RSA加解密，加签以及验签。

由于RSA算法是不对称加密算法，所以每次加密得到的数据都不相同，同理加签得到的数据每次也不一样。

简单的说下不对称算法，就是两把不同，但是完全匹配的秘钥，去进行加解密，公钥对外提供进行数据加密，私钥自己保存，对加密的数据进行解密。所以私钥不要泄露。

RSA算法原理：

1、任意互质的两个质数p,q。

2、得到连个质数的乘积n。

3、得到两个质数的欧元函数f(n)=(p-1) * (q-1)。

4、任取一个小于f(n)并与其互质的质数e。

5、存在一个数d，使得e^d % f(n) = 1。

6、则（n,e）为公钥，(n,d)为私钥。

加密：待加密数据t:

t^te% n = m(m为加密后的数据);

解密：m^d % n = t(t为原数据)

Java实现RSA算法加密解密，加签以及验签代码如下：

1、Base64工具类：

//Base64加密
public static String encryptBase64(byte[] key){
    return new String(Base64.encodeBase64(key));
}

//Base64解密
public static byte[] decryptBase64(String key) throws IOException {
    return new BASE64Decoder().decodeBuffer(key);
}

2、获取RSA秘钥对：

public static Map keyMap()throws Exception{
    KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
    keyPairGenerator.initialize(1024);
    KeyPair keyPair = keyPairGenerator.generateKeyPair();
    PublicKey publicKey = keyPair.getPublic();
    PrivateKey privateKey = keyPair.getPrivate();

    Map keyMap = new HashMap<>(2);
    keyMap.put(PUBLIC_KEY, publicKey);
    keyMap.put(PRIVATE_KEY, privateKey);
    return keyMap;
}

3、获取RSA公钥以及私钥分别保存到文件中：

public static void keyToFile(Map keymap)throws Exception{
    PublicKey publicKey = (PublicKey) keymap.get(PUBLIC_KEY);
    PrivateKey privateKey = (PrivateKey)keymap.get(PRIVATE_KEY);
    String encryptBase64PublicKey = encryptBase64(publicKey.getEncoded());
    String encryptBase64PrivateKey = encryptBase64(privateKey.getEncoded());
    FileWriter fw = new FileWriter("src/main/resources/pubKey.txt");//按需要保存路径，下同

    FileWriter fw1 = new FileWriter("src/main/resources/priKey.txt");
    fw.write(encryptBase64PublicKey);
    fw.flush();
    fw.close();
    fw1.write(encryptBase64PrivateKey);
    fw1.flush();
    fw1.close();
}

4、从文件中获取公钥：

public static RSAPublicKey getPublicKeyForFile() throws Exception {
    File file = new File("src/main/resources/pubKey.txt");

    FileInputStream fis = new FileInputStream(file);
    BufferedReader br = new BufferedReader(new InputStreamReader(fis));
    String readLine = null;
    StringBuffer sb = new StringBuffer();
    while ((readLine = br.readLine()) != null) {
        sb.append(readLine);
    }
    String publicKeyStr = sb.toString();
    System.out.println("从文件获取到的公钥：" + publicKeyStr);
    //Base64解密
    byte[] decryptBase64 = GetKey.decryptBase64(publicKeyStr);
    //选取密钥编码规则
    X509EncodedKeySpec keySpec = new X509EncodedKeySpec(decryptBase64);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    RSAPublicKey rsaPublicKey = (RSAPublicKey) keyFactory.generatePublic(keySpec);
    return rsaPublicKey;
}

5、从文件中获取私钥：

//从文件中获取私钥
public static RSAPrivateKey getPrivateKeyForFile() throws Exception {
    FileInputStream fis = new FileInputStream("src/main/resources/priKey.keyStore");
    BufferedReader br = new BufferedReader(new InputStreamReader(fis));
    String readLine = null;
    StringBuffer sb = new StringBuffer();
    while ((readLine = br.readLine()) != null) {
        sb.append(readLine);
    }
    String privateKey = sb.toString();
    System.out.println("从文件获取到的私钥：" + privateKey);
    //Base64解密
    byte[] bytes = GetKey.decryptBase64(privateKey);
    PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(bytes);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyFactory.generatePrivate(pkcs8EncodedKeySpec);
    return rsaPrivateKey;
}

6.公钥加密/私钥解密：

public static byte[] encryptOrDecrypt(Key key, byte[] data, int mode) throws Exception {
    //加密算法：RSA/ECB/PKCS1Padding

    ByteArrayOutputStream out = new ByteArrayOutputStream();

    //提供者
    Provider provider = new BouncyCastleProvider();
    Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", provider);
    cipher.init(mode, key);
    int blockSize = cipher.getBlockSize();
    int length = data.length;
    int num = length / blockSize + 1;
    int cache = blockSize;
    byte[] bytes = null;
    for (int i = 0; i < num; i++) {
        if (i == num - 1) {
            cache = length % blockSize;
            if (cache == 0) {
                return out.toByteArray();
            }
        }
        bytes = cipher.doFinal(data, i * blockSize, cache);
        out.write(bytes);
    }
    return out.toByteArray();
}

7.RSA私钥加签：

 public static String addSign(PrivateKey privateKey, String context)throws Exception{
        //加签算法：SHA1WithRSA

	Signature signature = Signature.getInstance("SHA1WithRSA");
        signature.initSign(privateKey);
        signature.update(context.getBytes("utf-8"));
        byte[] sign = signature.sign();
        return encryptBase64(sign);
    }

8.RSA公钥验签：

public static boolean verifySign(PublicKey publicKey, String context, String signData)throws Exception{
        Signature signature = Signature.getInstance("SHA1WithRSA");
        signature.initVerify(publicKey);
        byte[] bytes = decryptBase64(signData);
        signature.update(context.getBytes("utf-8"));
        boolean verify = signature.verify(bytes);
        return verify;
    }

9.主测试类：

public class Sign {

  private final static String PUBLIC_KEY = "PUBLIC_KEY";
  private final static String PRIVATE_KEY = "PRIVATE_KEY";

public static void main(String[] args) { try {

		Map map = keyMap();
		keyToFile(map);

		RSAPublicKey rsaPublicKey = getPublicKeyForFile();

		System.out.println("rsaPublicKey公钥是：" + rsaPublicKey);

		RSAPrivateKey rsaPrivateKey = getPrivateKeyForFile();

		System.out.println("rsaPublicKey私钥是：" + rsaPrivateKey);

		String data = "这是一个加密字符串"

		//加密

		byte[] encrypt = encryptOrDecrypt(rsaPublicKey, data.getBytes("utf-8"), Cipher.ENCRYPT_MODE);	

		String s = encryptBase64(encrypt);
		System.out.println("加密后的数据：" + s);

//解密 byte[] decrypt = encryptOrDecrypt (rsaPrivateKey, decryptBase64( s ) , Cipher. DECRYPT_MODE );
System. out.println("解 密后的数据 " + new String( decrypt ));

		//加签

		String signData = addSign(rsaPrivateKey, data);	

		System.out.println("加签后的数据：" + signData);

		//验签

		boolean b = verifySign(rsaPublicKey, data, signData);
		System.out.println("验签得到的布尔值为：" + b);

 	} catch (Exception e) {
        e.printStackTrace();
    }
}

最后要说明的是要导入这个包：

<dependency>
    <groupId>org.bouncycastlegroupId>
    <artifactId>bcprov-jdk16artifactId>
    <version>1.46version>
dependency>