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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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package sun.security.validator;

import java.util.*;

import java.security.*;
import java.security.cert.*;

import javax.security.auth.x500.X500Principal;
import sun.security.action.GetBooleanAction;
import sun.security.provider.certpath.AlgorithmChecker;
import sun.security.provider.certpath.PKIXExtendedParameters;
import sun.security.util.SecurityProperties;

/**
 * Validator implementation built on the PKIX CertPath API. This
 * implementation will be emphasized going forward.
 * <p>
 * Note that the validate() implementation tries to use a PKIX validator
 * if that appears possible and a PKIX builder otherwise. This increases
 * performance and currently also leads to better exception messages
 * in case of failures.
 * <p>
 * {@code PKIXValidator} objects are immutable once they have been created.
 * Please DO NOT add methods that can change the state of an instance once
 * it has been created.
 *
 * @author Andreas Sterbenz
 */
public final class PKIXValidator extends Validator {

    /**
     * Flag indicating whether to enable revocation check for the PKIX trust
     * manager. Typically, this will only work if the PKIX implementation
     * supports CRL distribution points as we do not manually setup CertStores.
     */
    private final static boolean checkTLSRevocation =
        AccessController.doPrivileged
            (new GetBooleanAction("com.sun.net.ssl.checkRevocation"));

    // enable use of the validator if possible
    private final static boolean TRY_VALIDATOR = true;

    /**
     * System or security property that if set (or set to "true"), allows trust
     * anchor certificates to be used if they do not have the proper CA
     * extensions. Set to false if prop is not set, or set to any other value.
     */
    private static final boolean ALLOW_NON_CA_ANCHOR = allowNonCaAnchor();
    private static boolean allowNonCaAnchor() {
        String prop = SecurityProperties
                .privilegedGetOverridable("jdk.security.allowNonCaAnchor");
        return prop != null && (prop.isEmpty() || prop.equalsIgnoreCase("true"));
    }

    private final Set<X509Certificate> trustedCerts;
    private final PKIXBuilderParameters parameterTemplate;
    private int certPathLength = -1;

    // needed only for the validator
    private final Map<X500Principal, List<PublicKey>> trustedSubjects;
    private final CertificateFactory factory;

    private final boolean plugin;

    PKIXValidator(String variant, Collection<X509Certificate> trustedCerts) {
        super(TYPE_PKIX, variant);
        if (trustedCerts instanceof Set) {
            this.trustedCerts = (Set<X509Certificate>)trustedCerts;
        } else {
            this.trustedCerts = new HashSet<X509Certificate>(trustedCerts);
        }
        Set<TrustAnchor> trustAnchors = new HashSet<TrustAnchor>();
        for (X509Certificate cert : trustedCerts) {
            trustAnchors.add(new TrustAnchor(cert, null));
        }
        try {
            parameterTemplate = new PKIXBuilderParameters(trustAnchors, null);
        } catch (InvalidAlgorithmParameterException e) {
            throw new RuntimeException("Unexpected error: " + e.toString(), e);
        }
        setDefaultParameters(variant);

        // initCommon();
        if (TRY_VALIDATOR) {
            if (TRY_VALIDATOR == false) {
                return;
            }
            trustedSubjects = new HashMap<X500Principal, List<PublicKey>>();
            for (X509Certificate cert : trustedCerts) {
                X500Principal dn = cert.getSubjectX500Principal();
                List<PublicKey> keys;
                if (trustedSubjects.containsKey(dn)) {
                    keys = trustedSubjects.get(dn);
                } else {
                    keys = new ArrayList<PublicKey>();
                    trustedSubjects.put(dn, keys);
                }
                keys.add(cert.getPublicKey());
            }
            try {
                factory = CertificateFactory.getInstance("X.509");
            } catch (CertificateException e) {
                throw new RuntimeException("Internal error", e);
            }
            plugin = variant.equals(VAR_PLUGIN_CODE_SIGNING);
        } else {
            plugin = false;
        }
    }

    PKIXValidator(String variant, PKIXBuilderParameters params) {
        super(TYPE_PKIX, variant);
        trustedCerts = new HashSet<X509Certificate>();
        for (TrustAnchor anchor : params.getTrustAnchors()) {
            X509Certificate cert = anchor.getTrustedCert();
            if (cert != null) {
                trustedCerts.add(cert);
            }
        }
        parameterTemplate = params;

        // initCommon();
        if (TRY_VALIDATOR) {
            if (TRY_VALIDATOR == false) {
                return;
            }
            trustedSubjects = new HashMap<X500Principal, List<PublicKey>>();
            for (X509Certificate cert : trustedCerts) {
                X500Principal dn = cert.getSubjectX500Principal();
                List<PublicKey> keys;
                if (trustedSubjects.containsKey(dn)) {
                    keys = trustedSubjects.get(dn);
                } else {
                    keys = new ArrayList<PublicKey>();
                    trustedSubjects.put(dn, keys);
                }
                keys.add(cert.getPublicKey());
            }
            try {
                factory = CertificateFactory.getInstance("X.509");
            } catch (CertificateException e) {
                throw new RuntimeException("Internal error", e);
            }
            plugin = variant.equals(VAR_PLUGIN_CODE_SIGNING);
        } else {
            plugin = false;
        }
    }

    public Collection<X509Certificate> getTrustedCertificates() {
        return trustedCerts;
    }

    /**
     * Returns the length of the last certification path that is validated by
     * CertPathValidator. This is intended primarily as a callback mechanism
     * for PKIXCertPathCheckers to determine the length of the certification
     * path that is being validated. It is necessary since engineValidate()
     * may modify the length of the path.
     *
     * @return the length of the last certification path passed to
     *   CertPathValidator.validate, or -1 if it has not been invoked yet
     */
    public int getCertPathLength() { // mutable, should be private
        return certPathLength;
    }

    /**
     * Set J2SE global default PKIX parameters. Currently, hardcoded to disable
     * revocation checking. In the future, this should be configurable.
     */
    private void setDefaultParameters(String variant) {
        if ((variant == Validator.VAR_TLS_SERVER) ||
                (variant == Validator.VAR_TLS_CLIENT)) {
            parameterTemplate.setRevocationEnabled(checkTLSRevocation);
        } else {
            parameterTemplate.setRevocationEnabled(false);
        }
    }

    /**
     * Return the PKIX parameters used by this instance. An application may
     * modify the parameters but must make sure not to perform any concurrent
     * validations.
     */
    public PKIXBuilderParameters getParameters() { // mutable, should be private
        return parameterTemplate;
    }

    @Override
    X509Certificate[] engineValidate(X509Certificate[] chain,
            Collection<X509Certificate> otherCerts,
            List<byte[]> responseList,
            AlgorithmConstraints constraints,
            Object parameter) throws CertificateException {
        if ((chain == null) || (chain.length == 0)) {
            throw new CertificateException
                ("null or zero-length certificate chain");
        }


        // Use PKIXExtendedParameters for timestamp and variant additions
        PKIXBuilderParameters pkixParameters = null;
        try {
            pkixParameters = new PKIXExtendedParameters(
                    (PKIXBuilderParameters) parameterTemplate.clone(),
                    (parameter instanceof Timestamp) ?
                            (Timestamp) parameter : null,
                    variant);
        } catch (InvalidAlgorithmParameterException e) {
            // ignore exception
        }

        // add a new algorithm constraints checker
        if (constraints != null) {
            pkixParameters.addCertPathChecker(
                    new AlgorithmChecker(constraints, variant));
        }

        // attach it to the PKIXBuilderParameters.
        if (!responseList.isEmpty()) {
            addResponses(pkixParameters, chain, responseList);
        }

        if (TRY_VALIDATOR) {
            // check that chain is in correct order and check if chain contains
            // trust anchor
            X500Principal prevIssuer = null;
            for (int i = 0; i < chain.length; i++) {
                X509Certificate cert = chain[i];
                X500Principal dn = cert.getSubjectX500Principal();

                if (i == 0) {
                    if (trustedCerts.contains(cert)) {
                        return new X509Certificate[] {chain[0]};
                    }
                } else {
                    if (!dn.equals(prevIssuer)) {
                        // chain is not ordered correctly, call builder instead
                        return doBuild(chain, otherCerts, pkixParameters);
                    }
                    // Check if chain[i] is already trusted. It may be inside
                    // trustedCerts, or has the same dn and public key as a cert
                    // inside trustedCerts. The latter happens when a CA has
                    // updated its cert with a stronger signature algorithm in JRE
                    // but the weak one is still in circulation.
                    if (trustedCerts.contains(cert) ||          // trusted cert
                            (trustedSubjects.containsKey(dn) && // replacing ...
                             trustedSubjects.get(dn).contains(  // ... weak cert
                                cert.getPublicKey()))) {
                        // Remove and call validator on partial chain [0 .. i-1]
                        X509Certificate[] newChain = new X509Certificate[i];
                        System.arraycopy(chain, 0, newChain, 0, i);
                        return doValidate(newChain, pkixParameters);
                    }
                }
                prevIssuer = cert.getIssuerX500Principal();
            }

            // apparently issued by trust anchor?
            X509Certificate last = chain[chain.length - 1];
            X500Principal issuer = last.getIssuerX500Principal();
            X500Principal subject = last.getSubjectX500Principal();
            if (trustedSubjects.containsKey(issuer) &&
                    isSignatureValid(trustedSubjects.get(issuer), last)) {
                return doValidate(chain, pkixParameters);
            }

            // don't fallback to builder if called from plugin/webstart
            if (plugin) {
                // Validate chain even if no trust anchor is found. This
                // allows plugin/webstart to make sure the chain is
                // otherwise valid
                if (chain.length > 1) {
                    X509Certificate[] newChain =
                        new X509Certificate[chain.length-1];
                    System.arraycopy(chain, 0, newChain, 0, newChain.length);

                    // temporarily set last cert as sole trust anchor
                    try {
                        pkixParameters.setTrustAnchors
                            (Collections.singleton(new TrustAnchor
                                (chain[chain.length-1], null)));
                    } catch (InvalidAlgorithmParameterException iape) {
                        // should never occur, but ...
                        throw new CertificateException(iape);
                    }
                    doValidate(newChain, pkixParameters);
                }
                // if the rest of the chain is valid, throw exception
                // indicating no trust anchor was found
                throw new ValidatorException
                    (ValidatorException.T_NO_TRUST_ANCHOR);
            }
            // otherwise, fall back to builder
        }

        return doBuild(chain, otherCerts, pkixParameters);
    }

    private boolean isSignatureValid(List<PublicKey> keys,
            X509Certificate sub) {
        if (plugin) {
            for (PublicKey key: keys) {
                try {
                    sub.verify(key);
                    return true;
                } catch (Exception ex) {
                    continue;
                }
            }
            return false;
        }
        return true; // only check if PLUGIN is set
    }

    private static X509Certificate[] toArray(CertPath path, TrustAnchor anchor)
            throws CertificateException {
        X509Certificate trustedCert = anchor.getTrustedCert();
        if (trustedCert == null) {
            throw new ValidatorException
                ("TrustAnchor must be specified as certificate");
        }

        verifyTrustAnchor(trustedCert);

        List<? extends java.security.cert.Certificate> list =
                                                path.getCertificates();
        X509Certificate[] chain = new X509Certificate[list.size() + 1];
        list.toArray(chain);
        chain[chain.length - 1] = trustedCert;
        return chain;
    }

    /**
     * Set the check date (for debugging).
     */
    private void setDate(PKIXBuilderParameters params) {
        @SuppressWarnings("deprecation")
        Date date = validationDate;
        if (date != null) {
            params.setDate(date);
        }
    }

    private X509Certificate[] doValidate(X509Certificate[] chain,
            PKIXBuilderParameters params) throws CertificateException {
        try {
            setDate(params);

            // do the validation
            CertPathValidator validator = CertPathValidator.getInstance("PKIX");
            CertPath path = factory.generateCertPath(Arrays.asList(chain));
            certPathLength = chain.length;
            PKIXCertPathValidatorResult result =
                (PKIXCertPathValidatorResult)validator.validate(path, params);

            return toArray(path, result.getTrustAnchor());
        } catch (GeneralSecurityException e) {
            throw new ValidatorException
                ("PKIX path validation failed: " + e.toString(), e);
        }
    }

    /**
     * Verify that a trust anchor certificate is a CA certificate.
     */
    private static void verifyTrustAnchor(X509Certificate trustedCert)
        throws ValidatorException {

        // skip check if jdk.security.allowNonCAAnchor system property is set
        if (ALLOW_NON_CA_ANCHOR) {
            return;
        }

        // allow v1 trust anchor certificates
        if (trustedCert.getVersion() < 3) {
            return;
        }

        // check that the BasicConstraints cA field is not set to false
        if (trustedCert.getBasicConstraints() == -1) {
            throw new ValidatorException
                ("TrustAnchor with subject \"" +
                 trustedCert.getSubjectX500Principal() +
                 "\" is not a CA certificate");
        }

        // check that the KeyUsage extension, if included, asserts the
        // keyCertSign bit
        boolean[] keyUsageBits = trustedCert.getKeyUsage();
        if (keyUsageBits != null && !keyUsageBits[5]) {
            throw new ValidatorException
                ("TrustAnchor with subject \"" +
                 trustedCert.getSubjectX500Principal() +
                 "\" does not have keyCertSign bit set in KeyUsage extension");
        }
    }

    private X509Certificate[] doBuild(X509Certificate[] chain,
        Collection<X509Certificate> otherCerts,
        PKIXBuilderParameters params) throws CertificateException {

        try {
            setDate(params);

            // setup target constraints
            X509CertSelector selector = new X509CertSelector();
            selector.setCertificate(chain[0]);
            params.setTargetCertConstraints(selector);

            // setup CertStores
            Collection<X509Certificate> certs =
                                        new ArrayList<X509Certificate>();
            certs.addAll(Arrays.asList(chain));
            if (otherCerts != null) {
                certs.addAll(otherCerts);
            }
            CertStore store = CertStore.getInstance("Collection",
                                new CollectionCertStoreParameters(certs));
            params.addCertStore(store);

            // do the build
            CertPathBuilder builder = CertPathBuilder.getInstance("PKIX");
            PKIXCertPathBuilderResult result =
                (PKIXCertPathBuilderResult)builder.build(params);

            return toArray(result.getCertPath(), result.getTrustAnchor());
        } catch (GeneralSecurityException e) {
            throw new ValidatorException
                ("PKIX path building failed: " + e.toString(), e);
        }
    }

    /**
     * For OCSP Stapling, add responses that came in during the handshake
     * into a {@code PKIXRevocationChecker} so we can evaluate them.
     *
     * @param pkixParams the pkixParameters object that will be used in
     * path validation.
     * @param chain the chain of certificates to verify
     * @param responseList a {@code List} of zero or more byte arrays, each
     * one being a DER-encoded OCSP response (per RFC 6960).  Entries
     * in the List must match the order of the certificates in the
     * chain parameter.
     */
    private static void addResponses(PKIXBuilderParameters pkixParams,
            X509Certificate[] chain, List<byte[]> responseList) {

        if (pkixParams.isRevocationEnabled()) {
            try {
                // Make a modifiable copy of the CertPathChecker list
                PKIXRevocationChecker revChecker = null;
                List<PKIXCertPathChecker> checkerList =
                        new ArrayList<>(pkixParams.getCertPathCheckers());

                // Find the first PKIXRevocationChecker in the list
                for (PKIXCertPathChecker checker : checkerList) {
                    if (checker instanceof PKIXRevocationChecker) {
                        revChecker = (PKIXRevocationChecker)checker;
                        break;
                    }
                }

                // If we still haven't found one, make one
                if (revChecker == null) {
                    revChecker = (PKIXRevocationChecker)CertPathValidator.
                            getInstance("PKIX").getRevocationChecker();
                    checkerList.add(revChecker);
                }

                // Each response in the list should be in parallel with
                // the certificate list.  If there is a zero-length response
                // treat it as being absent.  If the user has provided their
                // own PKIXRevocationChecker with pre-populated responses, do
                // not overwrite them with the ones from the handshake.
                Map<X509Certificate, byte[]> responseMap =
                        revChecker.getOcspResponses();
                int limit = Integer.min(chain.length, responseList.size());
                for (int idx = 0; idx < limit; idx++) {
                    byte[] respBytes = responseList.get(idx);
                    if (respBytes != null && respBytes.length > 0 &&
                            !responseMap.containsKey(chain[idx])) {
                        responseMap.put(chain[idx], respBytes);
                    }
                }

                // Add the responses and push it all back into the
                // PKIXBuilderParameters
                revChecker.setOcspResponses(responseMap);
                pkixParams.setCertPathCheckers(checkerList);
            } catch (NoSuchAlgorithmException exc) {
                // This should not occur, but if it does happen then
                // stapled OCSP responses won't be part of revocation checking.
                // Clients can still fall back to other means of revocation
                // checking.
            }
        }
    }
}
