It turns out the system I was on really uses /lib/systemd/system/kamailio.service, despite /etc/init.d/kamailio also existing.

I was able to make it work by following the Systemd process:

mkdir /etc/default/kamailio.d/

edit /etc/default/kamailio.d/voipmonitor

add lines:

SSLKEYLOG_UDP='127.0.0.1:1234'
LD_PRELOAD="/usr/local/src/voipmonitor-git/tools/ssl_keylogger/sslkeylog.so /usr/lib/x86_64-linux-gnu/libssl.so.3"

The keys are captured by the VoIPmonitor sniffer and everything works as expected from there. I'd be happy to explain further to anyone interested in this setup.

On Sun, Jan 28, 2024 at 3:20 AM Sergey Safarov <s.safarov@gmail.com> wrote:

You can check this PR

https://github.com/kamailio/kamailio/pull/2785

On Fri, Jan 26, 2024 at 8:58 PM Calvin E. via sr-users <sr-users@lists.kamailio.org> wrote:

I've been tasked to use LD_PRELOAD to log SSL keys for TLS connections using a Diffie-Hellman cipher. The first attempt did not work, so I wanted to sanity check whether Kamailio's TLS support is built in such a way that would defeat LD_PRELOAD.

The instructions from the vendor are to update /etc/init.d/kamailio like this:

env SSLKEYLOG_UDP='127.0.0.1:1234' LD_PRELOAD="/usr/local/src/voipmonitor-git/tools/ssl_keylogger/sslkeylog.so /usr/lib/x86_64-linux-gnu/libssl.so.3" \
    start-stop-daemon --start --quiet --pidfile $PIDFILE \
                --exec $DAEMON -- $OPTIONS || log_failure_msg " already running"

Is there anything special in Kamailio (5.7.3 on Debian 12) that would prevent this from working? Not necessarily something to defeat a keylogger, but maybe the way tls.so gets loaded?

The only discrepancy I've noticed is the vendor docs refer to libssl.so.3 not libssl.so.1, but the vendor said that should be OK.

I'd love to hear from someone already using VoIPmonitor with Diffie-Hellman ciphers and Kamailio.

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