source: mod_gnutls/docs/mod_gnutls_manual.mdwn @ bce7907

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1% `mod_gnutls` Manual
2
3* * * * *
4
5`mod_gnutls` is a module for the Apache web server that provides HTTPS
6(HTTP over Transport Layer Security (TLS) or the older Secure Sockets
7Layer (SSL)) using the GnuTLS library.  More information about the
8module can be found at [the project's website](https://mod.gnutls.org/).
9
10* * * * *
11
12Compilation & Installation
13==========================
14
15`mod_gnutls` uses the `./configure && make && make install` mechanism
16common to many Open Source programs.  Most of the dirty work is
17handled by either `./configure` or Apache's `apxs` utility. If you have
18built Apache modules before, there shouldn't be any surprises for you.
19
20The interesting options you can pass to configure are:
21
22`--with-apxs=PATH`
23:   This option is used to specify the location of the apxs utility that
24    was installed as part of apache. Specify the location of the
25    binary, not the directory it is located in.
26
27`--with-libgnutls=PATH`
28:   Full path to the libgnutls-config program.
29
30`--with-apr-memcache=PREFIX`
31:   Prefix to where apr\_memcache is installed.
32
33`--help`
34:   Provides a list of all available configure options.
35
36* * * * *
37
38Integration
39===========
40
41To activate `mod_gnutls` just add the following line to your httpd.conf
42and restart Apache:
43
44    LoadModule gnutls_module modules/mod_gnutls.so
45
46* * * * *
47
48Configuration Directives
49========================
50
51`GnuTLSEnable`
52--------------
53
54Enable GnuTLS for this virtual host
55
56    GnuTLSEnable [on|off]
57
58Default: *off*\
59Context: virtual host
60
61This directive enables SSL/TLS Encryption for a Virtual Host.
62
63`GnuTLSCache`
64-------------
65
66Configure SSL Session Cache
67
68    GnuTLSCache [dbm|gdbm|memcache|none] [PATH|SERVERLIST|-]
69
70Default: `GnuTLSCache none`\
71Context: server config
72
73This directive configures the SSL Session Cache for `mod_gnutls`.
74This could be shared between machines of different architectures.
75
76`dbm` (Requires Berkeley DBM)
77:   Uses the default Berkeley DB backend of APR DBM to cache SSL
78    Sessions results.  The argument is a relative or absolute path to
79    be used as the DBM Cache file. This is compatible with most
80    operating systems, but needs the Apache Runtime to be compiled
81    with Berkeley DBM support.
82
83`gdbm`
84:   Uses the GDBM backend of APR DBM to cache SSL Sessions results.
85
86    The argument is a relative or absolute path to be used as the DBM Cache
87    file.  This is the recommended option.
88
89`memcache`
90:   Uses a memcached server to cache the SSL Session.
91
92    The argument is a space separated list of servers. If no port
93    number is supplied, the default of 11211 is used.  This can be
94    used to share a session cache between all servers in a cluster.
95
96`none`
97:   Turns off all caching of SSL Sessions.
98
99    This can significantly reduce the performance of `mod_gnutls` since
100    even followup connections by a client must renegotiate parameters
101    instead of reusing old ones.  This is the default, since it
102    requires no configuration.
103
104`GnuTLSCacheTimeout`
105--------------------
106
107Timeout for SSL Session Cache expiration
108
109    GnuTLSCacheTimeout SECONDS
110
111Default: `GnuTLSCacheTimeout 300`\
112Context: server config
113
114Sets the timeout for SSL Session Cache entries expiration.  This
115directive is valid even if Session Tickets are used, and indicates the
116expiration time of the ticket in seconds.
117
118`GnuTLSSessionTickets`
119----------------------
120
121Enable Session Tickets for the server
122
123    GnuTLSSessionTickets [on|off]
124
125Default: `off`\
126Context: server config, virtual host
127
128To avoid storing data for TLS session resumption it is allowed to
129provide client with a ticket, to use on return.  Use for servers with
130limited storage, and don't combine with GnuTLSCache. For a pool of
131servers this option is not recommended since the tickets are unique
132for the issuing server only.
133
134
135`GnuTLSCertificateFile`
136-----------------------
137
138Set to the PEM Encoded Server Certificate
139
140    GnuTLSCertificateFile FILEPATH
141
142Default: *none*\
143Context: server config, virtual host
144
145Takes an absolute or relative path to a PEM-encoded X.509 certificate to
146use as this Server's End Entity (EE) certificate. If you need to supply
147certificates for intermediate Certificate Authorities (iCAs), they
148should be listed in sequence in the file, from EE to the iCA closest to
149the root CA. Optionally, you can also include the root CA's certificate
150as the last certificate in the list.
151
152`GnuTLSKeyFile`
153---------------
154
155Set to the PEM Encoded Server Certificate
156
157    GnuTLSCertificateFile FILEPATH
158
159Default: *none*\
160Context: server config, virtual host
161
162Takes an absolute or relative path to the Server Private Key.  This
163key cannot currently be password protected.
164
165**Security Warning:**\
166 This private key must be protected. It is read while Apache is still
167running as root, and does not need to be readable by the nobody or
168apache user.
169
170`GnuTLSPGPCertificateFile`
171--------------------------
172
173Set to a base64 Encoded Server OpenPGP Certificate
174
175    GnuTLSPGPCertificateFile FILEPATH
176
177Default: *none*\
178Context: server config, virtual host
179
180Takes an absolute or relative path to a base64 Encoded OpenPGP
181Certificate to use as this Server's Certificate.
182
183`GnuTLSPGPKeyFile`
184------------------
185
186Set to the Server OpenPGP Secret Key
187
188    GnuTLSPGPKeyFile FILEPATH
189
190Default: *none*\
191Context: server config, virtual host
192
193Takes an absolute or relative path to the Server Private Key. This key
194cannot currently be password protected.
195
196**Security Warning:**\
197 This private key must be protected. It is read while Apache is still
198running as root, and does not need to be readable by the nobody or
199apache user.
200
201`GnuTLSClientVerify`
202--------------------
203
204Enable Client Certificate Verification\
205
206    GnuTLSClientVerify [ignore|request|require]
207
208Default: `ignore`\
209Context: server config, virtual host, directory, .htaccess
210
211This directive controls the use of SSL Client Certificate
212Authentication. If used in the .htaccess context, it can force TLS
213re-negotiation.
214
215`ignore`
216:   `mod_gnutls` will ignore the contents of any SSL Client Certificates
217    sent. It will not request that the client sends a certificate.
218
219`request`
220:   The client certificate will be requested, but not required.
221    The Certificate will be validated if sent.  The output of the
222    validation status will be stored in the `SSL_CLIENT_VERIFY`
223    environment variable and can be `SUCCESS`, `FAILED` or `NONE`.
224
225`require`
226:   A Client certificate will be required. Any requests without a valid
227    client certificate will be denied.  The `SSL_CLIENT_VERIFY`
228    environment variable will only be set to `SUCCESS`.
229
230`GnuTLSClientCAFile`
231--------------------
232
233Set to the PEM Encoded Certificate Authority Certificate
234
235    GnuTLSClientCAFile FILEPATH
236
237Default: *none*
238Context: server config, virtual host
239
240Takes an absolute or relative path to a PEM Encoded Certificate to use
241as a Certificate Authority with Client Certificate Authentication.
242This file may contain a list of trusted authorities.
243
244`GnuTLSPGPKeyringFile`
245----------------------
246
247Set to a base64 Encoded key ring
248
249    GnuTLSPGPKeyringFile FILEPATH
250
251Default: *none*\
252Context: server config, virtual host
253
254Takes an absolute or relative path to a base64 Encoded Certificate
255list (key ring) to use as a means of verification of Client
256Certificates.  This file should contain a list of trusted signers.
257
258`GnuTLSDHFile`
259--------------
260
261Set to the PKCS \#3 encoded Diffie Hellman parameters
262
263    GnuTLSDHFile FILEPATH
264
265Default: *none*\
266Context: server config, virtual host
267
268Takes an absolute or relative path to a PKCS \#3 encoded DH
269parameters.Those are used when the DHE key exchange method is enabled.
270You can generate this file using `certtool --generate-dh-params --bits
2712048`.  If not set `mod_gnutls` will use the included parameters.
272
273`GnuTLSSRPPasswdFile`
274---------------------
275
276Set to the SRP password file for SRP ciphersuites
277
278    GnuTLSSRPPasswdFile FILEPATH
279
280Default: *none*\
281Context: server config, virtual host
282
283Takes an absolute or relative path to an SRP password file. This is
284the same format as used in libsrp.  You can generate such file using
285the command `srptool --passwd /etc/tpasswd --passwd-conf
286/etc/tpasswd.conf -u test` to set a password for user test.  This
287password file holds the username, a password verifier and the
288dependency to the SRP parameters.
289
290`GnuTLSSRPPasswdConfFile`
291-------------------------
292
293Set to the SRP password.conf file for SRP ciphersuites
294
295    GnuTLSSRPPasswdConfFile FILEPATH
296
297Default: *none*\
298Context: server config, virtual host
299
300Takes an absolute or relative path to an SRP password.conf file. This
301is the same format as used in `libsrp`.  You can generate such file
302using the command `srptool --create-conf /etc/tpasswd.conf`.  This
303file holds the SRP parameters and is associate with the password file
304(the verifiers depends on these parameters).
305
306`GnuTLSPriorities`
307------------------
308
309Set the allowed ciphers, key exchange algorithms, MACs and compression
310methods
311
312    GnuTLSPriorities NORMAL:+CIPHER_0:+CIPHER_1:...:+CIPHER_N
313
314Default: *none*\
315Context: server config, virtual host
316
317Takes a semi-colon separated list of ciphers, key exchange methods
318Message authentication codes and compression methods to enable.
319The allowed keywords are specified in the `gnutls_priority_init()`
320function of GnuTLS.
321
322Full details can be found at [the GnuTLS documentation](http://gnutls.org/manual/html_node/Priority-Strings.html#Priority-Strings).
323In brief you can specify a set of ciphersuites from the choices:
324
325`NONE`
326:   The empty list.
327
328`EXPORT`
329:   A list with all the supported cipher combinations
330    including the `EXPORT` strength algorithms.
331
332`PERFORMANCE`
333:   A list with all the secure cipher combinations sorted in terms of performance.
334
335`NORMAL`
336:   A list with all the secure cipher combinations sorted
337    with respect to security margin (subjective term).
338
339`SECURE`
340:   A list with all the secure cipher combinations including
341    the 256-bit ciphers sorted with respect to security margin.
342
343Additionally you can add or remove algorithms using the `+` and `!`
344prefixes respectively.
345
346For example, in order to disable the `ARCFOUR` cipher from the `NORMAL` set
347you can use the string `NORMAL:!ARCFOUR-128`
348
349Other options such as the protocol version and the compression method
350can be specified using the `VERS-` and `COMP-` prefixes.
351
352So in order to remove or add a specific TLS version from the `NORMAL`
353set, use `NORMAL:!VERS-SSL3.0`.  And to enable zlib compression use
354`NORMAL:+COMP-DEFLATE`.
355
356
357However it is recommended not to add compression at this level.  With
358the `NONE` set, in order to be usable, you have to specify a complete
359set of combinations of protocol versions, cipher algorithms
360(`AES-128-CBC`), key exchange algorithms (`RSA`), message
361authentication codes (`SHA1`) and compression methods (`COMP-NULL`).
362
363You can find a list of all supported Ciphers, Versions, MACs, etc.  by
364running `gnutls-cli --list`.
365
366The special keyword `%COMPAT` will disable some security features such
367as protection against statistical attacks to ciphertext data in order to
368achieve maximum compatibility (some broken mobile clients need this).
369
370`GnuTLSExportCertificates`
371--------------------------
372
373Export the PEM encoded certificates to CGIs
374
375    GnuTLSExportCertificates [on|off]
376
377Default: `off`\
378Context: server config, virtual host
379
380This directive enables exporting the full certificates of the server and
381the client to CGI scripts. The exported certificates will be PEM-encoded
382(if X.509) or ASCII-armored (if OpenPGP).
383With GnuTLSExportCertificates enabled, `mod_gnutls` exports the same
384environment variables to the CGI process as `mod_ssl`.
385
386* * * * *
387
388Configuration Examples
389======================
390
391Simple Standard SSL Example
392---------------------------
393
394The following is an example of standard SSL Hosting, using one IP
395Addresses for each virtual host
396
397     # Load the module into Apache.
398     LoadModule gnutls_module modules/mod_gnutls.so
399     GnuTLSCache gdbm /var/cache/www-tls-cache
400     GnuTLSCacheTimeout 500
401     # With normal SSL Websites, you need one IP Address per-site.
402     Listen 1.2.3.1:443
403     Listen 1.2.3.2:443
404     Listen 1.2.3.3:443
405     Listen 1.2.3.4:443
406     <VirtualHost 1.2.3.1:443>
407     GnuTLSEnable on
408     GnuTLSPriorities NONE:+AES-128-CBC:+3DES-CBC:+ARCFOUR-128:+RSA:+DHE-RSA:+DHE-DSS:+SHA1:+MD5:+COMP-NULL
409     DocumentRoot /www/site1.example.com/html
410     ServerName site1.example.com:443
411     GnuTLSCertificateFile conf/ssl/site1.crt
412     GnuTLSKeyFile conf/ss/site1.key
413     </VirtualHost>
414     <VirtualHost 1.2.3.2:443>
415     # This virtual host enables SRP authentication
416     GnuTLSEnable on
417     GnuTLSPriorities NORMAL:+SRP
418     DocumentRoot /www/site2.example.com/html
419     ServerName site2.example.com:443
420     GnuTLSSRPPasswdFile conf/ssl/tpasswd.site2
421     GnuTLSSRPPasswdConfFile conf/ssl/tpasswd.site2.conf
422     </VirtualHost>
423     <VirtualHost 1.2.3.3:443>
424     # This server enables SRP, OpenPGP and X.509 authentication.
425     GnuTLSEnable on
426     GnuTLSPriorities NORMAL:+SRP:+SRP-RSA:+SRP-DSS
427     DocumentRoot /www/site3.example.com/html
428     ServerName site3.example.com:443
429     GnuTLSCertificateFile conf/ssl/site3.crt
430     GnuTLSKeyFile conf/ss/site3.key
431     GnuTLSClientVerify ignore
432     GnuTLSPGPCertificateFile conf/ss/site3.pub.asc
433     GnuTLSPGPKeyFile conf/ss/site3.sec.asc
434     GnuTLSSRPPasswdFile conf/ssl/tpasswd.site3
435     GnuTLSSRPPasswdConfFile conf/ssl/tpasswd.site3.conf
436     </VirtualHost>
437     <VirtualHost 1.2.3.4:443>
438     GnuTLSEnable on
439     # %COMPAT disables some security features to enable maximum compatibility with clients.
440     GnuTLSPriorities NONE:+AES-128-CBC:+ARCFOUR-128:+RSA:+SHA1:+MD5:+COMP-NULL:%COMPAT
441     DocumentRoot /www/site4.example.com/html
442     ServerName site4.example.com:443
443     GnuTLSCertificateFile conf/ssl/site4.crt
444     GnuTLSKeyFile conf/ss/site4.key
445     </VirtualHost>
446
447Server Name Indication Example
448------------------------------
449
450`mod_gnutls` can also use "Server Name Indication", as specified in
451RFC 3546.  This allows hosting many SSL Websites, with a Single IP
452Address.  Currently all the recent browsers support this
453standard. Here is an example, using SNI: ` `
454
455
456     # Load the module into Apache.
457     LoadModule gnutls_module modules/mod_gnutls.so
458     # With normal SSL Websites, you need one IP Address per-site.
459     Listen 1.2.3.1:443
460     # This could also be 'Listen *:443',
461     # just like '*:80' is common for non-https
462     # No caching. Enable session tickets. Timeout is still used for
463     # ticket expiration.
464     GnuTLSCacheTimeout 600
465     # This tells apache, that for this IP/Port combination, we want to use
466     # Name Based Virtual Hosting. In the case of Server Name Indication,
467     # it lets mod_gnutls pick the correct Server Certificate.
468     NameVirtualHost 1.2.3.1:443
469     <VirtualHost 1.2.3.1:443>
470     GnuTLSEnable on
471     GnuTLSSessionTickets on
472     GnuTLSPriorities NORMAL
473     DocumentRoot /www/site1.example.com/html
474     ServerName site1.example.com:443
475     GnuTLSCertificateFile conf/ssl/site1.crt
476     GnuTLSKeyFile conf/ss/site1.key
477     </VirtualHost>
478     <VirtualHost 1.2.3.1:443>
479     GnuTLSEnable on
480     GnuTLSPriorities NORMAL
481     DocumentRoot /www/site2.example.com/html
482     ServerName site2.example.com:443
483     GnuTLSCertificateFile conf/ssl/site2.crt
484     GnuTLSKeyFile conf/ss/site2.key
485     </VirtualHost>
486     <VirtualHost 1.2.3.1:443>
487     GnuTLSEnable on
488     GnuTLSPriorities NORMAL
489     DocumentRoot /www/site3.example.com/html
490     ServerName site3.example.com:443
491     GnuTLSCertificateFile conf/ssl/site3.crt
492     GnuTLSKeyFile conf/ss/site3.key
493     </VirtualHost>
494     <VirtualHost 1.2.3.1:443>
495     GnuTLSEnable on
496     GnuTLSPriorities NORMAL
497     DocumentRoot /www/site4.example.com/html
498     ServerName site4.example.com:443
499     GnuTLSCertificateFile conf/ssl/site4.crt
500     GnuTLSKeyFile conf/ss/site4.key
501     </VirtualHost>
502
503
504* * * * *
505
506Performance Issues
507==================
508
509`mod_gnutls` by default uses conservative settings for the server.
510You can fine tune the configuration to reduce the load on a busy
511server.  The following examples do exactly this:
512
513
514     # Load the module into Apache.
515     LoadModule gnutls_module modules/mod_gnutls.so
516     # Using 4 memcache servers to distribute the SSL Session Cache.
517     GnuTLSCache memcache "mc1.example.com mc2.example.com mc3.example.com mc4.example.com"
518     GnuTLSCacheTimeout 600
519     Listen 1.2.3.1:443
520     NameVirtualHost 1.2.3.1:443
521     <VirtualHost 1.2.3.1:443>
522     GnuTLSEnable on
523     # Here we disable the Perfect forward secrecy ciphersuites (DHE)
524     # and disallow AES-256 since AES-128 is just fine.
525     GnuTLSPriorities NORMAL:!DHE-RSA:!DHE-DSS:!AES-256-CBC:%COMPAT
526     DocumentRoot /www/site1.example.com/html
527     ServerName site1.example.com:443
528     GnuTLSCertificateFile conf/ssl/site1.crt
529     GnuTLSKeyFile conf/ss/site1.key
530     </VirtualHost>
531     <VirtualHost 1.2.3.1:443>
532     GnuTLSEnable on
533     # Here we instead of disabling the DHE ciphersuites we use
534     # Diffie Hellman parameters of smaller size than the default (2048 bits).
535     # Using small numbers from 768 to 1024 bits should be ok once they are
536     # regenerated every few hours.
537     # Use "certtool --generate-dh-params --bits 1024" to get those
538     GnuTLSDHFile /etc/apache2/dh.params
539     GnuTLSPriorities NORMAL:!AES-256-CBC:%COMPAT
540     DocumentRoot /www/site2.example.com/html
541     ServerName site2.example.com:443
542     GnuTLSCertificateFile conf/ssl/site2.crt
543     GnuTLSKeyFile conf/ss/site2.key
544     </VirtualHost>
545
546* * * * *
547
548Environment Variables
549=====================
550
551`mod_gnutls` exports the following environment variables to scripts.
552These are compatible with `mod_ssl`.
553
554`HTTPS`
555-------
556
557Can be `on` or `off`
558
559`SSL_VERSION_LIBRARY`
560---------------------
561
562The version of the GnuTLS library
563
564`SSL_VERSION_INTERFACE`
565-----------------------
566
567The version of this module
568
569`SSL_PROTOCOL`
570--------------
571
572The SSL or TLS protocol name (such as `TLS 1.0` etc.)
573
574`SSL_CIPHER`
575------------
576
577The SSL or TLS cipher suite name
578
579`SSL_COMPRESS_METHOD`
580---------------------
581
582The negotiated compression method (`NULL` or `DEFLATE`)
583
584`SSL_SRP_USER`
585--------------
586
587The SRP username used for authentication (only set when
588`GnuTLSSRPPasswdFile` and `GnuTLSSRPPasswdConfFile` are configured).
589
590`SSL_CIPHER_USEKEYSIZE` & `SSL_CIPHER_ALGKEYSIZE`
591-------------------------------------------------
592
593The number if bits used in the used cipher algorithm.
594
595This does not fully reflect the security level since the size of
596RSA or DHE key exchange parameters affect the security level too.
597
598`SSL_DH_PRIME_BITS`
599-------------------
600
601The number if bits in the modulus for the DH group, if DHE or static
602DH is used.
603
604This will not be set if DH is not used.
605
606`SSL_CIPHER_EXPORT`
607-------------------
608
609`True` or `False`. Whether the cipher suite negotiated is an export one.
610
611`SSL_SESSION_ID`
612----------------
613
614The session ID negotiated in this session. Can be the same during client
615reloads.
616
617`SSL_CLIENT_V_REMAIN`
618---------------------
619
620The number of days until the client's certificate is expired.
621
622`SSL_CLIENT_V_START`
623--------------------
624
625The activation time of client's certificate.
626
627`SSL_CLIENT_V_END`
628------------------
629
630The expiration time of client's certificate.
631
632`SSL_CLIENT_S_DN`
633-----------------
634
635The distinguished name of client's certificate in RFC2253 format.
636
637`SSL_CLIENT_I_DN`
638-----------------
639
640The SSL or TLS cipher suite name
641
642`SSL_CLIENT_S_AN%`
643------------------
644
645These will contain the alternative names of the client certificate (`%` is
646a number starting from zero).
647
648The values will be prepended by `DNSNAME:`, `RFC822NAME:` or `URI:`
649depending on the type.
650
651If it is not supported the value `UNSUPPORTED` will be set.
652
653`SSL_SERVER_M_SERIAL`
654---------------------
655
656The serial number of the server's certificate.
657
658`SSL_SERVER_M_VERSION`
659----------------------
660
661The version of the server's certificate.
662
663`SSL_SERVER_A_SIG`
664------------------
665
666The algorithm used for the signature in server's certificate.
667
668`SSL_SERVER_A_KEY`
669------------------
670
671The public key algorithm in server's certificate.
672
673`SSL_SERVER1_CERT`
674------------------
675
676The PEM-encoded server certificate.
677
678`SSL_SERVER_CERT_TYPE`
679----------------------
680
681The certificate type can be `X.509` or `OPENPGP`.
682
683`SSL_CLIENT_CERT_TYPE`
684----------------------
685
686The certificate type can be `X.509` or `OPENPGP`.
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