randomness of identifiers

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Holger Freyther holger at freyther.de
Thu Oct 5 08:33:49 UTC 2017


> On 5. Oct 2017, at 15:35, Harald Welte <laforge at gnumonks.org> wrote:
> 
> Hi Holger,

Hi,


>> Picking something like RAND_bytes of OpenSSL for TMSIs seems to be the
>> best way. It will re-seed itself (and we are not forking). 
> 
> Ok, then let's do that.

Maybe to expand on the "forking" part. OpenSSL didn't (and might not do
it right now) re-seed on fork. This created some security issues on other
platforms (maybe the most noticeable was Android, e.g. two processes
generating the same random numbers).



>> If the OpenSSL dependency is too bad (license compatibility, the move to the Apache license
>> could help us here for GPLv3+ software) 
> 
> Yes, the new apache-style license makes this less of a headache.
> 
> So then we conclude for now:
> 
> * TMSIs and other temp identifiers: openssl RAND_bytes()
> * random challenges for authentication: also RAND_bytes, or getrandom()?
> * secret key generation (which we don't implement, so far: ?

I would use RAND_bytes() in all of these cases


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