How to achieve adverting toward only central devices in the same application?

Question

We would like to achieve following:

Only peripheral devices should advertise data toward only central devices in the same application. 
 advertising data by peripheral devices should be protected from malicious people.

TylerD · Accepted Answer

Yes, anything you put into the advertising packets can be easily detected by any other user who has just the basic knowledge of BLE and a phone. If there are some sensitive data in the advertisements that you do not want to expose to everybody, then the only way around that is encrypting the data somehow. 
 Have a look at this blog about advertising and other BLE basics: https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/bluetooth-smart-and-the-nordics-softdevices-part-1 There is a section that talks about whitelisting . It answers your second question, about limiting who can connect to your peripheral. Even if the advertisements can be heard by any other device in the range of your peripheral, you can still use whitelisting to limit which devices are allowed to connect. 
 The limitation with whitelisting is that you need to know in advance the addresses of the "trusted" devices. If you do not have that information available, then an alternative solution could be to implement some application level security check. For example: whenever a central connects to your peripheral, you require some custom passkey exchange or similar to be executed, before the central is allowed to get access to any sensitive data. If the passkey exchange (or whatever handshake mechanism you define) fails, then the peripheral can drop the connection.

How to achieve adverting toward only central devices in the same application?

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