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Goal (short description)

Communication between the User Agent and the home proxy is encrypted using TLS.

Applicability

We enable end-users of domain A to communicate with their home proxy based on TLS:

      User Agent A  ->  proxy domainA 

Prerequisites

This example is based on

  • Debian 4r0
  • OpenSER version 1.2 with tls

Configuration  


  • If TLS support is not included in your installation, get OpenSER 1.2 with TLS. This example uses the source code at
    http://www.openser.org/pub/openser/latest/src/openser-1.2.0-tls_src.tar.gz
  • Carefully observe the installation notes:
    http://www.openser.org/mos/view/-OpenSER-Installation-Notes/
  • Special care should be taken to install the packages:
    • mysql-server
    • libmysqlclient-dev
    • libssl0.9.8-dev
  • Make sure you build openser including TLS. There are several options, like changing the line in the makefile to the following:
    TLS=1
    and that you include mysql support:
    make all include_modules="mysql"
    make install
  • note that the compiled version puts openser in different directory compared to the openser package. The config file is in
    /usr/local/etc/openser/openser.cfg
    and the modules are in
    /usr/local/lib/openser/modules
    and the certificate information is in
    /usr/local/etc/openser/tls/user 
  • run mysqldb.sh to create the database
  • add the certificate chain of domainA and domainB in PEM format to the CA list file in
    /usr/local/etc/openser/user/user-calist.pem
    You can open the file in a text editor and add the certificate string at the end of the file. 
  • put the private key and public key of the server certificate in
    /usr/local/etc/openser/tls/user/user_privkey.pem and
    /usr/local/etc/openser/tls/user/user_cert.pem
    (you're free to choose file names and locations, these are the config defaults)

This example config shows the necessary minimal elements:

No Format
 # #----------- global configuration parameters -----------------------
debug=3     3
fork=yes
log_stderror=no  no
children=4
sip_warning=yes
 
# disable these if you do not allow UDP. UDP is obligatory
# in the SIP RFC
listen=<sip server IP address>
port=5060
 
disable_tls = 0
listen = tls:<sip server IP address>:5061
tls_verify_server = 1
tls_verify_client = 1
tls_require_client_certificate = 0
tls_method = TLSv1
tls_certificate = "/usr/local/etc/openser/tls/user/user-cert.pem"
tls_private_key = "/usr/local/etc/openser/tls/user/user-privkey.pem"
tls_ca_list =         "/usr/local/etc/openser/tls/user/user-calist.pem"
alias="domainA.net"
mpath="/usr/local/lib/openser/modules/"
loadmodule "mysql.so"
loadmodule "sl.so"
loadmodule "tm.so"
loadmodule "rr.so"
loadmodule "maxfwd.so"
loadmodule "usrloc.so"
loadmodule "registrar.so"
loadmodule "textops.so"
loadmodule "mi_fifo.so"
loadmodule "uri_db.so"
loadmodule "auth.so"
loadmodule "auth_db.so"
loadmodule "xlog.so"
 
# ----------------- setting module-specific parameters ---------------
modparam("mi_fifo", "fifo_name", "/tmp/openser_fifo")
# change the read-write mysql account password and adjust this line:
modparam("usrloc", "db_mode", 2)
modparam("usrloc", "db_url", "mysql://openser:openserrw@localhost/openser")
 
# change the read-only mysql account password and adjust this line:
modparam("auth_db", "db_url", "mysql://openserro:openserro@localhost/openser")
modparam("auth_db", "calculate_ha1", yes)
modparam("auth_db", "password_column", "password")
 
modparam("rr", "enable_full_lr", 1)
 
# -------------------------   request routing logic -------------------
# main routing logic
route{
               # initial sanity checks -- messages with
               # max_forwards==0, or excessively long requests
               if (!mf_process_maxfwd_header("10")) {
                               sl_send_reply("483","Too Many Hops");
                               exit;
               };
               if (msg:len >=   2048 ) {
                               sl_send_reply("513", "Message too big");
                               exit;
               };
               # if somene claims to belong to our domain in From,
               # challenge him (skip REGISTERs -- we will chalenge them later)
               if (from_uri==myself) {
                       setflag(1);
                       if ( (method=="INVITE" || method=="SUBSCRIBE" || method=="MESSAGE")
                       &&   !(src_ip==myself) ) {
                if                 if  (!(proxy_authorize("domainA", "subscriber" ))) {
                                       proxy_challenge("domainA","0");
                                       exit;
                               };
                               if (!check_from()) {
                                       log("LOG: From Cheating attempt in INVITE");
                                       sl_send_reply("403",
                                                 "That is ugly -- use From=id next time (OB)");
                                       exit;
                               };
                       };
               }
               else if ( method=="INVITE" && uri!=myself ) {
                       sl_send_reply("403", "No relaying");
                       exit;
               };
 
       
        # we record-route all messages -- to make sure that
               # subsequent messages will go through our proxy; that's
               # particularly good if upstream and downstream entities
               # use different transport protocol
               if (!method=="REGISTER")
                               record_route();
               # subsequent messages withing a dialog should take the
               # path determined by record-routing
               if (loose_route()) {
                               # mark routing logic in request
                               append_hf("P-hint: rr-enforced\r\n");
                               route(1);
               };
 
       
        # check for requests targeted out of our domain
               # see recipe on proxy-proxy TLS
       
       
        # if the request is for other domain use UsrLoc
               # (in case, it does not work, use the following command
               # with proper names and addresses in it)
               if (uri==myself) {
                               if (method=="REGISTER") {
                                               # digest authentication
                                               if (!www_authorize("domainA", "subscriber")) {
                                                               www_challenge("domainA", "0");
                                                               exit;
                                               };
                                               save("location");
                                               exit;
                               };
                               lookup("aliases");
                               if (!uri==myself) {
                                               append_hf("P-hint: outbound alias\r\n");
                                               route(1);
                               };
               };
               route(1)
}
route[1] {
               if (!t_relay()) {
                               sl_reply_error();
               };
               exit;
}

Test

Make sure that the certificate chain (CA list) is installed on the UA. For instance, when using Eyebeam 1.5 under MS Windows, import the chain (in PEM format with file extension .cer) into the windows certificate store by double clicking.

...

  • Invalid TLS version: though TLS 1.0 should be used according to the SIP RFC, TLS 2/3 is supported by both proxies and UAs
  • Client certificate verification should be disabled
  • CA certificate cannot be verified: make sure the correct chain is on the server and on the UA
  • Common name of the server certificate does not match DNS name of the server


OS specific help

Reminder: this example is based on a compiled version of openSER where the config is in /usr/local/etc/openser and the certificates are in /usr/local/etc/openser/tls/user, which might differ when installed from packages.

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