Improve resilient OCSP certificate revocation checker

[madislm]

AUT-2981

Signed-off-by: Madis Jaagup Laurson <[email protected]>

[mrts]

Should this extend CertificateRevocationCheckFailedException? UserCertificateOCSPException errors prevent determining revocation status and should be caught through that common type.

[mrts]

How about this:

Suggested change

By default, OCSP responder certificates must have the Key Usage extension with Digital Signature. To accept responder certificates that lack the Key Usage extension or do not assert Digital Signature in it, pass `false` as the last `isKeyUsageRequired` argument of the `AiaOcspServiceConfiguration`, `DesignatedOcspServiceConfiguration` or `FallbackOcspServiceConfiguration` constructor. If the Key Usage extension is present, it must still not contain Certificate Signing, the Extended Key Usage extension must still contain OCSP Signing, and the certificate must still not be a CA certificate. For AIA services, the setting applies only to delegated responder certificates, not to the issuer CA signing its own responses. The setting of a fallback configuration does not propagate to its `nextFallbackConfiguration`.

The examples require OCSP responder certificates to have the Key Usage extension. To accept responder certificates that lack the Key Usage extension, pass `false` as the last `isKeyUsageRequired` argument of the `AiaOcspServiceConfiguration`, `DesignatedOcspServiceConfiguration` or `FallbackOcspServiceConfiguration` constructor. If the Key Usage extension is present, it must contain Digital Signature or Non Repudiation and must not contain Certificate Signing. The Extended Key Usage extension must still contain OCSP Signing, and the certificate must still not be a CA certificate. For AIA services, the setting applies only to delegated responder certificates, not to the issuer CA signing its own responses. The setting of a fallback configuration does not propagate to its `nextFallbackConfiguration`.

[mrts]

Suggested change

	true // Require the Key Usage extension with Digital Signature in responder certificates.
	true // Require the Key Usage extension in responder certificates.

[mrts]

Suggested change

	true // Require the Key Usage extension with Digital Signature in responder certificates.
	true // Require the Key Usage extension in responder certificates.

[mrts]

I think validateKeyUsageDigitalSignature() and validateKeyUsageNotCertificateSigning() can be merged into one validateKeyUsageOcspSigning() for consistency:

    /**
     * The flag controls whether Key Usage must be present. If present, Key Usage must include
     * Digital Signature or Non Repudiation and must not include Certificate Signing.
     */
    public static void validateKeyUsageOcspSigning(X509Certificate certificate, boolean isKeyUsageRequired) throws OCSPCertificateException {
        Objects.requireNonNull(certificate, "certificate");
        final boolean[] keyUsage = certificate.getKeyUsage();
        if (keyUsage == null) {
            if (!isKeyUsageRequired) {
                return;
            }
            throw new OCSPCertificateException("Certificate " + certificate.getSubjectX500Principal() +
                " does not contain the Key Usage extension required for OCSP response signing");
        }
        final boolean hasDigitalSignature = keyUsage.length > KEY_USAGE_DIGITAL_SIGNATURE_BIT_INDEX
            && keyUsage[KEY_USAGE_DIGITAL_SIGNATURE_BIT_INDEX];
        // RFC 5280 section 4.2.1.12 also permits Non Repudiation for OCSP signing.
        final boolean hasNonRepudiation = keyUsage.length > KEY_USAGE_NON_REPUDIATION_BIT_INDEX
            && keyUsage[KEY_USAGE_NON_REPUDIATION_BIT_INDEX];
        if (!hasDigitalSignature && !hasNonRepudiation) {
            throw new OCSPCertificateException("Certificate " + certificate.getSubjectX500Principal() +
                " Key Usage extension does not contain Digital Signature or Non Repudiation, which is required for OCSP response signing");
        }
        if (keyUsage.length > KEY_USAGE_KEY_CERT_SIGN_BIT_INDEX && keyUsage[KEY_USAGE_KEY_CERT_SIGN_BIT_INDEX]) {
            throw new OCSPCertificateException("Certificate " + certificate.getSubjectX500Principal() +
                " Key Usage extension contains Certificate Signing, which is not allowed for OCSP responder");
        }
    }