Identity Module

Alexander Christ

Cologne University of Applied Sciences

Edited by

Alexander Christ

Revision History
Revision $Revision: 5901 $$Date: 2007-03-29$

Table of Contents

1. Admin Guide
1.1. Overview
1.2. Dependencies
1.2.1. OpenSIPS Modules
1.2.2. External Libraries or Applications
1.3. Exported Parameters
1.3.1. privKey (string)
1.3.2. authCert (string)
1.3.3. certUri (string)
1.3.4. verCert (string)
1.3.5. caList (string)
1.3.6. crlList (string)
1.3.7. useCrls (integer)
1.4. Exported Functions
1.4.1. authservice()
1.4.2. verifier()
1.5. Known Limitations

List of Examples

1.1. Set privKey parameter
1.2. Set authCert parameter
1.3. Set certUri parameter
1.4. Set verCert parameter
1.5. Set caList parameter
1.6. Set crlList parameter
1.7. Set privKey parameter
1.8. authservice() usage
1.9. verifier() usage

Chapter 1. Admin Guide

1.1. Overview

This module adds support for SIP Identity (see RFC 4474).

1.2. Dependencies

1.2.1. OpenSIPS Modules

The following modules must be loaded before this module:

  • No dependencies on other OpenSIPS modules.

1.2.2. External Libraries or Applications

The following libraries or applications must be installed before running OpenSIPS with this module loaded:

  • openssl (libssl).

1.3. Exported Parameters

1.3.1. privKey (string)

Filename of private RSA-key of authentication service. This file must be in PEM format.

Example 1.1. Set privKey parameter

...
modparam("identity", "privKey", "/etc/openser/privkey.pem")
...

1.3.2. authCert (string)

Filename of certificate which belongs to privKey. This file must be in PEM format.

Example 1.2. Set authCert parameter

...
modparam("identity", "authCert", "/etc/openser/cert.pem")
...

1.3.3. certUri (string)

URI from which the certificate of the authentication service can be acquired. This string will be placed in the Identity-Info header.

Example 1.3. Set certUri parameter

...
modparam("identity", "certUri", "http://www.myserver.com/cert.pem")
...

1.3.4. verCert (string)

Path containing certificates for the verifier. Certificates must be in PEM format. The URI in the Identity-Info header field is used to find the corresponding certificate for the request. For this purpose the verifier replaces every character which is not alphanumeric, no _ and no . with a -. A . at the beginning of the URI is forbidden. If the URI is http://www.test.com/cert.pem the verifier will look for the file http---www.test.com-cert.pem, for example. It is also possible to store a whole certificate chain in a file. In this case certificates must be in right order, end certificate first.

Example 1.4. Set verCert parameter

...
modparam("identity", "verCert", "/etc/openser/verCert/")
...

1.3.5. caList (string)

File containing all trusted (root) certificates for the verifier. Certificates must be in PEM format.

Example 1.5. Set caList parameter

...
modparam("identity", "caList", "/etc/openser/caList.pem")
...

1.3.6. crlList (string)

File containing certificate revocation lists (crls) for the verifier. Setting this parameter is only necessary if useCrls is set to 1.

Example 1.6. Set crlList parameter

...
modparam("identity", "crlList", "/etc/openser/crls.pem")
...

1.3.7. useCrls (integer)

Switch to decide whether to use revocation lists (1) or not (0).

Default value is 0.

Example 1.7. Set privKey parameter

...
modparam("identity", "useCrls", 1)
...

1.4. Exported Functions

1.4.1.  authservice()

This function performs the steps of an authentication service. Before you call this function, you have to ensure that

  • the server is responsible for this request (from URI matches local SIP domain)

  • the sender of the request is authorized to claim the identity given in the From header field.

This function returns the following values:
  • -3: Date header field does not match validity period of cert. Identity header has not been added.

  • -2: message out of time (e.g. message to old), Identity header has not been added.

  • -1: An error occurred.

  • 1: everything OK, Identity header has been added.

This function can be used from REQUEST_ROUTE.

Example 1.8. authservice() usage

...
# CANCEL and ACK cannot be challenged
if (($rm=="CANCEL") || ($rm"ACK"))
{
    route(1); # forward
    exit;
}

# some clients (e.g. Kphone) do not answer, when a BYE is challenged
if ($rm=="BYE")
{
    route(1); # forward
    exit;
}

### Authentication Service ###

# check whether I am authoritative
if(!$fu=~".*@mysipdomain.de")
{
    route(1); # forward
    exit;
}

if(!proxy_authorize("mysipdomain.de","subscriber"))
{
    proxy_challenge("mysipdomain.de","0");
    exit;
}

if (!db_check_from())
{
    sl_send_reply("403", "Use From=ID");
    exit;
}
consume_credentials();
        
authservice();
switch($retcode)
{
    case -3:
        xlog("L_DBG" ,"authservice: Date header field does not match validity period of cert\n");
        break;
    case -2:
        xlog("L_DBG" ,"authservice: msg out of time (max. +- 10 minutes allowed)\n");
        break;
    case -1:
        xlog("L_DBG" ,"authservice: ERROR, returnvalue: -1\n");
        break;
    case 1:
        xlog("L_DBG" ,"authservice: everything OK\n");
        break;
    default:
        xlog("L_DBG" ,"unknown returnvalue of authservice\n");
        
}

route(1); #forward with ($retcode=1) or without ($retcode!=1) Identity header
...

1.4.2.  verifier()

This function performs the steps of an verifier. The returned code tells you the result of the verification:

  • -438: Signature does not correspond to the message. 438-response should be send.

  • -437: Certificate cannot be validated. 437-response should be send.

  • -436: Certificate is not available. 436-response should be send.

  • -428: Message does not have an Identity header. 428-response should be send.

  • -3: Error verifying Date header field.

  • -2: Authentication service is not authoritative.

  • -1: An unknown error occurred.

  • 1: verification OK

This function can be used from REQUEST_ROUTE.

Example 1.9. verifier() usage

...
# we have to define the same exceptions as we did for the authentication service
if (($rm=="CANCEL") || ($rm"ACK")) 
{ 
    route(1); # forward
    exit;
}
    
if ($rm=="BYE")
{
    route(1); # forward
    exit;
}
   
verifier();
switch($retcode)
{
    case -438:
        xlog("L_DBG" ,"verifier: returnvalue: -438\n");
        sl_send_reply("438", "Invalid Identity Header");
        exit;
        break;
    case -437:
        xlog("L_DBG" ,"verifier: returnvalue: -437\n");
        sl_send_reply("437", "Unsupported Certificate");
        exit;
        break;
    case -436:
        xlog("L_DBG" ,"verifier: returnvalue: -436\n");
        sl_send_reply("436", "Bad Identity-Info");
        exit;
        break;
    case -428:
        xlog("L_DBG" ,"verifier: returnvalue: -428\n");
        sl_send_reply("428", "Use Identity Header");
        exit;
        break;
    case -3:
        xlog("L_DBG" ,"verifier: error verifying Date header field\n");
        exit;
        break;
    case -2:
        xlog("L_DBG" ,"verifier: authentication service is not authoritative\n");
        exit;
        break;
    case -1:
        xlog("L_DBG" ,"verifier: ERROR, returnvalue: -1\n");
        exit;
        break;
    case 1:
        xlog("L_DBG" ,"verifier: verification OK\n");
        route(1); # forward
        exit;
        break;
    default:
        xlog("L_DBG" ,"unknown returnvalue of verifier\n");
        exit;
}
exit;
...

1.5. Known Limitations

  • Certificates are not downloaded. They have to be stored locally.

  • Call-IDs of valid requests containing an Identity header are not recorded. Hence the verifier does not provide full replay protection.

  • Authentication service and verifier use the original request. Changes resulting from message processing in OpenSER script are ignored.