Java で、AES または DES でテキストを暗号化・復号化する方法

以下の encrypt メソッドの引数に String でテキスト文字列を渡すと、暗号化されたものがバイト列で返ってくる。復号は decrypt の引数にそのバイト列を渡す。両メソッド共、crypt_spec 引数に AES を指定すれば AES で暗号するし、DES を指定すれば DES で暗号化する。


import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;

// CHANGE THIS VALUE DEPENDING ON WHAT YOU WANT
public static final int MESSAGE_LENGTH = 1024;

/**
 * @param text
 *            Message to encrypt
 * @param secret_key
 *            Secret Key
 * @param crypt_spec
 *            Crypt algorithm like "AES" or "DES"
 * @return Encrypted Byte Strings
 */
public byte[] encrypt(String text, byte[] secret_key, String crypt_spec)
    throws InvalidKeyException, IllegalBlockSizeException, IOException,
    BadPaddingException {

SecretKeySpec sKey = new SecretKeySpec(secret_key, crypt_spec);
byte[] secret = new byte[MESSAGE_LENGTH];

try {
    Cipher cipher = Cipher.getInstance(crypt_spec);
    cipher.init(Cipher.ENCRYPT_MODE, sKey);
    secret = cipher.doFinal(text.getBytes());
} catch (Exception e) {
    System.out.println(this.getClass().getName()
            + ".encrypt: Exception:");
    e.printStackTrace();
}
return secret;
}

/**
 * @param b
 *            Encypted Byte Message
 * @param crypt_spec
 *            Crypt Algorithm like "AES" or "DES"
 * @return Decrypted String
 */
public String decrypt(byte[] b, byte[] secret_key, String crypt_spec)
    throws InvalidKeyException, IllegalBlockSizeException, IOException,
    BadPaddingException {

SecretKeySpec sKey = new SecretKeySpec(secret_key, crypt_spec);
byte[] secret = new byte[MESSAGE_LENGTH];

try {
    Cipher cipher = Cipher.getInstance(crypt_spec);
    cipher.init(Cipher.DECRYPT_MODE, sKey);
    secret = cipher.doFinal(b);
} catch (Exception e) {
    System.out.println(this.getClass().getName()
            + ".decrypt: Exception:");
    e.printStackTrace();
}
return new String(secret);
}