mod\_gnutls Manual 0.1\ July 2011 ======================= * * * * * Contents -------- 1. Compilation & Installation 2. Integration 3. Configuration Directives\ - GnuTLSCache - GnuTLSCacheTimeout - GnuTLSSessionTickets - GnuTLSCertificateFile - GnuTLSKeyFile - GnuTLSPGPCertificateFile - GnuTLSPGPKeyFile - GnuTLSClientVerify - GnuTLSClientCAFile - GnuTLSPGPKeyringFile - GnuTLSEnable - GnuTLSDHFile - GnuTLSRSAFile - GnuTLSSRPPasswdFile - GnuTLSSRPPasswdConfFile - GnuTLSPriorities - GnuTLSExportCertificates 4. Configuration Examples\ - Simple Standard SSL Example - Server Name Indication Example 5. Performance Issues 6. Environment Variables 7. Credits * * * * * Compilation & Installation -------------------------- mod\_gnutls uses the "configure/make/make install" mechanism common to many Open Source programs.\ Most of the dirty work is handled by either configure or Apache's apxs utility.\ If you have built Apache modules before, there shouldn't be any surprises for you.\ The interesting options you can pass to configure are:\ \ --with-apxs=PATH\ This option is used to specify the location of the apxs utility that was installed as part of apache.\ Specify the location of the binary, not the directory it is located in.\ \ --with-libgnutls=PATH\ Full path to the libgnutls-config program.\ \ --with-apr-memcache=PREFIX\ Prefix to where apr\_memcache is installed.\ \ --help\ Provides a list of all available configure options. * * * * * Integration ----------- To activate mod\_gnutls just add the following line to your httpd.conf and restart Apache: `LoadModule gnutls_module modules/mod_gnutls.so` * * * * * Configuration Directives: ------------------------- #### GnuTLSCache ##### Description: Configure SSL Session Cache\ ##### Syntax:        GnuTLSCache [*dbm*|*gdbm*|*memcache*|*none*] [path|server list|-]\ ##### Default:       GnuTLSCache none\ ##### Context:       server config\ This directive configures the SSL Session Cache for mod\_gnutls.\ This could be shared between machines of different architectures. **dbm (Requires Berkeley DBM)**\ Uses the default Berkeley DB backend of APR DBM to cache SSL Sessions results.\ The argument is a relative or absolute path to be used as the DBM Cache file.\ This is compatible with most operating systems, but needs the Apache Runtime to be compiled with Berkeley DBM support.\ **gdbm**\ Uses the GDBM backend of APR DBM to cache SSL Sessions results.\ The argument is a relative or absolute path to be used as the DBM Cache file.\ This is the recommended option.\ **memcache**\ Uses a memcached server to cache the SSL Session.\ The argument is a space separated list of servers. If no port number is supplied, the default of 11211 is used.\ This can be used to share a session cache between all servers in a cluster.\ **none**\ Turns off all caching of SSL Sessions.\ This can significantly reduce the performance of mod\_gnutls since even followup connections by a client must renegotiate parameters instead of reusing old ones.\ This is the default, since it requires no configuration.\ #### GnuTLSCacheTimeout ##### Description: Timeout for SSL Session Cache expiration\ ##### Syntax:        GnuTLSCacheTimeout *seconds*\ ##### Default:       GnuTLSCacheTimeout 300\ ##### Context:       server config\ Sets the timeout for SSL Session Cache entries expiration.\ This directive is valid even if Session Tickets are used, and indicates the expiration time of the ticket in seconds. #### GnuTLSSessionTickets ##### Description: Enable Session Tickets for the server\ ##### Syntax:        GnuTLSSessionTickets [ *on* | *off* ]\ ##### Default:       *off*\ ##### Context:       server config, virtual host\ To avoid storing data for TLS session resumption it is allowed to provide client with a ticket, to use on return.\ Use for servers with limited storage, and don't combine with GnuTLSCache.\ For a pool of servers this option is not recommended since the tickets are unique for the issuing server only. #### GnuTLSCertificateFile ##### Description: Set to the PEM Encoded Server Certificate\ ##### Syntax:        GnuTLSCertificateFile *file-path*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to a PEM-encoded X.509 certificate to use as this Server's End Entity (EE) certificate. If you need to supply certificates for intermediate Certificate Authorities (iCAs), they should be listed in sequence in the file, from EE to the iCA closest to the root CA. Optionally, you can also include the root CA's certificate as the last certificate in the list. #### GnuTLSKeyFile ##### Description: Set to the PEM Encoded Server Certificate\ ##### Syntax:        GnuTLSCertificateFile *file-path*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to the Server Private Key.\ This key cannot currently be password protected. **Security Warning:**\ This private key must be protected. It is read while Apache is still running as root, and does not need to be readable by the nobody or apache user. #### GnuTLSPGPCertificateFile ##### Description: Set to a base64 Encoded Server OpenPGP Certificate\ ##### Syntax:        GnuTLSPGPCertificateFile *file-path*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to a base64 Encoded OpenPGP Certificate to use as this Server's Certificate. #### GnuTLSPGPKeyFile ##### Description: Set to the Server OpenPGP Secret Key\ ##### Syntax:        GnuTLSPGPKeyFile *file-path*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to the Server Private Key. This key cannot currently be password protected. **Security Warning:**\ This private key must be protected. It is read while Apache is still running as root, and does not need to be readable by the nobody or apache user. #### GnuTLSClientVerify ##### Description: Enable Client Certificate Verification\ ##### Syntax:        GnuTLSClientVerify [ *ignore* | *request* | *require* ]\ ##### Default:       *ignore*\ ##### Context:       server config, virtual host, directory, .htaccess\ This directive controls the use of SSL Client Certificate Authentication.\ If used in the .htaccess context, it can force TLS re-negotiation. **ignore**\ mod\_gnutls will ignore the contents of any SSL Client Certificates sent.\ It will not request that the client sends a certificate.\ **request**\ The client certificate will be requested, but not required.\ The Certificate will be validated if sent.\ The output of the validation status will be stored in the SSL\_CLIENT\_VERIFY environment variable and can be "SUCCESS", "FAILED" or "NONE".\ **require**\ A Client certificate will be required. Any requests without a valid client certificate will be denied.\ The SSL\_CLIENT\_VERIFY environment variable will only be set to "SUCCESS". #### GnuTLSClientCAFile ##### Description: Set to the PEM Encoded Certificate Authority Certificate\ ##### Syntax:        GnuTLSClientCAFile *file-path*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to a PEM Encoded Certificate to use as a Certificate Authority with Client Certificate Authentication.\ This file may contain a list of trusted authorities.\ #### GnuTLSPGPKeyringFile ##### Description: Set to a base64 Encoded key ring\ ##### Syntax:        GnuTLSPGPKeyringFile *file-path*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to a base64 Encoded Certificate list (key ring) to use as a means of verification of Client Certificates.\ This file should contain a list of trusted signers. #### GnuTLSEnable ##### Description: Enable GnuTLS for this virtual host\ ##### Syntax:        GnuTLSEnable [ *on* | *off* ] \ ##### Default:       *off*\ ##### Context:       virtual host\ This directive enables SSL/TLS Encryption for a Virtual Host. #### GnuTLSDHFile ##### Description: Set to the PKCS \#3 encoded Diffie Hellman parameters\ ##### Syntax:        GnuTLSDHFile *file-path* \ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to a PKCS \#3 encoded DH parameters.\ Those are used when the DHE key exchange method is enabled.\ You can generate this file using "certtool --generate-dh-params --bits 2048".\ If not set mod\_gnutls will use the included parameters. #### GnuTLSSRPPasswdFile ##### Description: Set to the SRP password file for SRP ciphersuites\ ##### Syntax:        GnuTLSSRPPasswdFile *file-path* \ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to an SRP password file. This is the same format as used in libsrp.\ You can generate such file using the command "srptool --passwd /etc/tpasswd --passwd-conf /etc/tpasswd.conf -u test" to set a password for user test.\ This password file holds the username, a password verifier and the dependency to the SRP parameters. #### GnuTLSSRPPasswdConfFile ##### Description: Set to the SRP password.conf file for SRP ciphersuites\ ##### Syntax:        GnuTLSSRPPasswdConfFile *file-path* \ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes an absolute or relative path to an SRP password.conf file. This is the same format as used in libsrp.\ You can generate such file using the command "srptool --create-conf /etc/tpasswd.conf".\ This file holds the SRP parameters and is associate with the password file (the verifiers depends on these parameters). #### GnuTLSPriorities ##### Description: Set the allowed ciphers, key exchange algorithms, MACs and compression methods\ ##### Syntax:        GnuTLSPriorities *+cipher0:+cipher1:...:+cipherN*\ ##### Default:       *none*\ ##### Context:       server config, virtual host\ Takes a semi-colon separated list of ciphers, key exchange methods\ Message authentication codes and compression methods to enable.\ The allowed keywords are specified in the gnutls\_priority\_init() function of GnuTLS.\ It's documentation can be found at [Core GnuTLS functions](http://www.gnu.org/software/gnutls/manual/html_node/Core-functions.html#Core-functions).\ In brief you can specify a set of ciphersuites from the choices:\ - **NONE**: The empty list. - **EXPORT**: A list with all the supported cipher combinations including the "EXPORT" strength algorithms. - **PERFORMANCE**: A list with all the secure cipher combinations sorted in terms of performance. - **NORMAL**: A list with all the secure cipher combinations sorted with respect to security margin (subjective term). - **SECURE**: A list with all the secure cipher combinations including the 256-bit ciphers sorted with respect to security margin. Additionally you can add or remove algorithms using the "+" and "!" prefixes respectively.\ That is in order to disable the ARCFOUR cipher from the "NORMAL" set you can use the string **NORMAL**:!ARCFOUR-128\ Other options such as the protocol version and the compression method can be specified using the **VERS-** and **COMP-** prefixes.\ So in order to remove or add a specific TLS version from the "NORMAL" set use **NORMAL:!VERS-SSL3.0**.\ To enable zlib compression use **NORMAL:+COMP-DEFLATE**.\ However it is recommended not to add compression at this level.\ With the "NONE" set, in order to be usable, you have to specify a complete set of combinations of protocol versions,\ cipher algorithms (**AES-128-CBC**), key exchange algorithms (**RSA**), message authentication codes (**SHA1**) and compression methods (**COMP-NULL**).\ \ All the supported algorithms are:\ - **Ciphers**: AES-256-CBC, AES-128-CBC, CAMELLIA-256-CBC, CAMELLIA-128-CBC, ARCFOUR-128, 3DES-CBC, ARCFOUR-40 - **Key exchange methods**: RSA, DHE-RSA, DHE-DSS, SRP, SRP-RSA, SRP-DSS, ANON-DH - **Message authentication codes**: SHA1, MD5 - **Compression methods**: COMP-DEFLATE, COMP-NULL - **Protocol versions**: VERS-TLS1.1, VERS-TLS1.0, VERS-SSL3.0 The special keyword "%COMPAT" will disable some security features such as protection against statistical attacks to ciphertext data in order to achieve maximum compatibility (some broken mobile clients need this). #### GnuTLSExportCertificates ##### Description: Export the PEM encoded certificates to CGIs\ ##### Syntax:        GnuTLSExportCertificates [ *on* | *off* ]\ ##### Default:       *off*\ ##### Context:       server config, virtual host\ This directive enables exporting the full certificates of the server and the client to CGI scripts. The exported certificates will be PEM-encoded (if X.509) or ASCII-armored (if OpenPGP).\ With GnuTLSExportCertificates enabled, mod\_gnutls exports the same environment variables as mod\_ssl. * * * * * Configuration Examples ---------------------- #### Simple Standard SSL Example: The following is an example of standard SSL Hosting, using one IP Addresses for each virtual host ` # Load the module into Apache. LoadModule gnutls_module modules/mod_gnutls.so GnuTLSCache gdbm /var/cache/www-tls-cache GnuTLSCacheTimeout 500 # With normal SSL Websites, you need one IP Address per-site. Listen 1.2.3.1:443 Listen 1.2.3.2:443 Listen 1.2.3.3:443 Listen 1.2.3.4:443 GnuTLSEnable on GnuTLSPriorities NONE:+AES-128-CBC:+3DES-CBC:+ARCFOUR-128:+RSA:+DHE-RSA:+DHE-DSS:+SHA1:+MD5:+COMP-NULL DocumentRoot /www/site1.example.com/html ServerName site1.example.com:443 GnuTLSCertificateFile conf/ssl/site1.crt GnuTLSKeyFile conf/ss/site1.key # This virtual host enables SRP authentication GnuTLSEnable on GnuTLSPriorities NORMAL:+SRP DocumentRoot /www/site2.example.com/html ServerName site2.example.com:443 GnuTLSSRPPasswdFile conf/ssl/tpasswd.site2 GnuTLSSRPPasswdConfFile conf/ssl/tpasswd.site2.conf # This server enables SRP, OpenPGP and X.509 authentication. GnuTLSEnable on GnuTLSPriorities NORMAL:+SRP:+SRP-RSA:+SRP-DSS DocumentRoot /www/site3.example.com/html ServerName site3.example.com:443 GnuTLSCertificateFile conf/ssl/site3.crt GnuTLSKeyFile conf/ss/site3.key GnuTLSClientVerify ignore GnuTLSPGPCertificateFile conf/ss/site3.pub.asc GnuTLSPGPKeyFile conf/ss/site3.sec.asc GnuTLSSRPPasswdFile conf/ssl/tpasswd.site3 GnuTLSSRPPasswdConfFile conf/ssl/tpasswd.site3.conf GnuTLSEnable on # %COMPAT disables some security features to enable maximum compatibility with clients. GnuTLSPriorities NONE:+AES-128-CBC:+ARCFOUR-128:+RSA:+SHA1:+MD5:+COMP-NULL:%COMPAT DocumentRoot /www/site4.example.com/html ServerName site4.example.com:443 GnuTLSCertificateFile conf/ssl/site4.crt GnuTLSKeyFile conf/ss/site4.key ` #### Server Name Indication Example: mod\_gnutls can also use 'Server Name Indication', as specified in RFC 3546.\ This allows hosting many SSL Websites, with a Single IP Address.\ Currently all the recent browsers support this standard.\ Here is an example, using SNI:\ ` ` \# Load the module into Apache.\ LoadModule gnutls\_module modules/mod\_gnutls.so\ \# With normal SSL Websites, you need one IP Address per-site.\ Listen 1.2.3.1:443\ \# This could also be 'Listen \*:443',\ \# just like '\*:80' is common for non-https\ \# No caching. Enable session tickets. Timeout is still used for\ \# ticket expiration.\ GnuTLSCacheTimeout 600\ \# This tells apache, that for this IP/Port combination, we want to use\ \# Name Based Virtual Hosting. In the case of Server Name Indication,\ \# it lets mod\_gnutls pick the correct Server Certificate.\ NameVirtualHost 1.2.3.1:443\ \\ GnuTLSEnable on\ GnuTLSSessionTickets on\ GnuTLSPriorities NORMAL\ DocumentRoot /www/site1.example.com/html\ ServerName site1.example.com:443\ GnuTLSCertificateFile conf/ssl/site1.crt\ GnuTLSKeyFile conf/ss/site1.key\ \\ \\ GnuTLSEnable on\ GnuTLSPriorities NORMAL\ DocumentRoot /www/site2.example.com/html\ ServerName site2.example.com:443\ GnuTLSCertificateFile conf/ssl/site2.crt\ GnuTLSKeyFile conf/ss/site2.key\ \\ \\ GnuTLSEnable on\ GnuTLSPriorities NORMAL\ DocumentRoot /www/site3.example.com/html\ ServerName site3.example.com:443\ GnuTLSCertificateFile conf/ssl/site3.crt\ GnuTLSKeyFile conf/ss/site3.key\ \\ \\ GnuTLSEnable on\ GnuTLSPriorities NORMAL\ DocumentRoot /www/site4.example.com/html\ ServerName site4.example.com:443\ GnuTLSCertificateFile conf/ssl/site4.crt\ GnuTLSKeyFile conf/ss/site4.key\ \\ * * * * * Performance Issues: ------------------- mod\_gnutls by default uses conservative settings for the server.\ You can fine tune the configuration to reduce the load on a busy server.\ The following examples do exactly this:\ ` # Load the module into Apache. LoadModule gnutls_module modules/mod_gnutls.so # Using 4 memcache servers to distribute the SSL Session Cache. GnuTLSCache memcache "mc1.example.com mc2.example.com mc3.example.com mc4.example.com" GnuTLSCacheTimeout 600 Listen 1.2.3.1:443 NameVirtualHost 1.2.3.1:443 GnuTLSEnable on # Here we disable the Perfect forward secrecy ciphersuites (DHE) # and disallow AES-256 since AES-128 is just fine. GnuTLSPriorities NORMAL:!DHE-RSA:!DHE-DSS:!AES-256-CBC:%COMPAT DocumentRoot /www/site1.example.com/html ServerName site1.example.com:443 GnuTLSCertificateFile conf/ssl/site1.crt GnuTLSKeyFile conf/ss/site1.key GnuTLSEnable on # Here we instead of disabling the DHE ciphersuites we use # Diffie Hellman parameters of smaller size than the default (2048 bits). # Using small numbers from 768 to 1024 bits should be ok once they are # regenerated every few hours. # Use "certtool --generate-dh-params --bits 1024" to get those GnuTLSDHFile /etc/apache2/dh.params GnuTLSPriorities NORMAL:!AES-256-CBC:%COMPAT DocumentRoot /www/site2.example.com/html ServerName site2.example.com:443 GnuTLSCertificateFile conf/ssl/site2.crt GnuTLSKeyFile conf/ss/site2.key ` * * * * * Environment Variables: ---------------------- mod\_gnutls exports the following environment variables to scripts.\ These are compatible with mod\_ssl. ###### HTTPS Can be "on" or "off" ###### SSL\_VERSION\_LIBRARY The version of the gnutls library ###### SSL\_VERSION\_INTERFACE The version of this module ###### SSL\_PROTOCOL The SSL or TLS protocol name (such as "TLS 1.0" etc.) ###### SSL\_CIPHER The SSL or TLS cipher suite name ###### SSL\_COMPRESS\_METHOD The negotiated compression method (NULL or DEFLATE) ###### SSL\_SRP\_USER The SRP username used for authentication (only set when GnuTLSSRPPasswdFile and GnuTLSSRPPasswdConfFile are configured). ###### SSL\_CIPHER\_USEKEYSIZE & SSL\_CIPHER\_ALGKEYSIZE The number if bits used in the used cipher algorithm. This does not fully reflect the security level since the size of RSA or DHE key exchange parameters affect the security level too. ###### SSL\_CIPHER\_EXPORT True or False. Whether the cipher suite negotiated is an export one. ###### SSL\_SESSION\_ID The session ID negotiated in this session. Can be the same during client reloads. ###### SSL\_CLIENT\_V\_REMAIN The number of days until the client's certificate is expired. ###### SSL\_CLIENT\_V\_START The activation time of client's certificate. ###### SSL\_CLIENT\_V\_END The expiration time of client's certificate. ###### SSL\_CLIENT\_S\_DN The distinguished name of client's certificate in RFC2253 format. ###### SSL\_CLIENT\_I\_DN The SSL or TLS cipher suite name ###### SSL\_CLIENT\_S\_AN% These will contain the alternative names of the client certificate (% is a number starting from zero). The values will be prepended by "DNSNAME:", "RFC822NAME:" or "URI:" depending on the type. If it is not supported the value "UNSUPPORTED" will be set. ###### SSL\_SERVER\_M\_SERIAL The serial number of the server's certificate. ###### SSL\_SERVER\_M\_VERSION The version of the server's certificate. ###### SSL\_SERVER\_A\_SIG The algorithm used for the signature in server's certificate. ###### SSL\_SERVER\_A\_KEY The public key algorithm in server's certificate. ###### SSL\_SERVER\_CERT The PEM-encoded server certificate. ###### SSL\_SERVER\_CERT\_TYPE The certificate type can be X.509 or OPENPGP.