/*
 * Copyright (c) 2002, 2012, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * 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).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.security.validator;

import java.io.IOException;
import java.util.*;

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

import javax.security.auth.x500.X500Principal;

import sun.security.x509.X509CertImpl;
import sun.security.x509.NetscapeCertTypeExtension;
import sun.security.util.DerValue;
import sun.security.util.DerInputStream;
import sun.security.util.DerOutputStream;
import sun.security.util.ObjectIdentifier;

import sun.security.provider.certpath.AlgorithmChecker;
import sun.security.provider.certpath.UntrustedChecker;

/**
 * A simple validator implementation. It is based on code from the JSSE
 * X509TrustManagerImpl. This implementation is designed for compatibility with
 * deployed certificates and previous J2SE versions. It will never support
 * more advanced features and will be deemphasized in favor of the PKIX
 * validator going forward.
 * <p>
 * {@code SimpleValidator} 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 SimpleValidator extends Validator {

    // Constants for the OIDs we need

    final static String OID_BASIC_CONSTRAINTS = "2.5.29.19";

    final static String OID_NETSCAPE_CERT_TYPE = "2.16.840.1.113730.1.1";

    final static String OID_KEY_USAGE = "2.5.29.15";

    final static String OID_EXTENDED_KEY_USAGE = "2.5.29.37";

    final static String OID_EKU_ANY_USAGE = "2.5.29.37.0";

    final static ObjectIdentifier OBJID_NETSCAPE_CERT_TYPE =
        NetscapeCertTypeExtension.NetscapeCertType_Id;

    private final static String NSCT_SSL_CA =
                                NetscapeCertTypeExtension.SSL_CA;

    private final static String NSCT_CODE_SIGNING_CA =
                                NetscapeCertTypeExtension.OBJECT_SIGNING_CA;

    /**
     * The trusted certificates as:
     * Map (X500Principal)subject of trusted cert -> List of X509Certificate
     * The list is used because there may be multiple certificates
     * with an identical subject DN.
     */
    private final Map<X500Principal, List<X509Certificate>>
                                            trustedX500Principals;

    /**
     * Set of the trusted certificates. Present only for
     * getTrustedCertificates().
     */
    private final Collection<X509Certificate> trustedCerts;

    SimpleValidator(String variant, Collection<X509Certificate> trustedCerts) {
        super(TYPE_SIMPLE, variant);
        this.trustedCerts = trustedCerts;
        trustedX500Principals =
                        new HashMap<X500Principal, List<X509Certificate>>();
        for (X509Certificate cert : trustedCerts) {
            X500Principal principal = cert.getSubjectX500Principal();
            List<X509Certificate> list = trustedX500Principals.get(principal);
            if (list == null) {
                // this actually should be a set, but duplicate entries
                // are not a problem and we can avoid the Set overhead
                list = new ArrayList<X509Certificate>(2);
                trustedX500Principals.put(principal, list);
            }
            list.add(cert);
        }
    }

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

    /**
     * Perform simple validation of chain. The arguments otherCerts and
     * parameter are ignored.
     */
    @Override
    X509Certificate[] engineValidate(X509Certificate[] chain,
            Collection<X509Certificate> otherCerts,
            AlgorithmConstraints constraints,
            Object parameter) throws CertificateException {
        if ((chain == null) || (chain.length == 0)) {
            throw new CertificateException
                ("null or zero-length certificate chain");
        }

        // make sure chain includes a trusted cert
        chain = buildTrustedChain(chain);

        Date date = validationDate;
        if (date == null) {
            date = new Date();
        }

        // create distrusted certificates checker
        UntrustedChecker untrustedChecker = new UntrustedChecker();

        // create default algorithm constraints checker
        TrustAnchor anchor = new TrustAnchor(chain[chain.length - 1], null);
        AlgorithmChecker defaultAlgChecker = new AlgorithmChecker(anchor);

        // create application level algorithm constraints checker
        AlgorithmChecker appAlgChecker = null;
        if (constraints != null) {
            appAlgChecker = new AlgorithmChecker(anchor, constraints);
        }

        // verify top down, starting at the certificate issued by
        // the trust anchor
        int maxPathLength = chain.length - 1;
        for (int i = chain.length - 2; i >= 0; i--) {
            X509Certificate issuerCert = chain[i + 1];
            X509Certificate cert = chain[i];

            // check untrusted certificate
            try {
                // Untrusted checker does not care about the unresolved
                // critical extensions.
                untrustedChecker.check(cert, Collections.<String>emptySet());
            } catch (CertPathValidatorException cpve) {
                throw new ValidatorException(
                    "Untrusted certificate: " + cert.getSubjectX500Principal(),
                    ValidatorException.T_UNTRUSTED_CERT, cert, cpve);
            }

            // check certificate algorithm
            try {
                // Algorithm checker does not care about the unresolved
                // critical extensions.
                defaultAlgChecker.check(cert, Collections.<String>emptySet());
                if (appAlgChecker != null) {
                    appAlgChecker.check(cert, Collections.<String>emptySet());
                }
            } catch (CertPathValidatorException cpve) {
                throw new ValidatorException
                        (ValidatorException.T_ALGORITHM_DISABLED, cert, cpve);
            }

            // no validity check for code signing certs
            if ((variant.equals(VAR_CODE_SIGNING) == false)
                        && (variant.equals(VAR_JCE_SIGNING) == false)) {
                cert.checkValidity(date);
            }

            // check name chaining
            if (cert.getIssuerX500Principal().equals(
                        issuerCert.getSubjectX500Principal()) == false) {
                throw new ValidatorException
                        (ValidatorException.T_NAME_CHAINING, cert);
            }

            // check signature
            try {
                cert.verify(issuerCert.getPublicKey());
            } catch (GeneralSecurityException e) {
                throw new ValidatorException
                        (ValidatorException.T_SIGNATURE_ERROR, cert, e);
            }

            // check extensions for CA certs
            if (i != 0) {
                maxPathLength = checkExtensions(cert, maxPathLength);
            }
        }

        return chain;
    }

    private int checkExtensions(X509Certificate cert, int maxPathLen)
            throws CertificateException {
        Set<String> critSet = cert.getCriticalExtensionOIDs();
        if (critSet == null) {
            critSet = Collections.<String>emptySet();
        }

        // Check the basic constraints extension
        int pathLenConstraint =
                checkBasicConstraints(cert, critSet, maxPathLen);

        // Check the key usage and extended key usage extensions
        checkKeyUsage(cert, critSet);

        // check Netscape certificate type extension
        checkNetscapeCertType(cert, critSet);

        if (!critSet.isEmpty()) {
            throw new ValidatorException
                ("Certificate contains unknown critical extensions: " + critSet,
                ValidatorException.T_CA_EXTENSIONS, cert);
        }

        return pathLenConstraint;
    }

    private void checkNetscapeCertType(X509Certificate cert,
            Set<String> critSet) throws CertificateException {
        if (variant.equals(VAR_GENERIC)) {
            // nothing
        } else if (variant.equals(VAR_TLS_CLIENT)
                || variant.equals(VAR_TLS_SERVER)) {
            if (getNetscapeCertTypeBit(cert, NSCT_SSL_CA) == false) {
                throw new ValidatorException
                        ("Invalid Netscape CertType extension for SSL CA "
                        + "certificate",
                        ValidatorException.T_CA_EXTENSIONS, cert);
            }
            critSet.remove(OID_NETSCAPE_CERT_TYPE);
        } else if (variant.equals(VAR_CODE_SIGNING)
                || variant.equals(VAR_JCE_SIGNING)) {
            if (getNetscapeCertTypeBit(cert, NSCT_CODE_SIGNING_CA) == false) {
                throw new ValidatorException
                        ("Invalid Netscape CertType extension for code "
                        + "signing CA certificate",
                        ValidatorException.T_CA_EXTENSIONS, cert);
            }
            critSet.remove(OID_NETSCAPE_CERT_TYPE);
        } else {
            throw new CertificateException("Unknown variant " + variant);
        }
    }

    /**
     * Get the value of the specified bit in the Netscape certificate type
     * extension. If the extension is not present at all, we return true.
     */
    static boolean getNetscapeCertTypeBit(X509Certificate cert, String type) {
        try {
            NetscapeCertTypeExtension ext;
            if (cert instanceof X509CertImpl) {
                X509CertImpl certImpl = (X509CertImpl)cert;
                ObjectIdentifier oid = OBJID_NETSCAPE_CERT_TYPE;
                ext = (NetscapeCertTypeExtension)certImpl.getExtension(oid);
                if (ext == null) {
                    return true;
                }
            } else {
                byte[] extVal = cert.getExtensionValue(OID_NETSCAPE_CERT_TYPE);
                if (extVal == null) {
                    return true;
                }
                DerInputStream in = new DerInputStream(extVal);
                byte[] encoded = in.getOctetString();
                encoded = new DerValue(encoded).getUnalignedBitString()
                                                                .toByteArray();
                ext = new NetscapeCertTypeExtension(encoded);
            }
            Boolean val = (Boolean)ext.get(type);
            return val.booleanValue();
        } catch (IOException e) {
            return false;
        }
    }

    private int checkBasicConstraints(X509Certificate cert,
            Set<String> critSet, int maxPathLen) throws CertificateException {

        critSet.remove(OID_BASIC_CONSTRAINTS);
        int constraints = cert.getBasicConstraints();
        // reject, if extension missing or not a CA (constraints == -1)
        if (constraints < 0) {
            throw new ValidatorException("End user tried to act as a CA",
                ValidatorException.T_CA_EXTENSIONS, cert);
        }

        // if the certificate is self-issued, ignore the pathLenConstraint
        // checking.
        if (!X509CertImpl.isSelfIssued(cert)) {
            if (maxPathLen <= 0) {
                throw new ValidatorException("Violated path length constraints",
                    ValidatorException.T_CA_EXTENSIONS, cert);
            }

            maxPathLen--;
        }

        if (maxPathLen > constraints) {
            maxPathLen = constraints;
        }

        return maxPathLen;
    }

    /*
     * Verify the key usage and extended key usage for intermediate
     * certificates.
     */
    private void checkKeyUsage(X509Certificate cert, Set<String> critSet)
            throws CertificateException {

        critSet.remove(OID_KEY_USAGE);
        // EKU irrelevant in CA certificates
        critSet.remove(OID_EXTENDED_KEY_USAGE);

        // check key usage extension
        boolean[] keyUsageInfo = cert.getKeyUsage();
        if (keyUsageInfo != null) {
            // keyUsageInfo[5] is for keyCertSign.
            if ((keyUsageInfo.length < 6) || (keyUsageInfo[5] == false)) {
                throw new ValidatorException
                        ("Wrong key usage: expected keyCertSign",
                        ValidatorException.T_CA_EXTENSIONS, cert);
            }
        }
    }

    /**
     * Build a trusted certificate chain. This method always returns a chain
     * with a trust anchor as the final cert in the chain. If no trust anchor
     * could be found, a CertificateException is thrown.
     */
    private X509Certificate[] buildTrustedChain(X509Certificate[] chain)
            throws CertificateException {
        List<X509Certificate> c = new ArrayList<X509Certificate>(chain.length);
        // scan chain starting at EE cert
        // if a trusted certificate is found, append it and return
        for (int i = 0; i < chain.length; i++) {
            X509Certificate cert = chain[i];
            X509Certificate trustedCert = getTrustedCertificate(cert);
            if (trustedCert != null) {
                c.add(trustedCert);
                return c.toArray(CHAIN0);
            }
            c.add(cert);
        }

        // check if we can append a trusted cert
        X509Certificate cert = chain[chain.length - 1];
        X500Principal subject = cert.getSubjectX500Principal();
        X500Principal issuer = cert.getIssuerX500Principal();
        List<X509Certificate> list = trustedX500Principals.get(issuer);
        if (list != null) {
            X509Certificate trustedCert = list.iterator().next();
            c.add(trustedCert);
            return c.toArray(CHAIN0);
        }

        // no trusted cert found, error
        throw new ValidatorException(ValidatorException.T_NO_TRUST_ANCHOR);
    }

    /**
     * Return a trusted certificate that matches the input certificate,
     * or null if no such certificate can be found. This method also handles
     * cases where a CA re-issues a trust anchor with the same public key and
     * same subject and issuer names but a new validity period, etc.
     */
    private X509Certificate getTrustedCertificate(X509Certificate cert) {
        Principal certSubjectName = cert.getSubjectX500Principal();
        List<X509Certificate> list = trustedX500Principals.get(certSubjectName);
        if (list == null) {
            return null;
        }

        Principal certIssuerName = cert.getIssuerX500Principal();
        PublicKey certPublicKey = cert.getPublicKey();

        for (X509Certificate mycert : list) {
            if (mycert.equals(cert)) {
                return cert;
            }
            if (!mycert.getIssuerX500Principal().equals(certIssuerName)) {
                continue;
            }
            if (!mycert.getPublicKey().equals(certPublicKey)) {
                continue;
            }

            // All tests pass, this must be the one to use...
            return mycert;
        }
        return null;
    }

}