Re: [mosquitto-dev] library clientid not random enough

[Roger Light <roger@xxxxxxxxxx>]

Hi Nick,

Good point, cheers.

Roger



On Mon, Feb 15, 2016 at 9:16 PM, Nicholas O'Leary <nick.oleary@xxxxxxxxx> wrote:
> Hi,
>
> One thing to bear in mind is that pid would be susceptible to clashes if you
> had two devices set to connect on boot that are turned on at the same moment
> (ie, power is restored simultaneously). If they are running identical
> software images, the processes IDs are likely to be the same.
>
> Nick
>
> On 15 February 2016 at 21:05, Roger Light <roger@xxxxxxxxxx> wrote:
>>
>> Hi Stefan,
>>
>> That sounds pretty reasonable to me. Aside from the pid, /dev/random
>> isn't very portable anyway - a better solution would be the openssl
>> random functions if available.
>>
>> Cheers,
>>
>> Roger
>>
>>
>> On Wed, Feb 10, 2016 at 9:30 AM, Stefan May <stefan.may@xxxxxxx> wrote:
>> > Hi,
>> >
>> > I found some log messages at the mosquitto broker regarding
>> > dis-/reconnects
>> > that were caused by clients using the same clientid. I'm using the
>> > automatic
>> > generation of clientids in the call mosquitto_new().
>> >
>> > So what exactly happens is the following: two clients starting
>> > *simultaneously* on different computers. Sometimes they get the same
>> > clientid.
>> >
>> > Digging into the library code I was searching for the seeding of PRNG
>> > and
>> > found it in mosquitto_lib_init(). The PRNG is only seeded with the
>> > current
>> > time, which can be equal on different computers. In my opinion it should
>> > be
>> > seeded not only with time, but with some better randomness, so that
>> > collisions between different clients are reduced. Is using time and
>> > getpid()
>> > a better candidate? Using /dev/random seems like breaking a fly on the
>> > wheel.
>> >
>> > tty, Stefan.
>> > --
>> > Stefan May
>> > Department MPS
>> >
>> > Deutsches Elektronen-Synchrotron DESY
>> > A Research Centre of the Helmholtz Association
>> > Notkestr. 85, 22607 Hamburg
>> >
>> > Phone: +49-40-8998-4636
>> > for guests: Bldg. 30/Rm. 419
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>
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