Java是一款非常流行的编程语言，广泛应用于各种领域。在实际的应用中，数据的加密和解密是很常见的需求。Java提供了许多加密解密算法，本文将简单介绍其中几种常见的算法。
一、对称加密算法
对称加密算法又叫私钥加密算法，是将加密和解密使用相同的密钥。常见的对称加密算法有DES、3DES、AES等。
- DES算法
DES（Data Encryption Standard）是一种经典的对称加密算法，它的密钥长度为56位。在使用DES算法时，需要先生成密钥，然后使用密钥加密明文，得到密文；再使用密钥解密密文，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。示例代码如下：
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算法
3DES（Triple DES）算法是在DES算法的基础上加强的一种加密算法，密钥长度为168位。3DES算法的加密解密过程类似于DES算法，可以使用Java提供的JCE库进行实现。示例代码如下：
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算法
AES（Advanced Encryption Standard）算法是一种高级加密标准，是目前最流行的对称加密算法之一。AES算法的密钥长度一般为128位、192位或256位。在Java中，也可以使用JCE库提供的AES加密解密功能。示例代码如下：
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、非对称加密算法
非对称加密算法又叫公钥加密算法，是加密和解密使用不同的密钥。常见的非对称加密算法有RSA算法。
- RSA算法
RSA算法是一种非对称加密算法，是一种基于大整数的数论加密算法。RSA算法的特点是公钥可以公开，密钥是私有的，因此安全性较高。在Java中，也可以使用JCE库提供的RSA加密解密功能。示例代码如下：
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)
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