3 =for comment openssl_manual_section:5
7 x509v3_config - X509 V3 certificate extension configuration format
11 Several of the OpenSSL utilities can add extensions to a certificate or
12 certificate request based on the contents of a configuration file.
14 Typically the application will contain an option to point to an extension
15 section. Each line of the extension section takes the form:
17 extension_name=[critical,] extension_options
19 If B<critical> is present then the extension will be critical.
21 The format of B<extension_options> depends on the value of B<extension_name>.
23 There are four main types of extension: I<string> extensions, I<multi-valued>
24 extensions, I<raw> and I<arbitrary> extensions.
26 String extensions simply have a string which contains either the value itself
27 or how it is obtained.
31 nsComment="This is a Comment"
33 Multi-valued extensions have a short form and a long form. The short form
34 is a list of names and values:
36 basicConstraints=critical,CA:true,pathlen:1
38 The long form allows the values to be placed in a separate section:
40 basicConstraints=critical,@bs_section
47 Both forms are equivalent.
49 The syntax of raw extensions is governed by the extension code: it can
50 for example contain data in multiple sections. The correct syntax to
51 use is defined by the extension code itself: check out the certificate
52 policies extension for an example.
54 If an extension type is unsupported then the I<arbitrary> extension syntax
55 must be used, see the L<ARBITRARY EXTENSIONS|/"ARBITRARY EXTENSIONS"> section for more details.
57 =head1 STANDARD EXTENSIONS
59 The following sections describe each supported extension in detail.
61 =head2 Basic Constraints.
63 This is a multi valued extension which indicates whether a certificate is
64 a CA certificate. The first (mandatory) name is B<CA> followed by B<TRUE> or
65 B<FALSE>. If B<CA> is B<TRUE> then an optional B<pathlen> name followed by an
66 non-negative value can be included.
70 basicConstraints=CA:TRUE
72 basicConstraints=CA:FALSE
74 basicConstraints=critical,CA:TRUE, pathlen:0
76 A CA certificate B<must> include the basicConstraints value with the CA field
77 set to TRUE. An end user certificate must either set CA to FALSE or exclude the
78 extension entirely. Some software may require the inclusion of basicConstraints
79 with CA set to FALSE for end entity certificates.
81 The pathlen parameter indicates the maximum number of CAs that can appear
82 below this one in a chain. So if you have a CA with a pathlen of zero it can
83 only be used to sign end user certificates and not further CAs.
88 Key usage is a multi valued extension consisting of a list of names of the
91 The supported names are: digitalSignature, nonRepudiation, keyEncipherment,
92 dataEncipherment, keyAgreement, keyCertSign, cRLSign, encipherOnly
97 keyUsage=digitalSignature, nonRepudiation
99 keyUsage=critical, keyCertSign
102 =head2 Extended Key Usage.
104 This extensions consists of a list of usages indicating purposes for which
105 the certificate public key can be used for,
107 These can either be object short names of the dotted numerical form of OIDs.
108 While any OID can be used only certain values make sense. In particular the
109 following PKIX, NS and MS values are meaningful:
113 serverAuth SSL/TLS Web Server Authentication.
114 clientAuth SSL/TLS Web Client Authentication.
115 codeSigning Code signing.
116 emailProtection E-mail Protection (S/MIME).
117 timeStamping Trusted Timestamping
118 msCodeInd Microsoft Individual Code Signing (authenticode)
119 msCodeCom Microsoft Commercial Code Signing (authenticode)
120 msCTLSign Microsoft Trust List Signing
121 msEFS Microsoft Encrypted File System
125 extendedKeyUsage=critical,codeSigning,1.2.3.4
126 extendedKeyUsage=serverAuth,clientAuth
129 =head2 Subject Key Identifier.
131 This is really a string extension and can take two possible values. Either
132 the word B<hash> which will automatically follow the guidelines in RFC3280
133 or a hex string giving the extension value to include. The use of the hex
134 string is strongly discouraged.
138 subjectKeyIdentifier=hash
141 =head2 Authority Key Identifier.
143 The authority key identifier extension permits two options. keyid and issuer:
144 both can take the optional value "always".
146 If the keyid option is present an attempt is made to copy the subject key
147 identifier from the parent certificate. If the value "always" is present
148 then an error is returned if the option fails.
150 The issuer option copies the issuer and serial number from the issuer
151 certificate. This will only be done if the keyid option fails or
152 is not included unless the "always" flag will always include the value.
156 authorityKeyIdentifier=keyid,issuer
159 =head2 Subject Alternative Name.
161 The subject alternative name extension allows various literal values to be
162 included in the configuration file. These include B<email> (an email address)
163 B<URI> a uniform resource indicator, B<DNS> (a DNS domain name), B<RID> (a
164 registered ID: OBJECT IDENTIFIER), B<IP> (an IP address), B<dirName>
165 (a distinguished name) and otherName.
167 The email option include a special 'copy' value. This will automatically
168 include and email addresses contained in the certificate subject name in
171 The IP address used in the B<IP> options can be in either IPv4 or IPv6 format.
173 The value of B<dirName> should point to a section containing the distinguished
174 name to use as a set of name value pairs. Multi values AVAs can be formed by
175 prefacing the name with a B<+> character.
177 otherName can include arbitrary data associated with an OID: the value
178 should be the OID followed by a semicolon and the content in standard
179 L<ASN1_generate_nconf(3)|ASN1_generate_nconf(3)> format.
183 subjectAltName=email:copy,email:my@other.address,URI:http://my.url.here/
184 subjectAltName=IP:192.168.7.1
185 subjectAltName=IP:13::17
186 subjectAltName=email:my@other.address,RID:1.2.3.4
187 subjectAltName=otherName:1.2.3.4;UTF8:some other identifier
189 subjectAltName=dirName:dir_sect
198 =head2 Issuer Alternative Name.
200 The issuer alternative name option supports all the literal options of
201 subject alternative name. It does B<not> support the email:copy option because
202 that would not make sense. It does support an additional issuer:copy option
203 that will copy all the subject alternative name values from the issuer
204 certificate (if possible).
208 issuserAltName = issuer:copy
211 =head2 Authority Info Access.
213 The authority information access extension gives details about how to access
214 certain information relating to the CA. Its syntax is accessOID;location
215 where I<location> has the same syntax as subject alternative name (except
216 that email:copy is not supported). accessOID can be any valid OID but only
217 certain values are meaningful, for example OCSP and caIssuers.
221 authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
222 authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html
225 =head2 CRL distribution points.
227 This is a multi-valued extension whose options can be either in name:value pair
228 using the same form as subject alternative name or a single value representing
229 a section name containing all the distribution point fields.
231 For a name:value pair a new DistributionPoint with the fullName field set to
232 the given value both the cRLissuer and reasons fields are omitted in this case.
234 In the single option case the section indicated contains values for each
235 field. In this section:
237 If the name is "fullname" the value field should contain the full name
238 of the distribution point in the same format as subject alternative name.
240 If the name is "relativename" then the value field should contain a section
241 name whose contents represent a DN fragment to be placed in this field.
243 The name "CRLIssuer" if present should contain a value for this field in
244 subject alternative name format.
246 If the name is "reasons" the value field should consist of a comma
247 separated field containing the reasons. Valid reasons are: "keyCompromise",
248 "CACompromise", "affiliationChanged", "superseded", "cessationOfOperation",
249 "certificateHold", "privilegeWithdrawn" and "AACompromise".
254 crlDistributionPoints=URI:http://myhost.com/myca.crl
255 crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl
257 Full distribution point example:
259 crlDistributionPoints=crldp1_section
263 fullname=URI:http://myhost.com/myca.crl
264 CRLissuer=dirName:issuer_sect
265 reasons=keyCompromise, CACompromise
272 =head2 Issuing Distribution Point
274 This extension should only appear in CRLs. It is a multi valued extension
275 whose syntax is similar to the "section" pointed to by the CRL distribution
276 points extension with a few differences.
278 The names "reasons" and "CRLissuer" are not recognized.
280 The name "onlysomereasons" is accepted which sets this field. The value is
281 in the same format as the CRL distribution point "reasons" field.
283 The names "onlyuser", "onlyCA", "onlyAA" and "indirectCRL" are also accepted
284 the values should be a boolean value (TRUE or FALSE) to indicate the value of
285 the corresponding field.
289 issuingDistributionPoint=critical, @idp_section
293 fullname=URI:http://myhost.com/myca.crl
295 onlysomereasons=keyCompromise, CACompromise
303 =head2 Certificate Policies.
305 This is a I<raw> extension. All the fields of this extension can be set by
306 using the appropriate syntax.
308 If you follow the PKIX recommendations and just using one OID then you just
309 include the value of that OID. Multiple OIDs can be set separated by commas,
312 certificatePolicies= 1.2.4.5, 1.1.3.4
314 If you wish to include qualifiers then the policy OID and qualifiers need to
315 be specified in a separate section: this is done by using the @section syntax
316 instead of a literal OID value.
318 The section referred to must include the policy OID using the name
319 policyIdentifier, cPSuri qualifiers can be included using the syntax:
323 userNotice qualifiers can be set using the syntax:
325 userNotice.nnn=@notice
327 The value of the userNotice qualifier is specified in the relevant section.
328 This section can include explicitText, organization and noticeNumbers
329 options. explicitText and organization are text strings, noticeNumbers is a
330 comma separated list of numbers. The organization and noticeNumbers options
331 (if included) must BOTH be present. If you use the userNotice option with IE5
332 then you need the 'ia5org' option at the top level to modify the encoding:
333 otherwise it will not be interpreted properly.
337 certificatePolicies=ia5org,1.2.3.4,1.5.6.7.8,@polsect
341 policyIdentifier = 1.3.5.8
342 CPS.1="http://my.host.name/"
343 CPS.2="http://my.your.name/"
348 explicitText="Explicit Text Here"
349 organization="Organisation Name"
350 noticeNumbers=1,2,3,4
352 The B<ia5org> option changes the type of the I<organization> field. In RFC2459
353 it can only be of type DisplayText. In RFC3280 IA5Strring is also permissible.
354 Some software (for example some versions of MSIE) may require ia5org.
356 =head2 Policy Constraints
358 This is a multi-valued extension which consisting of the names
359 B<requireExplicitPolicy> or B<inhibitPolicyMapping> and a non negative integer
360 value. At least one component must be present.
364 policyConstraints = requireExplicitPolicy:3
367 =head2 Inhibit Any Policy
369 This is a string extension whose value must be a non negative integer.
376 =head2 Name Constraints
378 The name constraints extension is a multi-valued extension. The name should
379 begin with the word B<permitted> or B<excluded> followed by a B<;>. The rest of
380 the name and the value follows the syntax of subjectAltName except email:copy
381 is not supported and the B<IP> form should consist of an IP addresses and
382 subnet mask separated by a B</>.
386 nameConstraints=permitted;IP:192.168.0.0/255.255.0.0
388 nameConstraints=permitted;email:.somedomain.com
390 nameConstraints=excluded;email:.com
395 The OCSP No Check extension is a string extension but its value is ignored.
402 =head1 DEPRECATED EXTENSIONS
404 The following extensions are non standard, Netscape specific and largely
405 obsolete. Their use in new applications is discouraged.
407 =head2 Netscape String extensions.
409 Netscape Comment (B<nsComment>) is a string extension containing a comment
410 which will be displayed when the certificate is viewed in some browsers.
414 nsComment = "Some Random Comment"
416 Other supported extensions in this category are: B<nsBaseUrl>,
417 B<nsRevocationUrl>, B<nsCaRevocationUrl>, B<nsRenewalUrl>, B<nsCaPolicyUrl>
418 and B<nsSslServerName>.
421 =head2 Netscape Certificate Type
423 This is a multi-valued extensions which consists of a list of flags to be
424 included. It was used to indicate the purposes for which a certificate could
425 be used. The basicConstraints, keyUsage and extended key usage extensions are
428 Acceptable values for nsCertType are: B<client>, B<server>, B<email>,
429 B<objsign>, B<reserved>, B<sslCA>, B<emailCA>, B<objCA>.
432 =head1 ARBITRARY EXTENSIONS
434 If an extension is not supported by the OpenSSL code then it must be encoded
435 using the arbitrary extension format. It is also possible to use the arbitrary
436 format for supported extensions. Extreme care should be taken to ensure that
437 the data is formatted correctly for the given extension type.
439 There are two ways to encode arbitrary extensions.
441 The first way is to use the word ASN1 followed by the extension content
442 using the same syntax as L<ASN1_generate_nconf(3)|ASN1_generate_nconf(3)>.
445 1.2.3.4=critical,ASN1:UTF8String:Some random data
447 1.2.3.4=ASN1:SEQUENCE:seq_sect
454 It is also possible to use the word DER to include the raw encoded data in any
457 1.2.3.4=critical,DER:01:02:03:04
460 The value following DER is a hex dump of the DER encoding of the extension
461 Any extension can be placed in this form to override the default behaviour.
464 basicConstraints=critical,DER:00:01:02:03
468 There is no guarantee that a specific implementation will process a given
469 extension. It may therefore be sometimes possible to use certificates for
470 purposes prohibited by their extensions because a specific application does
471 not recognize or honour the values of the relevant extensions.
473 The DER and ASN1 options should be used with caution. It is possible to create
474 totally invalid extensions if they are not used carefully.
479 If an extension is multi-value and a field value must contain a comma the long
480 form must be used otherwise the comma would be misinterpreted as a field
481 separator. For example:
483 subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
485 will produce an error but the equivalent form:
487 subjectAltName=@subject_alt_section
489 [subject_alt_section]
490 subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
494 Due to the behaviour of the OpenSSL B<conf> library the same field name
495 can only occur once in a section. This means that:
497 subjectAltName=@alt_section
504 will only recognize the last value. This can be worked around by using the form:
513 The X509v3 extension code was first added to OpenSSL 0.9.2.
515 Policy mappings, inhibit any policy and name constraints support was added in
518 The B<directoryName> and B<otherName> option as well as the B<ASN1> option
519 for arbitrary extensions was added in OpenSSL 0.9.8
523 L<req(1)|req(1)>, L<ca(1)|ca(1)>, L<x509(1)|x509(1)>,
524 L<ASN1_generate_nconf(3)|ASN1_generate_nconf(3)>