JEP 124: Enhance the Certificate Revocation-Checking API

Revocation checking is the mechanism to determine the revocation status of a certificate. If it is revoked, it is considered invalid and should not be used. Currently as of JDK 7, the PKIX implementation of java.security.cert.CertPathValidator  includes a revocation checking implementation that supports both OCSP and CRLs, the two main methods of checking revocation. However, there are very few options that allow you to configure the behavior. You can always implement your own revocation checker, but that's a lot of work.

JEP 124 (Enhance the Certificate Revocation-Checking API) is one of the 11 new security features in JDK 8. This feature enhances the java.security.cert API to support various revocation settings such as best-effort checking, end-entity certificate checking, and mechanism-specific options and parameters. Let's describe each of these in more detail and show some examples.

The features are provided through a new class named PKIXRevocationChecker. A PKIXRevocationChecker instance is returned by a PKIX CertPathValidator as follows:

CertPathValidator cpv = CertPathValidator.getInstance("PKIX");
PKIXRevocationChecker prc = (PKIXRevocationChecker)cpv.getRevocationChecker();

You can now set various revocation options by calling different methods of the returned PKIXRevocationChecker object. For example, the best-effort option (called soft-fail) allows the revocation check to succeed if the status cannot be obtained due to a network connection failure or an overloaded server. It is enabled as follows:

prc.setOptions(Enum.setOf(Option.SOFT_FAIL)); 

When the SOFT_FAIL option is specified, you can still obtain any exceptions that may have been thrown due to network issues. This can be useful if you want to log this information or treat it as a warning. You can obtain these exceptions by calling the getSoftFailExceptions method:

List<CertPathValidatorException> exceptions = prc.getSoftFailExceptions();

Another new option called ONLY_END_ENTITY allows you to only check the revocation status of the end-entity certificate. This can improve performance, but you should be careful using this option, as the revocation status of CA certificates will not be checked. To set more than one option, simply specify them together, for example:

prc.setOptions(Enum.setOf(Option.SOFT_FAIL, Option.ONLY_END_ENTITY));

By default, PKIXRevocationChecker will try to check the revocation status of a certificate using OCSP first, and then CRLs as a fallback. However, you can switch the order using the PREFER_CRLS option, or disable the fallback altogether using the NO_FALLBACK option. For example, here is how you would only use CRLs to check the revocation status:

prc.setOptions(Enum.setOf(Option.PREFER_CRLS, Option.NO_FALLBACK));

There are also a number of other useful methods which allow you to specify various options such as the OCSP responder URI, the trusted OCSP responder certificate, and OCSP request extensions. However, one of the most useful features is the ability to specify a cached OCSP response with the setOCSPResponse method. This can be quite useful if the OCSPResponse has already been obtained, for example in a protocol that uses OCSP stapling.

After you have set all of your preferred options, you must add the PKIXRevocationChecker to your PKIXParameters object as one of your custom CertPathCheckers before you validate the certificate chain, as follows:

PKIXParameters params = new PKIXParameters(keystore);
params.addCertPathChecker(prc);
CertPathValidatorResult result = cpv.validate(path, params);

Early access binaries of JDK 8 can be downloaded from http://jdk8.java.net/download.html

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Sean Mullan

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