# CertificatePathValidator.java

    /*
     *  Licensed to the Apache Software Foundation (ASF) under one
     *  or more contributor license agreements.  See the NOTICE file
     *  distributed with this work for additional information
     *  regarding copyright ownership.  The ASF licenses this file
     *  to you under the Apache License, Version 2.0 (the
     *  "License"); you may not use this file except in compliance
     *  with the License.  You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     *  Unless required by applicable law or agreed to in writing,
     *  software distributed under the License is distributed on an
     *   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
     *  KIND, either express or implied.  See the License for the
     *  specific language governing permissions and limitations
     *  under the License.
     */
    package org.apache.synapse.transport.certificatevalidation.pathvalidation;

    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.synapse.transport.certificatevalidation.*;

    import java.security.*;
    import java.security.cert.X509Certificate;
    import java.util.List;
    import java.security.cert.*;
    import java.util.*;

    /**
     * Used to validate the revocation status of a certificate chain acquired from the peer. A revocation verifier
     * (OCSP or CRL) should be given. Must be used only once when validating certificate chain for an SSLSession.
     * Create a new instance if need to be reused because the path validation process is state-full.
     * Not thread safe
     */
    public class CertificatePathValidator {
        private PathChecker pathChecker;

        // Certificate Chain with Root CA certificate (eg: peer cert, issuer cert, root cert)
        List<X509Certificate> fullCertChain;
        // Certificate Chain without Root CA certificate. (eg: peer cert, issuer cert)
        List<X509Certificate> certChain;
        private static final Log log = LogFactory.getLog(CertificatePathValidator.class);

        public CertificatePathValidator(X509Certificate[] certChainArray, RevocationVerifier verifier) {
            this.pathChecker = new PathChecker(certChainArray, verifier);
            init(certChainArray);
        }

        /**
         * Here revocation status checking is started from one below the root certificate in the chain (certChain).
         * Since ssl implementation ensures that at least one certificate in the chain is trusted,
         * we can logically say that the root is trusted.
         */
        private void init(X509Certificate[] certChainArray) {
            X509Certificate[] partCertChainArray = new X509Certificate[certChainArray.length-1];
            System.arraycopy(certChainArray,0,partCertChainArray,0,partCertChainArray.length);
            certChain = Arrays.asList(partCertChainArray);
            fullCertChain = Arrays.asList(certChainArray);

          /*  for (int i = 0; i < certChainArray.length; i++) {
                fullCertChain.add(certChainArray[i]);
                if (i < certChainArray.length - 1)
                    certChain.add(certChainArray[i]);
            }*/
        }

        /**
         * Certificate Path Validation process
         *
         * @throws CertificateVerificationException
         *          if validation process fails.
         */
        public void validatePath() throws Exception {
            String jceProvider = getPreferredJceProvider();
            String providerClass;
            if (jceProvider.equals(Constants.BOUNCY_CASTLE_PROVIDER)) {
                providerClass = "org.bouncycastle.jce.provider.BouncyCastleProvider";
            } else if (jceProvider.equals(Constants.BOUNCY_CASTLE_FIPS_PROVIDER)) {
                providerClass = "org.bouncycastle.jcajce.provider.BouncyCastleFipsProvider";
            } else {
                throw new NoSuchProviderException("Configured JCE provider " + jceProvider + " is not supported");
            }
            Security.addProvider((Provider) Class.forName(providerClass).getDeclaredConstructor().newInstance());
            CollectionCertStoreParameters params = new CollectionCertStoreParameters(fullCertChain);
            try {
                CertStore store = CertStore.getInstance("Collection", params, jceProvider);

                // create certificate path
                CertificateFactory fact = CertificateFactory.getInstance("X.509", jceProvider);

                CertPath certPath = fact.generateCertPath(certChain);
                TrustAnchor trustAnchor = new TrustAnchor(fullCertChain.get(fullCertChain.size() - 1), null);
                Set<TrustAnchor> trust = Collections.singleton(trustAnchor);

                // perform validation
                CertPathValidator validator = CertPathValidator.getInstance("PKIX", jceProvider);
                PKIXParameters param = new PKIXParameters(trust);

                param.addCertPathChecker(pathChecker);
                param.setRevocationEnabled(false);
                param.addCertStore(store);
                param.setDate(new Date());

                validator.validate(certPath, param);

                log.info("Certificate path validated");
            } catch (CertPathValidatorException e) {
                throw new CertificateVerificationException("Certificate Path Validation failed on certificate number "
                        + e.getIndex() + ", details: " + e.getMessage(), e);
            } catch (Exception e) {
                throw new CertificateVerificationException("Certificate Path Validation failed", e);
            }
        }

        /**
         * This method returns the preferred JCE provider to be used.
         *
         * @return
         */
        private static String getPreferredJceProvider() {
            String provider = System.getProperty("security.jce.provider");
            if (provider != null && provider.equalsIgnoreCase(Constants.BOUNCY_CASTLE_FIPS_PROVIDER)) {
                return Constants.BOUNCY_CASTLE_FIPS_PROVIDER;
            }
            return Constants.BOUNCY_CASTLE_PROVIDER;
        }
    }