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I used the BLE example from here.

But any device can read and write to the advertised characteristic. Is there a way to make the data inaccessible to other devices except for my app somehow. What I would really like to do is something like SDP and then connect and exchange data over RFCOMM but it seems impossible to do so in esp32. I have done it using bluez library on Linux but in case of esp32 I found only one library btstack that is impossible to use with esp-idf because of lack of CMakeLists.txt. Is there some way I can achieve what I want?

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In general terms, you could simply require a client to authenticate first. This would require a bit of a deviation from the example you linked to (which actually only handles reading of the characteristic) to handle multiple connections and their state, but it should be pretty straightforward.

The Arduino BLE library seems to lack sending quite a bit of information via the callbacks, so you just know there's a connect or disconnect or a write to a characteristic, and not which devices did. This means you won't be able to handle multiple connections at the same time, but making sure you reset your authentication state whenever you receive a connect or disconnect should be enough to prevent anyone but your own client from "talking" to your device.

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  • thanks, I'll try implementing this flow and update you as soon as I can. – Ryosuke Jan 8 '20 at 14:16

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