5 x509v3_config - X509 V3 certificate extension configuration format
9 Several of the OpenSSL utilities can add extensions to a certificate or
10 certificate request based on the contents of a configuration file.
12 Typically the application will contain an option to point to an extension
13 section. Each line of the extension section takes the form:
15 extension_name=[critical,] extension_options
17 If B<critical> is present then the extension will be critical.
19 The format of B<extension_options> depends on the value of B<extension_name>.
21 There are four main types of extension: I<string> extensions, I<multi-valued>
22 extensions, I<raw> and I<arbitrary> extensions.
24 String extensions simply have a string which contains either the value itself
25 or how it is obtained.
29 nsComment="This is a Comment"
31 Multi-valued extensions have a short form and a long form. The short form
32 is a list of names and values:
34 basicConstraints=critical,CA:true,pathlen:1
36 The long form allows the values to be placed in a separate section:
38 basicConstraints=critical,@bs_section
45 Both forms are equivalent.
47 The syntax of raw extensions is governed by the extension code: it can
48 for example contain data in multiple sections. The correct syntax to
49 use is defined by the extension code itself: check out the certificate
50 policies extension for an example.
52 If an extension type is unsupported then the I<arbitrary> extension syntax
53 must be used, see the L<ARBITRART EXTENSIONS|/"ARBITRARY EXTENSIONS"> section for more details.
55 =head1 STANDARD EXTENSIONS
57 The following sections describe each supported extension in detail.
59 =head2 Basic Constraints.
61 This is a multi valued extension which indicates whether a certificate is
62 a CA certificate. The first (mandatory) name is B<CA> followed by B<TRUE> or
63 B<FALSE>. If B<CA> is B<TRUE> then an optional B<pathlen> name followed by an
64 non-negative value can be included.
68 basicConstraints=CA:TRUE
70 basicConstraints=CA:FALSE
72 basicConstraints=critical,CA:TRUE, pathlen:0
74 A CA certificate B<must> include the basicConstraints value with the CA field
75 set to TRUE. An end user certificate must either set CA to FALSE or exclude the
76 extension entirely. Some software may require the inclusion of basicConstraints
77 with CA set to FALSE for end entity certificates.
79 The pathlen parameter indicates the maximum number of CAs that can appear
80 below this one in a chain. So if you have a CA with a pathlen of zero it can
81 only be used to sign end user certificates and not further CAs.
86 Key usage is a multi valued extension consisting of a list of names of the
89 The supporte names are: digitalSignature, nonRepudiation, keyEncipherment,
90 dataEncipherment, keyAgreement, keyCertSign, cRLSign, encipherOnly
95 keyUsage=digitalSignature, nonRepudiation
97 keyUsage=critical, keyCertSign
100 =head2 Extended Key Usage.
102 This extensions consists of a list of usages indicating purposes for which
103 the certificate public key can be used for,
105 These can either be object short names of the dotted numerical form of OIDs.
106 While any OID can be used only certain values make sense. In particular the
107 following PKIX, NS and MS values are meaningful:
111 serverAuth SSL/TLS Web Server Authentication.
112 clientAuth SSL/TLS Web Client Authentication.
113 codeSigning Code signing.
114 emailProtection E-mail Protection (S/MIME).
115 timeStamping Trusted Timestamping
116 msCodeInd Microsoft Individual Code Signing (authenticode)
117 msCodeCom Microsoft Commercial Code Signing (authenticode)
118 msCTLSign Microsoft Trust List Signing
119 msSGC Microsoft Server Gated Crypto
120 msEFS Microsoft Encrypted File System
121 nsSGC Netscape Server Gated Crypto
125 extendedKeyUsage=critical,codeSigning,1.2.3.4
126 extendedKeyUsage=nsSGC,msSGC
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 preceeding 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 ASN1_generate_nconf() 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 that supports all the literal options of
228 subject alternative name. Of the few software packages that currently interpret
229 this extension most only interpret the URI option.
231 Currently each option will set a new DistributionPoint with the fullName
232 field set to the given value.
234 Other fields like cRLissuer and reasons cannot currently be set or displayed:
235 at this time no examples were available that used these fields.
239 crlDistributionPoints=URI:http://myhost.com/myca.crl
240 crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl
242 =head2 Certificate Policies.
244 This is a I<raw> extension. All the fields of this extension can be set by
245 using the appropriate syntax.
247 If you follow the PKIX recommendations and just using one OID then you just
248 include the value of that OID. Multiple OIDs can be set separated by commas,
251 certificatePolicies= 1.2.4.5, 1.1.3.4
253 If you wish to include qualifiers then the policy OID and qualifiers need to
254 be specified in a separate section: this is done by using the @section syntax
255 instead of a literal OID value.
257 The section referred to must include the policy OID using the name
258 policyIdentifier, cPSuri qualifiers can be included using the syntax:
262 userNotice qualifiers can be set using the syntax:
264 userNotice.nnn=@notice
266 The value of the userNotice qualifier is specified in the relevant section.
267 This section can include explicitText, organization and noticeNumbers
268 options. explicitText and organization are text strings, noticeNumbers is a
269 comma separated list of numbers. The organization and noticeNumbers options
270 (if included) must BOTH be present. If you use the userNotice option with IE5
271 then you need the 'ia5org' option at the top level to modify the encoding:
272 otherwise it will not be interpreted properly.
276 certificatePolicies=ia5org,1.2.3.4,1.5.6.7.8,@polsect
280 policyIdentifier = 1.3.5.8
281 CPS.1="http://my.host.name/"
282 CPS.2="http://my.your.name/"
287 explicitText="Explicit Text Here"
288 organization="Organisation Name"
289 noticeNumbers=1,2,3,4
291 The B<ia5org> option changes the type of the I<organization> field. In RFC2459
292 it can only be of type DisplayText. In RFC3280 IA5Strring is also permissible.
293 Some software (for example some versions of MSIE) may require ia5org.
295 =head2 Policy Constraints
297 This is a multi-valued extension which consisting of the names
298 B<requireExplicitPolicy> or B<inhibitPolicyMapping> and a non negative intger
299 value. At least one component must be present.
303 policyConstraints = requireExplicitPolicy:3
306 =head2 Inhibit Any Policy
308 This is a string extension whose value must be a non negative integer.
315 =head2 Name Constraints
317 The name constraints extension is a multi-valued extension. The name should
318 begin with the word B<permitted> or B<excluded> followed by a B<;>. The rest of
319 the name and the value follows the syntax of subjectAltName except email:copy
320 is not supported and the B<IP> form should consist of an IP addresses and
321 subnet mask separated by a B</>.
325 nameConstraints=permitted;IP:192.168.0.0/255.255.0.0
327 nameConstraints=permitted;email:.somedomain.com
329 nameConstraints=excluded;email:.com
331 =head1 DEPRECATED EXTENSIONS
333 The following extensions are non standard, Netscape specific and largely
334 obsolete. Their use in new applications is discouraged.
336 =head2 Netscape String extensions.
338 Netscape Comment (B<nsComment>) is a string extension containing a comment
339 which will be displayed when the certificate is viewed in some browsers.
343 nsComment = "Some Random Comment"
345 Other supported extensions in this category are: B<nsBaseUrl>,
346 B<nsRevocationUrl>, B<nsCaRevocationUrl>, B<nsRenewalUrl>, B<nsCaPolicyUrl>
347 and B<nsSslServerName>.
350 =head2 Netscape Certificate Type
352 This is a multi-valued extensions which consists of a list of flags to be
353 included. It was used to indicate the purposes for which a certificate could
354 be used. The basicConstraints, keyUsage and extended key usage extensions are
357 Acceptable values for nsCertType are: B<client>, B<server>, B<email>,
358 B<objsign>, B<reserved>, B<sslCA>, B<emailCA>, B<objCA>.
361 =head1 ARBITRARY EXTENSIONS
363 If an extension is not supported by the OpenSSL code then it must be encoded
364 using the arbitrary extension format. It is also possible to use the arbitrary
365 format for supported extensions. Extreme care should be taken to ensure that
366 the data is formatted correctly for the given extension type.
368 There are two ways to encode arbitrary extensions.
370 The first way is to use the word ASN1 followed by the extension content
371 using the same syntax as ASN1_generate_nconf(). For example:
373 1.2.3.4=critical,ASN1:UTF8String:Some random data
375 1.2.3.4=ASN1:SEQUENCE:seq_sect
382 It is also possible to use the word DER to include the raw encoded data in any
385 1.2.3.4=critical,DER:01:02:03:04
388 The value following DER is a hex dump of the DER encoding of the extension
389 Any extension can be placed in this form to override the default behaviour.
392 basicConstraints=critical,DER:00:01:02:03
396 There is no guarantee that a specific implementation will process a given
397 extension. It may therefore be sometimes possible to use certificates for
398 purposes prohibited by their extensions because a specific application does
399 not recognize or honour the values of the relevant extensions.
401 The DER and ASN1 options should be used with caution. It is possible to create
402 totally invalid extensions if they are not used carefully.
407 If an extension is multi-value and a field value must contain a comma the long
408 form must be used otherwise the comma would be misinterpreted as a field
409 separator. For example:
411 subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
413 will produce an error but the equivalent form:
415 subjectAltName=@subject_alt_section
417 [subject_alt_section]
418 subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
422 Due to the behaviour of the OpenSSL B<conf> library the same field name
423 can only occur once in a section. This means that:
425 subjectAltName=@alt_section
432 will only recognize the last value. This can be worked around by using the form:
441 The X509v3 extension code was first added to OpenSSL 0.9.2.
443 Policy mappings, name constraints, inhibit any policy and name
444 constraints support was added in OpenSSL 0.9.8
446 The B<directoryName> and B<otherName> option as well as the B<ASN1> option
447 for arbitrary extensions was added in OpenSSL 0.9.8
451 L<req(1)|req(1)>, L<ca(1)|ca(1)>, L<x509(1)|x509(1)>