocted a
Java calculator based on Curt and Ken's programs. With the calculator, you can generate
VCRPlus+® numbers for channels less than 64. Enter the date, start time, program length,
and channel number. Presto! Out pops the VCRPlus+® code for that show. You predict
numbers by entering future dates.
In November 1994, when the New York Times exclusive right to publish VCRPlus numbers
in its area expired, every excluded newspaper in the market joined the VCRPlus program.
The code is big business.
EXAMPLE (accurate in 1994 but may be incorrect at later times.
Gemstar changes things.) Gemstar designed a code which deliberately obscures patterns. The rules change within the
system, Curt Welch says, but basically the cipher uses the following devices: scramble digits,
assume constants, lookup values in tables, and generate final results with equations.
Let's look at a simple case to illustrate how the code works. Suppose you looked up your show
and found the VCRPlus+® code 5 in the TV listing. What does that tell the VCR? A number,
but the number isn't 5. First the VCR decoder adds the month, January, (1) to the code (5) to
get 6; that's the number. But there's more. Now the decoder converts the number 6 to a 5-bit
binary number (00110)--the kind that computers understand, just zeros and ones.
This number encodes the start time (T2 T1 T0) of your show and the channel (C1 C0) that it's on.
The digits of the time and channel, however, are scrambled in the binary number 6 as the table
shows:
The decoder identifies the start time from the table: T2 T1 T0 = 010, which is binary for the
number 2. It looks up "2" in a table similar to the one below to get the real start time: 7:30 p.m.
| 0 |
6:30 p |
| 1 |
4:00 p |
| 2 |
7:30 p |
| 3 |
4:30 p |
| 4 |
3:30 p |
| 5 |
5:30 p |
| 6 |
6:00 p |
| 7 |
2:30 p |
The channel (C1 C0 = 01) is the number 1, but first the decoder knows to apply a rule (add 1) to
arrive at the real channel which is 2.
The VCRPlus code number, 5, is a single digit. This tells the decoder to assume the day of the
month is the first and the show length is 30 minutes.
The VCR decoder gets the current month (December) and the day today (the 27th) from its
internal clock and assumes the month you want to record is January because the first of December
is long past. So it cranks in next month's number in its calculations. The year doesn't matter.
The VCR can only record shows up to a month in advance using VCRPlus+ codes.
The VCR now has the information it needs so it starts recording your show on Channel 2 at 7:30
p.m. on 1 January 2000 and stops recording 30 minutes later. |
