hash - 多个 JWT 的匹配哈希 JWT

Question

我使用 bcryptjs 对用户的刷新 token 进行哈希处理，然后再将其存储到数据库中。

当将散列字符串与 JWT 进行比较时，以下内容似乎总是评估为 true，我在 https://bcrypt-generator.com/ 上也得到了相同的行为

例如，哈希值 $2a$10$z4rwnyg.cVtP2SHt3lYj7.aGeAzonmmzbxqCzi2UW3SQj6famGaqW 与以下两个 JWT 匹配

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiI2NTZlODdkNi1jMmVkLTRmN2ItOTU2Zi00NDFhMWU1NjA2MmQiLCJpYXQiOjE2Mzk1OTg2MDISimV4cCI6MTY0MjE 5MDYwMn0.aJlzFHhBMGO4J7vlOudqOrOFnL1P-yEGrREgdaCXlxU

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiI2NTZlODdkNi1jMmVkLTRmN2ItOTU2Zi00NDFhMWU1NjA2MmQiLCJpYXQiOjE2Mzk2MDY4ODgsImV4cCI6MTY0MjE 5ODg4OH0.vo4HKLXuQbT0Yb0j21M4xl-rakxyE5wINjuGdkPuSJY

您也可以在网站上验证它们是否都产生“匹配”

1. 转到https://bcrypt-generator.com/并打开浏览器控制台。

2. 在控制台中输入这些行:

   > var jwt1 = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiI2NTZlODdkNi1jMmVkLTRmN2ItOTU2Zi00NDFhMWU1NjA2MmQiLCJpYXQiOjE2Mzk1OTg2MDIsImV4cCI6MTY0MjE5MDYwMn0.aJlzFHhBMGO4J7vlOudqOrOFnL1P-yEGrREgdaCXlxU"
   < undefined
   
   > var jwt2 = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiI2NTZlODdkNi1jMmVkLTRmN2ItOTU2Zi00NDFhMWU1NjA2MmQiLCJpYXQiOjE2Mzk2MDY4ODgsImV4cCI6MTY0MjE5ODg4OH0.vo4HKLXuQbT0Yb0j21M4xl-rakxyE5wINjuGdkPuSJY"
   < undefined
   
   > var h = "$2a$10$z4rwnyg.cVtP2SHt3lYj7.aGeAzonmmzbxqCzi2UW3SQj6famGaqW"
   < undefined
   

3. 然后在控制台中输入这些行，观察它们如何返回true:

   > bcrypt.compareSync(jwt1, h)
   < true
   > bcrypt.compareSync(jwt2, h)
   < true
   

---

这是我自己的 JS 代码，它也重现了哈希匹配:

// Login Logic

const refresh_token: string = jwt.sign({ userId }, authSecrets.refresh_secret, { expiresIn: '30d' });

const hash_refresh = bcrypt.hashSync(refresh_token);

await UserModel.update({
    id: user.id,
    refresh_token: hash_refresh,
});

// Refresh logic
// 'value' is the payload after using joi to validate it 

const claims: any = jwt.verify(value.refresh_token, authSecrets.refresh_secret);

user = await UserModel.get(claims.userId);

if (!bcrypt.compareSync(value.refresh_token, user.refresh_token)) {
    // This never happens with any JWT!
    return response(401, 'Refresh Token is incorrect');
}

为什么会发生这种情况？字符串明显不同(尽管相差不是很多)。

Answer 1

哈希冲突是因为 bcrypt only hashes the first 72 bytes of input (在大多数实现中)。

这在 bcryptjs 和 bcrypt npm 包的自述文件中都有记录:

bcryptjs :

The maximum input length is 72 bytes (note that UTF8 encoded characters use up to 4 bytes) and the length of generated hashes is 60 characters.

bcrypt :

Per bcrypt implementation, only the first 72 bytes of a string are used. Any extra bytes are ignored when matching passwords. Note that this is not the first 72 characters. It is possible for a string to contain less than 72 characters, while taking up more than 72 bytes (e.g. a UTF-8 encoded string containing emojis).

(考虑到这是为了用户安全，这是一个客观上糟糕的设计......如果输入超过 72 字节(IMO)，bcryptjs 库确实应该始终抛出异常)

我注意到 bcrypt 是为人类提供的(即非随机)密码而设计的，而不是作为通用的消息摘要算法。鉴于您不需要向随机生成的密码添加盐(例如您的 refresh_token 值)，您可能应该使用 SHA-2 系列算法(例如 SHA-256，但不是 SHA-) 1)为此。