Java 标准库实现常见加密解密

一时兴起，好奇 Java 中常用的加解密是如何实现的，今天就 常见的 bas64编码解码、MD5、SHA256、HmacSHA256 做个简单小结，希望对各位有用。

环境：

• JDK: 17

以下内容基于 JDK 17 的自带工具库 实现，示例如下：

package com.example.util;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class MyCrypto {

    // base64 encode and decode
    public static String encodeBase64(String val) {
        return Base64.getEncoder().encodeToString(val.getBytes());
    }

    public static String decodeBase64(String b64Str) {
        return new String(Base64.getDecoder().decode(b64Str));
    }

    // md5 or sha256 encrypt
    public static String md5OrSha256(String val, String algorithm) {
        if (val == null) {
            val = "";
        }

        String Str = "";
        try {
            MessageDigest md = MessageDigest.getInstance(algorithm);
            md.update(val.getBytes());
            byte[] b = md.digest();

            int i;

            StringBuilder builder = new StringBuilder(32);

            for (int j = 0; j < b.length; j++) {
                i = b[j];
                if (i < 0) {
                    i += 256;
                }
                if (i < 16) {
                    builder.append("0");
                }

                builder.append(Integer.toHexString(i));
            }

            Str = builder.toString();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }

        // md5 -> 128 bits, sha256 -> 256 bits
        return Str;
    }

    private static String byteArrayToHexString(byte[] b) {
        StringBuilder builder = new StringBuilder();
        String stmp;
        for (int i = 0; i < b.length; i++) {
            stmp = Integer.toHexString(b[i] & 0XFF);
            if (stmp.length() == 1) builder.append('0');
            builder.append(stmp);
        }
        return builder.toString().toLowerCase();
    }

    public static String hmacSha256(String msg, String secret) {
        String hash = "";
        String algorithm = "HmacSHA256";

        try {
            Mac instance = Mac.getInstance(algorithm);
            SecretKeySpec secretKey = new SecretKeySpec(secret.getBytes(), algorithm);
            instance.init(secretKey);
            byte[] bytes = instance.doFinal(msg.getBytes());
            hash = byteArrayToHexString(bytes);
        } catch (NoSuchAlgorithmException| InvalidKeyException e) {
            e.printStackTrace();
        }

        return hash;
    }

    public static void main(String[] args) {
        String str = "hello, world";
        System.out.println(encodeBase64(str));
        System.out.println(decodeBase64(encodeBase64(str)));
        System.out.println(md5OrSha256(str, "MD5"));
        System.out.println(md5OrSha256(str, "SHA-256"));
        System.out.println(hmacSha256("hello, world", "secret"));
    }
}