javaspringspring-securitybcrypt

Why BCryptPasswordEncoder from Spring generate different outputs for same input?


I am using BCryptPasswordEncoder with Spring security. My expectation was that for the same input I will always get the same output. But for the same input I get different output. You could test it with the code snippet below:

String password = "123456"; 
PasswordEncoder passwordEncoder = new BCryptPasswordEncoder(); 
String encodedPassword = passwordEncoder.encode(password);
System.out.print(encodedPassword);

output: $2a$10$cYLM.qoXpeAzcZhJ3oXRLu9Slkb61LHyWW5qJ4QKvHEMhaxZ5qCPi

output2: $2a$10$KEvYX9yjj0f1X3Wl8S.KPuWzSWGyGM9ubI71NOm3ZNbJcwWN6agvW

output3: $2a$10$nCmrPtUaOLn5EI73VZ4Ouu1TmkSWDUxxD4N6A.8hPBWg43Vl.RLDC

Could someone explain, why BCryptPasswordEncoder behave like this?


Solution

  • public static void main(String[] args) {
      // spring 4.0.0
      org.springframework.security.crypto.password.PasswordEncoder encoder
       = new org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder();
    
       // $2a$10$lB6/PKg2/JC4XgdMDXyjs.dLC9jFNAuuNbFkL9udcXe/EBjxSyqxW
       // true
       // $2a$10$KbQiHKTa1WIsQFTQWQKCiujoTJJB7MCMSaSgG/imVkKRicMPwgN5i
       // true
       // $2a$10$5WfW4uxVb4SIdzcTJI9U7eU4ZwaocrvP.2CKkWJkBDKz1dmCh50J2
       // true
       // $2a$10$0wR/6uaPxU7kGyUIsx/JS.krbAA9429fwsuCyTlEFJG54HgdR10nK
       // true
       // $2a$10$gfmnyiTlf8MDmwG7oqKJG.W8rrag8jt6dNW.31ukgr0.quwGujUuO
       // true
    
        for (int i = 0; i < 5; i++) {
          // "123456" - plain text - user input from user interface
          String passwd = encoder.encode("123456");
    
          // passwd - password from database
          System.out.println(passwd); // print hash
    
          // true for all 5 iteration
          System.out.println(encoder.matches("123456", passwd));
        }
    }