1=pod
2
3=head1 NAME
4
5x509v3_config - X509 V3 certificate extension configuration format
6
7=head1 DESCRIPTION
8
9Several OpenSSL commands can add extensions to a certificate or
10certificate request based on the contents of a configuration file
11and CLI options such as B<-addext>.
12The syntax of configuration files is described in L<config(5)>.
13The commands typically have an option to specify the name of the configuration
14file, and a section within that file; see the documentation of the
15individual command for details.
16
17This page uses B<extensions> as the name of the section, when needed
18in examples.
19
20Each entry in the extension section takes the form:
21
22 name = [critical, ]value(s)
23
24If B<critical> is present then the extension will be marked as critical.
25
26If multiple entries are processed for the same extension name,
27later entries override earlier ones with the same name.
28
29The format of B<values> depends on the value of B<name>, many have a
30type-value pairing where the type and value are separated by a colon.
31There are four main types of extension:
32
33 string
34 multi-valued
35 raw
36 arbitrary
37
38Each is described in the following paragraphs.
39
40String extensions simply have a string which contains either the value itself
41or how it is obtained.
42
43Multi-valued extensions have a short form and a long form. The short form
44is a comma-separated list of names and values:
45
46 basicConstraints = critical, CA:true, pathlen:1
47
48The long form allows the values to be placed in a separate section:
49
50 [extensions]
51 basicConstraints = critical, @basic_constraints
52
53 [basic_constraints]
54 CA = true
55 pathlen = 1
56
57Both forms are equivalent.
58
59If an extension is multi-value and a field value must contain a comma the long
60form must be used otherwise the comma would be misinterpreted as a field
61separator. For example:
62
63 subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar
64
65will produce an error but the equivalent form:
66
67 [extensions]
68 subjectAltName = @subject_alt_section
69
70 [subject_alt_section]
71 subjectAltName = URI:ldap://somehost.com/CN=foo,OU=bar
72
73is valid.
74
75OpenSSL does not support multiple occurrences of the same field within a
76section. In this example:
77
78 [extensions]
79 subjectAltName = @alt_section
80
81 [alt_section]
82 email = steve@example.com
83 email = steve@example.org
84
85will only recognize the last value.  To specify multiple values append a
86numeric identifier, as shown here:
87
88 [extensions]
89 subjectAltName = @alt_section
90
91 [alt_section]
92 email.1 = steve@example.com
93 email.2 = steve@example.org
94
95The syntax of raw extensions is defined by the source code that parses
96the extension but should be documened.
97See L</Certificate Policies> for an example of a raw extension.
98
99If an extension type is unsupported, then the I<arbitrary> extension syntax
100must be used, see the L</ARBITRARY EXTENSIONS> section for more details.
101
102=head1 STANDARD EXTENSIONS
103
104The following sections describe the syntax of each supported extension.
105They do not define the semantics of the extension.
106
107=head2 Basic Constraints
108
109This is a multi-valued extension which indicates whether a certificate is
110a CA certificate. The first value is B<CA> followed by B<TRUE> or
111B<FALSE>. If B<CA> is B<TRUE> then an optional B<pathlen> name followed by a
112nonnegative value can be included.
113
114For example:
115
116 basicConstraints = CA:TRUE
117
118 basicConstraints = CA:FALSE
119
120 basicConstraints = critical, CA:TRUE, pathlen:1
121
122A CA certificate I<must> include the B<basicConstraints> name with the B<CA>
123parameter set to B<TRUE>. An end-user certificate must either have B<CA:FALSE>
124or omit the extension entirely.
125The B<pathlen> parameter specifies the maximum number of CAs that can appear
126below this one in a chain. A B<pathlen> of zero means the CA cannot sign
127any sub-CA's, and can only sign end-entity certificates.
128
129=head2 Key Usage
130
131Key usage is a multi-valued extension consisting of a list of names of
132the permitted key usages.  The defined values are: C<digitalSignature>,
133C<nonRepudiation>, C<keyEncipherment>, C<dataEncipherment>, C<keyAgreement>,
134C<keyCertSign>, C<cRLSign>, C<encipherOnly>, and C<decipherOnly>.
135
136Examples:
137
138 keyUsage = digitalSignature, nonRepudiation
139
140 keyUsage = critical, keyCertSign
141
142=head2 Extended Key Usage
143
144This extension consists of a list of values indicating purposes for which
145the certificate public key can be used.
146Each value can be either a short text name or an OID.
147The following text names, and their intended meaning, are known:
148
149 Value                  Meaning according to RFC 5280 etc.
150 -----                  ----------------------------------
151 serverAuth             SSL/TLS WWW Server Authentication
152 clientAuth             SSL/TLS WWW Client Authentication
153 codeSigning            Code Signing
154 emailProtection        E-mail Protection (S/MIME)
155 timeStamping           Trusted Timestamping
156 OCSPSigning            OCSP Signing
157 ipsecIKE               ipsec Internet Key Exchange
158 msCodeInd              Microsoft Individual Code Signing (authenticode)
159 msCodeCom              Microsoft Commercial Code Signing (authenticode)
160 msCTLSign              Microsoft Trust List Signing
161 msEFS                  Microsoft Encrypted File System
162
163While IETF RFC 5280 says that B<id-kp-serverAuth> and B<id-kp-clientAuth>
164are only for WWW use, in practice they are used for all kinds of TLS clients
165and servers, and this is what OpenSSL assumes as well.
166
167Examples:
168
169 extendedKeyUsage = critical, codeSigning, 1.2.3.4
170
171 extendedKeyUsage = serverAuth, clientAuth
172
173=head2 Subject Key Identifier
174
175The SKID extension specification has a value with three choices.
176If the value is the word B<none> then no SKID extension will be included.
177If the value is the word B<hash>, or by default for the B<x509>, B<req>, and
178B<ca> apps, the process specified in RFC 5280 section 4.2.1.2. (1) is followed:
179The keyIdentifier is composed of the 160-bit SHA-1 hash of the value of the BIT
180STRING subjectPublicKey (excluding the tag, length, and number of unused bits).
181
182Otherwise, the value must be a hex string (possibly with C<:> separating bytes)
183to output directly, however, this is strongly discouraged.
184
185Example:
186
187 subjectKeyIdentifier = hash
188
189=head2 Authority Key Identifier
190
191The AKID extension specification may have the value B<none>
192indicating that no AKID shall be included.
193Otherwise it may have the value B<keyid> or B<issuer>
194or both of them, separated by C<,>.
195Either or both can have the option B<always>,
196indicated by putting a colon C<:> between the value and this option.
197For self-signed certificates the AKID is suppressed unless B<always> is present.
198By default the B<x509>, B<req>, and B<ca> apps behave as if
199"none" was given for self-signed certificates and "keyid, issuer" otherwise.
200
201If B<keyid> is present, an attempt is made to
202copy the subject key identifier (SKID) from the issuer certificate except if
203the issuer certificate is the same as the current one and it is not self-signed.
204The hash of the public key related to the signing key is taken as fallback
205if the issuer certificate is the same as the current certificate.
206If B<always> is present but no value can be obtained, an error is returned.
207
208If B<issuer> is present, and in addition it has the option B<always> specified
209or B<keyid> is not present,
210then the issuer DN and serial number are copied from the issuer certificate.
211If this fails, an error is returned.
212
213Examples:
214
215 authorityKeyIdentifier = keyid, issuer
216
217 authorityKeyIdentifier = keyid, issuer:always
218
219=head2 Subject Alternative Name
220
221This is a multi-valued extension that supports several types of name
222identifier, including
223B<email> (an email address),
224B<URI> (a uniform resource indicator),
225B<DNS> (a DNS domain name),
226B<RID> (a registered ID: OBJECT IDENTIFIER),
227B<IP> (an IP address),
228B<dirName> (a distinguished name),
229and B<otherName>.
230The syntax of each is described in the following paragraphs.
231
232The B<email> option has a special C<copy> value, which will automatically
233include any email addresses contained in the certificate subject name in
234the extension.
235
236The IP address used in the B<IP> option can be in either IPv4 or IPv6 format.
237
238The value of B<dirName> is specifies the configuration section containing
239the distinguished name to use, as a set of name-value pairs.
240Multi-valued AVAs can be formed by prefacing the name with a B<+> character.
241
242The value of B<otherName> can include arbitrary data associated with an OID;
243the value should be the OID followed by a semicolon and the content in specified
244using the syntax in L<ASN1_generate_nconf(3)>.
245
246Examples:
247
248 subjectAltName = email:copy, email:my@example.com, URI:http://my.example.com/
249
250 subjectAltName = IP:192.168.7.1
251
252 subjectAltName = IP:13::17
253
254 subjectAltName = email:my@example.com, RID:1.2.3.4
255
256 subjectAltName = otherName:1.2.3.4;UTF8:some other identifier
257
258 [extensions]
259 subjectAltName = dirName:dir_sect
260
261 [dir_sect]
262 C = UK
263 O = My Organization
264 OU = My Unit
265 CN = My Name
266
267Non-ASCII Email Address conforming the syntax defined in Section 3.3 of RFC 6531
268are provided as otherName.SmtpUTF8Mailbox. According to RFC 8398, the email
269address should be provided as UTF8String. To enforce the valid representation in
270the certificate, the SmtpUTF8Mailbox should be provided as follows
271
272 subjectAltName=@alts
273 [alts]
274 otherName = 1.3.6.1.5.5.7.8.9;FORMAT:UTF8,UTF8String:nonasciiname.example.com
275
276=head2 Issuer Alternative Name
277
278This extension supports most of the options of subject alternative name;
279it does not support B<email:copy>.
280It also adds B<issuer:copy> as an allowed value, which copies any subject
281alternative names from the issuer certificate, if possible.
282
283Example:
284
285 issuerAltName = issuer:copy
286
287=head2 Authority Info Access
288
289This extension gives details about how to retrieve information that
290related to the certificate that the CA makes available. The syntax is
291B<access_id;location>, where B<access_id> is an object identifier
292(although only a few values are well-known) and B<location> has the same
293syntax as subject alternative name (except that B<email:copy> is not supported).
294
295Possible values for access_id include B<OCSP> (OCSP responder),
296B<caIssuers> (CA Issuers),
297B<ad_timestamping> (AD Time Stamping),
298B<AD_DVCS> (ad dvcs),
299B<caRepository> (CA Repository).
300
301Examples:
302
303 authorityInfoAccess = OCSP;URI:http://ocsp.example.com/,caIssuers;URI:http://myca.example.com/ca.cer
304
305 authorityInfoAccess = OCSP;URI:http://ocsp.example.com/
306
307=head2 CRL distribution points
308
309This is a multi-valued extension whose values can be either a name-value
310pair using the same form as subject alternative name or a single value
311specifying the section name containing all the distribution point values.
312
313When a name-value pair is used, a DistributionPoint extension will
314be set with the given value as the fullName field as the distributionPoint
315value, and the reasons and cRLIssuer fields will be omitted.
316
317When a single option is used, the value specifies the section, and that
318section can have the following items:
319
320=over 4
321
322=item fullname
323
324The full name of the distribution point, in the same format as the subject
325alternative name.
326
327=item relativename
328
329The value is taken as a distinguished name fragment that is set as the
330value of the nameRelativeToCRLIssuer field.
331
332=item CRLIssuer
333
334The value must in the same format as the subject alternative name.
335
336=item reasons
337
338A multi-value field that contains the reasons for revocation. The recognized
339values are: C<keyCompromise>, C<CACompromise>, C<affiliationChanged>,
340C<superseded>, C<cessationOfOperation>, C<certificateHold>,
341C<privilegeWithdrawn>, and C<AACompromise>.
342
343=back
344
345Only one of B<fullname> or B<relativename> should be specified.
346
347Simple examples:
348
349 crlDistributionPoints = URI:http://example.com/myca.crl
350
351 crlDistributionPoints = URI:http://example.com/myca.crl, URI:http://example.org/my.crl
352
353Full distribution point example:
354
355 [extensions]
356 crlDistributionPoints = crldp1_section
357
358 [crldp1_section]
359 fullname = URI:http://example.com/myca.crl
360 CRLissuer = dirName:issuer_sect
361 reasons = keyCompromise, CACompromise
362
363 [issuer_sect]
364 C = UK
365 O = Organisation
366 CN = Some Name
367
368=head2 Issuing Distribution Point
369
370This extension should only appear in CRLs. It is a multi-valued extension
371whose syntax is similar to the "section" pointed to by the CRL distribution
372points extension. The following names have meaning:
373
374=over 4
375
376=item fullname
377
378The full name of the distribution point, in the same format as the subject
379alternative name.
380
381=item relativename
382
383The value is taken as a distinguished name fragment that is set as the
384value of the nameRelativeToCRLIssuer field.
385
386=item onlysomereasons
387
388A multi-value field that contains the reasons for revocation. The recognized
389values are: C<keyCompromise>, C<CACompromise>, C<affiliationChanged>,
390C<superseded>, C<cessationOfOperation>, C<certificateHold>,
391C<privilegeWithdrawn>, and C<AACompromise>.
392
393=item onlyuser, onlyCA, onlyAA, indirectCRL
394
395The value for each of these names is a boolean.
396
397=back
398
399Example:
400
401 [extensions]
402 issuingDistributionPoint = critical, @idp_section
403
404 [idp_section]
405 fullname = URI:http://example.com/myca.crl
406 indirectCRL = TRUE
407 onlysomereasons = keyCompromise, CACompromise
408
409=head2 Certificate Policies
410
411This is a I<raw> extension that supports all of the defined fields of the
412certificate extension.
413
414Policies without qualifiers are specified by giving the OID.
415Multiple policies are comma-separated. For example:
416
417 certificatePolicies = 1.2.4.5, 1.1.3.4
418
419To include policy qualifiers, use the "@section" syntax to point to a
420section that specifies all the information.
421
422The section referred to must include the policy OID using the name
423B<policyIdentifier>. cPSuri qualifiers can be included using the syntax:
424
425 CPS.nnn = value
426
427where C<nnn> is a number.
428
429userNotice qualifiers can be set using the syntax:
430
431 userNotice.nnn = @notice
432
433The value of the userNotice qualifier is specified in the relevant section.
434This section can include B<explicitText>, B<organization>, and B<noticeNumbers>
435options. explicitText and organization are text strings, noticeNumbers is a
436comma separated list of numbers. The organization and noticeNumbers options
437(if included) must BOTH be present. Some software might require
438the B<ia5org> option at the top level; this changes the encoding from
439Displaytext to IA5String.
440
441Example:
442
443 [extensions]
444 certificatePolicies = ia5org, 1.2.3.4, 1.5.6.7.8, @polsect
445
446 [polsect]
447 policyIdentifier = 1.3.5.8
448 CPS.1 = "http://my.host.example.com/"
449 CPS.2 = "http://my.your.example.com/"
450 userNotice.1 = @notice
451
452 [notice]
453 explicitText = "Explicit Text Here"
454 organization = "Organisation Name"
455 noticeNumbers = 1, 2, 3, 4
456
457The character encoding of explicitText can be specified by prefixing the
458value with B<UTF8>, B<BMP>, or B<VISIBLE> followed by colon. For example:
459
460 [notice]
461 explicitText = "UTF8:Explicit Text Here"
462
463=head2 Policy Constraints
464
465This is a multi-valued extension which consisting of the names
466B<requireExplicitPolicy> or B<inhibitPolicyMapping> and a non negative integer
467value. At least one component must be present.
468
469Example:
470
471 policyConstraints = requireExplicitPolicy:3
472
473=head2 Inhibit Any Policy
474
475This is a string extension whose value must be a non negative integer.
476
477Example:
478
479 inhibitAnyPolicy = 2
480
481=head2 Name Constraints
482
483This is a multi-valued extension. The name should
484begin with the word B<permitted> or B<excluded> followed by a B<;>. The rest of
485the name and the value follows the syntax of subjectAltName except
486B<email:copy>
487is not supported and the B<IP> form should consist of an IP addresses and
488subnet mask separated by a B</>.
489
490Examples:
491
492 nameConstraints = permitted;IP:192.168.0.0/255.255.0.0
493
494 nameConstraints = permitted;email:.example.com
495
496 nameConstraints = excluded;email:.com
497
498=head2 OCSP No Check
499
500This is a string extension. It is parsed, but ignored.
501
502Example:
503
504 noCheck = ignored
505
506=head2 TLS Feature (aka Must Staple)
507
508This is a multi-valued extension consisting of a list of TLS extension
509identifiers. Each identifier may be a number (0..65535) or a supported name.
510When a TLS client sends a listed extension, the TLS server is expected to
511include that extension in its reply.
512
513The supported names are: B<status_request> and B<status_request_v2>.
514
515Example:
516
517 tlsfeature = status_request
518
519=head1 DEPRECATED EXTENSIONS
520
521The following extensions are non standard, Netscape specific and largely
522obsolete. Their use in new applications is discouraged.
523
524=head2 Netscape String extensions
525
526Netscape Comment (B<nsComment>) is a string extension containing a comment
527which will be displayed when the certificate is viewed in some browsers.
528Other extensions of this type are: B<nsBaseUrl>,
529B<nsRevocationUrl>, B<nsCaRevocationUrl>, B<nsRenewalUrl>, B<nsCaPolicyUrl>
530and B<nsSslServerName>.
531
532=head2 Netscape Certificate Type
533
534This is a multi-valued extensions which consists of a list of flags to be
535included. It was used to indicate the purposes for which a certificate could
536be used. The basicConstraints, keyUsage and extended key usage extensions are
537now used instead.
538
539Acceptable values for nsCertType are: B<client>, B<server>, B<email>,
540B<objsign>, B<reserved>, B<sslCA>, B<emailCA>, B<objCA>.
541
542=head1 ARBITRARY EXTENSIONS
543
544If an extension is not supported by the OpenSSL code then it must be encoded
545using the arbitrary extension format. It is also possible to use the arbitrary
546format for supported extensions. Extreme care should be taken to ensure that
547the data is formatted correctly for the given extension type.
548
549There are two ways to encode arbitrary extensions.
550
551The first way is to use the word ASN1 followed by the extension content
552using the same syntax as L<ASN1_generate_nconf(3)>.
553For example:
554
555 [extensions]
556 1.2.3.4 = critical, ASN1:UTF8String:Some random data
557 1.2.3.4.1 = ASN1:SEQUENCE:seq_sect
558
559 [seq_sect]
560 field1 = UTF8:field1
561 field2 = UTF8:field2
562
563It is also possible to use the word DER to include the raw encoded data in any
564extension.
565
566 1.2.3.4 = critical, DER:01:02:03:04
567 1.2.3.4.1 = DER:01020304
568
569The value following DER is a hex dump of the DER encoding of the extension
570Any extension can be placed in this form to override the default behaviour.
571For example:
572
573 basicConstraints = critical, DER:00:01:02:03
574
575=head1 WARNINGS
576
577There is no guarantee that a specific implementation will process a given
578extension. It may therefore be sometimes possible to use certificates for
579purposes prohibited by their extensions because a specific application does
580not recognize or honour the values of the relevant extensions.
581
582The DER and ASN1 options should be used with caution. It is possible to create
583invalid extensions if they are not used carefully.
584
585=head1 SEE ALSO
586
587L<openssl-req(1)>, L<openssl-ca(1)>, L<openssl-x509(1)>,
588L<ASN1_generate_nconf(3)>
589
590=head1 COPYRIGHT
591
592Copyright 2004-2021 The OpenSSL Project Authors. All Rights Reserved.
593
594Licensed under the Apache License 2.0 (the "License").  You may not use
595this file except in compliance with the License.  You can obtain a copy
596in the file LICENSE in the source distribution or at
597L<https://www.openssl.org/source/license.html>.
598
599=cut
600