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/**
 * 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
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 * Unless required by applicable law or agreed to in writing,
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package com.sun.org.apache.xml.internal.security.keys.keyresolver.implementations;

import java.security.Key;
import java.security.PublicKey;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.List;

import javax.crypto.SecretKey;

import com.sun.org.apache.xml.internal.security.encryption.EncryptedKey;
import com.sun.org.apache.xml.internal.security.encryption.XMLCipher;
import com.sun.org.apache.xml.internal.security.encryption.XMLEncryptionException;
import com.sun.org.apache.xml.internal.security.keys.keyresolver.KeyResolverSpi;
import com.sun.org.apache.xml.internal.security.keys.storage.StorageResolver;
import com.sun.org.apache.xml.internal.security.utils.EncryptionConstants;
import com.sun.org.apache.xml.internal.security.utils.XMLUtils;
import org.w3c.dom.Element;

The EncryptedKeyResolver is not a generic resolver.  It can
only be for specific instantiations, as the key being unwrapped will
always be of a particular type and will always have been wrapped by
another key which needs to be recursively resolved.
The EncryptedKeyResolver can therefore only be instantiated
with an algorithm.  It can also be instantiated with a key (the KEK) or
will search the static KeyResolvers to find the appropriate key.
Author:
Berin Lautenbach/**
 * The <code>EncryptedKeyResolver</code> is not a generic resolver.  It can
 * only be for specific instantiations, as the key being unwrapped will
 * always be of a particular type and will always have been wrapped by
 * another key which needs to be recursively resolved.
 *
 * The <code>EncryptedKeyResolver</code> can therefore only be instantiated
 * with an algorithm.  It can also be instantiated with a key (the KEK) or
 * will search the static KeyResolvers to find the appropriate key.
 *
 * @author Berin Lautenbach
 */
public class EncryptedKeyResolver extends KeyResolverSpi {

    
logging logging facility /** {@link org.apache.commons.logging} logging facility */
    private static java.util.logging.Logger log =
        java.util.logging.Logger.getLogger(EncryptedKeyResolver.class.getName());

    private Key kek;
    private String algorithm;
    private List<KeyResolverSpi> internalKeyResolvers;

    
Constructor for use when a KEK needs to be derived from a KeyInfo
list
Params:
algorithm – /**
     * Constructor for use when a KEK needs to be derived from a KeyInfo
     * list
     * @param algorithm
     */
    public EncryptedKeyResolver(String algorithm) {
        kek = null;
        this.algorithm = algorithm;
    }

    
Constructor used for when a KEK has been set
Params:
algorithm – 
kek – /**
     * Constructor used for when a KEK has been set
     * @param algorithm
     * @param kek
     */
    public EncryptedKeyResolver(String algorithm, Key kek) {
        this.algorithm = algorithm;
        this.kek = kek;
    }

    
This method is used to add a custom KeyResolverSpi to help resolve the KEK. 
Params:
realKeyResolver – /**
     * This method is used to add a custom {@link KeyResolverSpi} to help
     * resolve the KEK.
     *
     * @param realKeyResolver
     */
    public void registerInternalKeyResolver(KeyResolverSpi realKeyResolver) {
        if (internalKeyResolvers == null) {
            internalKeyResolvers = new ArrayList<KeyResolverSpi>();
        }
        internalKeyResolvers.add(realKeyResolver);
    }

    
@inheritDoc
/** @inheritDoc */
    public PublicKey engineLookupAndResolvePublicKey(
        Element element, String BaseURI, StorageResolver storage
    ) {
        return null;
    }

    
@inheritDoc
/** @inheritDoc */
    public X509Certificate engineLookupResolveX509Certificate(
        Element element, String BaseURI, StorageResolver storage
    ) {
        return null;
    }

    
@inheritDoc
/** @inheritDoc */
    public javax.crypto.SecretKey engineLookupAndResolveSecretKey(
        Element element, String BaseURI, StorageResolver storage
    ) {
        if (log.isLoggable(java.util.logging.Level.FINE)) {
            log.log(java.util.logging.Level.FINE, "EncryptedKeyResolver - Can I resolve " + element.getTagName());
        }

        if (element == null) {
            return null;
        }

        SecretKey key = null;
        boolean isEncryptedKey =
            XMLUtils.elementIsInEncryptionSpace(element, EncryptionConstants._TAG_ENCRYPTEDKEY);
        if (isEncryptedKey) {
            if (log.isLoggable(java.util.logging.Level.FINE)) {
                log.log(java.util.logging.Level.FINE, "Passed an Encrypted Key");
            }
            try {
                XMLCipher cipher = XMLCipher.getInstance();
                cipher.init(XMLCipher.UNWRAP_MODE, kek);
                if (internalKeyResolvers != null) {
                    int size = internalKeyResolvers.size();
                    for (int i = 0; i < size; i++) {
                        cipher.registerInternalKeyResolver(internalKeyResolvers.get(i));
                    }
                }
                EncryptedKey ek = cipher.loadEncryptedKey(element);
                key = (SecretKey) cipher.decryptKey(ek, algorithm);
            } catch (XMLEncryptionException e) {
                if (log.isLoggable(java.util.logging.Level.FINE)) {
                    log.log(java.util.logging.Level.FINE, e.getMessage(), e);
                }
            }
        }

        return key;
    }
}