Why we can't copy car remote patterns?

I have a set top box remote that I can use to control set top box as well as TV by using the set button on my stb remote.That remote can copy any remote IR pattern but when I tried it on a car remote it didn't worked.Do car remote uses different type of radiation?

• Do you mean a keyfob for an automobile? – Ale..chenski Sep 9 '18 at 5:40
• Cryptographic schemes are used, and the pattern has to change for each use. See security.stackexchange.com/q/43050/131754. – dim Sep 9 '18 at 5:58
• If I recall correctly, those kind of remotes use a predefined pattern, like $\pi$, and then they just iterate forward. So if you send 3, then the next time it expects a 1, the time after that a 4 and etc. But in reality it's larger chunks and some other values (I don't think it's $\pi$). And the search space is like 256 forward, so if you click with the remote while not being near then it's fine... as long as you don't click more than 256 times, or whatever your system has as search space - I won't post this as an answer because I'm not 100% sure. – Harry Svensson Sep 9 '18 at 6:43
• I am not available to write a full-blown answer now. But lookup OTP (one-time password) and PRNG (pseudo random generator). The answer is there. – dim Sep 9 '18 at 7:00
• There's a discussion of the cryptographic details of how they work at security.stackexchange.com/questions/43050/… ... but I'd guess that's offtopic here. The important thing is just that they change on each use, so a simple record and playback won't work. – Jules Sep 9 '18 at 8:16

Do car remote uses different type of radiation?

Yes.

TV remotes use infrared transmission. On many the LED is visible at the end of the remote. You can test the operation of an infrared LED using your camera phone as they are responsive in the infrared region.

Figure 1. IR LED testing using a digital camera. (Image mine.)

Car remotes use one-way radio signalling.

Figure 2. A Peugot 307 remote. Note there is no LED visible but there is what appears to be an inductor (top of PCB) and an antenna (to outer loop). Random image source.

How do they differ?

• Infrared requires line of sight to the receiver or enough reflective surface to bounce the infrared light. Point the remote into your hand and the television will not respond.
• Your car's remote control will work inside your pocket. This is the biggest clue that it is not using light as a transmission medium.

Your programmable remote control is for infrared remote only. It will not be able to receive radio signals from your car key.

• The other difference is that car central locking remotes typically use a generated sequence of pulses that changes with each use, and the car tracks which ones have been used, so that even if you did have a device to copy them it wouldn't be any use. Many of them aren't secure but a simple record & playback copy won't work either, you'd need something more sophisticated to make it work. – Jules Sep 9 '18 at 8:14
• How car get information about pattern that remote will send next time?If the car don't know the second pattern then any random radio wave pattern will unlock the car. – pra9 Sep 9 '18 at 10:02
• There is a common 'agreement' between the car and the key, based on an initial value and a calculation to get the next value. The details are generally covered by elaborate non-descolsure contracts. – Wouter van Ooijen Sep 9 '18 at 10:06
• @pra9 Why did you accept the answer if it did not answer your question? – Harry Svensson Sep 9 '18 at 10:28
• @pra9: I did answer the question that was asked. The encryption method is a separate question and if you don't understand after reading the links in the comments to your post then please ask a new question giving a link to the article and the part you don't understand. – Transistor Sep 9 '18 at 13:26