Secured Wireless Connectivity

Hi,

I am no engineer but I do have a concept that I am pursuing which begs the question:

Is it possible to have a master device which connects to only a particular type of slave devices? Its a little difficult for me to explain but by example this is what I mean:

Lets say that a cell phone brand-say Apple- came up with some technology that they wish to be exclusive to their iPhone device, this iPhone for whatever reason would need to have the capability of linking with various master devices in varying locations where any owner of an iPhone would have the capability of linking to these master devices. The master devices therefore, would need to be programmed to only recognize and be compatible with iPhone devices.

I know that WIFI works similar to this, automatically synching with a device once the WEP key has been programmed from master to slave but is there a way that a specified group of devices could immediately be recognized to synch with a master without having to provide a special code to be synched? Perhaps a microchip type that would immediately be recognized upon entering the range of the master? I ask this because my product must be exclusive technology that could not simply be taken advantage of by today's average smart phone.

Any advice with this matter would be greatly appreciated

Hmm. Given the constraints of no shared codes, the short answer is "not really".

Since you are seeking to uniquely authenticate one device to another, you have to define what is "unique" (or "exclusive") about that device. Stored cryptographic keys (as you mention) are probably the simplest approach, and hence are widely used. Indeed, there are an overwhelmingly large range of possibilities with regards to cryptographic authentication techniques so don't discount them prematurely, as perhaps one may suit your needs.

While you *can* also use some other (measurable) physical parameter [provided the space of possible "keys" is large enough] this is often difficult to define - and particularly control - from a manufacturing perspective. For example, "fingerprinting" of RF transmitters is used to identify/track specific devices. One way this may be achieved is by observing the rise/fall times/profile of the transmit power envelope, and since this will be influenced by the component values, tolerances, threshold voltages etc unique to a particular device this allows some distinguishibility between otherwise identical transmitters. In this way, a "key" is formed from the circuit parameters. The caveat is that the variation between devices is likely to be small and a function of temperature, battery etc and nearly impossible to define a priori.

A handy rule to remember is that secrets (such as keys, codes etc) CAN be embedded into devices, but are always potentially vunerable. In general, the greater the rewards for extracting a secret key/authentication protocol/etc from a device, the harder the bad guys will try Mechanically/chemically/optically removing the protective/active layers of embedded devices and reading the keys from flash memory via electron microscopy became a favoured technique over 15 years ago! Of course, the semiconductor manfuacturers have retaliated with a plethora of 'secure' devices (for example: **broken link removed**). This isn't meant to scare you off, rather it's just to help you put your problem into perspective