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com.hfg xml, html, svg, and bioinformatics utility library
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package com.hfg.security;

import java.io.File;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import com.hfg.util.FileUtil;

//------------------------------------------------------------------------------
/**
 * AES-related functions.
 *
 * @author J. Alex Taylor, hairyfatguy.com
 */
//------------------------------------------------------------------------------
// com.hfg XML/HTML Coding Library
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
// J. Alex Taylor, President, Founder, CEO, COO, CFO, OOPS hairyfatguy.com
// [email protected]
//------------------------------------------------------------------------------

public class AESUtil
{

    //--------------------------------------------------------------------------
    public static SecretKey generateKey()
        throws Exception
    {
        KeyGenerator generator = KeyGenerator.getInstance("AES");
        generator.init(128); // The AES key size in number of bits

        return generator.generateKey();
    }

    //--------------------------------------------------------------------------
    public static SecretKey generateKey(File inOutputDir)
        throws Exception
    {
        SecretKey key = generateKey();

        File file = new File(inOutputDir, "aes.key");
        FileUtil.writeBytes(file, key.getEncoded());

        // Set strict user-only permissions
        file.setReadable(false, false);
        file.setReadable(true, true);
        file.setWritable(false, false);
        file.setWritable(true, true);
        file.setExecutable(false, false);

        return key;
    }

    //--------------------------------------------------------------------------
    public static SecretKey readKey(File inFile)
    {
        SecretKey key = null;

        try
        {
            byte[] keyBytes = FileUtil.readBytes(inFile);
            key = new SecretKeySpec(keyBytes, 0, keyBytes.length, "AES");
        }
        catch (Exception e)
        {
            throw new RuntimeException(e);
        }

        return key;
    }

}