Passwords

A website requires its users to have passwords with a length of exactly 8 characters long and made of alpha-numeric characters.

1. How many passwords are possible?

2. What is the password entropy (n-bit security)?

Cracking passwords from the login page

Assuming that we use a password cracking tool that tries different login/password using the login page. We roughly estimates that:

• the login page returns a response in 100ms
• the cracking tool can spawn 100 threads sending such requests

1. How long would it take to:

   • brute-force the password for 1 user
   • brute force the password for m users

Cracking unsalted hash passwords

Assuming that we hack into their server and download their (lame) database of unsalted passwords. We roughly estimates that:

• computing a hash takes 10^(-9) seconds
• a table lookup takes 10^(-3) seconds (regardless the size of the table)
• testing whether two hashes are equal takes no time

1. For all types of attack, how long would it take to:

   • brute-force 1 specific password instance for m users
   • brute-force m specific password instances for 1 user
   • brute force n specific password instances for m users

2. If we use rainbow tables, how long would it take to:

   • crack the password of 1 user
   • crack the password of m users

Cracking salted hash passwords

Assuming now that the passwords are salted (each user has a different salt).

1. For all types of attack, how long would it take to:

   • brute-force 1 password for n users
   • brute-force m passwords for 1 user
   • brute force m passwords for n users

2. How about using rainbow tables on salted passwords?