If I change my server bcrypt can remember salt and decrypt Password,How can do that?

Question

I want to deploy my program to another server,my script can decrypt all passwords of my customers in database correctly?

//old server
const bcrypt = require("bcrypt");
const salt = bcrypt.genSalt();
password = bcrypt.hash("password", salt);

//new server 
const auth = bcrypt.compare(password, "password")

How can bcrypt decrypt passwords with a variable "salt" that is generated randomly?

Answer 1

BCrypt hashes are stored in one of two forms.

The more common is Modular Crypt Format and has the form...

$2y$10$kV7kssmFuFOydBewIp9ele8GMkWGDPpte6jGGDAabpsBmxtzWxfZW

Where:

• $ is a delimiter
• 2 indicates the algorithm is BCrypt
• y is the version of BCrypt
• 10 is the cost
• kV7kssmFuFOydBewIp9ele is the salt
• 8GMkWGDPpte6jGGDAabpsBmxtzWxfZW is the hash.

A more modern alternative is PHC string format which makes it more obvious which parts correspond to which values:

$bcrypt$v=98$r=10$cIF1Ev2ATA6/iYv4kddXCQ$qcrDoGjsiB2eLq1/vCZWiAZ8bEs4+Qs

In both cases, the string persisted to your database contains everything necessary to compare a candidate password: The hash, the salt, and the cost, the algorithm's name, and its version.