Bluetooth socket timeout, device pairing

[Oliver Fromme]

Hello Max,

Maksim Yevmenkin wrote:
 > Oliver,
 > 
 > > My Bluetooth Python module basically works now.
 > > However, I've got one small problem with pairing ...
 > > 
 > > I have entered an 8-character PIN code in hcsecd.conf.
 > > When I try to open a connection for the first time,
 > > the device (i.e. my Mindstorms NXT brick) asks me to
 > > enter the PIN code.  However, entering the code on
 > > the brick takes some time ...  I have to scroll
 > > through the alphabet and digits which is rather slow.
 > > I can enter at most 4 characters of the PIN code
 > > before the socket() call returns with ECONN
 > > ("Connection refused").
 > > 
 > > For now I'm using a short 4-character PIN code, but
 > > I would really like to use a longer one.  Where is
 > > the timeout defined for that?
 > 
 > its so called "LMP (link manager protocol) response timeout". its
 > defined in link manager, i.e. part of the device's firmware. v1.1 spec
 > seems to be implying that LMP response timeout should be set to 30
 > sec.
 > 
 > > Python's socket module has no timeout by default.
 > > I've also searched the net.bluetooth sysctls and
 > > increased all of the timeout values (half a dozen),
 > > but none of them seemed to have an effect on this
 > > particular problem.  So I think this value must be
 > > hardcoded somewhere.  Where do I have to look?
 > 
 > i'm afraid that you can not change LMP response timeout. there isn't
 > any defined command that would do that. i'm not sure why do you care
 > much about pin length. pin is only used once to generate link key and
 > as soon as link key is generated both devices should use it instead of
 > pin.

Thankyou very much for the explanation.

It was my impression that the length of the PIN code has
to do with the security (i.e. the longer, the better).
It seems I was wrong.

Is it correct that it would even be secure enough to use
the public default factory PIN code of the device ("1234")?
In that case I could skip the whole business of entering
a PIN code ...

Best regards
   Oliver

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