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 ARBITRARY EXTENSION 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. Normally this will only be done if the keyid option fails or
152 is not included: the "always" flag will always include the value.
155 =head2 Subject Alternative Name.
157 The subject alternative name extension allows various literal values to be
158 included in the configuration file. These include B<email> (an email address)
159 B<URI> a uniform resource indicator, B<DNS> (a DNS domain name), B<RID> (a
160 registered ID: OBJECT IDENTIFIER), B<IP> (an IP address), B<dirName>
161 (a distinguished name) and otherName.
163 The email option include a special 'copy' value. This will automatically
164 include and email addresses contained in the certificate subject name in
167 The value of B<dirName> should point to a section containing the distinguished
168 name to use as a set of name value pairs. Multi values AVAs can be formed by
169 preceeding the name with a B<+> character.
171 otherName can include arbitrary data associated with an OID: the value
172 should be the OID followed by a semicolon and the content in standard
173 ASN1_generate_nconf() format.
177 subjectAltName=email:copy,email:my@other.address,URI:http://my.url.here/
178 subjectAltName=email:my@other.address,RID:1.2.3.4
179 subjectAltName=otherName:1.2.3.4;UTF8:some other identifier
181 subjectAltName=dirName:dir_sect
190 =head2 Issuer Alternative Name.
192 The issuer alternative name option supports all the literal options of
193 subject alternative name. It does B<not> support the email:copy option because
194 that would not make sense. It does support an additional issuer:copy option
195 that will copy all the subject alternative name values from the issuer
196 certificate (if possible).
200 issuserAltName = issuer:copy
203 =head2 Authority Info Access.
205 The authority information access extension gives details about how to access
206 certain information relating to the CA. Its syntax is accessOID;location
207 where I<location> has the same syntax as subject alternative name (except
208 that email:copy is not supported). accessOID can be any valid OID but only
209 certain values are meaningful, for example OCSP and caIssuers.
213 authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
214 authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html
217 =head2 CRL distribution points.
219 This is a multi-valued extension that supports all the literal options of
220 subject alternative name. Of the few software packages that currently interpret
221 this extension most only interpret the URI option.
223 Currently each option will set a new DistributionPoint with the fullName
224 field set to the given value.
226 Other fields like cRLissuer and reasons cannot currently be set or displayed:
227 at this time no examples were available that used these fields.
231 crlDistributionPoints=URI:http://myhost.com/myca.crl
232 crlDistributionPoints=URI:http://my.com/my.crl,URI:http://oth.com/my.crl
234 =head2 Certificate Policies.
236 This is a B<raw> extension. All the fields of this extension can be set by
237 using the appropriate syntax.
239 If you follow the PKIX recommendations and just using one OID then you just
240 include the value of that OID. Multiple OIDs can be set separated by commas,
243 certificatePolicies= 1.2.4.5, 1.1.3.4
245 If you wish to include qualifiers then the policy OID and qualifiers need to
246 be specified in a separate section: this is done by using the @section syntax
247 instead of a literal OID value.
249 The section referred to must include the policy OID using the name
250 policyIdentifier, cPSuri qualifiers can be included using the syntax:
254 userNotice qualifiers can be set using the syntax:
256 userNotice.nnn=@notice
258 The value of the userNotice qualifier is specified in the relevant section.
259 This section can include explicitText, organization and noticeNumbers
260 options. explicitText and organization are text strings, noticeNumbers is a
261 comma separated list of numbers. The organization and noticeNumbers options
262 (if included) must BOTH be present. If you use the userNotice option with IE5
263 then you need the 'ia5org' option at the top level to modify the encoding:
264 otherwise it will not be interpreted properly.
268 certificatePolicies=ia5org,1.2.3.4,1.5.6.7.8,@polsect
272 policyIdentifier = 1.3.5.8
273 CPS.1="http://my.host.name/"
274 CPS.2="http://my.your.name/"
279 explicitText="Explicit Text Here"
280 organization="Organisation Name"
281 noticeNumbers=1,2,3,4
283 The B<ia5org> option changes the type of the I<organization> field. In RFC2459
284 it can only be of type DisplayText. In RFC3280 IA5Strring is also permissible.
285 Some software (for example some versions of MSIE) may require ia5org.
288 =head1 DEPRECATED EXTENSIONS
290 The following extensions are considered non standard, Netscape specific and
291 largely obsolete. Their use in new applications is discouraged.
293 =head2 Netscape String extensions.
295 Netscape Comment (B<nsComment>) is a string extension containing a comment
296 which will be displayed when the certificate is viewed in some browsers.
300 nsComment = "Some Random Comment"
302 Other supported extensions in this category are: B<nsBaseUrl>,
303 B<nsRevocationUrl>, B<nsCaRevocationUrl>, B<nsRenewalUrl>, B<nsCaPolicyUrl>
304 and B<nsSslServerName>.
307 =head2 Netscape Certificate Type
309 This is a multi-valued extensions which consists of a list of flags to be
310 included. It was used to indicate the purposes for which a certificate could
311 be used. The basicConstraints, keyUsage and extended key usage extensions are
314 Acceptable values for nsCertType are: B<client>, B<server>, B<email>,
315 B<objsign>, B<reserved>, B<sslCA>, B<emailCA>, B<objCA>.
318 =head1 ARBITRARY EXTENSIONS
320 If an extension is not supported by the OpenSSL code then it must be encoded
321 using the arbitrary extension format. It is also possible to use the arbitrary
322 format for supported extensions. Extreme care should be taken to ensure that
323 the data is formatted correctly for the given extension type.
325 There are two ways to encode arbitrary extensions.
327 The first way is to use the word ASN1 followed by the extension content
328 using the same syntax as ASN1_generate_nconf(). For example:
330 1.2.3.4=critical,ASN1:UTF8String:Some random data
332 1.2.3.4=ASN1:SEQUENCE:seq_sect
339 It is also possible to use the word DER to include the raw encoded data in any
342 1.2.3.4=critical,DER:01:02:03:04
345 The value following DER is a hex dump of the DER encoding of the extension
346 Any extension can be placed in this form to override the default behaviour.
349 basicConstraints=critical,DER:00:01:02:03
353 There is no guarantee that a specific implementation will process a given
354 extension. It may therefore be sometimes possible to use certificates for
355 purposes prohibited by their extensions because a specific application does
356 not recognize or honour the values of the relevant extensions.
358 The DER and ASN1 options should be used with caution. It is possible to create
359 totally invalid extensions if they are not used carefully.
364 If an extension is multi-value and a field value must contain a comma the long
365 form must be used otherwise the comma would be misinterpreted as a field
366 separator. For example:
368 subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
370 will produce an error but the equivalent form:
372 subjectAltName=@subject_alt_section
374 [subject_alt_section]
375 subjectAltName=URI:ldap://somehost.com/CN=foo,OU=bar
379 Due to the behaviour of the OpenSSL B<conf> library the same field name
380 can only occur once in a section. This means that:
382 subjectAltName=@alt_section
389 will only recognize the last value. This can be worked around by using the form: