Thanks Lee. One more question. How is the info transfered from the car to the fob which is a separate piece from the key?
> On May 25, 2016, at 10:57 AM, Lee Larson <leelar...@me.com> wrote: > > On May 24, 2016, at 7:22 PM, Harry Jacobson-Beyer <harr...@me.com> wrote: > >> Before I get to my question I want to to give you some background. >> >> I have a 2004 Toyota Sienna Van with 100,000+ miles. The key fob (you know >> the one with the unlock/lock buttons and the 3 open door buttons and the >> panic button) has been dropped several times over the past few year and >> finally gave out. I changed the battery and it still doesn’t work. >> >> I asked the toyota dealer about a new fob $100 for the fob and $50 to >> program it. I decided to just use the key and not replace the fob. >> >> My wife Sherry, the ebay maven in our family, went on ebay and found a third >> party fob for the car for ±$21. Instructions for programming the fob were >> included. >> >> I now have a workable replacement fob. Yeah! >> >> Without getting into the long and the short of it the instructions for >> programming the fob included inserting and removing the key, closing and >> opening the door 2 or 3 times, turning the ignition on and off, and pressing >> buttons on the fob. >> >> It’s magic. Now here’s the question: How does this work? what do those steps >> do and how is the information transferred to the fob? >> >> If anyone would like to see the complete instructions email me off list and >> I will send you a link to them. > > A few months ago we got a Prius. It came with only two smart key fobs and I > was kind of “irritated" when the dealership told me a third would be $350. > Those keys can’t have more than $10 of electronics in them. I decided to see > if it could be done more cheaply elsewhere, so I looked into how they work. > > Here’s how the current Toyota fobs work. > > When you program a key, it syncs a number in the key to one already in the > car’s computer. This is a seed for what’s called a pseudo-random number > generator. A pseudo-random number generator is a mathematical function that > generates a list of numbers which seems to be totally random, but actually is > completely determined by the starting seed. Since both the key and the car’s > computer have the same pseudo-random generator and the same seed, they can > generate the same pseudo-random numbers. > > When the car and the key come into radio contact, they compare numbers. If > the numbers match, the key can control the car. After a number is used, both > the key and the car throw it away and use the next number, so a thief can’t > decode everything by listening in on the conversation. A new number is used > every time you unlock a door or start your car. > > It’s actually a little more complicated than this. The computer in the car > searches forward 256 positions in the list for a match. So, if your toddler > gets hold of your key and sits on the couch pressing the lock button 257 or > more times, you might have to reprogram your key. > > Here’s where I think it gets downright despicable. > > Apparently, up until about 2013, Toyota sold locksmiths devices that could > program the key systems in their cars, and the magic incantation for syncing > an individual key was pretty easy to find. In 2014, they invoked the DMCA > (Digital Millennium Copyright Act) to keep their key programming secret. > According to the DMCA, it’s illegal for me or anyone else to reverse-engineer > the programming in my own car. Now, it’s pretty much only dealers who can > program the key systems in the cars. Repeat after me: “Dealer profit center." > > L^2 > > PS/ If anyone knows of a place around Louisville where I can get a Prius key > cheaply programmed, please let me know! > > > _______________________________________________ > MacGroup mailing list > Posting address: MacGroup@erdos.math.louisville.edu > Archive: <http://www.mail-archive.com/macgroup@erdos.math.louisville.edu/> > Answers to questions: <http://erdos.math.louisville.edu/macgroup/> _______________________________________________ MacGroup mailing list Posting address: MacGroup@erdos.math.louisville.edu Archive: <http://www.mail-archive.com/macgroup@erdos.math.louisville.edu/> Answers to questions: <http://erdos.math.louisville.edu/macgroup/>
