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--- testing_and_debugging_tls_connections [2012/07/13 09:25]
klaus3000 [Test TLS Connections with a Web Browser]
+++ — (current)
@@ Line 1: / Line 1: @@
-====== Testing and Debugging TLS Connections ======
-===== Test TLS Connections with a Web Browser =====
-Testing TLS connections is sometimes a bit tricky. You have to find a SIP client which supports TLS, and then if there are problems, you often do not know if the problem is caused by the SIP client or the SIP server.
-When using Kamailio as SIP proxy it is very easy to test TLS connections by using a web browser and configure Kamailio to accept HTTP(S) connections too. Just add the following config snippets to kamailio.cfg and restart Kamailio:
-<code>
-# to allow HTTP requests
-tcp_accept_no_cl=yes
-.
-.
-.
-# load web server module
-loadmodule "xhttp.so"
-.
-.
-.
-# xhttp event route
-event_route[xhttp:request] {
-  xhttp_reply("200", "OK", "text/html","<html><body>Received HTTP request to $hu from [$si:$sp] with protocol $proto</body></html>");
-}
-</code>
-Then point your browser to Kamailio and check if the configuration works:
-  - Try plain TCP (HTTP) connections: http://ip.address.ofyour.sipproxy:5060/
-  - If TCP works, try TLS (HTTPS) connections: https://ip.address.ofyour.sipproxy:5061/
-If the browser complains about invalid certificates, but after accepting the invalid certificate you receive the response from Kamailio, then TLS works technically, but you have problems with the certificate validation (e.g. Kamailio's certificate was not signed by a well known CA and you have to import the CA into the browser's certificate store).
-===== Test TLS Connections with OpenSSL =====
-This command is useful to connect to the TLS server without any certificate validation.
-  openssl s_client -connect 83.136.32.159:5061 -no_ssl2 -bugs
-For full debugging and inspection of all server certificates use "-showcerts" and "-debug":
-  openssl s_client -showcerts -debug -connect 83.136.32.159:5061 -no_ssl2 -bugs
-===== Debugging TLS Connections =====
-On the server side you can use the "ssldump" utility to see the TLS handshake, e.g. "ssldump port 5061". This will show you which party closes the TLS connection (e.g. sends "Alert" message) and maybe also the cause (e.g. "unknown CA"). Note: ssldump is quite old and sometimes fails to decode some TLS protocol elements.
-For example this is the ssldump trace from a failing handshake between Kamailio 3.3 and Eyebeam 1.5:
-<code>
-New TCP connection #1: pc177.example.com(51642) <-> sip.example.com(5061)
-1  0.0009 (0.0009)  C>S  Handshake
-      ClientHello
-        Version 3.1
-        cipher suites
-        TLS_DHE_RSA_WITH_AES_256_CBC_SHA
-        TLS_RSA_WITH_AES_256_CBC_SHA
-        TLS_DHE_DSS_WITH_AES_256_CBC_SHA
-        compression methods
-                  NULL
-2  0.0022 (0.0012)  S>C  Handshake
-      ServerHello
-        Version 3.1
-        session_id[0]=
-        cipherSuite         TLS_RSA_WITH_AES_256_CBC_SHA
-        compressionMethod                   NULL
-3  0.0022 (0.0000)  S>C  Handshake
-      Certificate
-4  0.0022 (0.0000)  S>C  Handshake
-      ServerHelloDone
-5  0.0038 (0.0016)  C>S  Alert
-    level           fatal
-    value           unknown_ca
-    0.0044 (0.0005)  C>S  TCP RST
-</code>
-Above trace clearly shows that the client closes the TLS/TCP connection due to "unknown_ca". This usually means that the client is configured to perform certificate validation but the validation failed. Either the signing CA is unknown to the client, or the intermediate certificates are missing. After adding the intermediate certificates to Kamailio's TLS configuration ("ca_list" parameter) Eyebeam accepted the certificate and the correct trace is:
-<code>
-New TCP connection #1: pc177.example.com(51733) <-> sip.example.com(5061)
-1  0.0009 (0.0009)  C>S  Handshake
-      ClientHello
-        Version 3.1
-        cipher suites
-        TLS_DHE_RSA_WITH_AES_256_CBC_SHA
-        TLS_RSA_WITH_AES_256_CBC_SHA
-        TLS_DHE_DSS_WITH_AES_256_CBC_SHA
-        compression methods
-                  NULL
-2  0.0024 (0.0015)  S>C  Handshake
-      ServerHello
-        Version 3.1
-        session_id[0]=
-        cipherSuite         TLS_RSA_WITH_AES_256_CBC_SHA
-        compressionMethod                   NULL
-3  0.0024 (0.0000)  S>C  Handshake
-      Certificate
-4  0.0024 (0.0000)  S>C  Handshake
-      ServerHelloDone
-5  0.0118 (0.0093)  C>S  Handshake
-      ClientKeyExchange
-6  0.0118 (0.0000)  C>S  ChangeCipherSpec
-7  0.0118 (0.0000)  C>S  Handshake
-8  0.0311 (0.0193)  S>C  ChangeCipherSpec
-9  0.0311 (0.0000)  S>C  Handshake
-10 0.0433 (0.0121)  C>S  application_data
-11 0.0433 (0.0000)  C>S  application_data
-12 0.1175 (0.0741)  S>C  application_data
-13 0.1185 (0.0010)  S>C  application_data
-</code>
-On the client side it is handy to use Wireshark to capture the SIPS traffic via connections attempts. Then verify the handshake to find out which party closes the connection. Wireshark is also handy to inspect the certificates exchanged in the TLS handshake, e.g. if the server also provided the proper server certificate and intermediate certificates.
-===== Decoding of TLS Connections with Wireshark =====
-Wireshark can be used to decode SSL/TLS sessions. To decode SSL/TLS connections, the following requirements must be fulfilled:
-  * The private key of the TLS server is known (maybe both keys are needed if mutual TLS (=client certificate) is used?)
-  * The TLS connections does not use a Diffie-Hellman cipher
-  * Wireshark captures the TLS session from the beginning (including the TLS handshake)
-To decode TLS connections configure Wireshark and Kamailio:
-  * Copy the server's private key to the PC running Wireshark. Then configure Wireshark to use this key:
-    * Edit → Preferences → Protocols → SSL → RSA Keys List: e.g.: //ip.address.of.server,5061,sip,c:\key.pem//
-  * If the server uses Diffie-Hellman (DH) Ciphers (depends on default compile time settings of libssl) you have to configure Kamailio to use other ciphers. See:
-    * http://kamailio.org/docs/modules/3.3.x/modules/tls.html#cipher_list and
-    * http://www.openssl.org/docs/apps/ciphers.html
-  * To make sure you capture the TLS handshake
-    * Close the SIP client
-    * Start Wireshark and start capturing
-    * Start the SIP client.
-If you have problems decoding the TLS session you should enable debugging in Wireshark: Edit -> Preferences -> Protocols -> SSL -> SSL Debug File
-===== TLS Clients =====
-Following a list of TLS clients and the certificate store they use (please extend):
-  * Eyebeam Windows: Windows certificate store
-  * QjSimple: select CA file in configuration dialog
-  * Internet Explorer: Windows certificate store
-  * Chrome: Windows certificate store
-  * Firefox: Dedicated Firefox certificate store

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