org.opendatakit.briefcase.util.CipherFactory.java Source code

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Here is the source code for org.opendatakit.briefcase.util.CipherFactory.java

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/*
 * Copyright (C) 2011 University of Washington.
 * 
 * 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.
 */

package org.opendatakit.briefcase.util;

import java.io.UnsupportedEncodingException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Cipher;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.opendatakit.briefcase.model.CryptoException;

/**
 * Handles the initialization of Cipher objects for the decryption of submission
 * and media files.
 * 
 * @author mitchellsundt@gmail.com
 * 
 */
public final class CipherFactory {

    private static final Log log = LogFactory.getLog(CipherFactory.class);
    private static final String SYMMETRIC_ALGORITHM = "AES/CFB/PKCS5Padding";
    private static final int IV_BYTE_LENGTH = 16;

    private final String instanceId;
    private final SecretKeySpec symmetricKey;
    private final byte[] ivSeedArray;
    private int ivCounter = 0;

    public CipherFactory(String instanceId, byte[] symmetricKeyBytes) throws CryptoException {

        this.instanceId = instanceId;
        symmetricKey = new SecretKeySpec(symmetricKeyBytes, SYMMETRIC_ALGORITHM);
        // construct the fixed portion of the iv -- the ivSeedArray
        // this is the md5 hash of the instanceID and the symmetric key
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(instanceId.getBytes("UTF-8"));
            md.update(symmetricKeyBytes);
            byte[] messageDigest = md.digest();
            ivSeedArray = new byte[IV_BYTE_LENGTH];
            for (int i = 0; i < IV_BYTE_LENGTH; ++i) {
                ivSeedArray[i] = messageDigest[(i % messageDigest.length)];
            }
        } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
            String msg = "Error constructing ivSeedArray";
            log.error(msg, e);
            throw new CryptoException(msg + " Cause: " + e);
        }
    }

    public Cipher getCipher(String context) throws InvalidKeyException, InvalidAlgorithmParameterException,
            NoSuchAlgorithmException, NoSuchPaddingException {
        ++ivSeedArray[ivCounter % ivSeedArray.length];
        ++ivCounter;
        IvParameterSpec baseIv = new IvParameterSpec(ivSeedArray);
        Cipher c = Cipher.getInstance(SYMMETRIC_ALGORITHM);

        c.init(Cipher.DECRYPT_MODE, symmetricKey, baseIv);
        return c;
    }

    public Cipher getCipher(String context, String fieldName)
            throws InvalidKeyException, InvalidAlgorithmParameterException, NoSuchAlgorithmException,
            NoSuchPaddingException, UnsupportedEncodingException {
        MessageDigest md = MessageDigest.getInstance("MD5");
        md.update(instanceId.getBytes("UTF-8"));
        md.update(symmetricKey.getEncoded());
        md.update(fieldName.getBytes("UTF-8"));
        byte[] messageDigest = md.digest();
        for (int i = 0; i < IV_BYTE_LENGTH; ++i) {
            ivSeedArray[i] = messageDigest[(i % messageDigest.length)];
        }
        IvParameterSpec baseIv = new IvParameterSpec(ivSeedArray);
        Cipher c = Cipher.getInstance(SYMMETRIC_ALGORITHM);

        c.init(Cipher.DECRYPT_MODE, symmetricKey, baseIv);
        return c;
    }
}