Main.java Source code

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Here is the source code for Main.java

Source

//package com.java2s;
/* 
 * Copyright (C) 2010 Giesecke & Devrient GmbH
 *
 * Licensed 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.
 */

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import android.util.Log;

public class Main {
    /**
     * Tag for logging
     */
    private static final String TAG = "Helper";
    /**
     * flag to indicate if the crypto-algorithms is initialized. 
     * This should only be done once, during a multi-part crypto-operation
     */
    private static boolean decryptInitialized = false;
    /**
     * Cipherobject to make decrypt operations
     */
    private static Cipher decryptCipher;

    /**
     * This method should be used to decrypt a block of data.
     * 
     * @param fileData the data to decrypt.
     * @param decryptionKey the key to initialize the cipher-algorithm.
     * @param decryptCompleted a flag, that indicates, that a multi-part decryption is to be
     *            completed. e.g. false, if the fileData consist of multiple
     *            parts. true, if the fileData consists only of one single part
     *            and so they could be decrypted in one operation.
     * 
     * @return the decrypted data.
     */
    public static byte[] decryptData(byte[] fileData, byte[] decryptionKey, boolean decryptCompleted) {

        // Initializing may only be done at the start of a multi-part
        // crypto-operation.
        // if it's a single part crypto-operation initialization must always be
        // done.
        if (!decryptInitialized) {
            // Initializing the cipher
            try {
                decryptCipher = Cipher.getInstance("AES");
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }

            try {
                SecretKeySpec keySpec = new SecretKeySpec(decryptionKey, "AES");
                decryptCipher.init(Cipher.DECRYPT_MODE, keySpec);
            } catch (Exception e) {
                Log.e(TAG, "Error while initializing decryption.");
                return null;
            }
            decryptInitialized = true;
        }

        // Decrypting
        try {
            if (!decryptCompleted) // done in case of multi-part operation
                fileData = decryptCipher.update(fileData);
            else
                // done in case of single part operation or to finish a
                // multi-part operation
                fileData = decryptCipher.doFinal(fileData);
        } catch (Exception e) {
            Log.e(TAG, "Error during decryption.");
            return null;
        }

        // at the and of an multi-part operation flags must be reset
        if (decryptCompleted)
            decryptInitialized = false;

        return fileData;
    }
}