source: mod_gnutls/docs/mod_gnutls_manual.mdwn @ 2aaf4f5

debian/masterdebian/stretch-backportsjessie-backportsupstream
Last change on this file since 2aaf4f5 was 999cdec, checked in by Daniel Kahn Gillmor <dkg@…>, 6 years ago

GnuTLSExportCertificates should control maximum size of exported certs

The server administrator should be able to control the maximum size of
the exported certificate environment variables. This will be done via
the existing GnuTLSExportCertificates environment variable.

This patch adds documentation of intended new feature and a test for
support. The test currently fails because the feature is not
implemented.

  • Property mode set to 100644
File size: 20.8 KB
Line 
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 [off|on|SIZE]
376
377Default: `off`\
378Context: server config, virtual host
379
380This directive configures exporting the full certificates of the
381server and the client to CGI scripts via the `SSL_SERVER_CERT` and
382`SSL_CLIENT_CERT` environment variables. The exported certificates
383will be PEM-encoded (if X.509) or ASCII-armored (if OpenPGP) up to the
384size given.  The type of the certificate will be exported in
385`SSL_SERVER_CERT_TYPE` and `SSL_CLIENT_CERT_TYPE`.
386
387SIZE should be an integer number of bytes, or may be written with a
388trailing `K` to indicate kibibytes.  `off` means the same thing as
389`0`, in which case the certificates will not be exported to the
390environment.  `on` is an alias for `16K`.  If a non-zero size is
391specified for this directive, but a certificate is too large to fit in
392the buffer, then the corresponding environment variable will contain
393the fixed string `GNUTLS_CERTIFICATE_SIZE_LIMIT_EXCEEDED`.
394
395With GnuTLSExportCertificates enabled, `mod_gnutls` exports the same
396environment variables to the CGI process as `mod_ssl`.
397
398* * * * *
399
400Configuration Examples
401======================
402
403Simple Standard SSL Example
404---------------------------
405
406The following is an example of standard SSL Hosting, using one IP
407Addresses for each virtual host
408
409     # Load the module into Apache.
410     LoadModule gnutls_module modules/mod_gnutls.so
411     GnuTLSCache gdbm /var/cache/www-tls-cache
412     GnuTLSCacheTimeout 500
413     # With normal SSL Websites, you need one IP Address per-site.
414     Listen 1.2.3.1:443
415     Listen 1.2.3.2:443
416     Listen 1.2.3.3:443
417     Listen 1.2.3.4:443
418     <VirtualHost 1.2.3.1:443>
419     GnuTLSEnable on
420     GnuTLSPriorities NONE:+AES-128-CBC:+3DES-CBC:+ARCFOUR-128:+RSA:+DHE-RSA:+DHE-DSS:+SHA1:+MD5:+COMP-NULL
421     DocumentRoot /www/site1.example.com/html
422     ServerName site1.example.com:443
423     GnuTLSCertificateFile conf/ssl/site1.crt
424     GnuTLSKeyFile conf/ss/site1.key
425     </VirtualHost>
426     <VirtualHost 1.2.3.2:443>
427     # This virtual host enables SRP authentication
428     GnuTLSEnable on
429     GnuTLSPriorities NORMAL:+SRP
430     DocumentRoot /www/site2.example.com/html
431     ServerName site2.example.com:443
432     GnuTLSSRPPasswdFile conf/ssl/tpasswd.site2
433     GnuTLSSRPPasswdConfFile conf/ssl/tpasswd.site2.conf
434     </VirtualHost>
435     <VirtualHost 1.2.3.3:443>
436     # This server enables SRP, OpenPGP and X.509 authentication.
437     GnuTLSEnable on
438     GnuTLSPriorities NORMAL:+SRP:+SRP-RSA:+SRP-DSS
439     DocumentRoot /www/site3.example.com/html
440     ServerName site3.example.com:443
441     GnuTLSCertificateFile conf/ssl/site3.crt
442     GnuTLSKeyFile conf/ss/site3.key
443     GnuTLSClientVerify ignore
444     GnuTLSPGPCertificateFile conf/ss/site3.pub.asc
445     GnuTLSPGPKeyFile conf/ss/site3.sec.asc
446     GnuTLSSRPPasswdFile conf/ssl/tpasswd.site3
447     GnuTLSSRPPasswdConfFile conf/ssl/tpasswd.site3.conf
448     </VirtualHost>
449     <VirtualHost 1.2.3.4:443>
450     GnuTLSEnable on
451     # %COMPAT disables some security features to enable maximum compatibility with clients.
452     GnuTLSPriorities NONE:+AES-128-CBC:+ARCFOUR-128:+RSA:+SHA1:+MD5:+COMP-NULL:%COMPAT
453     DocumentRoot /www/site4.example.com/html
454     ServerName site4.example.com:443
455     GnuTLSCertificateFile conf/ssl/site4.crt
456     GnuTLSKeyFile conf/ss/site4.key
457     </VirtualHost>
458
459Server Name Indication Example
460------------------------------
461
462`mod_gnutls` can also use "Server Name Indication", as specified in
463RFC 3546.  This allows hosting many SSL Websites, with a Single IP
464Address.  Currently all the recent browsers support this
465standard. Here is an example, using SNI: ` `
466
467
468     # Load the module into Apache.
469     LoadModule gnutls_module modules/mod_gnutls.so
470     # With normal SSL Websites, you need one IP Address per-site.
471     Listen 1.2.3.1:443
472     # This could also be 'Listen *:443',
473     # just like '*:80' is common for non-https
474     # No caching. Enable session tickets. Timeout is still used for
475     # ticket expiration.
476     GnuTLSCacheTimeout 600
477     # This tells apache, that for this IP/Port combination, we want to use
478     # Name Based Virtual Hosting. In the case of Server Name Indication,
479     # it lets mod_gnutls pick the correct Server Certificate.
480     NameVirtualHost 1.2.3.1:443
481     <VirtualHost 1.2.3.1:443>
482     GnuTLSEnable on
483     GnuTLSSessionTickets on
484     GnuTLSPriorities NORMAL
485     DocumentRoot /www/site1.example.com/html
486     ServerName site1.example.com:443
487     GnuTLSCertificateFile conf/ssl/site1.crt
488     GnuTLSKeyFile conf/ss/site1.key
489     </VirtualHost>
490     <VirtualHost 1.2.3.1:443>
491     GnuTLSEnable on
492     GnuTLSPriorities NORMAL
493     DocumentRoot /www/site2.example.com/html
494     ServerName site2.example.com:443
495     GnuTLSCertificateFile conf/ssl/site2.crt
496     GnuTLSKeyFile conf/ss/site2.key
497     </VirtualHost>
498     <VirtualHost 1.2.3.1:443>
499     GnuTLSEnable on
500     GnuTLSPriorities NORMAL
501     DocumentRoot /www/site3.example.com/html
502     ServerName site3.example.com:443
503     GnuTLSCertificateFile conf/ssl/site3.crt
504     GnuTLSKeyFile conf/ss/site3.key
505     </VirtualHost>
506     <VirtualHost 1.2.3.1:443>
507     GnuTLSEnable on
508     GnuTLSPriorities NORMAL
509     DocumentRoot /www/site4.example.com/html
510     ServerName site4.example.com:443
511     GnuTLSCertificateFile conf/ssl/site4.crt
512     GnuTLSKeyFile conf/ss/site4.key
513     </VirtualHost>
514
515
516* * * * *
517
518Performance Issues
519==================
520
521`mod_gnutls` by default uses conservative settings for the server.
522You can fine tune the configuration to reduce the load on a busy
523server.  The following examples do exactly this:
524
525
526     # Load the module into Apache.
527     LoadModule gnutls_module modules/mod_gnutls.so
528     # Using 4 memcache servers to distribute the SSL Session Cache.
529     GnuTLSCache memcache "mc1.example.com mc2.example.com mc3.example.com mc4.example.com"
530     GnuTLSCacheTimeout 600
531     Listen 1.2.3.1:443
532     NameVirtualHost 1.2.3.1:443
533     <VirtualHost 1.2.3.1:443>
534     GnuTLSEnable on
535     # Here we disable the Perfect forward secrecy ciphersuites (DHE)
536     # and disallow AES-256 since AES-128 is just fine.
537     GnuTLSPriorities NORMAL:!DHE-RSA:!DHE-DSS:!AES-256-CBC:%COMPAT
538     DocumentRoot /www/site1.example.com/html
539     ServerName site1.example.com:443
540     GnuTLSCertificateFile conf/ssl/site1.crt
541     GnuTLSKeyFile conf/ss/site1.key
542     </VirtualHost>
543     <VirtualHost 1.2.3.1:443>
544     GnuTLSEnable on
545     # Here we instead of disabling the DHE ciphersuites we use
546     # Diffie Hellman parameters of smaller size than the default (2048 bits).
547     # Using small numbers from 768 to 1024 bits should be ok once they are
548     # regenerated every few hours.
549     # Use "certtool --generate-dh-params --bits 1024" to get those
550     GnuTLSDHFile /etc/apache2/dh.params
551     GnuTLSPriorities NORMAL:!AES-256-CBC:%COMPAT
552     DocumentRoot /www/site2.example.com/html
553     ServerName site2.example.com:443
554     GnuTLSCertificateFile conf/ssl/site2.crt
555     GnuTLSKeyFile conf/ss/site2.key
556     </VirtualHost>
557
558* * * * *
559
560Environment Variables
561=====================
562
563`mod_gnutls` exports the following environment variables to scripts.
564These are compatible with `mod_ssl`.
565
566`HTTPS`
567-------
568
569Can be `on` or `off`
570
571`SSL_VERSION_LIBRARY`
572---------------------
573
574The version of the GnuTLS library
575
576`SSL_VERSION_INTERFACE`
577-----------------------
578
579The version of this module
580
581`SSL_PROTOCOL`
582--------------
583
584The SSL or TLS protocol name (such as `TLS 1.0` etc.)
585
586`SSL_CIPHER`
587------------
588
589The SSL or TLS cipher suite name
590
591`SSL_COMPRESS_METHOD`
592---------------------
593
594The negotiated compression method (`NULL` or `DEFLATE`)
595
596`SSL_SRP_USER`
597--------------
598
599The SRP username used for authentication (only set when
600`GnuTLSSRPPasswdFile` and `GnuTLSSRPPasswdConfFile` are configured).
601
602`SSL_CIPHER_USEKEYSIZE` & `SSL_CIPHER_ALGKEYSIZE`
603-------------------------------------------------
604
605The number if bits used in the used cipher algorithm.
606
607This does not fully reflect the security level since the size of
608RSA or DHE key exchange parameters affect the security level too.
609
610`SSL_DH_PRIME_BITS`
611-------------------
612
613The number if bits in the modulus for the DH group, if DHE or static
614DH is used.
615
616This will not be set if DH is not used.
617
618`SSL_CIPHER_EXPORT`
619-------------------
620
621`True` or `False`. Whether the cipher suite negotiated is an export one.
622
623`SSL_SESSION_ID`
624----------------
625
626The session ID negotiated in this session. Can be the same during client
627reloads.
628
629`SSL_CLIENT_V_REMAIN`
630---------------------
631
632The number of days until the client's certificate is expired.
633
634`SSL_CLIENT_V_START`
635--------------------
636
637The activation time of client's certificate.
638
639`SSL_CLIENT_V_END`
640------------------
641
642The expiration time of client's certificate.
643
644`SSL_CLIENT_S_DN`
645-----------------
646
647The distinguished name of client's certificate in RFC2253 format.
648
649`SSL_CLIENT_I_DN`
650-----------------
651
652The SSL or TLS cipher suite name
653
654`SSL_CLIENT_S_AN%`
655------------------
656
657These will contain the alternative names of the client certificate (`%` is
658a number starting from zero).
659
660The values will be prepended by `DNSNAME:`, `RFC822NAME:` or `URI:`
661depending on the type.
662
663If it is not supported the value `UNSUPPORTED` will be set.
664
665`SSL_SERVER_M_SERIAL`
666---------------------
667
668The serial number of the server's certificate.
669
670`SSL_SERVER_M_VERSION`
671----------------------
672
673The version of the server's certificate.
674
675`SSL_SERVER_A_SIG`
676------------------
677
678The algorithm used for the signature in server's certificate.
679
680`SSL_SERVER_A_KEY`
681------------------
682
683The public key algorithm in server's certificate.
684
685`SSL_SERVER_CERT`
686------------------
687
688The PEM-encoded (X.509) or ASCII-armored (OpenPGP) server certificate
689(see the `GnuTLSExportCertificates` directive).
690
691`SSL_SERVER_CERT_TYPE`
692----------------------
693
694The certificate type can be `X.509` or `OPENPGP`.
695
696`SSL_CLIENT_CERT`
697------------------
698
699The PEM-encoded (X.509) or ASCII-armored (OpenPGP) client certificate
700(see the `GnuTLSExportCertificates` directive).
701
702`SSL_CLIENT_CERT_TYPE`
703----------------------
704
705The certificate type can be `X.509` or `OPENPGP`.
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