Re: [Linphone-developers] b256 SAS implementation for bzrtp

[Johan Pascal]

Hi Eli,
thanks for your patch. I had a quick look at it and it seems fine.

Note that until recently bzrtp didn't consider on reception of Hello 
Packets the mandatory algorithm if a non mandatory was present in the 
Hello, which lead to a ZRTP key exchange failure if peer give only a non 
mandatory algo (as it may do) in the Hello packet and self support 
mandatory algo only.

This has been fixed now and also the mandatory algorithms are always 
added to the set of available one, even if it shall work without, in the 
self Hello packet which ensure backward compatibility with old versions 
of bzrtp.

About having a dedicated zrtp_cipher_suites setting in the linphonerc, I 
didn't really check it but as far as I understood if present it will 
have precedence on the srtp_crypto_suite(which remains in force when 
using SDES) setting, am I correct?

I'll try to review more accurately and push your patches by the end of 
the week.

regards,

Johan

On 10/03/15 11:48, Eli Burke wrote:
> Building on Ben Sartor’s excellent BZRTP patches to add support for the
> non-mandatory algorithms, here are patches to add the b256 SAS format.
> Instead of returning a 4 character SAS string like “7jb3” it will return
> two words such as “seabird:asteroid”. Per the RFC, the words come from
> the PGP Word List and should not be localized:
> http://en.wikipedia.org/w/index.php?title=PGP_word_list
>
> oRTP and ms2 need small patches to extend the length of the SAS variable
> in the eventData structure. liblinphone was patched to add linphonerc
> overrides for each set of algorithms. No default values are changed from
> stock Linphone: Ben’s patch sets sensible ZRTP defaults based on the
> config setting for “srtp_crypto_suites”, this patch adds e.g:
> zrtp_key_agreements_suites=MS_ZRTP_KEY_AGREEMENT_EC38
> zrtp_cipher_suites=MS_ZRTP_CIPHER_AES3
> zrtp_auth_suites=MS_ZRTP_AUTHTAG_HS80
> zrtp_hash_suites=MS_ZRTP_HASH_S256
> zrtp_sas_suites=MS_ZRTP_SAS_B256
> Note that due to the nature of the ZRTP spec, the mandatory algorithms
> are always added and used during the initial ZRTP handshake, so it is
> not necessary to specify B32 to be backwards compatible with older clients.
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