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Apache XML Security for Java supports XML-Signature Syntax and Processing, W3C Recommendation 12 February 2002, and XML Encryption Syntax and Processing, W3C Recommendation 10 December 2002. As of version 1.4, the library supports the standard Java API JSR-105: XML Digital Signature APIs.
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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
 *
 * 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.xml.security.encryption;

import java.io.IOException;

import org.apache.xml.security.c14n.CanonicalizationException;
import org.apache.xml.security.utils.XMLUtils;
import org.apache.xml.security.utils.resolver.ResourceResolver;
import org.apache.xml.security.utils.resolver.ResourceResolverException;
import org.apache.xml.security.signature.XMLSignatureInput;
import org.apache.xml.security.transforms.TransformationException;
import org.w3c.dom.Attr;

/**
 * XMLCipherInput is used to wrap input passed into the
 * XMLCipher encryption operations.
 *
 * In decryption mode, it takes a CipherData object and allows
 * callers to dereference the CipherData into the encrypted bytes that it
 * actually represents.  This takes care of all base64 encoding etc.
 *
 * While primarily an internal class, this can be used by applications to
 * quickly and easily retrieve the encrypted bytes from an EncryptedType
 * object
 *
 */
public class XMLCipherInput {

    private static final org.slf4j.Logger LOG =
        org.slf4j.LoggerFactory.getLogger(XMLCipherInput.class);

    /** The data we are working with */
    private CipherData cipherData;

    /** MODES */
    private int mode;

    private boolean secureValidation;

    /**
     * Constructor for processing encrypted octets
     *
     * @param data The CipherData object to read the bytes from
     * @throws XMLEncryptionException {@link XMLEncryptionException}
     */
    public XMLCipherInput(CipherData data) throws XMLEncryptionException {
        cipherData = data;
        mode = XMLCipher.DECRYPT_MODE;
        if (cipherData == null) {
            throw new XMLEncryptionException("CipherData is null");
        }
    }

    /**
     * Constructor for processing encrypted octets
     *
     * @param input The EncryptedType object to read
     * the bytes from.
     * @throws XMLEncryptionException {@link XMLEncryptionException}
     */
    public XMLCipherInput(EncryptedType input) throws XMLEncryptionException {
        cipherData = input == null ? null : input.getCipherData();
        mode = XMLCipher.DECRYPT_MODE;
        if (cipherData == null) {
            throw new XMLEncryptionException("CipherData is null");
        }
    }

    /**
     * Set whether secure validation is enabled or not. The default is false.
     */
    public void setSecureValidation(boolean secureValidation) {
        this.secureValidation = secureValidation;
    }

    /**
     * Dereferences the input and returns it as a single byte array.
     *
     * @throws XMLEncryptionException
     * @return The decripted bytes.
     */
    public byte[] getBytes() throws XMLEncryptionException {
        if (mode == XMLCipher.DECRYPT_MODE) {
            return getDecryptBytes();
        }
        return null;
    }

    /**
     * Internal method to get bytes in decryption mode
     * @return the decrypted bytes
     * @throws XMLEncryptionException
     */
    private byte[] getDecryptBytes() throws XMLEncryptionException {
        String base64EncodedEncryptedOctets = null;

        if (cipherData.getDataType() == CipherData.REFERENCE_TYPE) {
            // Fun time!
            LOG.debug("Found a reference type CipherData");
            CipherReference cr = cipherData.getCipherReference();

            // Need to wrap the uri in an Attribute node so that we can
            // Pass to the resource resolvers

            Attr uriAttr = cr.getURIAsAttr();
            XMLSignatureInput input = null;

            try {
                ResourceResolver resolver =
                    ResourceResolver.getInstance(uriAttr, null, secureValidation);
                input = resolver.resolve(uriAttr, null, secureValidation);
            } catch (ResourceResolverException ex) {
                throw new XMLEncryptionException(ex);
            }

            if (input != null) {
                LOG.debug("Managed to resolve URI \"{}\"", cr.getURI());
            } else {
                LOG.debug("Failed to resolve URI \"{}\"", cr.getURI());
            }

            // Lets see if there are any transforms
            Transforms transforms = cr.getTransforms();
            if (transforms != null) {
                LOG.debug("Have transforms in cipher reference");
                try {
                    org.apache.xml.security.transforms.Transforms dsTransforms =
                        transforms.getDSTransforms();
                    dsTransforms.setSecureValidation(secureValidation);
                    input = dsTransforms.performTransforms(input);
                } catch (TransformationException ex) {
                    throw new XMLEncryptionException(ex);
                }
            }

            try {
                return input.getBytes();
            } catch (IOException ex) {
                throw new XMLEncryptionException(ex);
            } catch (CanonicalizationException ex) {
                throw new XMLEncryptionException(ex);
            }

            // retrieve the cipher text
        } else if (cipherData.getDataType() == CipherData.VALUE_TYPE) {
            base64EncodedEncryptedOctets = cipherData.getCipherValue().getValue();
        } else {
            throw new XMLEncryptionException("CipherData.getDataType() returned unexpected value");
        }

        LOG.debug("Encrypted octets:\n{}", base64EncodedEncryptedOctets);

        return XMLUtils.decode(base64EncodedEncryptedOctets);
    }
}