master 优化数字签名的readme

Author: weileifrank

.idea/workspace.xml

@@ -236,13 +236,66 @@ public class MacDemo {
 > 总结: 
 >
 > 1. 数据通信
->
-> ```
 >  - 公钥加密, 私钥解密
 > 2. 数字签名:
 > - 私钥加密, 公钥解密
-> ```
+> 
 
 ### 数字签名的方法
 
 ![Logo](imgs/3.png)
+
+- 数字签名示例代码
+```$xslt
+public class SignatureDemo {
+    public static void main(String[] args) throws Exception {
+        String algorithm = "RSA";
+        String priPath = "test.pri";
+        String pubPath = "test.pub";
+        String input = "frank";
+//        RSAUtil.generateKeys(algorithm,priPath,pubPath);
+
+        PrivateKey privateKey = RSAUtil.getPrivateKey(priPath, algorithm);
+        PublicKey publicKey = RSAUtil.getPublicKey(pubPath, algorithm);
+
+        String signatureAlgorithm = "SHA256withRSA";
+        String signatured = getSignature(input, privateKey, signatureAlgorithm);
+
+        boolean verify = verifySignature(input, publicKey, signatureAlgorithm, signatured);
+        System.out.println(verify);
+    }
+
+    /**
+     * 生成签名字符串
+     * @param input  原文
+     * @param privateKey 私钥
+     * @param signatureAlgorithm 签名算法
+     * @return
+     * @throws Exception
+     */
+    public static String getSignature(String input, PrivateKey privateKey, String signatureAlgorithm) throws Exception {
+        Signature signature = Signature.getInstance(signatureAlgorithm);
+        signature.initSign(privateKey);
+        signature.update(input.getBytes());
+        byte[] sign = signature.sign();
+        return Base64.encode(sign);
+    }
+
+    /**
+     * 校验签名
+     * @param input 原文
+     * @param publicKey 公钥
+     * @param signatureAlgorithm 签名算法
+     * @param signatured 发送过来的签名
+     * @return
+     * @throws Exception
+     */
+    public static boolean verifySignature(String input, PublicKey publicKey, String signatureAlgorithm, String signatured) throws Exception {
+        Signature signature = Signature.getInstance(signatureAlgorithm);
+        signature.initVerify(publicKey);
+        signature.update(input.getBytes());
+        return signature.verify(Base64.decode(signatured));
+
+    }
+}
+```