Unix Password

Unix Password

1. old

   • storage
     • /etc/passwd
       • readable by all users
   • password creation
     • 1. 1st 8 characters of user password turned into 56 bit key.
       • vulnerability: reduction of attack surface
     • 2. key + 12 bit salt used to encrypt 64 bit string of 0s using DES
       • goal: prevent use of rainbow tables
     • 3. encryption run 25 times
       • goal: slow down brute force attempts
     • 4. convert result to 11 printable ASCII charaters for storage in /etc/passwd along with 12 bit salt
     • 5. when user enters password, the same process is run and the result is compared to stored value
   • attacks
     • pre-computed dictionary attack to find any user's password
       • have user names.
       • have salt

2. new

   • storage
     • /etc/passwd
       • readable by everyone
       • does not contain password!
       • contains settings info about account
     • /etc/shadow
       • password stored here
       • accessible directly by root and users in shadow group
       • users may only access & update through a program that provides access through special execute privilege
   • password creation
     • 1. key + full password used with MD5 (or SHA-1) to generate hashed output
     • 2. hashed output stored in /etc/shadow using base 64 encoding
   • improvements
     • /etc/shadow not world readable
     • full password is used rather than 1st eight characters