6.4 Passwords

6.4 Passwords

1. until early 2000's passwords were encrypted using the following process

   • password was translated into a DES key using ASCII
     • a plaintext string of 64 zeros was encrypted using the DES key
       • The cyphertext was then encrypted again using that same DES key
         • process was repeated 25 times
           • final cyphertext converted to ASCII and stored in etc/passwd

2. In actual fact this process was using DES to make a 1 way finction

   • given an encrypted password it would be difficult to find out what the password represents nb
     • it is not really encryption because there is no key that can be used to decrypt the scrambled form back into clear text

3. a 12 bit random salt is also used to prevent hashes being the same if 2 users have the same password

   • if 2 hashes in etc/passwd were the same you would know the users have the same password, if it was the same as yours you would know how to login as the other user

4. susceptible to dictionary attacks, see examples on page 20 of how a dictionary attack works

5. because etc/passwd is human readable anyone can get it and see the hashed passwords values

   • one way to combat this is to move hashed passwords from etc/passwd to etc/shadow
     • etc/shadow is only for storing encrypted passwords, so its possible to place tight security controls around it and restrict access
       • see example on pg 21-22
       • the main advantage is that although dictionary attacks are still possible its harder to get the file to compare hashes with your dictionary