Passwords: salts, hashes

In the previous post we saw that network and web site accounts with reasonable security use hash functions to protect passwords.

But even using a hash function isn’t enough, because the bad guys have rainbow tables. A rainbow table is a list of common passwords (like Password123) and their hash values. So if a site suffers a data breach exposing account data, a simple hash function won’t be much of a barrier, because the criminal can compare the hash values (in the breach data) against a rainbow table and recover many of the weaker passwords.

To counter rainbow tables, sites typically salt users’ passwords: when someone creates a password, the site generates some random characters (the salt), appends that to the user’s password, runs the salted password through the hash function, and then stores the hash value and the salt. When the user tries to log in, the site takes the password they typed, appends the salt stored with the user’s account, sends that through the hash function, and compares the hash values.

Salting hashes sets the bar a lot higher, because the criminal would need to compute a new rainbow table for each password (because each password will have a different salt).

This is why I get frustrated with fiction that makes it look easy to crack passwords. Any account worth hacking will likely be protected by some or all of the following safeguards:

  1. salted and hashed passwords
  2. a password policy enforcing complexity rules (e.g., your password has to be at least eight characters, has to include numbers and punctuation characters, and can’t look too much like a word)
  3. active response locking an account after too many failed attempts
  4. two-factor authentication (you log in with your username and password, but then the site won’t give you access until you enter a code it sends to your cell phone)

Active response in particular makes guessing passwords impractical. If your character is trying to break into a network or web site account, too many failed attempts are going to end up locking the target account. Your character is better off trying to steal the password with a phishing attack, social engineering, using a keylogger, exploiting a flaw in the “forgot my password” feature, or even a security camera pointed at the keyboard.

And an account protected by two-factor authentication is nearly unassailable, because your character would need the target’s password and their cell phone. Social engineering might be best here.

Advertisements

Author: carl

A web programmer and Linux system administrator who would like to be a writer.