1. TLS Module

Andrei Pelinescu-Onciul

   iptelorg GmbH

   Copyright © 2007 iptelorg GmbH
     __________________________________________________________________

   1.1. Overview
   1.2. Quick Start
   1.3. Important Notes
   1.4. Compiling the TLS Module
   1.5. TLS and Low Memory
   1.6. TLS Debugging
   1.7. Known Limitations
   1.8. Quick Certificate Howto
   1.9. Parameters

        1.9.1. tls_method (string)
        1.9.2. certificate (string)
        1.9.3. private_key (string)
        1.9.4. ca_list (string)
        1.9.5. crl (string)
        1.9.6. verify_certificate (boolean)
        1.9.7. verify_depth (integer)
        1.9.8. require_certificate (boolean)
        1.9.9. cipher_list (string)
        1.9.10. send_timeout (int)
        1.9.11. handshake_timeout (int)
        1.9.12. connection_timeout (int)
        1.9.13. tls_disable_compression (boolean)
        1.9.14. ssl_release_buffers (integer)
        1.9.15. ssl_free_list_max_len (integer)
        1.9.16. ssl_max_send_fragment (integer)
        1.9.17. ssl_read_ahead (boolean)
        1.9.18. send_close_notify (boolean)
        1.9.19. con_ct_wq_max (integer)
        1.9.20. ct_wq_max (integer)
        1.9.21. ct_wq_blk_size (integer)
        1.9.22. tls_log (int)
        1.9.23. tls_debug (int)
        1.9.24. low_mem_threshold1 (integer)
        1.9.25. low_mem_threshold2 (integer)
        1.9.26. tls_force_run (boolean)
        1.9.27. session_cache (boolean)
        1.9.28. session_id (str)
        1.9.29. renegotiation (boolean)
        1.9.30. config (string)

   1.10. Functions

        1.10.1. is_peer_verified()

   1.11. History

1.1. Overview

   This module implements the TLS transport for SIP-router using the
   OpenSSL library (http://www.openssl.org). To enable the TLS support
   this module must be loaded and enable_tls=yes must be added to the
   SIP-router config file

1.2. Quick Start

   Make sure you have a proper certificate and private key and either use
   the certificate and private_key module parameters, or make sure the
   certificate and key are in the same PEM file, named cert.pem an placed
   in [your-cfg-install-prefix]/etc/ser/. Don't forget to load the tls
   module and to enable TLS (add enable_tls=yes to your config).

   Example 1. quick start config
#...
loadmodule "modules/tls/tls.so"

modparam("tls", "private_key", "./andrei-test.pem")
modparam("tls", "certificate", "./andrei-test.pem")
modparam("tls", "ca_list", "./calist.pem")

enable_tls=yes

route{
        # ....
}

1.3. Important Notes

   The TLS module needs some special options enabled when compiling
   SIP-router. These options are enabled by default, however in case
   you're using a modified SIP-router version or Makefile, make sure that
   you enable -DUSE_TLS and -DTLS_HOOKS (or compile with make TLS_HOOKS=1
   which will take care of both options). To quickly check if your
   SIP-router version was compiled with these options, run ser -V and look
   for USE_TLS and TLS_HOOKS among the flags.

   This module includes several workarounds for various Openssl bugs (like
   compression and Kerberos using the wrong memory allocations functions,
   low memory problems a.s.o). On startup it will try to enable the needed
   workarounds based on the openssl library version. Each time a known
   problem is detected and a workaround is enabled, a message will be
   logged. In general it is recommended to compile this module on the same
   machine or a similar machine to where ser will be run or to link it
   statically with libssl. For example if on the compile machine openssl
   does not have the kerberos support enabled, but on the target machine a
   kerberos enabled openssl library is installed, ser cannot apply the
   needed workarounds and will refuse to start. The same thing will happen
   if the openssl versions are too different (to force ser startup anyway,
   see the tls_force_run module parameter).

   Try to avoid using keys larger then 1024 bytes. Large keys
   significantly slow down the TLS connection handshake, thus limiting the
   maximum SIP-router TLS connection rate.

   Compression is fully supported if you have a new enough Openssl version
   (starting with 0.9.8). Although there are some problems with zlib
   compression in currently deployed Openssl versions (up to and including
   0.9.8d, see openssl bug #1468), the TLS module will automatically
   switch to its own fixed version. Note however that starting with sr 3.1
   compression is not enabled by default, due to the huge extra memory
   consumption that it causes (about 10x more memory). To enable it use
   modparam("tls", "tls_disable_compression", 0) (see
   tls_disable_compression).

   The TLS module includes workarounds for the following known openssl
   bugs: openssl #1204 (disable SS_OP_TLS_BLOCK_PADDING_BUG if compression
   is enabled, for versions between 0.9.8 and 0.9.8c), openssl #1468 (fix
   zlib compression memory allocation), openssl #1467 (kerberos support
   will be disabled if the openssl version is less than 0.9.8e-beta1) and
   openssl #1491 (stop using tls in low memory situations due to the very
   high risk of openssl crashing or leaking memory). The bug reports can
   be viewed at http://rt.openssl.org/.

1.4. Compiling the TLS Module

   In most case compiling the TLS module is as simple as:
make -C modules/tls

   or
make modules modules=modules/tls

   or (compiling whole SIP-router and the tls module)
make all include_modules=tls

   .

   However in some cases the openssl library requires linking with other
   libraries. For example compiling the openssl library with kerberos and
   zlib-shared support will require linking the tls module with libkrb5
   and libz. In this case just add TLS_EXTRA_LIBS="library list" to make's
   command line. E.g.:
make TLS_EXTRA_LIBS="-lkrb5 -lz" all include_modules=tls

   In general, if SIP-router fails to start with a symbol not found error
   when trying to load the tls module (check the log), it means some
   needed library was not linked and it must be added to TLS_EXTRA_LIBS

1.5. TLS and Low Memory

   The openssl library doesn't handle very well low memory situations. If
   memory allocations start to fail (due to memory shortage), openssl can
   crash or cause memory leaks (making the memory shortage even worse). As
   of this writing all openssl versions were affected (includind 0.9.8e),
   see openssl bug #1491. The tls module has some workarounds for
   preventing this problem (see low_mem_treshold1 and low_mem_threshold2),
   however starting SIP-router with enough shared memory is higly
   recommended. When this is not possible a quick way to significantly
   reduce openssl memory usage it to disable compression (see
   tls_disable_compression).

1.6. TLS Debugging

   Debugging messages can be selectively enabled by recompiling the tls
   module with a combination of the following defines:
     * TLS_WR_DEBUG - debug messages for the write/send part.
     * TLS_RD_DEBUG - debug messages for the read/receive part.
     * TLS_BIO_DEBUG - debug messages for the custom BIO.

   Example 2. Compiling TLS with Debug Messages
make -C modules/tls extra_defs="-DTLS_WR_DEBUG -DTLS_RD_DEBUG"

   To change the level at which the debug messages are logged, change the
   tls_debug module parameter.

1.7. Known Limitations

   The private key must not encrypted (SIP-router cannot ask you for a
   password on startup).

   The TLS certificate verifications ignores the certificate name, subject
   altname and ip extensions, it just checks if the certificate is signed
   by a recognized CA. One can use the select framework to try to overcome
   this limitation (check in the script for the contents of various
   certificate fields), but this is not only slow, but also not exactly
   standard conforming (the verification should happen during TLS
   connection establishment and not after).

   TLS specific config reloading is not safe, so for now better don't use
   it, especially under heavy traffic.

   This documentation is incomplete. The RPCs are not documented here, but
   in doc/rpc_list/rpc_tls.txt or
   http://sip-router.org/docbook/sip-router/branch/master/rpc_list/rpc_lis
   t.html#rpc_exports.tls. The provided selects are not documented. A list
   with all the ones implemented by the tls module can be seen under
   doc/select_list/select_tls.txt or or
   http://sip-router.org/docbook/sip-router/branch/master/select_list/sele
   ct_list.html#select_list.tls.

1.8. Quick Certificate Howto

   There are various ways to create, sign certificates and manage small
   CAs (Certificate Authorities). If you want a GUI, try tinyca
   (http://tinyca.sm-zone.net/), a very nice and small CA management
   application. If you are in a hurry and everything you have are the
   installed openssl libraries and utilities, read on.

   Assumptions: we run our own CA.

   Warning: in this example no key is encrypted. The client and server
   private keys must not be encrypted (ser doesn't support encrypted
   keys), so make sure the corresponding files are readable only by
   trusted people. You should use a password for your CA private key.

Assumptions
------------

The default openssl configuration (usually /etc/ssl/openssl.cnf)
default_ca section is the one distributed with openssl and uses the default
directories:

...

default_ca      = CA_default            # The default ca section

[ CA_default ]

dir             = ./demoCA              # Where everything is kept
certs           = $dir/certs            # Where the issued certs are kept
crl_dir         = $dir/crl              # Where the issued crl are kept
database        = $dir/index.txt        # database index file.
#unique_subject = no                    # Set to 'no' to allow creation of
                                        # several ctificates with same subject.
new_certs_dir   = $dir/newcerts         # default place for new certs.

certificate     = $dir/cacert.pem       # The CA certificate
serial          = $dir/serial           # The current serial number
crlnumber       = $dir/crlnumber        # the current crl number
crl             = $dir/crl.pem          # The current CRL
private_key     = $dir/private/cakey.pem# The private key
RANDFILE        = $dir/private/.rand    # private random number file

...

If this is not the case create a new openssl config file that uses the above
paths for the default CA and add to all the openssl commands:
 -config filename. E.g.:
        openssl ca -config my_openssl.cnf -in ser1_cert_req.pem -out ser1_cert.p
em


Creating CA certificate
-----------------------
1. create CA dir
        mkdir ca
        cd ca

2. create ca dir structure and files  (see ca(1))
        mkdir demoCA #default CA name, edit /etc/ss/openssl.cnf
        mkdir  demoCA/private
        mkdir demoCA/newcerts
        touch demoCA/index.txt
        echo 01 >demoCA/serial
        echo 01 >demoCA/crlnumber

2. create CA private key
        openssl genrsa -out demoCA/private/cakey.pem 2048
        chmod 600 demoCA/private/cakey.pem

3. create CA self-signed certificate
        openssl req -out demoCA/cacert.pem   -x509 -new -key demoCA/private/cake
y.pem


Creating a server/client certificate
------------------------------------
1. create a certificate request (and its private key in privkey.pem)
        openssl req -out ser1_cert_req.pem -new -nodes
        WARNING: the organization name should be the same as in the ca certifica
te.

2. sign it with the ca certificate
        openssl ca -in ser1_cert_req.pem -out ser1_cert.pem

3. copy ser1_cert.pem to your ser config. dir


Setting sip-router to use the certificate
-----------------------------------------
1. create the ca list file:
        for each of your ca certificates that you intend to use do:
                cat cacert.pem >>calist.pem

2. copy your sip-router certificate, private key and ca list file to your
        intended machine (preferably in your sip-router configuration directory,
         this is the default place sip-router searches for).

3. set up sip-router.cfg to use the certificate
        if your ser certificate name is different from cert.pem or it is not
        placed in sip-router cfg. directory, add to your sip-router.cfg:
                modparam("tls", "certificate", "/path/cert_file_name")

4. set up sip-router to use the private key
        if your private key is not contained in the same file as the certificate
        (or the certificate name is not the default cert.pem), add to your
         sip-router.cfg:
                modparam("tls", "private_key", "/path/private_key_file")

5. set up sip-router to use the ca list (optional)
        add to your sip-router.cfg:
                modparam("tls", "ca_list", "/path/ca_list_file")

6. set up tls authentication options:
                modparam("tls", "verify_certificate", 1)
                modparam("tls", "require_certificate", 1)
        (for more information see the module parameters documentation)


Revoking a certificate and using a CRL
--------------------------------------
1. revoking a certificate:
        openssl ca -revoke bad_cert.pem

2. generate/update the certificate revocation list:
        openssl ca -gencrl -out my_crl.pem

3. copy my_crl.pem to your ser config. dir

4. set up sip-router to use the CRL:
                modparam("tls", "crl", "path/my_crl.pem")

1.9. Parameters

1.9.1. tls_method (string)

   Sets the SSL/TLS protocol method. Possible values are:
     * TLSv1 - only TLSv1 connections are accepted. This is the default
       and recommended method (if you want to be rfc3261 conformant don't
       change it).
     * SSLv3 - only SSLv3 connections are accepted
     * SSLv2 - only SSLv2 connections, for old clients. Note: you
       shouldn't use SSLv2 for anything which should be highly secure.
     * SSLv23 - any of the above methods will be accepted, with the
       following limitation: the initial SSL hello message must be V2 (in
       the initial hello all the supported protocols are advertised
       enabling switching to a higher and more secure version). This means
       connections from SSLv3 or TLSv1 clients will not be accepted.

   If rfc3261 conformance is desired, TLSv1 must be used. For
   compatibility with older clients SSLv23 is a good option.

   Example 3. Set tls_method parameter
...
modparam("tls", "tls_method", "TLSv1")
...

1.9.2. certificate (string)

   Sets the certificate file name. The certificate file can also contain
   the private key in PEM format.

   If the file name starts with a '.' the path will be relative to the
   working directory (at runtime). If it starts with a '/' it will be an
   absolute path and if it starts with anything else the path will be
   relative to the main config file directory (e.g.: for ser -f
   /etc/ser/ser.cfg it will be relative to /etc/ser/).

   Warning: try not to use certificate with keys longer then 1024 bytes.
   Longer keys will severely impact performance, in particular the TLS
   connection rate.

   The default value is [SER_CFG_DIR]/cert.pem.

   Example 4. Set certificate parameter
...
modparam("tls", "certificate", "/usr/local/etc/ser/my_certificate.pem")
...

1.9.3. private_key (string)

   Sets the private key file name.

   If the file name starts with a '.' the path will be relative to the
   working directory (at runtime). If it starts with a '/' it will be an
   absolute path and if it starts with anything else the path will be
   relative to the main config file directory (e.g.: for ser -f
   /etc/ser/ser.cfg it will be relative to /etc/ser/).

   Note: the private key can be contained in the same file as the
   certificate (just append it to the certificate file, e.g.: cat pkey.pem
   >> cert.pem)

   The default value is [SER_CFG_DIR]/cert.pem.

   Example 5. Set private_key parameter
...
modparam("tls", "private", "/usr/local/etc/ser/my_pkey.pem")
...

1.9.4. ca_list (string)

   Sets the CA list file name. This file contains a list of all the
   trusted CAs certificates. If a signature in a certificate chain belongs
   to one of the listed CAs, the authentication will succeed.

   If the file name starts with a '.' the path will be relative to the
   working directory (at runtime). If it starts with a '/' it will be an
   absolute path and if it starts with anything else the path will be
   relative to the main config file directory (e.g.: for ser -f
   /etc/ser/ser.cfg it will be relative to /etc/ser/).

   By default the CA file is not set.

   An easy way to create the CA list is to append each trusted trusted CA
   certificate in the PEM format to one file, e.g.: for f in
   trusted_cas/*.pem ; do cat "$f" >> ca_list.pem ; done .

   See also verify_certificate, verify_depth, require_certificate and crl.

   Example 6. Set ca_list parameter
...
modparam("tls", "ca_list", "/usr/local/etc/ser/ca_list.pem")
...

1.9.5. crl (string)

   Sets the certificate revocation list file name. This file contains a
   list of revoked certificates. Any attempt to verify a revoked
   certificate will fail.

   If not set, no crl list will be used.

   If the file name starts with a '.' the path will be relative to the
   working directory (at runtime). If it starts with a '/' it will be an
   absolute path and if it starts with anything else the path will be
   relative to the main config file directory (e.g.: for ser -f
   /etc/ser/ser.cfg it will be relative to /etc/ser/).

Note

   If set, require_certificate should also be set or it will not have any
   effect.

   By default the crl file is not set.

   To update the crl in a running ser, make sure you configure tls via a
   separate tls config file (the config modparam) and issue a tls.reload
   RPC call, e.g.:
 $ sercmd tls.reload

   A quick way to create the CRL in PEM format, using openssl is:
 $ openssl ca -gencrl -keyfile cacert.key -cert cacert.pem -out my_crl.pem

   my_crl.pem will contain the signed list of the revoked certificates.

   To revoke a certificate use something like:
 $ openssl ca -revoke bad_cert.pem -keyfile cacert.key -cert cacert.pem

   and then refresh the crl file using the command above.

   To display the CRL contents use:
 $ openssl crl -in crl.pem -noout -text

   See also ca_list, verify_certificate, verify_depth and
   require_certificate.

   Example 7. Set crl parameter
...
modparam("tls", "crl", "/usr/local/etc/ser/crl.pem")
...

1.9.6. verify_certificate (boolean)

   If enabled it will force certificate verification. For more information
   see the verify(1) openssl man page.

   Note: the certificate verification will always fail if the ca_list is
   empty.

   See also: ca_list, require_certificate, verify_depth.

   By default the certificate verification is off.

   Example 8. Set verify_certificate parameter
...
modparam("tls", "verify_certificate", 1)
...

1.9.7. verify_depth (integer)

   Sets how far up the certificate chain will the certificate verification
   go in the search for a trusted CA.

   See also: ca_list, require_certificate, verify_certificate,

   The default value is 9.

   Example 9. Set verify_depth parameter
...
modparam("tls", "verify_depth", 9)
...

1.9.8. require_certificate (boolean)

   When enabled it will require a certificate from a client. If the client
   does not offer a certificate and verify_certificate is on, the
   certificate verification will fail.

   The default value is off.

   Example 10. Set require_certificate parameter
...
modparam("tls", "require_certificate", 1)
...

1.9.9. cipher_list (string)

   Sets the list of accepted ciphers. The list consists of cipher strings
   separated by colons. For more information on the cipher list format see
   the cipher(1) openssl man page.

   The default value is not set (all the Openssl supported ciphers are
   enabled).

   Example 11. Set cipher_list parameter
...
modparam("tls", "cipher_list", "HIGH")
...

1.9.10. send_timeout (int)

   This parameter is obsolete and cannot be used in newer TLS versions (>
   sip-router 3.0). In these versions the send_timeout is replaced by
   tcp_send_timeout (common with all the tcp connections).

1.9.11. handshake_timeout (int)

   This parameter is obsolete and cannot be used in newer TLS versions (>
   sip-router 3.0). In these versions the handshake_timeout is replaced by
   tcp_connect_timeout (common with all the tcp connections).

1.9.12. connection_timeout (int)

   Sets the amount of time after which an idle TLS connection will be
   closed, if no I/O ever occured after the initial open. If an I/O event
   occurs, the timeout will be extended with tcp_connection_lifetime. The
   value is expressed in seconds.

   The default value is 10 min.

   If the value set is -1, the connection will never be close on idle.

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.connection_timeout.

   Example 12. Set connection_timeout parameter
...
modparam("tls", "connection_timeout", 60)
...

   Example 13. Set tls.connection_timeout at runtime
 $ sercmd cfg.set_now_int tls connection_timeout 180

1.9.13. tls_disable_compression (boolean)

   If set compression over SSL/TLS will be disabled. Note that compression
   uses a lot of memory (about 10x more then with the compression
   disabled), so if you want to minimize memory usage is a good idea to
   disable it.

   By default compression is disabled.

   Example 14. Set tls_disable_compression parameter
...
modparam("tls", "tls_disable_compression", 0) # enable
...

1.9.14. ssl_release_buffers (integer)

   Release internal OpenSSL read or write buffers as soon as they are no
   longer needed. Combined with ssl_free_list_max_len has the potential of
   saving a lot of memory ( ~ 32k per connection in the default
   configuration, or 16k + ssl_max_send_fragment). For sr versions > 3.0
   it makes little sense to disable it (0) since the tls module already
   has its own internal buffering.

   A value of -1 would not change this option from its openssl default.
   Use 0 or 1 for enable/disable.

   By default the value is 1 (enabled).

Note

   This option is supported only for OpenSSL versions >= 1.0.0. On all the
   other versions attempting to change the default will trigger an error.

   Example 15. Set ssl_release_buffers parameter
modparam("tls", "ssl_release_buffers", 1)

1.9.15. ssl_free_list_max_len (integer)

   Sets the maximum number of free memory chunks, that OpenSSL will keep
   per connection. Setting it to 0 would cause any unused memory chunk to
   be immediately freed, reducing the memory footprint. A too large value
   would result in extra memory consumption.

   Should be combined with ssl_release_buffers.

   A value of -1 has a special meaning: the OpenSSL default will be used
   (no attempt on changing the value will be made). For OpenSSL 1.0 the
   internal default is 32.

   By default the value is 0 (no freelist).

Note

   This option is supported only for OpenSSL versions >= 1.0.0. On all the
   other versions attempting to change the default will trigger an error.

   Example 16. Set ssl_freelist_max_len parameter
modparam("tls", "ssl_freelist_max_len", 0)

1.9.16. ssl_max_send_fragment (integer)

   Sets the maximum number of bytes (from the clear text) sent into one
   TLS or SSL record. Valid values are between 512 and 16384. Note however
   that even valid low values might not be big enough to allow a
   succesfull handshake (try minimum 1024).

   Lower values would lead to less memory usage, but values lower then the
   typical ser/sip-router write size would incur a slight performance
   penalty. Good values are bigger then the size of the biggest SIP packet
   one normally expects to forward. For example in most setups 2048 would
   be a good value.

Note

   Values on the lower side, even if valid (> 512), might not allow for a
   succesfull initial handshake. This happens if the certificate does not
   fit inside one send fragment. Values lower then 1024 should not be
   used. Even with higher values, if the handshake fails, try increasing
   the value.

   A value of -1 has a special meaning: the OpenSSL default will be used
   (no attempt on changing the value will be made).

   By default the value is -1 (the OpenSSL default, which at least in
   OpenSSL 1.0.0 is ~ 16k).

Note

   This option is supported only for OpenSSL versions >= 0.9.9. On all the
   other versions attempting to change the default will trigger an error.

   Example 17. Set ssl_max_send_fragment parameter
modparam("tls", "ssl_max_send_fragment", 4096)

1.9.17. ssl_read_ahead (boolean)

   Enables read ahead, reducing the number of internal OpenSSL BIO read()
   calls. This option has only debugging value, in normal circumstances it
   should not be changed from the default.

   When disabled OpenSSL will make at least 2 BIO read() calls per
   received record: one to get the record header and one to get the rest
   of the record.

   The TLS module buffers internally all read()s and defines its own fast
   BIO so enabling this option would only cause more memory consumption
   and a minor slow-down (extra memcpy).

   A value of -1 has a special meaning: the OpenSSL default will be used
   (no attempt on changing the value will be made).

   By default the value is 0 (disabled).

   Example 18. Set ssl_read_ahead parameter
modparam("tls", "ssl_read_ahead", 1)

1.9.18. send_close_notify (boolean)

   Enables/disables sending close notify alerts prior to closing the
   corresponding TCP connection. Sending the close notify prior to tcp
   shutdown is "nicer" from a TLS point of view, but it has a measurable
   performance impact. Default: off. Can be set at runtime
   (tls.send_close_notify).

   The default value is 0 (off).

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.send_close_notify.

   Example 19. Set send_close_notify parameter
...
modparam("tls", "send_close_notify", 1)
...

   Example 20. Set tls.send_close_notify at runtime
 $ sercmd cfg.set_now_int tls send_close_notify 1

1.9.19. con_ct_wq_max (integer)

   Sets the maximum allowed per connection clear-text send queue size in
   bytes. This queue is used when data cannot be encrypted and sent
   immediately because of an ongoing TLS/SSL level renegotiation.

   The default value is 65536 (64 Kb).

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.con_ct_wq_max.

   Example 21. Set con_ct_wq_max parameter
...
modparam("tls", "con_ct_wq_max", 1048576)
...

   Example 22. Set tls.con_ct_wq_max at runtime
 $ sercmd cfg.set_now_int tls con_ct_wq_max 1048576

1.9.20. ct_wq_max (integer)

   Sets the maximum total number of bytes queued in all the clear-text
   send queues. These queues are used when data cannot be encrypted and
   sent immediately because of an ongoing TLS/SSL level renegotiation.

   The default value is 10485760 (10 Mb).

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.ct_wq_max.

   Example 23. Set ct_wq_max parameter
...
modparam("tls", "ct_wq_max", 4194304)
...

   Example 24. Set tls.ct_wq_max at runtime
 $ sercmd cfg.set_now_int tls ct_wq_max 4194304

1.9.21. ct_wq_blk_size (integer)

   Minimum block size for the internal clear-text send queues (debugging /
   advanced tunning). Good values are multiple of typical datagram sizes.

   The default value is 4096.

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.ct_wq_blk_size.

   Example 25. Set ct_wq_blk_size parameter
...
modparam("tls", "ct_wq_blk_size", 2048)
...

   Example 26. Set tls.ct_wq_max at runtime
 $ sercmd cfg.set_now_int tls ct_wq_blk_size 2048

1.9.22. tls_log (int)

   Sets the log level at which TLS related messages will be logged.

   The default value is 3 (L_DBG).

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.log.

   Example 27. Set tls_log parameter
...
# ignore TLS messages if SIP-router is started with debug less than 10
modparam("tls", "tls_log", 10)
...

   Example 28. Set tls.log at runtime
 $ sercmd cfg.set_now_int tls log 10

1.9.23. tls_debug (int)

   Sets the log level at which TLS debug messages will be logged. Note
   that TLS debug messages are enabled only if the TLS module is compiled
   with debugging enabled (e.g. -DTLS_WR_DEBUG, -DTLS_RD_DEBUG or
   -DTLS_BIO_DEBUG).

   The default value is 3 (L_DBG).

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.debug.

   Example 29. Set tls_debug parameter
...
# ignore TLS debug messages if SIP-router is started with debug less than 10
modparam("tls", "tls_debug", 10)
...

   Example 30. Set tls.debug at runtime
 $ sercmd cfg.set_now_int tls debug 10

1.9.24. low_mem_threshold1 (integer)

   Sets the minimal free memory from which attempts to open or accept new
   TLS connections will start to fail. The value is expressed in KB.

   The default value depends on whether the openssl library used handles
   well low memory situations (openssl bug #1491). As of this writing this
   is not true for any openssl version (including 0.9.8e).

   If an ill-behaved openssl version is detected, a very conservative
   value is choosed, which depends on the maximum possible number of
   simultaneously created TLS connections (and hence on the process
   number).

   The following values have a special meaning:
     * -1 - use the default value
     * 0 - disable (TLS connections will not fail preemptively)

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.low_mem_threshold1.

   See also low_mem_threshold2.

   Example 31. Set low_mem_threshold1 parameter
...
modparam("tls", "low_mem_threshold1", -1)
...

   Example 32. Set tls.low_mem_threshold1 at runtime
 $ sercmd cfg.set_now_int tls low_mem_threshold1 2048

1.9.25. low_mem_threshold2 (integer)

   Sets the minimal free memory from which TLS operations on already
   established TLS connections will start to fail preemptively. The value
   is expressed in KB.

   The default value depends on whether the openssl library used handles
   well low memory situations (openssl bug #1491). As of this writing this
   is not true for any openssl version (including 0.9.8e).

   If an ill-behaved openssl version is detected, a very conservative
   value is choosed, which depends on the maximum possible number of
   simultaneously created TLS connections (and hence on the process
   number).

   The following values have a special meaning:
     * -1 - use the default value
     * 0 - disable (TLS operations will not fail preemptively)

   It can be changed also at runtime, via the RPC interface and config
   framework. The config variable name is tls.low_mem_threshold2.

   See also low_mem_threshold1.

   Example 33. Set low_mem_threshold2 parameter
...
modparam("tls", "low_mem_threshold2", -1)
...

   Example 34. Set tls.low_mem_threshold2 at runtime
 $ sercmd cfg.set_now_int tls low_mem_threshold2 1024

1.9.26. tls_force_run (boolean)

   If enabled SIP-router will start even if some of the openssl sanity
   checks fail (turn it on at your own risk).

   Currently failing any of the following sanity checks will not allow
   SIP-router to start:
     * the version of the library the TLS module was compiled with is "too
       different" from the library used at runtime. The versions should
       have the same major, minor and fix level (e.g.: 0.9.8a and 0.9.8c
       are ok, but 0.9.8 and 0.9.9 are not)
     * the openssl library used at compile time and the one used at
       runtime have different kerberos options

   By default tls_force_run is disabled.

   Example 35. Set tls_force_run parameter
...
modparam("tls", "tls_force_run", 11)
...

1.9.27. session_cache (boolean)

   If enabled SIP server will do caching of the TLS sessions data,
   generation a session_id and sending it back to client.

   By default TLS session caching is disabled (0).

   Example 36. Set session_cache parameter
...
modparam("tls", "session_cache", 1)
...

1.9.28. session_id (str)

   The value for session ID context, making sense when session caching is
   enabled.

   By default TLS session_id is "sip-router-tls-3.1".

   Example 37. Set session_id parameter
...
modparam("tls", "session_id", "my-session-id-context")
...

1.9.29. renegotiation (boolean)

   If enabled SIP server will allow renegotiations of TLS connection
   initiated by the client. This may expose to a security risk if the
   client is not a trusted peer and keeps renegotiating, consuming CPU and
   bandwidth resources.

   By default TLS renegotiation is disabled (0).

   Example 38. Set renegotiation parameter
...
modparam("tls", "renegotiation", 1)
...

1.9.30. config (string)

   Sets the name of the TLS specific config file.

   If set the TLS module will load a special config file, in which
   different TLS parameters can be specified on a per role (server or
   client) and domain basis (for now only IPs). The corresponding module
   parameters will be ignored.

   If the file name starts with a '.' the path will be relative to the
   working directory (at runtime). If it starts with a '/' it will be an
   absolute path and if it starts with anything else the path will be
   relative to the main config file directory (e.g.: for ser -f
   /etc/ser/ser.cfg it will be relative to /etc/ser/).

   By default no config file is specified.

   The following parameters can be set in the config file, for each
   domain:
     * tls_method
     * verify_certificate
     * require_certificate
     * private_key
     * certificate
     * verify_depth
     * ca_list
     * crl
     * cipher_list

   All the parameters that take filenames as values will be resolved using
   the same rules as for the tls config filename itself: starting with a
   '.' means relative to the working directory, a '/' means an absolute
   path and anything else a path relative to the directory of the current
   ser main config file.

   SIP-router acts as a server when it accepts a connection and as a
   client when it initiates a new connection by itself (it connects to
   something).

   Example 39. Short config file
[server:default]
method = TLSv1
verify_certificate = yes
require_certificate = yes
private_key = default_key.pem
certificate = default_cert.pem
ca_list = default_ca.pem
crl = default_crl.pem

[client:default]
verify_certificate = yes
require_certificate = yes

#more relaxed for connection on the loopback interface
[server:127.0.0.1:5061]
method = SSLv23
verify_certificate = yes
require_certificate = no
private_key = local_key.pem
certificate = local_cert.pem
verify_depth = 3
ca_list = local_ca.pem

   For a more complete example check the tls.cfg distributed with the
   SIP-router source (sip_router/modules/tls/tls.cfg).

   Example 40. Set config parameter
...
modparam("tls", "config", "/usr/local/etc/ser/tls.cfg")
...

   It can be changed also at runtime. The new config will not be loaded
   immediately, but after the first tls.reload RPC call.

   Example 41. Change and reload tls config at runtime
 $ sercmd cfg.set_now_string tls config "/usr/local/etc/ser/new_tls.cfg"
 $ sercmd tls.reload

1.10. Functions

1.10.1. is_peer_verified()

   Returns true if the connection on which the message was received is TLS
   , the peer presented an X509 certificate and the certificate chain
   verified ok. It can be used only in a request route.

   Example 42. is_peer_verified usage
        if (proto==TLS && !is_peer_verified()){
                sl_send_reply("400", "No certificate or verification failed");
                drop;
        }

1.11. History

   This module was put together by Jan Janak <jan@iptel.org> from code
   from the experimental tls core addon
   (http://cvs.berlios.de/cgi-bin/viewcvs.cgi/ser/experimental/tls/), code
   originally written by Peter Griffiths and later maintained by Cesc
   Santasusana and from an iptelorg tls code addon, written by Andrei
   Pelinescu-Onciul <andrei@iptel.org>. Jan also added support for
   multiple domains, a tls specific config, config reloading and a tls
   specific select framework.

   For ser/sr 3.1 most of the TLS specific code was completely re-written
   to add support for asynchrounous TLS and fix several long standing
   bugs.

   The code is currently maintained by Andrei Pelinescu-Onciul
   <andrei@iptel.org>.
