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 *  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
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 *    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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 *  KIND, either express or implied.  See the License for the
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package org.apache.cayenne.crypto.transformer.bytes;

import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.Key;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.ShortBufferException;
import javax.crypto.spec.IvParameterSpec;

import org.apache.cayenne.crypto.CayenneCryptoException;

/**
 * A {@link BytesDecryptor} that decrypts the provided bytes that were encrypted
 * by the complimentary {@link CbcEncryptor}. The object is stateful and is not
 * thread-safe.
 * 
 * @since 4.0
 */
class CbcDecryptor implements BytesDecryptor {

    private Cipher cipher;
    private int blockSize;

    CbcDecryptor(Cipher cipher) {
        this.cipher = cipher;
        this.blockSize = cipher.getBlockSize();
    }

    @Override
    public byte[] decrypt(byte[] input, int inputOffset, Key key) {
        try {
            return doDecrypt(input, inputOffset, key);
        } catch (Exception e) {
            throw new CayenneCryptoException("Error on decryption", e);
        }
    }

    private byte[] doDecrypt(byte[] input, int inputOffset, Key key) throws InvalidKeyException,
            InvalidAlgorithmParameterException, ShortBufferException, IllegalBlockSizeException, BadPaddingException {

        IvParameterSpec iv = iv(input, inputOffset);

        cipher.init(Cipher.DECRYPT_MODE, key, iv);

        int offset = inputOffset + blockSize;
        return cipher.doFinal(input, offset, input.length - offset);
    }

    IvParameterSpec iv(byte[] input, int inputOffset) {
        return new IvParameterSpec(input, inputOffset, blockSize);
    }
}