Hello Daniel,

Thanks for your answer.

I don’t see much in the debug logs. Except the SSL verification error, the rest looks like the normal SSL handshake and the TCP connection setup:

DEBUG: <core> [io_wait.h:598]: io_watch_del(): DBG: io_watch_del (0xa7edc0, 8, -1, 0x10) fd_no=2 called

DEBUG: <core> [tcp_read.c:1490]: release_tcpconn(): releasing con 0x7f9191b1ade0, state -2, fd=8, id=8 ([<SfB IP1>]:56267 -> [<SfB IP1>]:5061)

DEBUG: <core> [tcp_read.c:1491]: release_tcpconn(): extra_data 0x7f9191b39318

DEBUG: <core> [tcp_main.c:3243]: handle_tcp_child(): reader response= 7f9191b1ade0, -2 from 0

DEBUG: tls [tls_server.c:663]: tls_h_close(): Closing SSL connection 0x7f9191b39318

DEBUG: <core> [ip_addr.c:229]: print_ip(): tcpconn_new: new tcp connection: <SfB IP1>

DEBUG: <core> [tcp_main.c:985]: tcpconn_new(): on port 56269, type 3

DEBUG: <core> [tcp_main.c:1295]: tcpconn_add(): hashes: 3769:3996:3198, 9

DEBUG: <core> [io_wait.h:376]: io_watch_add(): DBG: io_watch_add(0xa25be0, 30, 2, 0x7f9191b1ade0), fd_no=20

DEBUG: <core> [io_wait.h:598]: io_watch_del(): DBG: io_watch_del (0xa25be0, 30, -1, 0x0) fd_no=21 called

DEBUG: <core> [tcp_main.c:4131]: handle_tcpconn_ev(): sending to child, events 1

DEBUG: <core> [tcp_main.c:3813]: send2child(): selected tcp worker 1 12(4808) for activity on [tls:<LOCAL IP>:5061], 0x7f9191b1ade0

DEBUG: <core> [tcp_read.c:1566]: handle_io(): received n=8 con=0x7f9191b1ade0, fd=8

DEBUG: tls [tls_server.c:197]: tls_complete_init(): completing tls connection initialization

DEBUG: tls [tls_server.c:226]: tls_complete_init(): Using initial TLS domain TLSs<default> (dom 0x7f9191861e98 ctx 0x7f9191887a10 sn [])

DEBUG: tls [tls_domain.c:703]: sr_ssl_ctx_info_callback(): SSL handshake started

DEBUG: <core> [tcp_main.c:2430]: tcpconn_do_send(): sending...

DEBUG: <core> [tcp_main.c:2464]: tcpconn_do_send(): after real write: c= 0x7f9191b1ade0 n=6692 fd=8

DEBUG: <core> [tcp_main.c:2465]: tcpconn_do_send(): buf=#012#026#003#003

DEBUG: <core> [io_wait.h:376]: io_watch_add(): DBG: io_watch_add(0xa7edc0, 8, 2, 0x7f9191b1ade0), fd_no=1

DEBUG: <core> [tcp_main.c:2430]: tcpconn_do_send(): sending...

DEBUG: <core> [tcp_main.c:2464]: tcpconn_do_send(): after real write: c= 0x7f9191b1ade0 n=7 fd=8

DEBUG: <core> [tcp_main.c:2465]: tcpconn_do_send(): buf=#012#025#003#003

ERROR: tls [tls_util.h:42]: tls_err_ret(): TLS accept:error:14089086:SSL routines:ssl3_get_client_certificate:certificate verify failed

ERROR: <core> [tcp_read.c:1330]: tcp_read_req(): ERROR: tcp_read_req: error reading

Maybe you can see some hint there that I don’t see?

Cheers, Francisco.

From: Daniel-Constantin Mierla [mailto:miconda@gmail.com]
Sent: Wednesday, October 25, 2017 14:50
To: Kamailio (SER) - Users Mailing List <sr-users@lists.kamailio.org>; Francisco Valentin Vinagrero <francisco.valentin.vinagrero@cern.ch>
Subject: Re: [SR-Users] Mutual TLS with Skype for Business 2015

Hello,

On 25.10.17 11:32, Francisco Valentin Vinagrero wrote:

Hello,

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.

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:

ERROR: tls [tls_util.h:42]: tls_err_ret(): TLS accept:error:14089086:SSL routines:ssl3_get_client_certificate:certificate verify failed

ERROR: <core> [tcp_read.c:1330]: tcp_read_req(): ERROR: tcp_read_req: error reading

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)

[server:default]

method = TLSv1+

verify_certificate = yes

require_certificate = yes

private_key = /usr/local/etc/kamailio/tls/key_gw_sfb.pem

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

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

[client:default]

method = TLSv1+

verify_certificate = yes

require_certificate = yes

private_key = /usr/local/etc/kamailio/tls/key_gw_sfb.pem

certificate = /usr/local/etc/kamailio/tls/cert_gw_sfb.pem

ca_list = /usr/local/etc/kamailio/tls/myca_and_sfbca.pem

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.

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.

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?

afaik, the certificate validation is done by the libssl, kamailio is not doing much in this respect and no dns query inside kamailio tls module. Maybe some parameters must be set when asking for validation.

If you run with debug=3 inside kamailio.cfg, do you see any log messages that can help in identifying why it fails?

Cheers,
Daniel

--

Daniel-Constantin Mierla

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