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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.security.AccessController;
import java.security.PrivilegedAction;
import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.spec.IvParameterSpec;

import org.apache.xml.security.utils.ClassLoaderUtils;
import org.apache.xml.security.utils.EncryptionConstants;

public final class XMLCipherUtil {

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

    private static final boolean gcmUseIvParameterSpec =
        AccessController.doPrivileged((PrivilegedAction)
            () -> Boolean.getBoolean("org.apache.xml.security.cipher.gcm.useIvParameterSpec"));

    /**
     * Build an AlgorithmParameterSpec instance used to initialize a Cipher instance
     * for block cipher encryption and decryption.
     *
     * @param algorithm the XML encryption algorithm URI
     * @param iv the initialization vector
     * @return the newly constructed AlgorithmParameterSpec instance, appropriate for the
     *         specified algorithm
     */
    public static AlgorithmParameterSpec constructBlockCipherParameters(String algorithm, byte[] iv, Class callingClass) {
        if (EncryptionConstants.ALGO_ID_BLOCKCIPHER_AES128_GCM.equals(algorithm)
                || EncryptionConstants.ALGO_ID_BLOCKCIPHER_AES192_GCM.equals(algorithm)
                || EncryptionConstants.ALGO_ID_BLOCKCIPHER_AES256_GCM.equals(algorithm)) {
            return constructBlockCipherParametersForGCMAlgorithm(algorithm, iv, callingClass);
        } else {
            LOG.debug("Saw non-AES-GCM mode block cipher, returning IvParameterSpec: {}", algorithm);
            return new IvParameterSpec(iv);
        }
    }

    public static AlgorithmParameterSpec constructBlockCipherParameters(boolean gcmAlgorithm, byte[] iv, Class callingClass) {
        if (gcmAlgorithm) {
            return constructBlockCipherParametersForGCMAlgorithm("AES/GCM/NoPadding", iv, callingClass);
        } else {
            LOG.debug("Saw non-AES-GCM mode block cipher, returning IvParameterSpec");
            return new IvParameterSpec(iv);
        }
    }

    private static AlgorithmParameterSpec constructBlockCipherParametersForGCMAlgorithm(String algorithm, byte[] iv, Class callingClass) {
        if (gcmUseIvParameterSpec) {
            // This override allows to support Java 1.7+ with (usually older versions of) third-party security
            // providers which support or even require GCM via IvParameterSpec rather than GCMParameterSpec,
            // e.g. BouncyCastle <= 1.49 (really <= 1.50 due to a semi-related bug).
            LOG.debug("Saw AES-GCM block cipher, using IvParameterSpec due to system property override: {}", algorithm);
            return new IvParameterSpec(iv);
        }

        LOG.debug("Saw AES-GCM block cipher, attempting to create GCMParameterSpec: {}", algorithm);

        try {
            // This class only added in Java 1.7. So load reflectively until Santuario starts targeting a minimum of Java 1.7.
            Class gcmSpecClass = ClassLoaderUtils.loadClass("javax.crypto.spec.GCMParameterSpec", callingClass);

            // XML Encryption 1.1 mandates a 128-bit Authentication Tag for AES GCM modes.
            AlgorithmParameterSpec gcmSpec = (AlgorithmParameterSpec) gcmSpecClass.getConstructor(int.class, byte[].class)
                    .newInstance(128, iv);
            LOG.debug("Successfully created GCMParameterSpec");
            return gcmSpec;
        } catch (Exception e) {
            // This handles the case of Java < 1.7 with a third-party security provider that
            // supports GCM mode using only an IvParameterSpec, such as BouncyCastle.
            LOG.debug("Failed to create GCMParameterSpec, falling back to returning IvParameterSpec", e);
            return new IvParameterSpec(iv);
        }
    }
}