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  • Case ID: 115673
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When do encryption keys exchange?

MC

I have a problem with bonding with a static passkey. I have some sensors, which have a static passkey hardcoded in them. If I want to bond with them, I have to provide this passkey from my custom central app, which uses s120 and SDK 8.1.0. For the past few days I wasn't able to make a successfull bond, because I keep getting BLE_GAP_SEC_STATUS_AUTH_REQ from the sensor. I can't find much information on what to do in this case. I can bond with MCP just fine.

I compared log file from MCP and sniffer trace from my central bonding attempt and they are different in one very impotant aspect. MCP exchanges keys and encrypts the connection before trying to authenticate the link. Default behavioral of the device manage in SDK 8.1.0 is not the same. If I call dm_security_setup_req it only forces authentication without previous key exchange. This is why authentication fails. If I go into debug mode, I can see that keys are always 0. Does anyone have any suggestions about this matter? Are there any examples that mimic MCP behavioral?

Edit: added trace logs for windows phone, s120 and MCP log file, all done with the same sensor (which uses TI stack).

Windows phone pairing attempt: windows_pairing_with_adv.pcapng

S120 pairing attempt: s120_central_pairing.pcapng

MCP log file: log.txt

Android bonding attempt: android_bonding.pcapng

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    I'm confused. I thought the lower picture was S120? The pairing request is sent in that picture. What do you mean by sending pairing request prior to authentication? The authentication is part of the pairing process, it is not done before the pairing request is sent. Please upload the sniffer files instead of pictures, and mark clearly what trace is from what device. You send a pairing request by calling sd_ble_gap_authenticate(). You can do this directly, or you can let device manager handle this for you, then you should call dm_security_setup_req(). If you call this, the central will request to pair/bond if the peer is not bonded, if it is bonded, the link will be re-encrypted using existing bond information.

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    I'm confused. I thought the lower picture was S120? The pairing request is sent in that picture. What do you mean by sending pairing request prior to authentication? The authentication is part of the pairing process, it is not done before the pairing request is sent. Please upload the sniffer files instead of pictures, and mark clearly what trace is from what device. You send a pairing request by calling sd_ble_gap_authenticate(). You can do this directly, or you can let device manager handle this for you, then you should call dm_security_setup_req(). If you call this, the central will request to pair/bond if the peer is not bonded, if it is bonded, the link will be re-encrypted using existing bond information.

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