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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 onTLS:

User Agent A — TLS — > proxy domainA

Prerequisites

  • Linux machine
  • SER version 2.0rc or higher
  • Server certificate and private key in PEM fomrat
  • CA list - list of trusted authorities in PEM format

If you use binary package, see if it supports TLS. command ser -V should show something like

ser -V
version: ser 2.0.0-rc1 (i386/linux)
flags: STATS: Off, USE_IPV6, USE_TCP, USE_TLS ......

and tls module (tls.so) has to located in module directory (depends on distribution and package i.e. /usr/local/lib/ser/modules)

Otherwise you have to recompile SER from source. Download daily snaphot from iptel.org or from CVS.

Make everything

make group_include="standard" include_modules="tls" all

Install it (and make before)

make group_include="standard" include_modules="tls" install

You can adjust compiled modules by group_include, include_modules and exclude_modules parameters.
Print-modules parameter show set of modules that will compiled.

make group_include="standard" include_modules="tls" print-modules

Configuration  

# ----------- global configuration parameters ------------------------

debug=3         # debug level (cmd line: -dddddddddd)
#memdbg=10 # memory debug message level
#memlog=10 # memory statistics log level
log_facility=LOG_LOCAL0 # sets the facility used for logging (see syslog(3))

/* Uncomment these lines to enter debugging mode 
fork=no
log_stderror=yes
*/

check_via=no    # (cmd. line: -v)
dns=no          # (cmd. line: -r)
rev_dns=no      # (cmd. line: -R)
#port=5060
children=2
#user=ser
#group=ser
#disable_core=yes #disables core dumping
#open_fd_limit=1024 # sets the open file descriptors limit
#mhomed=yes  # usefull for multihomed hosts, small performance penalty
#disable_tcp=yes 
#tcp_accept_aliases=yes # accepts the tcp alias via option (see NEWS)

enable_tls=yes

alias=domainA

listen=tcp:1.2.3.4:5060
listen=udp:1.2.3.4:5060
listen=tls:1.2.3.4:50


#

# ------------------ module loading ----------------------------------

loadmodule "/usr/local/lib/ser/modules/sl.so"
loadmodule "/usr/local/lib/ser/modules/tm.so"
loadmodule "/usr/local/lib/ser/modules/rr.so"
loadmodule "/usr/local/lib/ser/modules/textops.so"
loadmodule "/usr/local/lib/ser/modules/maxfwd.so"
loadmodule "/usr/local/lib/ser/modules/usrloc.so"
loadmodule "/usr/local/lib/ser/modules/registrar.so"
loadmodule "/usr/local/lib/ser/modules/ctl.so"
loadmodule "/usr/local/lib/ser/modules/tls.so"
loadmodule "/usr/local/lib/ser/modules/xlog.so"

# ----------------- setting module-specific parameters ---------------

# -- usrloc params --
# use memory
modparam("usrloc", "db_mode",   0)

# -- rr params --
# add value to ;lr param to make some broken UAs happy
modparam("rr", "enable_full_lr", 1)

# ctl params
# by default ctl listens on unixs:/tmp/ser_ctl if no other address is
# specified in modparams; this is also the default for sercmd
modparam("ctl", "binrpc", "unixs:/tmp/ser_ctl")
# listen on the "standard" fifo for backward compatibility
modparam("ctl", "fifo", "fifo:/tmp/ser_fifo")
# listen on tcp, localhost
#modparam("ctl", "binrpc", "tcp:localhost:2046")


modparam("tls", "private_key", "/etc/certs/key.pem")
modparam("tls", "ca_list", "/etc/certs/ca_list.pem")
modparam("tls", "certificate", "/etc/certs/cert.pem")
modparam("tls", "tls_log", 2)
modparam("tls", "handshake_timeout", 10)
modparam("tls", "send_timeout", 10)

modparam("tls", "require_certificate", 0)
modparam("tls", "verify_certificate", 1)
modparam("tls", "tls_method", "TLSv1")
#modparam("tls", "tls_method", "SSLv23")


# -------------------------  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_reply("483","Too Many Hops");
		break;
	}
	if (msg:len >=  max_len ) {
		sl_reply("1024", "Message too big");
		break;
	}
 

	if (proto==TLS) {
	    xlog("L_INFO","TLS Method: %rm RURI: %ru, TLSmy : %@tls.my.subject TLSpeer : %@tls.peer.subject %@tls.peer.issuer verified: %@tls.peer.verified  \n  "); 
	    
	}

	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(FORWARD);
		break;
	}

	if (!uri==myself) {
		# mark routing logic in request
		append_hf("P-hint: outbound\r\n");
		if (uri=~".*@domainB") {

			if (t_relay_to_tls("sip.domainB","5061")) {
				xlog("L_INFO","TLS DomainB Method: %rm RURI: \n  "); 
			}
			else {sl_reply_error();}
    			break;
		}
		route(FORWARD);
		break;
	}

	# 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") {
			save_contacts("location");
			break;
		}

		# native SIP destinations are handled using our USRLOC DB
		if (!lookup_contacts("location")) {
			sl_reply("404", "Not Found");
			break;
		}
		append_hf("P-hint: usrloc applied\r\n");
		
	}
	route(FORWARD);
}

route[FORWARD]
{
	# send it out now; use stateful forwarding as it works reliably
	# even for UDP2TCP
	}
	if (!t_relay()) {
	    sl_reply_error();	
	}
}


OS specific help

Validation, confirmation tests

Configure a UA to use TLS. Under MS Windows, good examples is Eyebeam 1.5. Make sure to choose 'TLS' as the protocol in the settings and register with the proxy. Use the diagnostic tools of the UA to see if any problems occur. Common problems are:

  • Invalid TLS version: though TLS 1.0 should be used according to the SIP RFC, SSL 2/3
  • certificate verification
  • Common name of the server certificate does not match DNS name of the server


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