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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m trying to replace two old Audiocodes gateways (used to interconnect our Skype for Business infrastructure to the PSTN) with a new Kamailio cluster.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am having some trouble to get the TLS mutual authentication working with Kamailio. For the moment, I’m just trying to receive the incoming OPTIONS from SfB, but I get all the time certificate verification errors:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">ERROR: tls [tls_util.h:42]: tls_err_ret(): TLS accept:error:14089086:SSL routines:ssl3_get_client_certificate:certificate verify failed<o:p></o:p></p>
<p class="MsoNormal">ERROR: <core> [tcp_read.c:1330]: tcp_read_req(): ERROR: tcp_read_req: error reading<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My tls.cfg is quite simple, with the same config for client and server (and one single listen=tls:<my IP>:5061 in the Kamailio.cfg file)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[server:default]<o:p></o:p></p>
<p class="MsoNormal">method = TLSv1+<o:p></o:p></p>
<p class="MsoNormal">verify_certificate = yes<o:p></o:p></p>
<p class="MsoNormal">require_certificate = yes<o:p></o:p></p>
<p class="MsoNormal">private_key = /usr/local/etc/kamailio/tls/key_gw_sfb.pem <o:p>
</o:p></p>
<p class="MsoNormal">certificate = /usr/local/etc/kamailio/tls/cert_gw_sfb.pem # => This certificate’s Subject is the DNS alias for the cluster, with all the kamailios in the cluster as Subject Alternative Names<o:p></o:p></p>
<p class="MsoNormal">ca_list = /usr/local/etc/kamailio/tls/myca_and_sfbca.pem # => Kamailio and Skype for Business are signed by different CAs, so here I concatenated all intermediate and root CAs<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[client:default]<o:p></o:p></p>
<p class="MsoNormal">method = TLSv1+<o:p></o:p></p>
<p class="MsoNormal">verify_certificate = yes<o:p></o:p></p>
<p class="MsoNormal">require_certificate = yes<o:p></o:p></p>
<p class="MsoNormal">private_key = /usr/local/etc/kamailio/tls/key_gw_sfb.pem<o:p></o:p></p>
<p class="MsoNormal"><span lang="FR">certificate = /usr/local/etc/kamailio/tls/cert_gw_sfb.pem<o:p></o:p></span></p>
<p class="MsoNormal">ca_list = /usr/local/etc/kamailio/tls/myca_and_sfbca.pem<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">When I run Kamailio, I can see incoming OPTIONS from Microsoft Exchange Unified Messaging (UM), whose certificate I verify without any issues. UM presents a certificate issued for a single machine, so no Subject Alternative Names (SANs)
are involved.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The problem comes with the TLS handshake for the Skype Mediation pool. They have a certificate with Subject = DNS alias and all the physical machines that are behind the alias appear listed as Subject Alternative Names (SANs) in the certificate.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As the only difference between UM and Skype’s Mediation is the certificate’s Subject, I think I am missing something on my configuration to validate the SANs instead of the subject. Is the TLS module doing any reverse DNS lookup to verify
this?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Francisco. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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