Java是一款非常流行的程式語言，廣泛應用於各種領域。在實際的應用中，資料的加密和解密是很常見的需求。 Java提供了許多加密解密演算法，本文將簡單介紹其中幾種常見的演算法。
一、對稱加密演算法
對稱加密演算法又叫私鑰加密演算法，是將加密和解密使用相同的金鑰。常見的對稱加密演算法有DES、3DES、AES等。
DES（Data Encryption Standard）是一種經典的對稱加密演算法，它的金鑰長度為56位元。使用DES演算法時，需要先生成金鑰，然後使用金鑰加密明文，得到密文；再使用金鑰解密密文，得到明文。在Java中，可以使用JCE（Java Cryptography Extension）提供的DES加密解密功能。範例程式碼如下：
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.NoSuchAlgorithmException;
public class DESUtil {
private static final String ALGORITHM = "DES";
public static String encrypt(String content, String key) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), ALGORITHM);
Cipher cipher = Cipher.getInstance(ALGORITHM);
byte[] byteContent = content.getBytes();
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] result = cipher.doFinal(byteContent);
return parseByte2HexStr(result);
}
public static String decrypt(String content, String key) throws Exception {
byte[] decryptFrom = parseHexStr2Byte(content);
SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), ALGORITHM);
Cipher cipher = Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] result = cipher.doFinal(decryptFrom);
return new String(result);
}
private static String parseByte2HexStr(byte[] buf) {
StringBuilder sb = new StringBuilder();
for (byte b : buf) {
String hex = Integer.toHexString(b & 0xFF);
if (hex.length() == 1) {
hex = '0' + hex;
}
sb.append(hex.toUpperCase());
}
return sb.toString();
}
private static byte[] parseHexStr2Byte(String hexStr) {
if (hexStr.length() < 1) {
return null;
}
byte[] result = new byte[hexStr.length() / 2];
for (int i = 0; i < hexStr.length() / 2; i++) {
int high = Integer.parseInt(hexStr.substring(i * 2, i * 2 + 1), 16);
int low = Integer.parseInt(hexStr.substring(i * 2 + 1, i * 2 + 2), 16);
result[i] = (byte) (high * 16 + low);
}
return result;
}
public static void main(String[] args) throws Exception {
String content = "Hello World!";
String key = "12345678";
String encrypt = encrypt(content, key);
System.out.println("加密后：" + encrypt);
String decrypt = decrypt(encrypt, key);
System.out.println("解密后：" + decrypt);
}
}3DES（Triple DES）演算法是在DES演算法的基礎上加強的一種加密演算法，金鑰長度為168位元. 3DES演算法的加密解密過程類似DES演算法，可以使用Java提供的JCE函式庫來實作。範例程式碼如下：
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.NoSuchAlgorithmException;
public class TripleDESUtil {
private static final String ALGORITHM = "DESede";
private static byte[] initKey() throws NoSuchAlgorithmException {
KeyGenerator kg = KeyGenerator.getInstance(ALGORITHM);
kg.init(168); // 3DES的密钥长度为168位
SecretKey secretKey = kg.generateKey();
return secretKey.getEncoded();
}
public static String encrypt(String content, byte[] key) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(key, ALGORITHM);
Cipher cipher = Cipher.getInstance(ALGORITHM);
byte[] byteContent = content.getBytes();
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] result = cipher.doFinal(byteContent);
return parseByte2HexStr(result);
}
public static String decrypt(String content, byte[] key) throws Exception {
byte[] decryptFrom = parseHexStr2Byte(content);
SecretKeySpec skeySpec = new SecretKeySpec(key, ALGORITHM);
Cipher cipher = Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] result = cipher.doFinal(decryptFrom);
return new String(result);
}
private static String parseByte2HexStr(byte[] buf) {
StringBuilder sb = new StringBuilder();
for (byte b : buf) {
String hex = Integer.toHexString(b & 0xFF);
if (hex.length() == 1) {
hex = '0' + hex;
}
sb.append(hex.toUpperCase());
}
return sb.toString();
}
private static byte[] parseHexStr2Byte(String hexStr) {
if (hexStr.length() < 1) {
return null;
}
byte[] result = new byte[hexStr.length() / 2];
for (int i = 0; i < hexStr.length() / 2; i++) {
int high = Integer.parseInt(hexStr.substring(i * 2, i * 2 + 1), 16);
int low = Integer.parseInt(hexStr.substring(i * 2 + 1, i * 2 + 2), 16);
result[i] = (byte) (high * 16 + low);
}
return result;
}
public static void main(String[] args) throws Exception {
String content = "Hello World!";
byte[] key = initKey();
String encrypt = encrypt(content, key);
System.out.println("加密后：" + encrypt);
String decrypt = decrypt(encrypt, key);
System.out.println("解密后：" + decrypt);
}
}AES（Advanced Encryption Standard）演算法是一種進階加密標準，是目前最受歡迎的對稱加密演算法之一。 AES演算法的金鑰長度一般為128位元、192位元或256位元。在Java中，也可以使用JCE函式庫提供的AES加密解密功能。範例程式碼如下：
import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.NoSuchAlgorithmException;
public class AESUtil {
private static final String ALGORITHM = "AES";
private static byte[] initKey() throws NoSuchAlgorithmException {
KeyGenerator kg = KeyGenerator.getInstance(ALGORITHM);
kg.init(128); // AES的密钥长度为128位、192位、256位
SecretKey secretKey = kg.generateKey();
return secretKey.getEncoded();
}
public static String encrypt(String content, byte[] key) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(key, ALGORITHM);
Cipher cipher = Cipher.getInstance(ALGORITHM);
byte[] byteContent = content.getBytes();
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] result = cipher.doFinal(byteContent);
return parseByte2HexStr(result);
}
public static String decrypt(String content, byte[] key) throws Exception {
byte[] decryptFrom = parseHexStr2Byte(content);
SecretKeySpec skeySpec = new SecretKeySpec(key, ALGORITHM);
Cipher cipher = Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] result = cipher.doFinal(decryptFrom);
return new String(result);
}
private static String parseByte2HexStr(byte[] buf) {
StringBuilder sb = new StringBuilder();
for (byte b : buf) {
String hex = Integer.toHexString(b & 0xFF);
if (hex.length() == 1) {
hex = '0' + hex;
}
sb.append(hex.toUpperCase());
}
return sb.toString();
}
private static byte[] parseHexStr2Byte(String hexStr) {
if (hexStr.length() < 1) {
return null;
}
byte[] result = new byte[hexStr.length() / 2];
for (int i = 0; i < hexStr.length() / 2; i++) {
int high = Integer.parseInt(hexStr.substring(i * 2, i * 2 + 1), 16);
int low = Integer.parseInt(hexStr.substring(i * 2 + 1, i * 2 + 2), 16);
result[i] = (byte) (high * 16 + low);
}
return result;
}
public static void main(String[] args) throws Exception {
String content = "Hello World!";
byte[] key = initKey();
String encrypt = encrypt(content, key);
System.out.println("加密后：" + encrypt);
String decrypt = decrypt(encrypt, key);
System.out.println("解密后：" + decrypt);
}
}二、非對稱加密演算法
非對稱加密演算法又叫公鑰加密演算法，是加密和解密使用不同的金鑰。常見的非對稱加密演算法有RSA演算法。
RSA演算法是一種非對稱加密演算法，是一種基於大整數的數論加密演算法。 RSA演算法的特點是公鑰可以公開，金鑰是私有的，因此安全性較高。在Java中，也可以使用JCE函式庫提供的RSA加密解密功能。範例程式碼如下：
import javax.crypto.Cipher;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
public class RSAUtil {
private static final String ALGORITHM = "RSA";
private static KeyPair getKeyPair(int keySize) throws NoSuchAlgorithmException {
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(ALGORITHM);
keyPairGenerator.initialize(keySize);
return keyPairGenerator.generateKeyPair();
}
public static String encrypt(String content, PublicKey publicKey) throws Exception {
Cipher cipher = Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] byteContent = content.getBytes();
byte[] result = cipher.doFinal(byteContent);
return parseByte2HexStr(result);
}
public static String decrypt(String content, PrivateKey privateKey) throws Exception {
byte[] decryptFrom = parseHexStr2Byte(content);
Cipher cipher = Cipher.getInstance(ALGORITHM);
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] result = cipher.doFinal(decryptFrom);
return new String(result);
}
private static String parseByte2HexStr(byte[] buf) {
StringBuilder sb = new StringBuilder();
for (byte b : buf) {
String hex = Integer.toHexString(b & 0xFF);
if (hex.length() == 1) {
hex = '0' + hex;
}
sb.append(hex.toUpperCase());
}
return sb.toString();
}
private static byte[] parseHexStr2Byte(String hexStr) {
if (hexStr.length() < 1) {
return null;
}
byte[] result = new byte[hexStr.length() / 2];
for (int i = 0; i < hexStr.length() / 2; i++) {
int high = Integer.parseInt(hexStr.substring(i * 2, i * 2 + 1), 16);
int low = Integer.parseInt(hexStr.substring(i * 2 + 1, i * 2 + 2), 16);
result[i] = (byte) (high * 16 + low);
}
return result;
}
public static void main(String[] args) throws Exception {
String content = "Hello World!";
KeyPair keyPair = getKeyPair(1024);
PublicKey publicKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();
String encrypt = encrypt(content, publicKey);
System.out.println("加密后：" + encrypt);
String decrypt = decrypt(encrypt, privateKey);
System.out.println("解密后：" + decrypt);
}
}以上就是幾種常見的Java實作的加密解密演算法。在實際的應用中，需要根據實際情況選擇適合自己的加密解密演算法，並根據具體的需求進行調整和最佳化。
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