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From:   Ordit Gross <ordit.gross@orcam.com>
Date:   Sun, 8 Mar 2020 17:42:53 +0200
Message-ID: <CAB+bgRanN9W4oH00rATmgarRnk4NXPXOdT2K+ZYDLMM1pYmtuQ@mail.gmail.com>
Subject: avoid cross-transport key derivation
To:     linux-bluetooth@vger.kernel.org
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hi all,

our application connects both to mobile (ble) and speakers (br/edr)
using bluez stack.
our controller is configured as follows:
current settings: powered connectable bondable ssp br/edr le secure-conn

ever since IOS started supporting CTKD (cross-transport key
derivation) at IOS13, pairing to mobile causes also link key
distribution and brief br/edr connection follows the ble connection.
I would like to avoid the link key distribution at the pairing stage.
the only way I was able to achieve that is by disabling either
secure-conn or ssp which is undesirable as disabling either of them
block other functionality.
what is the recommended approach?

** when br/edr is turned off we do not experience disconnections from
mobile app running with IOS13. and vis versa.
looking on HCI dump from mobile side the disconnections is initiated
from mobile side, however the application is not the one initiating
the disconnections.
any advice is greatly appreciated
Ordit