Thursday, March 8, 2012

More password cracking fun, with a twist.

The twist is, we wont be utilizing our CPU or GPU in the traditional sense of cracking a password hash. Let me explain.

In traditional password cracking, you have a hash file with hashes that you may have dumped from a database or operating system (like the sam file in windows or /etc/shadow in linux). You fire up your favorite password cracker like john the ripper, point to it your hash file and a wordlist then john does the rest. What's happening underneath the hood is that each word in the wordlist is ran through an algorithm (say md5 for example) and is thus converted to its hashed form. This hashed form of the word is then compared to the hashes in the hash file that was supplied to john the ripper. If there is a match, then the password was cracked.

Password crackers utilize the CPU or is some cases, the GPU, to do the computational work of converting the words in the wordlist files to their respective hash representations and then comparing them to a hash list. The amouont of words processed per second is dependent on the speed of the CPU or GPU and its not uncommon for password crackers like john and hashcat to process thousands of words per second.

Today, most of this processing work has gone into the cloud. There are many websites that offer password cracking services. You submit a hash, and withing a few seconds, if the hash is found, you will receive its plain text. Most of these services utilize rainbow tables which make for faster hash lookups, thus minimizing the time it takes to receive an answer.


While exploring some of the new tools in the recently released bactrack 5 R2, i came across this tool. This tool will accept a hash or a list of hashes in a file and the hash type. It will then utilize various web resources to find you the resulting password in plaintext (this means an internet connection is required).

Usage is simple.
# python MD5 -h "482c811da5d5b4bc6d497ffa98491e38"

Cracking hash: 482c811da5d5b4bc6d497ffa98491e38

Analyzing with md5hashcracker (

***** HASH CRACKED!! *****
The original string is: password123

The following hashes were cracked:

482c811da5d5b4bc6d497ffa98491e38 -> password123

Another useful utility is the hash identifier python script, which now comes bundled with hashcat in BT5 R2. This script aims to identify the hash type (md5, lm, ntlm, sha-1, etc)of given a hash. Just run the script and enter a hash and it the program will do its very best to identify the hash type. The findmyhash utility takes a hash type as one of its arguments so this hash identifier tool can be used to determine this.

usage: # python

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