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JCOSecretKeyAES.java

package edu.virtualschool.jco;

import java.security.SecureRandom;

import org.bouncycastle.crypto.StreamBlockCipher;
import org.bouncycastle.crypto.StreamCipher;
import org.bouncycastle.crypto.engines.AESLightEngine;
import org.bouncycastle.crypto.modes.CFBBlockCipher;
import org.bouncycastle.crypto.params.KeyParameter;

import edu.virtualschool.jwaa.RuntimeFault;

public class JCOSecretKeyAES extends JCOSymmetricKey
{
  final static int DEFAULT_KEY_LENGTH = 32;

  public JCOSecretKeyAES(int length)
  {
    this(createRandomBytes(length));
  }
  public JCOSecretKeyAES()
  {
    this(createRandomBytes(DEFAULT_KEY_LENGTH));
  }
  private static byte[] createRandomBytes(int length)
  {
    byte[] bytes = new byte[length];
    SecureRandom random = new SecureRandom();
    random.nextBytes(bytes);
    return bytes;
  }
  public JCOSecretKeyAES(String string)
  {
    this(JCOBase64.decode(string));
  }
  public JCOSecretKeyAES(byte[] bytes)
  {
    super(new KeyParameter(bytes));
    int length = bytes.length;
    if (length != 16 && length != 24 && length != 32)
      throw new RuntimeFault("key length not 16 or 24 or 32 bytes");
  }
  public byte[] encryptBytes(byte[] cleartext)
  {
    AESLightEngine blockCipher = new AESLightEngine();
    CFBBlockCipher cfbCipher = new CFBBlockCipher(blockCipher, 8);
    StreamCipher streamCipher = new StreamBlockCipher(cfbCipher);
    SecureRandom random = new SecureRandom();

    int blockSize = blockCipher.getBlockSize();
    byte[] iv = new byte[blockSize];
    random.nextBytes(iv);

    int length = cleartext.length + blockSize;
    byte[] plaintext = new byte[length];
    System.arraycopy(iv, 0, plaintext, 0, iv.length);
    System.arraycopy(cleartext, 0, plaintext, iv.length, cleartext.length);

    byte[] ciphertext = new byte[plaintext.length];
    streamCipher.init(true, key);
    streamCipher.processBytes(plaintext, 0, plaintext.length, ciphertext, 0);
    return ciphertext;
  }
  public byte[] decryptBytes(byte[] ciphertext) 
  {
    AESLightEngine blockCipher = new AESLightEngine();
    CFBBlockCipher cfbCipher = new CFBBlockCipher(blockCipher, 8);
    StreamCipher streamCipher = new StreamBlockCipher(cfbCipher);

    byte[] plaintext = new byte[ciphertext.length];
    streamCipher.init(false, key);
    streamCipher.processBytes(ciphertext, 0, ciphertext.length, plaintext, 0);
    
    int ivlength = blockCipher.getBlockSize();
    int messageLength = plaintext.length - ivlength;
    byte[] cleartext = new byte[messageLength];
    System.arraycopy(plaintext, ivlength, cleartext, 0, messageLength);
    return cleartext;
  }
  public final String getAlgorithm()
  {
    return "AES"; 
  }
  public final String getFormat()
  {
    return "RAW";
  }
  public final byte[] getEncoded()
  {
    return key.getKey();
  }
}