Question

剛開始接觸這種加密方式，而又對加密原理不瞭解時，很容易產生這種疑問❔：

對一個密碼，bcryptjs每次生成的hash都不一樣，那麼它是如何進行校驗的？

Basic verification

1. 雖然對同一個密碼，每次生成的hash不一樣，但是hash中包含了salt（hash產生過程：先隨機生成salt，salt跟password進行hash）；
2. 在下次校驗時，從hash中取出salt，salt跟password進行hash；得到的結果跟儲存在DB中的hash進行比對，compareSync中已經實現了這一過程：bcrypt.compareSync(password, hashFromDB);

Let Code tell you

const bcrypt = require('bcryptjs');

const password = "123";

// Step1: Generate Hash
// salt is different everytime, and so is hash
let salt = bcrypt.genSaltSync(10);// 10 is by default
console.log(salt);//$2a$10$TnJ1bdJ3JIzGZC/jVS.v3e
let hash = bcrypt.hashSync(password, salt); // salt is inclued in generated hash 
 

console.log(hash);//$2a$10$TnJ1bdJ3JIzGZC/jVS.v3eXlr3ns0hDxeRtlia0CPQfLJVaRCWJVS

// Step2: Verify Password
// when verify the password, get the salt from hash, and hashed again with password
let saltFromHash = hash.substr(0, 29);
console.log(saltFromHash);//$2a$10$TnJ1bdJ3JIzGZC/jVS.v3e
let newHash = bcrypt.hashSync(password, saltFromHash);
console.log(newHash);//$2a$10$TnJ1bdJ3JIzGZC/jVS.v3eXlr3ns0hDxeRtlia0CPQfLJVaRCWJVS
 

console.log(hash === newHash); //true

// back end compare
console.log(bcrypt.compareSync(password, hash)); //true

If you have any questions or any bugs are found, please feel free to contact me.

Your comments and suggestions are welcome!