multithreaded brute-force password hash cracker
crack threads keysize target
crack should attempt to find the password
associated to the target DES hash. It does this by trying all possible
lowercase alphabetic (a-z) passwords of length up to keysize. The
program should run with threads concurrent threads for speed.
Linux/Unix user passwords are never stored on the system. Instead, a
function called a hash is applied to the password. Then, the hashed
password is stored, traditionally in /etc/passwd or more recently in
/etc/shadow.
The classic hash function on Unix systems is crypt(3). To make things
harder on crackers, crypt also uses a two character string called a
salt which it combines with the password to create the hash.
Schematically:
password + salt ----crypt----> hash
The salt is visible in the hash as the first two characters. As an
example, a password ‘apple’ and salt ‘na’ become the hash
‘na3C5487Wz4zw’.
The crack program should extract the salt from
the first two characters of target, then repeatedly call crypt using
all possible passwords built of up to keysize lowercase alphabetic
characters.
When a match to target is found, the program should print the cracked
password and exit immediately. If the entire space of passwords is
searched with no match, the program should exit with no output.
See /export/mathcs/home/public/clair/bin/crack for a working version.
There is also a useful utility encode in the public os/demo_sec
directory. encode will encode passwords and salt into hashes. You can
also encode using the one line perl command:
perl -e 'print crypt("apple","na")'
Don’t forget to compile with the -lpthread and -lcrypt options.
The maximum allowed keysize is 8 (since crypt only uses the first 8
characters of the password anyway).
You might want to write this first as a single threaded program. Just
remember that crypt won’t work with multiple threads - you need to
switch to crypt_r.
You need to check passwords of length keysize, but don’t forget you
also need to check the shorter ones. The simplest way is probably to
write a function that checks all passwords which are exactly a given
length, and then have main call it in a loop from 1 to keysize.
For extra credit, add optional command line switches that allow searching for lowercase, uppercase, symbols, or combinations of them.
pthread_create(3)
pthread_join(3)
pthread_exit(3)
pthread_self(3)
pthread_mutex_init(3)
pthread_mutex_lock(3)
pthread_mutex_unlock(3)
crypt_r(3)
strcmp(3)
strcpy(3)
strncpy(3)