データの暗号化と復号化（ファイルと文字列 それぞれ）

TestFileCrypt.java

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotSame;

import java.io.BufferedReader;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

import org.junit.Test;

public class TestFileCrypt {
	private static final String ALG = "AES";
	private static final int KEYSIZE = 128;

	private static final int CASHE_SIZE = 2000;	//最低でも2000くらいとりましょう（性能のため）：HDDのブロックサイズと同じだと最高。

	private static final int CAPACITY_SB = 1024;	//StringBuilderの初期容量


	private static final String PLAINFILE = "secret/plain.dat";
	private static final String ENCRYPTFILE = "secret/encrypt.dat";
	private static final String DECRYPTFILE = "secret/decrypt.dat";

	@Test
	public void testTextCrypt() throws Exception{
		KeyGenerator keyGen = KeyGenerator.getInstance(ALG);
		keyGen.init(KEYSIZE);
		SecretKey key = keyGen.generateKey();

		String plainFileText = getFileString(new File(PLAINFILE));
		encryptFile(key, PLAINFILE, ENCRYPTFILE);
		String encryptFileText = getFileString(new File(ENCRYPTFILE));
		decryptFile(key, ENCRYPTFILE, DECRYPTFILE);
		String decryptFileText = getFileString(new File(DECRYPTFILE));

		assertNotSame( plainFileText, encryptFileText);
		assertEquals( plainFileText, decryptFileText);
	}


	/**
	 * ファイルの暗号化メソッド
	 * @param key
	 * @param plainFileName
	 * @param cryptFileName
	 * @throws Exception
	 */
	private static void encryptFile(SecretKey key, String plainFileName, String encryptFileName) throws Exception{
		Cipher cipher = Cipher.getInstance(ALG);
		cipher.init(Cipher.ENCRYPT_MODE, key);

		FileInputStream fis = null;
		FileOutputStream fos = null;

		try{
			fis = new FileInputStream(plainFileName);
			fos = new FileOutputStream(encryptFileName);
			// 暗号化ストリームを用意
			CipherInputStream cis = new CipherInputStream(fis, cipher);	//fisと同時にcloseされるのでclose不要（内側が閉じれば閉じる）

			byte[] buf = new byte[CASHE_SIZE];
			int i;
			while( (i = cis.read(buf)) != -1 ){
				fos.write(buf,0, i);
			}
		}finally{
			close(fis);
			close(fos);
		}
	}


	/**
	 * ファイルの復号化メソッド
	 * @param key
	 * @param encryptFileName
	 * @param decryptFileName
	 * @throws Exception
	 */
	private static void decryptFile(SecretKey key, String encryptFileName, String decryptFileName) throws Exception{
		Cipher cipher = Cipher.getInstance(ALG);
		cipher.init(Cipher.DECRYPT_MODE, key);

		FileInputStream fis = null;
		FileOutputStream fos = null;
		CipherOutputStream cos = null;

		try{
			fis = new FileInputStream(encryptFileName);
			fos = new FileOutputStream(decryptFileName);
			cos = new CipherOutputStream(fos, cipher);

			byte[] buf = new byte[CASHE_SIZE];
			int i;
			while( (i = fis.read(buf)) != -1 ){
				cos.write(buf, 0, i);
			}
		}finally{
			close(cos);	//closeしないと最後の一文字が切れてしまう。
			close(fos);
			close(fis);
		}
	}

	private static void close(Closeable c) throws Exception {
		try {
			if (c != null) {
				c.close();
			}
		} catch (Exception e) {
			throw new Exception(e);
		}
	}



	/**
	 * ファイルの中身をStringにして返す
	 * @param file
	 * @return
	 * @throws Exception
	 */
	private static String getFileString(File file) throws Exception{
		BufferedReader reader = null;
		StringBuilder result = new StringBuilder(CAPACITY_SB);
		try{
			reader = new BufferedReader(new FileReader(file));
			String line = null;
			while((line = reader.readLine()) != null){
				result.append(line);
			}
		}finally{
			reader.close();
		}
		return result.toString();
	}



	public static void main (String[] args) throws Exception {
		KeyGenerator keyGen = KeyGenerator.getInstance(ALG);
		keyGen.init(KEYSIZE);
		SecretKey key = keyGen.generateKey();

		System.out.println(getFileString(new File(PLAINFILE)));

		encryptFile(key, PLAINFILE, ENCRYPTFILE);
		System.out.println(getFileString(new File(ENCRYPTFILE)));

		decryptFile(key, ENCRYPTFILE, DECRYPTFILE);
		System.out.println(getFileString(new File(DECRYPTFILE)));
	}

}

TestTextCrypt.java

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotSame;

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;

import org.junit.Test;

public class TestTextCrypt {

	private static final String ALG = "AES";

	@Test
	public void testTextCrypt() throws Exception{
		String text = "abcdefg";
		String key = "asdfghjkloiuy67t";	//16文字（128bit）

		byte[] encrypted = encrypt(key, text);
		assertNotSame( new String( encrypted ), text);
		assertEquals( decrypt(key, encrypted), text );
	}


	/**
	 * 暗号化を行う
	 * @param key
	 * @param text
	 * @return
	 * @throws NoSuchAlgorithmException
	 * @throws NoSuchPaddingException
	 * @throws InvalidKeyException
	 * @throws IllegalBlockSizeException
	 * @throws BadPaddingException
	 */
	private byte[] encrypt(String key, String text) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
		//プロバイダに依存しない形式で秘密鍵を指定
		SecretKeySpec sksSpec = new SecretKeySpec(key.getBytes(), ALG);
		//暗号化および復号化の機能を提供するCipherオブジェクト生成
		Cipher cipher = Cipher.getInstance(ALG);
		cipher.init(Cipher.ENCRYPT_MODE, sksSpec);
		byte[] encrypted = cipher.doFinal(text.getBytes());
		return encrypted;
	}

	/**
	 * 復号化を行う
	 * @param key
	 * @param encrypted
	 * @return
	 * @throws NoSuchAlgorithmException
	 * @throws NoSuchPaddingException
	 * @throws InvalidKeyException
	 * @throws IllegalBlockSizeException
	 * @throws BadPaddingException
	 */
	private String decrypt(String key, byte[] encrypted) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
		SecretKeySpec sksSpec = new SecretKeySpec(key.getBytes(), ALG);
		Cipher cipher = Cipher.getInstance(ALG);
		cipher.init(Cipher.DECRYPT_MODE, sksSpec);
		byte[] decrypted = cipher.doFinal(encrypted);
		return new String(decrypted);
	}
}