ECDH (P-256 elliptic curve) in key exchanging phase

RE: ECDH (P-256 elliptic curve) in key exchanging phase

Einar Thorsrud — Wed, 08 Aug 2018 14:30:10 GMT

You have to download the library yourself. The simplest way to do it is to go to <SDK>nRF5_SDK_15.0.0_a53641a\external\micro-ecc\ and run the build_all script. It will download and build the micro-ecc library for you.

RE: ECDH (P-256 elliptic curve) in key exchanging phase

Bing — Wed, 08 Aug 2018 14:14:59 GMT

Thanks for your quickly reply. I compile the example "LE Secure Connections Multirole Example" in the directory SDKROOT\examples\ble_central_and_peripheral\experimental\ble_app_multirole_lesc, the keil mdk report the "micro_ecc_lib_nrf52.lib". After seaching the whole SDK, I can't find the lost library file. Where can I get it? Or could you give me some web links to guide us for generating of this library file ?

RE: ECDH (P-256 elliptic curve) in key exchanging phase

Einar Thorsrud — Wed, 08 Aug 2018 13:56:36 GMT

Hi,

LE Secure Connections is a secure pairing method that replaces LE legacy parring. Both are ways to pair/bond, i.e. exchange encryption keys to be used to encrypt the Bluetooth packet exchange between two peers. LE Secure Connection is the more secure of the two and should be the preferred pairing method if high security is more important than supporting legacy devices. (You can also support both).

The SDK has a example application that demonstrate its usage, the experimental LE Secure Connections Multirole Example.

Best regards,

Einar

RE: ECDH (P-256 elliptic curve) in key exchanging phase

Bing — Wed, 08 Aug 2018 13:45:07 GMT

Thanks Einar. Now I know the SDK support ECDH. But I still have doubt for how and when to use this BLE LESC module. Could you please give me a simple usage scenario.

RE: ECDH (P-256 elliptic curve) in key exchanging phase

Einar Thorsrud — Wed, 08 Aug 2018 12:43:41 GMT

Hi Wang,

The ECDH algorithm is used for LE Secure Connections, which is an enhanced security feature introduced in Bluetooth version 4.2. It is not implemented in the SoftDevice (BLE stack) itself, but rather in the SDK BLE LESC module. You can download the SDK from here and analyze the implementation.

Best regards,

Einar