概述

    在https://blog.csdn.net/chinoukin/article/details/100934995章节中，我介绍了用Hmac算法用于签名算法中的方法，本章节中将对常见的签名算法“SHA256withRSA”做一下分析与介绍。

此文由来

    当我在使用springcloud的oauth2时，经常会用到jwt作为用户身份的确认和鉴权。而我们知道jwt是由三部分组成，其中第三部分就是数字签名了，而springcloud的oauth2中的默认jwt签名算法为SHA256withRSA。

    下面通过调用OauthServer的{/oauth/token_key}接口来看一下返回情况：

HMAC与SHA256withRSA

    hmac做签名时需要指定一个secret和指定hamc算法，常见的hmac算法有hamcsha1、hamcsha256等，通常用hmac生成信息摘要后会再用RSA算法对其进行加密

    SHA256withRSA做签名则一步到位，需要先生成RSA密钥对，其中私钥用于签名，公钥用于验签。

    为了方便理解：

    hmac数字签名 =  rsa_encrypt(hmac(信息) + RSA私钥)

    SHA256withRSA数字签名 =  SHA256withRSA_encrypt(信息 + RSA私钥)

RSA密钥之PKCS#1、PKCS#8

    pkcs时密钥的语法标准，细心的同学应该会经常遇到PKCS#1,PKCS#8,PKCS#12等标准，具体所代表的含义这里不做赘述了。通常我们生成密钥对时，会对私钥进行加密，加密后的格式为PKCS#1或PKCS#8格式，而一般不会对公钥进行加密。对于开发者而言，JAVA中通常使用的是PKCS8格式的私钥，php、.net使用的是PKCS1格式的私钥。简单例子： 用openssl生成PKCS#1格式的私钥：openssl genrsa -des3 -out test.key 1024

通过文件首尾部能判断:

JAVA示例

  1.签名示例

import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.openssl.PEMWriter;
import org.bouncycastle.util.encoders.Base64;

import java.io.IOException;
import java.io.StringWriter;
import java.security.InvalidKeyException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
import java.security.Signature;
import java.security.SignatureException;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.util.HashMap;
import java.util.Map;

public class SignTest {

    /**
     * 生成没有加密的密钥对
     * @param algorithm
     * @param keysize
     * @return
     * @throws Exception
     */
    public static Map<String, Object> createKey(String algorithm,int keysize) throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(algorithm);
        keyPairGen.initialize(keysize);
        KeyPair keyPair = keyPairGen.generateKeyPair();

        //通过对象 KeyPair 获取RSA公私钥对象RSAPublicKey RSAPrivateKey
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();

        //公私钥对象存入map中
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put("publicKey", publicKey);
        keyMap.put("privateKey", privateKey);
        return keyMap;
    }

    /**
     * 生成加过密的密钥对 pkcs#1格式私钥 pkcs#8格式公钥
     *
     * @param algorithm
     * @param keysize
     * @param privateKeyPwd
     * @return
     * @throws Exception
     */
    public static Map<String, Object> createEncryKeyStr(String algorithm, int keysize, String privateKeyPwd) throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(algorithm);
        keyPairGen.initialize(keysize);
        KeyPair keyPair = keyPairGen.generateKeyPair();

        //通过对象 KeyPair 获取RSA公私钥对象RSAPublicKey RSAPrivateKey
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();

        String pubKeyStr = new String(Base64.encode(publicKey.getEncoded())); //pkcs8格式
        String priKeyStr = new String(Base64.encode(privateKey.getEncoded())); //pkcs8格式
        System.out.println(priKeyStr);//从输出结果可以知道是PKCS#8格式的

        //私钥加密
        String privateKeyStr = privateKeyPwdToPKCS1(privateKey, privateKeyPwd);//使用BC加密私钥格式会被转为PKSC#1格式
        System.out.println(privateKeyStr);
        System.out.println(privateKeyNoPwdToPKCS1(privateKey));

        //公私钥对象存入map中
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put("publicKeyStr", pubKeyStr);
        keyMap.put("privateKeyStr", privateKeyStr);
        return keyMap;
    }

    /**
     * 将私钥转为PKCS#1格式私钥（加密）
     *
     * @param privateKey
     * @param filePasswd
     * @return
     */
    private static String privateKeyPwdToPKCS1(PrivateKey privateKey, String filePasswd) {
        Security.addProvider(new BouncyCastleProvider());
        StringWriter sw = new StringWriter();
        PEMWriter writer = new PEMWriter(sw);
        try {
            writer.writeObject(privateKey, "DESEDE", filePasswd.toCharArray(),
                    new SecureRandom());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (writer != null) {
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return sw.toString();
    }

    /**
     * 将私钥转为PKCS#1格式私钥（没有加密）
     * @param privateKey
     * @return
     */
    private static String privateKeyNoPwdToPKCS1(PrivateKey privateKey){
        Security.addProvider(new BouncyCastleProvider());
        StringWriter sw = new StringWriter();
        PEMWriter writer = new PEMWriter(sw);
        try {
            writer.writeObject(privateKey);
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                if(writer !=null){
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return sw.toString();
    }


    public static final String SIGNATURE_ALGORITHM = "SHA256withRSA";
    public static final String ENCODE_ALGORITHM = "SHA-256";
    public static final String PLAIN_TEXT = "test string";

    /**
     * 签名
     * @param privateKey  私钥
     * @param plainText 明文
     * @return
     */
    public static byte[] sign(PrivateKey privateKey, String plainText) {
        MessageDigest messageDigest;
        byte[] signed = null;
        try {
            messageDigest = MessageDigest.getInstance(ENCODE_ALGORITHM);
            messageDigest.update(plainText.getBytes());
            byte[] outputDigest_sign = messageDigest.digest();
            System.out.println("SHA-256编码后-----》"
                    + org.apache.commons.codec.binary.Base64.encodeBase64String(outputDigest_sign));
            Signature Sign = Signature.getInstance(SIGNATURE_ALGORITHM);
            Sign.initSign(privateKey);
            Sign.update(outputDigest_sign);
            signed = Sign.sign();
            System.out.println("SHA256withRSA签名后-----》"
                    + org.apache.commons.codec.binary.Base64.encodeBase64String(signed));
        } catch (NoSuchAlgorithmException | InvalidKeyException | SignatureException e) {
            e.printStackTrace();
        }
        return signed;
    }

    /**
     * 验签
     * @param publicKey 公钥
     * @param plain_text 明文
     * @param signed 签名
     */
    public static boolean verifySign(PublicKey publicKey, String plain_text, byte[] signed) {
        MessageDigest messageDigest;
        boolean SignedSuccess=false;
        try {
            messageDigest = MessageDigest.getInstance(ENCODE_ALGORITHM);
            messageDigest.update(plain_text.getBytes());
            byte[] outputDigest_verify = messageDigest.digest();
            //System.out.println("SHA-256加密后-----》" +bytesToHexString(outputDigest_verify));
            Signature verifySign = Signature.getInstance(SIGNATURE_ALGORITHM);
            verifySign.initVerify(publicKey);
            verifySign.update(outputDigest_verify);
            SignedSuccess = verifySign.verify(signed);
            System.out.println("验证成功？---" + SignedSuccess);

        } catch (NoSuchAlgorithmException | InvalidKeyException | SignatureException e) {
            e.printStackTrace();
        }
        return SignedSuccess;
    }


    /**
     * bytes[]换成16进制字符串
     *
     * @param src
     * @return
     */
    public static String bytesToHexString(byte[] src) {
        StringBuilder stringBuilder = new StringBuilder("");
        if (src == null || src.length <= 0) {
            return null;
        }
        for (int i = 0; i < src.length; i++) {
            int v = src[i] & 0xFF;
            String hv = Integer.toHexString(v);
            if (hv.length() < 2) {
                stringBuilder.append(0);
            }
            stringBuilder.append(hv);
        }
        return stringBuilder.toString();
    }


    public static void main(String[] args) throws Exception {
        Map<String, Object> keyMap = createKey("RSA", 2048);
        PublicKey publicKey = (PublicKey) keyMap.get("publicKey");
        PrivateKey privateKey = (PrivateKey) keyMap.get("privateKey");
        byte[] signBytes = sign(privateKey, PLAIN_TEXT);
        System.out.println(verifySign(publicKey, PLAIN_TEXT, signBytes));
        
    }
}

  2.签发JWT示例

import com.cyq.CheckResult;
import io.jsonwebtoken.Claims;
import io.jsonwebtoken.ExpiredJwtException;
import io.jsonwebtoken.JwtBuilder;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;
import io.jsonwebtoken.SignatureException;
import org.bouncycastle.util.encoders.Base64;

import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.security.Key;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.time.OffsetDateTime;
import java.time.ZoneId;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

/**
 * maven依赖
 *
 * <dependency>
 * <groupId>io.jsonwebtoken</groupId>
 * <artifactId>jjwt</artifactId>
 * <version>0.9.0</version>
 * </dependency>
 */

/**
 * @author cyq
 */
public class JwtUtils {

    public static void main(String[] args) throws Exception {
        // 签发jwt(签名算法hmac256)
        System.out.println("签发jwt(签名算法hmac256):");
        String jwt = createJWT("123", "jwt_hmac256", 60);
        System.out.println(jwt);
        // 解析
        SecretKey secretKey = generalKey();
        Claims claims = parseJWT(jwt, secretKey);
        System.out.println(claims);


        // 签发jwt(签名算法SHA256withRSA)
        System.out.println("\n签发jwt(签名算法SHA256withRSA):");
        Map<String, Object> keyMaps = createRSAKey(2048);
        String jwt2 = createJWT2("456", "jwt_SHA256withRSA", 60, (RSAPrivateKey) keyMaps.get("privateKey"));
        System.out.println(jwt2);
        // 解析
        Claims claims2 = parseJWT(jwt2, (RSAPublicKey) keyMaps.get("publicKey"));
        System.out.println(claims2);

    }

    /**
     * 签发JWT
     * @param id
     * @param subject 可以是JSON数据 尽可能少
     * @param ttlMillis
     * @return String
     *
     */
    public static String createJWT(String id, String subject, long ttlMillis) {
        SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.HS256;// HmacSha256

        OffsetDateTime now = OffsetDateTime.now(ZoneId.of("Asia/Shanghai"));
        //Date now = new Date(nowMillis);
        SecretKey secretKey = generalKey();

        JwtBuilder builder = Jwts.builder()
                .setId(id)
                .setSubject(subject)   // 主题
                .setIssuer("user")     // 签发者
                .setIssuedAt(Date.from(now.toInstant()))      // 签发时间
                .signWith(signatureAlgorithm, secretKey); // 签名算法以及密匙
        if (ttlMillis >= 0) {
            OffsetDateTime expTime = now.plusSeconds(ttlMillis);
            builder.setExpiration(Date.from(expTime.toInstant())); // 过期时间
        }
        return builder.compact();
    }

    /**
     * 签发JWT
     * @param id
     * @param subject 可以是JSON数据 尽可能少
     * @param ttlMillis
     * @return String
     *
     */
    public static String createJWT2(String id, String subject, long ttlMillis, RSAPrivateKey privateKey) {
        SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.RS256;// SHA256withRSA
        OffsetDateTime now = OffsetDateTime.now(ZoneId.of("Asia/Shanghai"));

        JwtBuilder builder = Jwts.builder()
                .setId(id)
                .setSubject(subject)   // 主题
                .setIssuer("user")     // 签发者
                .setIssuedAt(Date.from(now.toInstant()))      // 签发时间
                .signWith(signatureAlgorithm, privateKey); // 签名算法以及密匙
        if (ttlMillis >= 0) {
            OffsetDateTime expTime = now.plusSeconds(ttlMillis);
            builder.setExpiration(Date.from(expTime.toInstant())); // 过期时间
        }
        return builder.compact();
    }

    /**
     * 生成没有加密的密钥对
     * @param keysize
     * @return
     * @throws Exception
     */
    public static Map<String, Object> createRSAKey(int keysize) throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("rsa");
        keyPairGen.initialize(keysize);
        KeyPair keyPair = keyPairGen.generateKeyPair();

        //通过对象 KeyPair 获取RSA公私钥对象RSAPublicKey RSAPrivateKey
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();

        //公私钥对象存入map中
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put("publicKey", publicKey);
        keyMap.put("privateKey", privateKey);
        return keyMap;
    }


    public static SecretKey generalKey() {
        byte[] encodedKey = Base64.decode("testjwt");
        SecretKey key = new SecretKeySpec(encodedKey, 0, encodedKey.length, "AES");
        return key;
    }

    /**
     *
     * 解析JWT字符串
     * @param jwt
     * @return
     * @throws Exception
     */
    public static Claims parseJWT(String jwt, Key key) throws Exception {
        return Jwts.parser()
                .setSigningKey(key)
                .parseClaimsJws(jwt)
                .getBody();
    }


    /**
     * 验证JWT
     * @param jwtStr
     * @return
     */
    public static CheckResult validateJWT(String jwtStr, Key key) {
        CheckResult checkResult = new CheckResult();
        Claims claims = null;
        try {
            claims = parseJWT(jwtStr, key);
            checkResult.setSuccess(true);
            checkResult.setClaims(claims);
        } catch (ExpiredJwtException e) {
            e.printStackTrace();
            checkResult.setErrCode("JWT_ERRCODE_EXPIRE");
            checkResult.setSuccess(false);
        } catch (SignatureException e) {
            e.printStackTrace();
            checkResult.setErrCode("JWT_ERRCODE_FAIL");
            checkResult.setSuccess(false);
        } catch (Exception e) {
            e.printStackTrace();
            checkResult.setErrCode("JWT_ERRCODE_FAIL");
            checkResult.setSuccess(false);
        }
        return checkResult;
    }
}