shirriff@sprite.berkeley.edu (Ken Shirriff) (04/28/91)
In article <GUEST.91Apr26180111@geech.ai.mit.edu> guest@geech.ai.mit.edu (Guest Account) writes: >For those of you who have heard of VCR PLUS+, does anyone know how the >date, channel, start time and stop time are encoded into the program >number? I was wondering the same thing a couple days ago. After studying the codes for a few minutes, I figured they must be encrypted in some way. Maybe it's a conspiracy to force people to buy TV guides? Ken Shirriff shirriff@sprite.Berkeley.EDU
guest@geech.ai.mit.edu (Guest Account) (04/30/91)
For those of you who have heard of VCR PLUS+, does anyone know how the date, channel, start time and stop time are encoded into the program number? Here are examples: 4-23; Channel 25; 20:00; 23:00 ==> 473323 4-23; Channel 38; 20:00; 23:00 ==> 716694 4-21; Channel 4; 21:00; 23:00 ==> 9711 I can't make rhyme or reason out of it, Watson. ---SHERLOCK HOLMES
strong@tc.fluke.COM (Norm Strong) (04/30/91)
In article <GUEST.91Apr26180111@geech.ai.mit.edu> guest@geech.ai.mit.edu (Guest Account) writes: }For those of you who have heard of VCR PLUS+, does anyone know how the }date, channel, start time and stop time are encoded into the program }number? Here are examples: } }4-23; Channel 25; 20:00; 23:00 ==> 473323 }4-23; Channel 38; 20:00; 23:00 ==> 716694 }4-21; Channel 4; 21:00; 23:00 ==> 9711 } }I can't make rhyme or reason out of it, Watson. That's the whole idea! That's what the company is selling--the code. -- Norm Strong (strong@tc.fluke.com) 2528 31st S. Seattle WA 98144 USA
jgk@osc.COM (Joe Keane) (05/02/91)
In article <GUEST.91Apr29180522@geech.ai.mit.edu> guest@geech.ai.mit.edu (Guest Account) writes: >For those of you who have heard of VCR PLUS+, does anyone know how the >date, channel, start time and stop time are encoded into the program >number? Here are examples: I'm curious about this too. I doubt these guys hired professional cryptographers to design their encoding scheme, so i bet it's not hard to break. Does anyone have information on the scheme? Failing that, does anyone have a large number of examples they'd like to send me? -- Joe Keane, amateur cryptographer jgk@osc.com (...!uunet!stratus!osc!jgk)
ts@cup.portal.com (Tim W Smith) (05/03/91)
Why do you assume that they did not hire cryptographers? The company that makes this thing is in Pasadena, California. The only rational reason a company making a gadget like this would be in Pasadena would be if they are from Caltech or JPL or both. Assuming that they want to protect these codes, I would expect people from Caltech or JPL to be smart enough to either hire a cryptographer or to learn enough about cryptography themselves to make this a hard problem. Tim Smith ps: I think that they can make this problem very hard without using sophisticated cryptographic methods. For instance, with 100K or so of ROM (quite feasible in a device this size), they could simply use a table lookup scheme as part of the encoding process. If these tables are well constructed, to break this you might either have to have a nearly complete set of encodings, or take the device apart and disassemble the software.
mackay@eecae.ee.msu.edu (James F. MacKay) (05/06/91)
jgk@osc.COM (Joe Keane) writes: >In article <GUEST.91Apr29180522@geech.ai.mit.edu> guest@geech.ai.mit.edu >(Guest Account) writes: >>For those of you who have heard of VCR PLUS+, does anyone know how the >>date, channel, start time and stop time are encoded into the program >>number? Here are examples: >I'm curious about this too. I doubt these guys hired professional >cryptographers to design their encoding scheme, so i bet it's not hard to >break. Does anyone have information on the scheme? Failing that, does anyone >have a large number of examples they'd like to send me? >-- >Joe Keane, amateur cryptographer >jgk@osc.com (...!uunet!stratus!osc!jgk) Has anyone considered how much information is in this short code? I've tried a few encoding schemes that I might use in designing a code and can't seem to figure out how they put so much info in so little space.
shirriff@sprite.berkeley.edu (Ken Shirriff) (05/07/91)
In article <1991May6.165343.5041@msuinfo.cl.msu.edu> mackay@eecae.ee.msu.edu (James F. MacKay) writes: >Has anyone considered how much information is in this short code? I've >tried a few encoding schemes that I might use in designing a code and >can't seem to figure out how they put so much info in so little space. The trick is they use variable length codes. Common things are short and uncommon things are long (kind of like Huffman encoding.) Assuming normal shows start on half hours and are 30, 60, or 90 minutes long and there are 50 channels and 7 days gives us 48x3x50x7=50400 possibilities. This matches the common numbers being about 4-5 digits long. Also, low channel numbers seem to have shorter codes than high channel numbers. On the other hand movies that, for example, start at 3:14 and go 98 minutes have long codes of about 10 digits. Assuming shows start any time during the day and go less than 24 hours on 100 channels gives us 24x60x24x60x100x7= 1.4x10^9 which fits in 10 digits. So there seems to be a short code for typical shows and a long code for arbitrary shows. I don't know if there are 2 codes, or more in between, or the same code varying in length somehow. Disclaimer: this is based on a few minutes of examining the numbers in the tv guide. So I may be wrong. P.S. Has anyone asked sci.crypt if they have ideas? Ken Shirriff shirriff@sprite.Berkeley.EDU
robertl@bucsf.bu.edu (Robert La Ferla) (05/07/91)
To everyone who has brought this subject up, please read rec.video because they have discussed this and there is a group of people working on cracking the code. -rob