AI-generated Key Takeaways
-
The
X509Extension
interface defines methods for handling extensions in X.509 v3 certificates and v2 CRLs (Certificate Revocation Lists), allowing for the inclusion of additional attributes and management of the certification hierarchy. -
Extensions can be marked as critical or non-critical, with critical extensions requiring recognition by certificate/CRL-using systems to avoid rejection.
-
The
getExtensionValue
method provides access to the DER-encoded OCTET STRING of an extension value, which can be processed by classes understanding the specific extension type. -
The interface includes methods to retrieve sets of critical and non-critical extension OIDs and to check for the presence of unsupported critical extensions.
Known Indirect Subclasses |
Interface for an X.509 extension.
The extensions defined for X.509 v3
Certificates
and v2
CRLs
(Certificate Revocation
Lists) provide methods
for associating additional attributes with users or public keys,
for managing the certification hierarchy, and for managing CRL
distribution. The X.509 extensions format also allows communities
to define private extensions to carry information unique to those
communities.
Each extension in a certificate/CRL may be designated as critical or non-critical. A certificate/CRL-using system (an application validating a certificate/CRL) must reject the certificate/CRL if it encounters a critical extension it does not recognize. A non-critical extension may be ignored if it is not recognized.
The ASN.1 definition for this is:
Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension Extension ::= SEQUENCE { extnId OBJECT IDENTIFIER, critical BOOLEAN DEFAULT FALSE, extnValue OCTET STRING -- contains a DER encoding of a value -- of the type registered for use with -- the extnId object identifier value }
getExtensionValue
method returns the DER-encoded OCTET STRING of the
extension value (i.e., the extnValue
). This can then
be handled by a Class that understands the extension.
Public Method Summary
abstract Set<String> |
getCriticalExtensionOIDs()
Gets a Set of the OID strings for the extension(s) marked
CRITICAL in the certificate/CRL managed by the object
implementing this interface.
|
abstract byte[] |
getExtensionValue(String oid)
Gets the DER-encoded OCTET string for the extension value
(extnValue) identified by the passed-in
oid
String. |
abstract Set<String> |
getNonCriticalExtensionOIDs()
Gets a Set of the OID strings for the extension(s) marked
NON-CRITICAL in the certificate/CRL managed by the object
implementing this interface.
|
abstract boolean |
hasUnsupportedCriticalExtension()
Check if there is a critical extension that is not supported.
|
Public Methods
public abstract Set<String> getCriticalExtensionOIDs ()
Gets a Set of the OID strings for the extension(s) marked CRITICAL in the certificate/CRL managed by the object implementing this interface. Here is sample code to get a Set of critical extensions from an X509Certificate and print the OIDs:
X509Certificate cert = null;
try (InputStream inStrm = new FileInputStream("DER-encoded-Cert")) {
CertificateFactory cf = CertificateFactory.getInstance("X.509");
cert = (X509Certificate)cf.generateCertificate(inStrm);
}
Set<String> critSet = cert.getCriticalExtensionOIDs();
if (critSet != null && !critSet.isEmpty()) {
System.out.println("Set of critical extensions:");
for (String oid : critSet) {
System.out.println(oid);
}
}
Returns
- a Set (or an empty Set if none are marked critical) of the extension OID strings for extensions that are marked critical. If there are no extensions present at all, then this method returns null.
public abstract byte[] getExtensionValue (String oid)
Gets the DER-encoded OCTET string for the extension value
(extnValue) identified by the passed-in oid
String.
The oid
string is
represented by a set of nonnegative whole numbers separated
by periods.
For example:
OID (Object Identifier) | Extension Name |
---|---|
2.5.29.14 | SubjectKeyIdentifier |
2.5.29.15 | KeyUsage |
2.5.29.16 | PrivateKeyUsage |
2.5.29.17 | SubjectAlternativeName |
2.5.29.18 | IssuerAlternativeName |
2.5.29.19 | BasicConstraints |
2.5.29.30 | NameConstraints |
2.5.29.33 | PolicyMappings |
2.5.29.35 | AuthorityKeyIdentifier |
2.5.29.36 | PolicyConstraints |
Parameters
oid | the Object Identifier value for the extension. |
---|
Returns
- the DER-encoded octet string of the extension value or null if it is not present.
public abstract Set<String> getNonCriticalExtensionOIDs ()
Gets a Set of the OID strings for the extension(s) marked NON-CRITICAL in the certificate/CRL managed by the object implementing this interface. Here is sample code to get a Set of non-critical extensions from an X509CRL revoked certificate entry and print the OIDs:
CertificateFactory cf = null;
X509CRL crl = null;
try (InputStream inStrm = new FileInputStream("DER-encoded-CRL")) {
cf = CertificateFactory.getInstance("X.509");
crl = (X509CRL)cf.generateCRL(inStrm);
}
byte[] certData = <DER-encoded certificate data>
ByteArrayInputStream bais = new ByteArrayInputStream(certData);
X509Certificate cert = (X509Certificate)cf.generateCertificate(bais);
X509CRLEntry badCert =
crl.getRevokedCertificate(cert.getSerialNumber());
if (badCert != null) {
Set<String> nonCritSet = badCert.getNonCriticalExtensionOIDs();
if (nonCritSet != null)
for (String oid : nonCritSet) {
System.out.println(oid);
}
}
Returns
- a Set (or an empty Set if none are marked non-critical) of the extension OID strings for extensions that are marked non-critical. If there are no extensions present at all, then this method returns null.
public abstract boolean hasUnsupportedCriticalExtension ()
Check if there is a critical extension that is not supported.
Returns
true
if a critical extension is found that is not supported, otherwisefalse
.