source: mod_gnutls/doc/mod_gnutls_manual.md @ 33d812d

asyncioproxy-ticket
Last change on this file since 33d812d was 87d7f89, checked in by Fiona Klute <fiona.klute@…>, 10 months ago

Send OCSP nonce only if GnuTLSOCSPCheckNonce is enabled

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1* * * * *
2
3`mod_gnutls` is a module for the Apache web server that provides HTTPS
4(HTTP over Transport Layer Security (TLS)) using the GnuTLS library.
5More information about the module can be found at
6[the project's website](https://mod.gnutls.org/).
7
8* * * * *
9
10Compilation & Installation
11==========================
12
13`mod_gnutls` uses the `./configure && make && make install` mechanism
14common to many Open Source programs.  Most of the dirty work is
15handled by either `./configure` or Apache's `apxs` utility. If you have
16built Apache modules before, there shouldn't be any surprises for you.
17
18The interesting options you can pass to configure are:
19
20`--with-apxs=PATH` 
21:   This option is used to specify the location of the apxs utility that
22    was installed as part of apache. Specify the location of the
23    binary, not the directory it is located in.
24
25`--with-apu-config=PATH`
26:   Path to APR Utility Library config tool (`apu-1-config`)
27
28`--help`
29:   Provides a list of all available configure options.
30
31It is recommended to run `make check` before installation. If your
32system doesn't have a loopback device with IPv6 and IPv4 support or
33`localhost` does not resolve to at least one of `[::1]` and
34`127.0.0.1`, you may have to set the `TEST_HOST` or `TEST_IP`
35environment variables when running `./configure` to make the test
36suite work correctly.
37
38* * * * *
39
40Integration
41===========
42
43To activate `mod_gnutls` just add the following line to your httpd.conf
44and restart Apache:
45
46    LoadModule gnutls_module modules/mod_gnutls.so
47
48Module Dependencies
49-------------------
50
51`mod_gnutls` uses the Apache HTTPD [Shared Object
52Cache](http://httpd.apache.org/docs/current/en/socache.html) to cache
53[OCSP responses for OCSP stapling](#gnutlsocspcache) and [TLS
54sessions](#gnutlscache). To use either cache you need to load a
55suitable `mod_socache_PROVIDER` module, which should be provided by
56your Apache installation.
57
58It is recommended to load at least `mod_socache_shmcb`. If that module
59is loaded `mod_gnutls` will [enable OCSP stapling by
60default](#gnutlsocspstapling), without needing any further
61configuration other than a [certificate chain](#gnutlscertificatefile)
62with OCSP support.
63
64* * * * *
65
66Configuration Directives
67========================
68
69General Options
70---------------
71
72### GnuTLSEnable
73
74Enable GnuTLS for this virtual host
75
76    GnuTLSEnable [on|off]
77
78Default: *off*\
79Context: virtual host
80
81This directive enables SSL/TLS Encryption for a Virtual Host.
82
83### GnuTLSCache
84
85Configure TLS Session Cache
86
87    GnuTLSCache (shmcb|dbm|memcache|...|none)[:PARAMETERS]
88
89Default: `GnuTLSCache none`\
90Context: server config
91
92This directive configures the TLS Session Cache for `mod_gnutls`. This
93could be shared between machines of different architectures. If the
94selected cache implementation is not thread-safe, access is serialized
95using the `gnutls-cache` mutex.
96
97Which cache implementations are available depends on your Apache
98installation and configuration, `mod_gnutls` can use any socache
99provider. In general you will need to load a `mod_socache_PROVIDER`
100module. Common options are described below, please check the Apache
101HTTPD documentation for details on available providers and their
102configuration.
103
104`shmcb`
105:   Uses a shared memory segment. This is a high performance local
106    cache. The parameter is a relative or absolute path to be used if
107    the local shared memory implementation requires one, followed by
108    the cache size in bytes enclosed in parentheses.
109
110    Example: `shmcb:cache/gnutls_cache(65536)`
111
112`dbm`
113:   Uses a DBM cache file. The parameter is a relative or absolute
114    path to be used as the DBM cache file.
115
116    Example: `dbm:cache/gnutls_cache`
117
118`memcache`
119:   Uses memcached server(s) to cache TLS session data. The parameter
120    is a comma separated list of servers (host:port). This can be used
121    to share a session cache between all servers in a cluster.
122
123    Example: `memcache:memcache.example.com:12345,memcache2.example.com:12345`
124
125`none`
126:   Turns off all caching of TLS sessions.
127
128    This can significantly reduce the performance of `mod_gnutls`
129    since even followup connections by a client must renegotiate
130    parameters instead of reusing old ones. This is the default, since
131    it requires no configuration.
132
133    Session tickets are an alternative to using a session cache,
134    please see `GnuTLSSessionTickets`. Note that for TLS 1.3 GnuTLS
135    supports resumption using session tickets only as of version
136    3.6.4.
137
138### GnuTLSCacheTimeout
139
140Timeout for TLS Session Cache expiration
141
142    GnuTLSCacheTimeout SECONDS
143
144Default: `GnuTLSCacheTimeout 300`\
145Context: server config, virtual host
146
147Sets the expiration timeout for cached TLS sessions.
148
149### GnuTLSSessionTickets
150
151Enable Session Tickets for the server
152
153    GnuTLSSessionTickets [on|off]
154
155Default: `on` with GnuTLS 3.6.4 and newer, `off` otherwise\
156Context: server config, virtual host
157
158Session tickets allow TLS session resumption without session state
159stored on the server, using encrypted tickets provided to the clients
160instead. Tickets are an alternative to using a session cache, and
161currently the only session resumption mechanism in TLS 1.3. For a pool
162of servers this option is not recommended since the tickets are bound
163to the issuing server only.
164
165If this option is set in the global configuration, virtual hosts
166without a `GnuTLSSessionTickets` setting will use the global setting.
167
168*Warning:* With GnuTLS version before 3.6.4 the master key that
169protects the tickets is generated only on server start, and there is
170no mechanism to roll over the key. If session tickets are enabled it
171is highly recommended to restart the server regularly to protect past
172sessions in case an attacker gains access to server memory. GnuTLS
1733.6.4 introduced an automatic TOTP-based key rollover, so this warning
174does not apply any more and tickets are enabled by default.
175
176### GnuTLSDHFile
177
178Use the provided PKCS \#3 encoded Diffie-Hellman parameters
179
180    GnuTLSDHFile FILEPATH
181
182Default: *none*\
183Context: server config, virtual host
184
185By default `mod_gnutls` uses the DH parameters included with GnuTLS
186corresponding to the security level of the configured private keys.
187
188If you need to use different DH parameters, you can provide a PEM file
189containing them in PKCS \#3 encoding using this option. Please see the
190"[Parameter
191generation](https://gnutls.org/manual/html_node/Parameter-generation.html)"
192section of the GnuTLS documentation for a short discussion of the
193security implications.
194
195### GnuTLSPriorities
196
197Set the allowed protocol versions, ciphers, key exchange algorithms,
198MACs and compression methods
199
200    GnuTLSPriorities NORMAL:+CIPHER_0:+CIPHER_1:...:+CIPHER_N
201
202Default: `NORMAL`\
203Context: server config, virtual host
204
205Sets the allowed protocol version(s), ciphers, key exchange methods,
206message authentication codes, and other TLS parameters for the server.
207The parameter is a GnuTLS priority string as described in the
208[the GnuTLS documentation](https://gnutls.org/manual/html_node/Priority-Strings.html).
209
210For example, to disable TLS 1.0 use `NORMAL:-VERS-TLS1.0`.
211
212### GnuTLSP11Module
213
214Load this PKCS #11 module.
215
216    GnuTLSP11Module PATH_TO_LIBRARY
217
218Default: *none*\
219Context: server config
220
221Load this PKCS #11 provider module, instead of the system
222defaults. May occur multiple times to load multiple modules.
223
224### GnuTLSPIN
225
226Set the PIN to be used to access encrypted key files or PKCS #11 objects.
227
228    GnuTLSPIN XXXXXX
229
230Default: *none*\
231Context: server config, virtual host
232
233Takes a string to be used as a PIN for the protected objects in
234a security module, or as a key to be used to decrypt PKCS #8, PKCS #12,
235or openssl encrypted keys.
236
237### GnuTLSSRKPIN
238
239Set the SRK PIN to be used to access the TPM.
240
241    GnuTLSSRKPIN XXXXXX
242
243Default: *none*\
244Context: server config, virtual host
245
246Takes a string to be used as a PIN for the protected objects in
247the TPM module.
248
249### GnuTLSExportCertificates
250
251Export the PEM encoded certificates to CGIs
252
253    GnuTLSExportCertificates [off|on|SIZE]
254
255Default: `off`\
256Context: server config, virtual host
257
258This directive configures exporting the full certificates of the
259server and the client to CGI scripts via the `SSL_SERVER_CERT` and
260`SSL_CLIENT_CERT` environment variables. The exported certificates
261will be PEM-encoded, limited to the given size. The type of the
262certificate will be exported in `SSL_SERVER_CERT_TYPE` and
263`SSL_CLIENT_CERT_TYPE`.
264
265SIZE should be an integer number of bytes, or may be written with a
266trailing `K` to indicate kibibytes.  `off` means the same thing as
267`0`, in which case the certificates will not be exported to the
268environment. `on` is an alias for `16K`. If a non-zero size is
269specified for this directive, but a certificate is too large to fit in
270the buffer, then the corresponding environment variable will contain
271the fixed string `GNUTLS_CERTIFICATE_SIZE_LIMIT_EXCEEDED`.
272
273With GnuTLSExportCertificates enabled, `mod_gnutls` exports the same
274environment variables to the CGI process as `mod_ssl`.
275
276X.509 Certificate Authentication
277--------------------------------
278
279### GnuTLSCertificateFile
280
281Set the PEM encoded server certificate or certificate chain
282
283    GnuTLSCertificateFile FILEPATH
284
285Default: *none*\
286Context: server config, virtual host
287
288FILEPATH is an absolute or relative path to a file containing the
289PEM-encoded X.509 certificate to use as this Server's End Entity (EE)
290certificate, and optionally those of the issuing Certificate
291Authorities (CAs). If the file contains multiple certificates they
292must be ordered from EE to the CA closest to the root CA.
293
294Including the full certificate chain is highly recommended because the
295CA certificates are needed for [OCSP stapling](#ocsp-stapling-configuration).
296
297Since version 0.7 this can be a PKCS #11 URL instead of a file.
298
299On Linux and other Unix-like systems you can create the file with a
300command like this (assuming "CA 1" issued the server certificate and
301has been issued by "Root CA" itself):
302
303        $ cat server.pem ca-1.pem root-ca.pem >server-chain.pem
304
305### GnuTLSKeyFile
306
307Set to the PEM Encoded Server Private Key
308
309    GnuTLSKeyFile FILEPATH
310
311Default: *none*\
312Context: server config, virtual host
313
314Takes an absolute or relative path to the Server Private Key. Set
315`GnuTLSPIN` if the key file is encrypted.
316
317Since version 0.7 this can be a PKCS #11 URL.
318
319**Security Warning:**\
320This private key must be protected. It is read while Apache is still
321running as root, and does not need to be readable by the nobody or
322apache user.
323
324### GnuTLSClientVerify
325
326Enable client certificate verification
327
328    GnuTLSClientVerify [ignore|request|require]
329
330Default: `ignore`\
331Context: server config, virtual host, directory, .htaccess
332
333This directive controls if clients need to authenticate with a
334certificate to access resources. If a mode other than `ignore` is used
335in a directory context the server may request post-handshake
336authentication (TLS 1.3 only, see below). Trusted CAs for certificate
337validation are set using [`GnuTLSClientCAFile`](#gnutlsclientcafile).
338
339`ignore`
340:   `mod_gnutls` will not request certificates from clients, and allow
341    any requests.
342
343`request`
344:   Client certificates will be requested, but requests are still
345    allowed if the client does not send one or the provided
346    certificate is invalid. If the client authenticates, the
347    certificate validation status will be stored in the
348    [`SSL_CLIENT_VERIFY`](#ssl_client_verify) environment variable and
349    can be `SUCCESS`, `FAILED` or `NONE`.
350
351`require`
352:   Client certificate authentication will be required for access. If
353    set at server or virtual host level TLS connections from clients
354    without a valid certificate will be denied. If set at directory
355    level any requests without a valid client certificate will be
356    denied with a 403 Forbidden error. The `SSL_CLIENT_VERIFY`
357    environment variable will be set to `SUCCESS` if access is
358    allowed, additional [environment
359    variables](#environment-variables) will hold details on the client
360    certificate.
361
362When using TLS 1.3 `mod_gnutls` will request [post-handshake
363authentication](https://tools.ietf.org/html/rfc8446#section-4.6.2) as
364necessary if the client announced support during the handshake. With
365TLS versions 1.2 and earlier `mod_gnutls` supports client
366authentication only during the initial handshake.
367
368If you want clients that do not support TLS 1.3 at all or do not
369support the post-handshake authentication extension to have access to
370resources that require authentication, you can set `GnuTLSClientVerify
371request` at the server or virtual host level so clients can
372authenticate during the initial handshake.
373
374### GnuTLSClientCAFile
375
376Set the PEM encoded Certificate Authority list to use for X.509 base
377client authentication
378
379    GnuTLSClientCAFile FILEPATH
380
381Default: *none*
382Context: server config, virtual host
383
384Takes an absolute or relative path to a PEM Encoded Certificate to use
385as a Certificate Authority with Client Certificate Authentication.
386This file may contain a list of trusted authorities.
387
388SRP Authentication
389------------------
390
391### GnuTLSSRPPasswdFile
392
393Set to the SRP password file for SRP ciphersuites
394
395    GnuTLSSRPPasswdFile FILEPATH
396
397Default: *none*\
398Context: server config, virtual host
399
400Takes an absolute or relative path to an SRP password file. This is
401the same format as used in libsrp.  You can generate such file using
402the command `srptool --passwd /etc/tpasswd --passwd-conf
403/etc/tpasswd.conf -u test` to set a password for user test.  This
404password file holds the username, a password verifier and the
405dependency to the SRP parameters.
406
407### GnuTLSSRPPasswdConfFile
408
409Set to the SRP password.conf file for SRP ciphersuites
410
411    GnuTLSSRPPasswdConfFile FILEPATH
412
413Default: *none*\
414Context: server config, virtual host
415
416Takes an absolute or relative path to an SRP password.conf file. This
417is the same format as used in `libsrp`.  You can generate such file
418using the command `srptool --create-conf /etc/tpasswd.conf`.  This
419file holds the SRP parameters and is associate with the password file
420(the verifiers depends on these parameters).
421
422TLS Proxy Configuration
423-----------------------
424
425### GnuTLSProxyEngine
426
427Enable TLS proxy connections for this virtual host
428
429    GnuTLSProxyEngine [on|off]
430
431Default: *off*\
432Context: virtual host
433
434This directive enables support for TLS proxy connections for a virtual
435host.
436
437### GnuTLSProxyCAFile
438
439Set to the PEM encoded Certificate Authority Certificate
440
441    GnuTLSProxyCAFile FILEPATH
442
443Default: *none*\
444Context: server config, virtual host
445
446Takes an absolute or relative path to a PEM encoded certificate to use
447as a Certificate Authority when verifying certificates provided by
448proxy back end servers. This file may contain a list of trusted
449authorities. If not set, verification of TLS back end servers will
450always fail due to lack of a trusted CA.
451
452### GnuTLSProxyCRLFile
453
454Set to the PEM encoded Certificate Revocation List
455
456    GnuTLSProxyCRLFile FILEPATH
457
458Default: *none*\
459Context: server config, virtual host
460
461Takes an absolute or relative path to a PEM encoded Certificate
462Revocation List to use when verifying certificates provided by proxy
463back end servers. The file may contain a list of CRLs.
464
465### GnuTLSProxyCertificateFile
466
467Set to the PEM encoded Client Certificate
468
469    GnuTLSProxyCertificateFile FILEPATH
470
471Default: *none*\
472Context: server config, virtual host
473
474Takes an absolute or relative path to a PEM encoded X.509 certificate
475to use as this Server's End Entity (EE) client certificate for TLS
476client authentication in proxy TLS connections. If you need to supply
477certificates for intermediate Certificate Authorities (iCAs), they
478should be listed in sequence in the file, from EE to the iCA closest
479to the root CA. Optionally, you can also include the root CA's
480certificate as the last certificate in the list.
481
482If not set, TLS client authentication will be disabled for TLS proxy
483connections. If set, `GnuTLSProxyKeyFile` must be set as well to
484provide the matching private key.
485
486### GnuTLSProxyKeyFile
487
488Set to the PEM encoded Private Key
489
490    GnuTLSProxyKeyFile FILEPATH
491
492Default: *none*\
493Context: server config, virtual host
494
495Takes an absolute or relative path to the Private Key matching the
496certificate configured using the `GnuTLSProxyCertificateFile`
497directive. This key cannot currently be password protected.
498
499**Security Warning:**\
500This private key must be protected. It is read while Apache is still
501running as root, and does not need to be readable by the nobody or
502apache user.
503
504### GnuTLSProxyPriorities
505
506Set the allowed ciphers, key exchange algorithms, MACs and compression
507methods for proxy connections
508
509    GnuTLSProxyPriorities NORMAL:+CIPHER_0:+CIPHER_1:...:+CIPHER_N
510
511Default: `NORMAL`\
512Context: server config, virtual host
513
514Sets the allowed protocol version(s), ciphers, key exchange methods,
515message authentication codes, and other TLS parameters for TLS proxy
516connections. Like for `GnuTLSPriorities` the parameter is a GnuTLS
517priority string as described in the
518[the GnuTLS documentation](https://gnutls.org/manual/html_node/Priority-Strings.html).
519
520OCSP Stapling Configuration
521---------------------------
522
523OCSP stapling, formally known as the TLS Certificate Status Request
524extension, allows the server to provide the client with a cached OCSP
525response for its certificate during the handshake. With OCSP stapling
526the client does not have to send an OCSP request to the issuer CA to
527check the certificate status, which offers privacy and performance
528advantages, and avoids the security issue of how to handle errors that
529prevent the client from getting a response.
530
531With TLS 1.2 stapling can be used only for the server certificate.
532TLS 1.3 supports stapling for all transmitted certificates.
533Mod\_gnutls will staple for as many consecutive certificates in the
534certificate chain as possible, ideally all except the root CA.
535
536Mod\_gnutls enables OCSP stapling by default if possible. The following
537requirements must be met:
538
539* OCSP responses are verified using the issuer CAs of the certificates
540  being checked, so the CAs must be included in
541  [`GnuTLSCertificateFile`](#gnutlscertificatefile). Providing the
542  whole certificate chain (including the root CA) is recommended.
543
544* Mod\_gnutls needs a cache to store OCSP responses for stapling. If
545  [mod\_socache\_shmcb](http://httpd.apache.org/docs/current/en/mod/mod_socache_shmcb.html)
546  is loaded mod\_gnutls can set up the cache without additional
547  configuration, for other options see
548  [`GnuTLSOCSPCache`](#gnutlsocspcache).
549
550* The certificates must contain OCSP access URIs using HTTP so
551  mod_gnutls can fetch responses, alternatively you may provide
552  responses using [`GnuTLSOCSPResponseFile`](#gnutlsocspresponsefile).
553
554If a server certificate contains the "must-staple" extension (X.509
555TLS Feature extension defined in [RFC
5567633](https://tools.ietf.org/html/rfc7633)) and the configuration does
557not support stapling mod_gnutls will refuse to start.
558
559By default mod\_gnutls regularly refreshes the cached OCSP responses
560in the background, see
561[`GnuTLSOCSPAutoRefresh`](#gnutlsocspautorefresh) for details.
562
563### GnuTLSOCSPStapling
564
565Enable OCSP stapling for this (virtual) host.
566
567    GnuTLSOCSPStapling [On|Off]
568
569Default: *on* if requirements are met, *off* otherwise\
570Context: server config, virtual host
571
572Stapling is activated by default if the requirements [listed
573above](#ocsp-stapling-configuration) are met.
574
575If the server certificate requires stapling ("must-staple") or
576`GnuTLSOCSPStapling` is explicitly set to `on` unmet requirements are
577an error.
578
579OCSP cache updates are serialized using the `gnutls-ocsp` mutex.
580
581### GnuTLSOCSPCache
582
583OCSP stapling cache configuration
584
585        GnuTLSOCSPCache (shmcb|memcache|...|none)[:PARAMETERS]
586
587Default: `shmcb:gnutls_ocsp_cache`\
588Context: server config
589
590This directive configures the OCSP stapling cache, and uses the same
591syntax as [`GnuTLSCache`](#gnutlscache). Please check there for
592details.
593
594The default should be reasonable for most servers and requires
595[mod\_socache\_shmcb](http://httpd.apache.org/docs/current/en/mod/mod_socache_shmcb.html)
596to be loaded. Servers with very many virtual hosts may need to
597increase the default cache size via the parameters string, those with
598few virtual hosts and memory constraints could save a few KB by reducing
599it. Note that `mod_socache_dbm` has a size constraint for entries that
600is generally too small for OCSP responses.
601
602If the selected cache implementation is not thread-safe, access
603is serialized using the `gnutls-ocsp-cache` mutex.
604
605### GnuTLSOCSPAutoRefresh
606
607Regularly refresh cached OCSP responses independent of TLS handshakes?
608
609    GnuTLSOCSPAutoRefresh [On|Off]
610
611Default: *on*\
612Context: server config, virtual host
613
614By default `mod_gnutls` will regularly refresh the cached OCSP
615responses, regardless of whether they are used. This has advantages
616over updating OCSP responses only when a TLS handshake needs them:
617
618* Handshakes are not delayed by updating the OCSP response cache
619  first.
620
621* Updating the cached response before it expires can hide short
622  unavailability of the OCSP responder, if a repeated request is
623  successful before the cache expires (see below).
624
625The interval to the next request is determined as follows: After a
626successful OCSP request the next one is scheduled for a random period
627between `GnuTLSOCSPFuzzTime` and half of it before
628`GnuTLSOCSPCacheTimeout` expires. For example, if the cache timeout is
6293600 seconds and the fuzz time 600 seconds, the next request will be
630sent after 3000 to 3300 seconds. If the validity period of the
631response expires before then, the selected interval is halved until it
632is smaller than the time until expiry. If an OCSP request fails, it is
633retried after `GnuTLSOCSPFailureTimeout`.
634
635Regularly updating the OCSP cache requires `mod_watchdog`,
636`mod_gnutls` will fall back to updating the OCSP cache during
637handshakes if `mod_watchdog` is not available or this option is set to
638`Off`.
639
640### GnuTLSOCSPCheckNonce
641
642Send nonces in OCSP requests and verify them in responses.
643
644    GnuTLSOCSPCheckNonce [On|Off]
645
646Default: *off*\
647Context: server config, virtual host
648
649If `GnuTLSOCSPCheckNonce` is enabled, `mod_gnutls` will send nonces in
650OCSP requests and verify them in responses. Responses without a nonce
651or with a mismatching one will be considered invalid and discarded.
652
653This option is disabled by default because many CAs do not support the
654OCSP nonce extension. The likely reason for that is the use of
655pre-produced responses, as described in [RFC 6960, Section
6562.5](https://tools.ietf.org/html/rfc6960#section-2.5).
657
658### GnuTLSOCSPResponseFile
659
660Read OCSP responses for stapling from these files (one or more)
661instead of sending a request over HTTP.
662
663    GnuTLSOCSPResponseFile /path/to/response.der [...]
664
665Default: *empty*\
666Context: server config, virtual host
667
668The first listed file must contain a response for the server
669certificate, responses for intermediate CAs may be added in the order
670they appear in [GnuTLSCertificateFile](#gnutlscertificatefile). You
671can revert to the default fetch mechanism for a specific certificate
672(including the server certificate) by giving the empty string (`""`)
673instead of a file path.
674
675The response files must be updated externally, for example using a
676cron job. This option is an alternative to the server fetching OCSP
677responses over HTTP. Reasons to use this option include:
678
679* Performing OCSP requests separate from the web server (e.g. to share
680  responses across a server cluster).
681* The issuer CA uses an access method other than HTTP, or doesn't
682  include an OCSP URL in the certificate.
683* Testing
684
685You can use a GnuTLS `ocsptool` command like the following to create
686and update the response file:
687
688    ocsptool --ask --nonce --load-issuer ca_cert.pem \
689        --load-cert server_cert.pem --outfile ocsp_response.der
690
691Additional error checking is highly recommended. You may have to
692remove the `--nonce` option if the OCSP responder of your CA does not
693support nonces.
694
695### GnuTLSOCSPCacheTimeout
696
697Cache timeout for OCSP responses
698
699    GnuTLSOCSPCacheTimeout SECONDS
700
701Default: *3600*\
702Context: server config, virtual host
703
704Cached OCSP responses will be refreshed after the configured number of
705seconds. How long this timeout should reasonably be depends on your
706CA, namely how often its OCSP responder is updated and how long
707responses are valid. Note that a response will not be cached beyond
708its lifetime as denoted in the `nextUpdate` field of the response.
709
710### GnuTLSOCSPFailureTimeout
711
712Wait this many seconds before retrying a failed OCSP request.
713
714    GnuTLSOCSPFailureTimeout SECONDS
715
716Default: *300*\
717Context: server config, virtual host
718
719Retries of failed OCSP requests must be rate limited to avoid
720overloading both the server using mod_gnutls and the CA's OCSP
721responder. A shorter value increases the load on both sides, a longer
722one means that stapling will remain disabled for longer after a failed
723request. The auto-refresh mechanism updates OCSP responses before they
724expire and can cover short unavailability of OCSP responders, see
725[`GnuTLSOCSPAutoRefresh`](#gnutlsocspautorefresh) for details.
726
727### GnuTLSOCSPFuzzTime
728
729Update the cached OCSP response up to this time before the cache expires
730
731    GnuTLSOCSPFuzzTime SECONDS
732
733Default: *larger of GnuTLSOCSPCacheTimeout / 8 and GnuTLSOCSPFailureTimeout \* 2*\
734Context: server config, virtual host
735
736Refreshing the cached response before it expires hides short OCSP
737responder unavailability. See `GnuTLSOCSPAutoRefresh` for how this
738value is used, using at least twice `GnuTLSOCSPFailureTimeout` is
739recommended.
740
741### GnuTLSOCSPSocketTimeout
742
743Timeout for TCP sockets used to send OCSP requests
744
745    GnuTLSOCSPFailureTimeout SECONDS
746
747Default: *6*\
748Context: server config, virtual host
749
750Stalled OCSP requests must time out after a while to prevent stalling
751the server too much. However, if the timeout is too short requests may
752fail with a slow OCSP responder or high latency network
753connection. This parameter allows you to adjust the timeout if
754necessary.
755
756Note that this is not an upper limit for the completion of an OCSP
757request but a socket timeout. The connection will time out if there is
758no activity (successful send or receive) at all for the configured
759time.
760
761* * * * *
762
763Configuration Examples
764======================
765
766Minimal Example
767---------------
768
769A minimal server configuration using mod_gnutls might look like this
770(other than the default setup):
771
772```apache
773# Load mod_gnutls into Apache.
774LoadModule gnutls_module modules/mod_gnutls.so
775
776Listen 192.0.2.1:443
777
778<VirtualHost _default_:443>
779        # Standard virtual host stuff
780        DocumentRoot /www/site1.example.com/html
781        ServerName site1.example.com:443
782
783        # Minimal mod_gnutls setup: enable, and set credentials
784        GnuTLSEnable on
785        GnuTLSCertificateFile conf/tls/site1_cert_chain.pem
786        GnuTLSKeyFile conf/tls/site1_key.pem
787</VirtualHost>
788```
789
790This gives you an HTTPS site using the GnuTLS `NORMAL` set of
791ciphersuites. OCSP stapling will be enabled if the server certificate
792contains an OCSP URI, `conf/tls/site1_cert_chain.pem` contains the
793issuer certificate in addition to the server's, and
794[mod\_socache\_shmcb](http://httpd.apache.org/docs/current/en/mod/mod_socache_shmcb.html)
795is loaded. With Gnutls 3.6.4 or newer session tickets are enabled,
796too.
797
798Virtual Hosts with Server Name Indication
799-----------------------------------------
800
801`mod_gnutls` supports Server Name Indication (SNI), as specified in
802[RFC 6066, Section 3](https://tools.ietf.org/html/rfc6066#section-3).
803This allows hosting many TLS websites with a single IP address, you
804can just add virtual host configurations. All recent browsers support
805this standard. Here is an example using SNI:
806
807```apache
808# Load the module into Apache.
809LoadModule gnutls_module modules/mod_gnutls.so
810# This example server uses session tickets, no cache.
811GnuTLSSessionTickets on
812
813# SNI allows hosting multiple sites using one IP address. This
814# could also be 'Listen *:443', just like '*:80' is common for
815# non-HTTPS
816Listen 198.51.100.1:443
817
818<VirtualHost _default_:443>
819        GnuTLSEnable on
820        DocumentRoot /www/site1.example.com/html
821    ServerName site1.example.com:443
822        GnuTLSCertificateFile conf/tls/site1.crt
823        GnuTLSKeyFile conf/tls/site1.key
824</VirtualHost>
825
826<VirtualHost _default_:443>
827        GnuTLSEnable on
828        DocumentRoot /www/site2.example.com/html
829        ServerName site2.example.com:443
830        GnuTLSCertificateFile conf/tls/site2.crt
831        GnuTLSKeyFile conf/tls/site2.key
832</VirtualHost>
833
834<VirtualHost _default_:443>
835        GnuTLSEnable on
836        DocumentRoot /www/site3.example.com/html
837        ServerName site3.example.com:443
838        GnuTLSCertificateFile conf/tls/site3.crt
839        GnuTLSKeyFile conf/tls/site3.key
840        # Enable HTTP/2
841        Protocols h2 http/1.1
842</VirtualHost>
843```
844
845Virtual Hosts without SNI
846-------------------------
847
848If you need to support clients that do not use SNI, you have to use a
849unique IP address/port combination for each virtual host. In this
850example all virtual hosts use the default port for HTTPS (443) and
851different IP addresses.
852
853```apache
854# Load the module into Apache.
855LoadModule gnutls_module modules/mod_gnutls.so
856# This example server uses a session cache.
857GnuTLSCache dbm:/var/cache/www-tls-cache
858GnuTLSCacheTimeout 1200
859
860# Without SNI you need one IP Address per site. The IP addresses
861# are listed separately for clarity, you could also use "Listen 443"
862# to use that port on all available IP addresses.
863Listen 192.0.2.1:443
864Listen 192.0.2.2:443
865Listen 192.0.2.3:443
866
867<VirtualHost 192.0.2.1:443>
868        GnuTLSEnable on
869        GnuTLSPriorities SECURE128
870        DocumentRoot /www/site1.example.com/html
871        ServerName site1.example.com:443
872        GnuTLSCertificateFile conf/tls/site1.crt
873        GnuTLSKeyFile conf/tls/site1.key
874</VirtualHost>
875
876<VirtualHost 192.0.2.2:443>
877    # This virtual host enables SRP authentication
878        GnuTLSEnable on
879        GnuTLSPriorities NORMAL:+SRP
880        DocumentRoot /www/site2.example.com/html
881        ServerName site2.example.com:443
882        GnuTLSSRPPasswdFile conf/tls/tpasswd.site2
883        GnuTLSSRPPasswdConfFile conf/tls/tpasswd.site2.conf
884</VirtualHost>
885
886<VirtualHost 192.0.2.3:443>
887        # This server enables SRP and X.509 authentication.
888        GnuTLSEnable on
889        GnuTLSPriorities NORMAL:+SRP:+SRP-RSA:+SRP-DSS
890        DocumentRoot /www/site3.example.com/html
891        ServerName site3.example.com:443
892        GnuTLSCertificateFile conf/tls/site3.crt
893        GnuTLSKeyFile conf/tls/site3.key
894        GnuTLSSRPPasswdFile conf/tls/tpasswd.site3
895        GnuTLSSRPPasswdConfFile conf/tls/tpasswd.site3.conf
896</VirtualHost>
897```
898
899OCSP Stapling Example
900---------------------
901
902This is an example with a customized OCSP stapling configuration. What
903is a resonable cache timeout varies depending on how long your CA's
904OCSP responses are valid. Some CAs provide responses that are valid
905for multiple days, in that case timeout and fuzz time could be
906significantly larger.
907
908```apache
909# Load the module into Apache.
910LoadModule gnutls_module modules/mod_gnutls.so
911# A 64K cache is more than enough for one response
912GnuTLSOCSPCache shmcb:ocsp_cache(65536)
913
914Listen 192.0.2.1:443
915
916<VirtualHost _default_:443>
917        GnuTLSEnable           On
918        DocumentRoot           /www/site1.example.com/html
919        ServerName             site1.example.com:443
920        GnuTLSCertificateFile  conf/tls/site1_cert_chain.pem
921        GnuTLSKeyFile          conf/tls/site1_key.pem
922        GnuTLSOCSPStapling     On
923        # The cached OCSP response is kept for up to 4 hours,
924        # with updates scheduled every 3 to 3.5 hours.
925        GnuTLSOCSPCacheTimeout 21600
926        GnuTLSOCSPFuzzTime     3600
927</VirtualHost>
928```
929
930* * * * *
931
932Environment Variables
933=====================
934
935`mod_gnutls` exports the following environment variables to scripts.
936These are compatible with `mod_ssl`.
937
938`HTTPS`
939-------
940
941Can be `on` or `off`
942
943`SSL_VERSION_LIBRARY`
944---------------------
945
946The version of the GnuTLS library
947
948`SSL_VERSION_INTERFACE`
949-----------------------
950
951The version of this module
952
953`SSL_PROTOCOL`
954--------------
955
956The SSL or TLS protocol name (such as `TLS 1.0` etc.)
957
958`SSL_CIPHER`
959------------
960
961The SSL or TLS cipher suite name
962
963`SSL_COMPRESS_METHOD`
964---------------------
965
966The negotiated compression method (`NULL` or `DEFLATE`)
967
968`SSL_SRP_USER`
969--------------
970
971The SRP username used for authentication (only set when
972`GnuTLSSRPPasswdFile` and `GnuTLSSRPPasswdConfFile` are configured).
973
974`SSL_CIPHER_USEKEYSIZE` & `SSL_CIPHER_ALGKEYSIZE`
975-------------------------------------------------
976
977The number if bits used in the used cipher algorithm.
978
979This does not fully reflect the security level since the size of
980RSA or DHE key exchange parameters affect the security level too.
981
982`SSL_DH_PRIME_BITS`
983-------------------
984
985The number if bits in the modulus for the DH group, if DHE or static
986DH is used.
987
988This will not be set if DH is not used.
989
990`SSL_CIPHER_EXPORT`
991-------------------
992
993`True` or `False`. Whether the cipher suite negotiated is an export one.
994
995`SSL_SESSION_ID`
996----------------
997
998The session ID negotiated in this session. Can be the same during client
999reloads.
1000
1001`SSL_CLIENT_VERIFY`
1002-------------------
1003
1004Verification status of the client's certificate, if any. May be
1005`SUCCESS`, `FAILED` or `NONE`. See
1006[`GnuTLSClientVerify`](#gnutlsclientverify).
1007
1008`SSL_CLIENT_V_REMAIN`
1009---------------------
1010
1011The number of days until the client's certificate is expired.
1012
1013`SSL_CLIENT_V_START`
1014--------------------
1015
1016The activation time of client's certificate.
1017
1018`SSL_CLIENT_V_END`
1019------------------
1020
1021The expiration time of client's certificate.
1022
1023`SSL_CLIENT_S_DN`
1024-----------------
1025
1026The distinguished name of client's certificate in RFC2253 format.
1027
1028`SSL_CLIENT_I_DN`
1029-----------------
1030
1031The distinguished name of the issuer of the client's certificate in
1032RFC2253 format.
1033
1034`SSL_CLIENT_S_AN%`
1035------------------
1036
1037These will contain the alternative names of the client certificate (`%` is
1038a number starting from zero).
1039
1040The values will be prepended by `DNSNAME:`, `RFC822NAME:` or `URI:`
1041depending on the type.
1042
1043If it is not supported the value `UNSUPPORTED` will be set.
1044
1045`SSL_SERVER_M_SERIAL`
1046---------------------
1047
1048The serial number of the server's certificate.
1049
1050`SSL_SERVER_M_VERSION`
1051----------------------
1052
1053The version of the server's certificate.
1054
1055`SSL_SERVER_A_SIG`
1056------------------
1057
1058The algorithm used for the signature in server's certificate.
1059
1060`SSL_SERVER_A_KEY`
1061------------------
1062
1063The public key algorithm in server's certificate.
1064
1065`SSL_SERVER_CERT`
1066------------------
1067
1068The PEM-encoded (X.509) server certificate (see the
1069`GnuTLSExportCertificates` directive).
1070
1071`SSL_SERVER_CERT_TYPE`
1072----------------------
1073
1074The certificate type will be `X.509`.
1075
1076`SSL_CLIENT_CERT`
1077------------------
1078
1079PEM-encoded (X.509) client certificate, if any (see the
1080`GnuTLSExportCertificates` directive).
1081
1082`SSL_CLIENT_CERT_TYPE`
1083----------------------
1084
1085The certificate type will be `X.509`, if any.
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