Bug#774517: grub-pc: README material to help in troubleshooting password setting

[Yann Dirson]

Package: grub-pc
Version: 2.02~beta2-19
Severity: wishlist
Tags: patch

When setting up grub to password-protect commandline edition (see
configuration hints in my comment to #545163), it can take some effort
in case of error to determine whether the password is wrong, or
whether it is wrongly entered because of the keyboard layout.

What I wanted to do is to check that the password I expected was the
one in the password_pbkdf2 statement, which required a bit of work,
since grub-mkpasswd-pbkdf2 generates a new salt on each run.

The attached python script generates the hashed password from the
password and the salt.  Comparison is lefta as an exercise through
visual inspection :)
-------------- next part --------------
#!/usr/bin/python

from Crypto.Hash import SHA512
import pbkdf2
import sys

# default grub-mkpasswd-pbkdf2 settings
ITERATIONS = 10000
LENGTH = 64

def unpack(s):
    if s:
       return chr(int(s[:2], base=16)) + unpack(s[2:])
    return ''

_, passwd, salt = sys.argv

print pbkdf2.PBKDF2(passwd, unpack(salt),
                    iterations=ITERATIONS,
                    digestmodule=SHA512).hexread(LENGTH).upper()