Re: [Linphone-developers] patch to add zrtp-hash support to linphone - updated ZRTP library

[Guillaume Beraudo]

Hi Werner,

Thanks for the information.

Regarding the patches from Eli, they were reverted as it crashed when
adding video to an audio-only call.

I'll look at the issue when I get some free time.


Cheers,

Guillaume Beraudo


On Tue, Mar 26, 2013 at 09:51:40AM +0100, Werner Dittmann wrote:
> A ew ZRTP version is ready in Github that supports protocol version 
> negotiation
> function described in RFC6189, section 4.1.1.
> 
> This is necessary because we may see some updates to the ZRTP protocol 
> handling
> and this will require a new protocol version. The protocol negotiation 
> provides
> interoperability between old and new ZRTP protocol versions. The drawback 
> here is
> that these new features added some interface changes, albeit just a few one.
> 
> According to RCF6189 each supported ZRTP version requires an own zrtp-hash 
> attribute
> in SDP. Thus I added a function to get the number of supported versions and 
> extended
> the function that reads the hello-hash to accept an index.
> 
> The new function to get the number of supported versions:
> 
>      /**
>       * Get number of supported ZRTP protocol versions.
>       *
>       * @param zrtpContext
>       *    Pointer to the opaque ZrtpContext structure.
>       *
>       * @return the number of supported ZRTP protocol versions.
>       */
>      int32_t zrtp_getNumberSupportedVersions(ZrtpContext* zrtpContext);
> 
> I did a quick check of the patches that Eli did and IMHO the Linphone function
>   ortp_zrtp_get_hello_hash(...)
> needs to be called in a loop, similar to (pseudo code):
> 
> ...
> int32_t index = zrtp_getNumberSupportedVersions(ZrtpContext* zrtpContext);
> for (int i = 0; i < index; i++) {
>    ortp_zrtp_get_hello_hash(ctx, version, version_len, hello_hash, 
> hello_hash_len, index);
>    add sdp attribute(hello_hash);
> }
> ...
> 
> To get this working the existing ortp_zrtp_get_hello_hash() needs a new 
> parameter that
> carries the index. zrtp_getHelloHash(ZrtpContext* zrtpContext, int32_t index) 
> requires
> this index to get to correct hello hash string.
> 
> I would recomend to move to the new ZRTP core lib and apply the proposed 
> enhacments to
> the Linphone code. For the time being only one ZRTP protocol version is 
> active and thus
> this library is interoperable with older ZRTP libraries.
> 
> 
> Werner
> 
> Am 15.02.2013 22:52, schrieb Eli Burke:
> > With some assistance from Werner Dittmann and Guillaume Beraudo, I've 
> > created patches to add zrtp-hash support to Linphone. At present this will 
> > add the hash of the ZrtpHello message to outgoing SDP messages but will not 
> > verify an incoming hash. Assuming the patches are accepted I'll add support 
> > for verification as well.
> > 
> > These patches (one to Linphone and one to its oRTP submodule) will allow 
> > Linphone to use ZRTP when connected to Freeswitch in proxy-media mode. 
> > Freeswitch contains special case logic that looks for the 'zrtp-hash' 
> > attribute in the SDP media definition of two clients and assigns the same 
> > SSRC to each channel. Without it, ZRTP fails because the SSRC gets changed 
> > and the internal packet hash will not match.
> > 
> > To the linphone developers: I've tried to match your style and coding 
> > standards to the best of my ability, but if there are any problems, please 
> > let me know. There are brief comments attached to most of the changes but I 
> > can expand upon them, or if you wish to make modifications I'd be happy to 
> > test them.
> > 
> > -Eli
> > 
> > 
> > 
> > _______________________________________________
> > Linphone-developers mailing list
> > address@hidden
> > https://lists.nongnu.org/mailman/listinfo/linphone-developers
> > 
> 
> 
> -- 
> ----------------------------------------------
> Werner Dittmann    address@hidden
> Tel +49 173 44 37 659
> PGP key: 82EF5E8B
> 
> _______________________________________________
> Linphone-developers mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/linphone-developers