1756d405cc
make 'req' check the config file syntax before it adds extensions. Added info in the documentation as well.
224 lines
7.4 KiB
Text
224 lines
7.4 KiB
Text
OpenSSL X509V3 extension configuration: preliminary documentation.
|
|
|
|
INTRODUCTION.
|
|
|
|
For OpenSSL 0.9.2 the extension code has be considerably enhanced. It is now
|
|
possible to add and print out common X509 V3 certificate and CRL extensions.
|
|
|
|
For more information about the meaning of extensions see:
|
|
|
|
http://www.imc.org/ietf-pkix/
|
|
http://home.netscape.com/eng/security/certs.html
|
|
|
|
PRINTING EXTENSIONS.
|
|
|
|
Extension values are automatically printed out for supported extensions.
|
|
|
|
openssl x509 -in cert.pem -text
|
|
openssl crl -in crl.pem -text
|
|
|
|
will give information in the extension printout, for example:
|
|
|
|
|
|
X509v3 extensions:
|
|
X509v3 Basic Constraints:
|
|
CA:TRUE
|
|
X509v3 Subject Key Identifier:
|
|
73:FE:F7:59:A7:E1:26:84:44:D6:44:36:EE:79:1A:95:7C:B1:4B:15
|
|
X509v3 Authority Key Identifier:
|
|
keyid:73:FE:F7:59:A7:E1:26:84:44:D6:44:36:EE:79:1A:95:7C:B1:4B:15, DirName:/C=AU/ST=Some-State/O=Internet Widgits Pty Ltd/Email=email@1.address/Email=email@2.address, serial:00
|
|
X509v3 Key Usage:
|
|
Certificate Sign, CRL Sign
|
|
X509v3 Subject Alternative Name:
|
|
email:email@1.address, email:email@2.address
|
|
|
|
CONFIGURATION FILES.
|
|
|
|
The OpenSSL utilities 'ca' and 'req' can now have extension sections listing
|
|
which certificate extensions to include. In each case a line:
|
|
|
|
x509_extensions = extension_section
|
|
|
|
indicates which section contains the extensions. In the case of 'req' the
|
|
extension section is used when the -x509 option is present to create a
|
|
self signed root certificate.
|
|
|
|
You can also add extensions to CRLs: a line
|
|
|
|
crl_extensions = crl_extension_section
|
|
|
|
will include extensions when the -gencrl option is used with the 'ca' utility.
|
|
You can add any extension to a CRL but of the supported extensions only
|
|
issuerAltName and authorityKeyIdentifier make any real sense. Note: these are
|
|
CRL extensions NOT CRL *entry* extensions which cannot currently be generated.
|
|
CRL entry extensions can be displayed.
|
|
|
|
EXTENSION SYNTAX.
|
|
|
|
Extensions have the basic form:
|
|
|
|
extension_name=[critical,] extension_options
|
|
|
|
the use of the critical option makes the extension critical. Extreme caution
|
|
should be made when using the critical flag. If an extension is marked
|
|
as critical then any client that does not understand the extension should
|
|
reject it as invalid. Some broken software will reject certificates which
|
|
have *any* critical extensions (these violates PKIX but we have to live
|
|
with it).
|
|
|
|
There are three main types of extension, string extensions, multi valued
|
|
extensions, and raw extensions.
|
|
|
|
String extensions simply have a string which defines the value of the or how
|
|
it is obtained.
|
|
|
|
For example:
|
|
|
|
nsComment="This is a Comment"
|
|
|
|
Multi valued extensions have a short form and a long form. The short form
|
|
is a list of names and values:
|
|
|
|
basicConstraints=critical,CA:true,pathlen:1
|
|
|
|
The long form allows the values to be placed in a separate section:
|
|
|
|
basicConstraints=critical,@bs_section
|
|
|
|
[bs_section]
|
|
|
|
CA=true
|
|
pathlen=1
|
|
|
|
Both forms are equivalent. However it should be noted that in some cases the
|
|
same name can appear multiple times, for example,
|
|
|
|
subjectAltName=email:steve@here,email:steve@there
|
|
|
|
in this case an equivalent long form is:
|
|
|
|
subjectAltName=@alt_section
|
|
|
|
[alt_section]
|
|
|
|
email.1=steve@here
|
|
email.2=steve@there
|
|
|
|
This is because the configuration file code cannot handle the same name
|
|
occurring twice in the same extension.
|
|
|
|
Raw extensions allow arbitrary data to be placed in an extension. For
|
|
example
|
|
|
|
1.2.3.4=critical,RAW:01:02:03:04
|
|
1.2.3.4=RAW:01020304
|
|
|
|
The value following RAW is a hex dump of the extension contents. Any extension
|
|
can be placed in this form to override the default behaviour. For example:
|
|
|
|
basicConstraints=critical,RAW:00:01:02:03
|
|
|
|
WARNING: raw extensions should be used with caution. It is possible to create
|
|
totally invalid extensions unless care is taken.
|
|
|
|
CURRENTLY SUPPORTED EXTENSIONS.
|
|
|
|
Literal String extensions.
|
|
|
|
In each case the 'value' of the extension is placed directly in the extension.
|
|
Currently supported extensions in this category are: nsBaseUrl, nsRevocationUrl
|
|
nsCaRevocationUrl, nsRenewalUrl, nsCaPolicyUrl, nsSslServerName and
|
|
nsComment.
|
|
|
|
For example:
|
|
|
|
nsComment="This is a test comment"
|
|
|
|
Bit Strings.
|
|
|
|
Bit string extensions just consist of a list of suppported bits, currently
|
|
two extensions are in this category: PKIX keyUsage and the Netscape specific
|
|
nsCertType.
|
|
|
|
nsCertType (netscape certificate type) takes the flags: client, server, email,
|
|
objsign, reserved, sslCA, emailCA, objCA.
|
|
|
|
keyUsage (PKIX key usage) takes the flags: digitalSignature, nonRepudiation,
|
|
keyEncipherment, dataEncipherment, keyAgreement, keyCertSign, cRLCertSign,
|
|
encipherOnly, decipherOnly.
|
|
|
|
For example:
|
|
|
|
nsCertType=server
|
|
|
|
keyUsage=critical, digitalSignature, nonRepudiation
|
|
|
|
|
|
Basic Constraints.
|
|
|
|
Basic constraints is a multi valued extension that supports a CA and an
|
|
optional pathlen option. The CA option takes the values true and false and
|
|
pathlen takes an integer. Note if the CA option is false the pathlen option
|
|
should be omitted.
|
|
|
|
Examples:
|
|
|
|
basicConstraints=CA:TRUE
|
|
basicConstraints=critical,CA:TRUE, pathlen:10
|
|
|
|
NOTE: for a CA to be considered valid it must have the CA option set to
|
|
TRUE. An end user certificate MUST NOT have the CA value set to true.
|
|
According to PKIX recommendations it should exclude the extension entirely
|
|
however some software may require CA set to FALSE for end entity certificates.
|
|
|
|
Subject Key Identifier.
|
|
|
|
This is really a string extension and can take two possible values. Either
|
|
a hex string giving details of the extension value to include or the word
|
|
'hash' which then automatically follow PKIX guidelines in selecting and
|
|
appropriate key identifier. The use of the hex string is strongly discouraged.
|
|
|
|
Example: subjectKeyIdentifier=hash
|
|
|
|
Authority Key Identifier.
|
|
|
|
The authority key identifier extension permits two options. keyid and issuer:
|
|
both can take the optional value "always".
|
|
|
|
If the keyid option is present an attempt is made to copy the subject key
|
|
identifier from the parent certificate. If the value "always" is present
|
|
then an error is returned if the option fails.
|
|
|
|
The issuer option copies the issuer and serial number from the issuer
|
|
certificate. Normally this will only be done if the keyid option fails or
|
|
is not included: the "always" flag will always include the value.
|
|
|
|
Subject Alternative Name.
|
|
|
|
The subject alternative name extension allows various literal values to be
|
|
included in the configuration file. These include "email" (an email address)
|
|
"URI" a uniform resource indicator, "DNS" (a DNS domain name), RID (a
|
|
registered ID: OBJECT IDENTIFIER) and IP (and IP address).
|
|
|
|
Also the email option include a special 'copy' value. This will automatically
|
|
include and email addresses contained in the certificate subject name in
|
|
the extension.
|
|
|
|
Examples:
|
|
|
|
subjectAltName=email:copy,email:my@other.address,URL:http://my.url.here/
|
|
subjectAltName=email:my@other.address,RID:1.2.3.4
|
|
|
|
Issuer Alternative Name.
|
|
|
|
The issuer alternative name option supports all the literal options of
|
|
subject alternative name. It does *not* support the email:copy option because
|
|
that would not make sense. It does support and additional issuer:copy option
|
|
that will copy all the subject alternative name values from the issuer
|
|
certificate (if possible).
|
|
|
|
Display only extensions.
|
|
|
|
Some extensions are only partially supported and currently are only displayed
|
|
but cannot be set. These include private key usage period, CRL number, and
|
|
CRL reason.
|