Java中常用的加密算法有DES、AES、RSA等。以下是這些算法的應用示例：
import javax.crypto.*;
import javax.crypto.spec.DESKeySpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.spec.InvalidKeySpecException;
public class DESExample {
public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidKeySpecException, BadPaddingException, IllegalBlockSizeException {
String plaintext = "Hello, world!";
String keyString = "mysecretkey"; // 密鑰，長度必須為8字節
// 生成密鑰
SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
DESKeySpec desKeySpec = new DESKeySpec(keyString.getBytes());
SecretKey secretKey = keyFactory.generateSecret(desKeySpec);
// 創建加密器
Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, secretKey);
// 加密
byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
System.out.println("Encrypted: " + new String(encryptedBytes));
// 創建解密器
cipher.init(Cipher.DECRYPT_MODE, secretKey);
// 解密
byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
System.out.println("Decrypted: " + new String(decryptedBytes));
}
}
import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
public class AESExample {
public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
String plaintext = "Hello, world!";
String keyString = "mysecretkey123456"; // 密鑰，長度必須為16字節
// 生成密鑰
Key key = new SecretKeySpec(keyString.getBytes(), "AES");
// 創建加密器
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key);
// 加密
byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
System.out.println("Encrypted: " + new String(encryptedBytes));
// 創建解密器
cipher.init(Cipher.DECRYPT_MODE, key);
// 解密
byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
System.out.println("Decrypted: " + new String(decryptedBytes));
}
}
import javax.crypto.Cipher;
import java.nio.charset.StandardCharsets;
import java.security.*;
public class RSAExample {
public static void main(String[] args) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
String plaintext = "Hello, world!";
// 生成密鑰對
KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
keyGen.initialize(2048);
KeyPair keyPair = keyGen.generateKeyPair();
PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();
// 創建加密器
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
// 加密
byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));
System.out.println("Encrypted: " + new String(encryptedBytes));
// 創建解密器
cipher.init(Cipher.DECRYPT_MODE, privateKey);
// 解密
byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
System.out.println("Decrypted: " + new String(decryptedBytes));
}
}
以上示例分別演示了DES、AES和RSA加密算法的使用方法，包括生成密鑰、創建加密器、加密和解密操作。請注意，密鑰的長度必須滿足算法要求，否則會拋出異常。加密和解密時使用的密鑰必須匹配。
