Ophcrack is a special kind of Linux distro that focuses primarily on password cracking, Ophcrack is basically a free open source program that requires a Linux based environment to run. Ophcrack can be used to crack passwords for Windows XP, Vista and Windows 7.
How does Ophcrack Work?
To understand how ophcrack cracks password we must first learn about how Windows stores password.
Any computer system that requires password authentication must contain a database of passwords, either hashed or in plaintext.
Windows uses a thing called MD5 Hashes, so what it basically does is when you type a password and create it, it creates a cryptographic hash.
Now hashes don’t work both ways, what that means is you can create a hash from a password, but you can take a hash and change it back to text because you can’t easily decrypt them.
So, how does Ophcrack decrypts password?
Ophcrack uses tables more formally known as rainbow tables.
Rainbow tables are pre-computed tables that contain a list of hundreds of millions of hashes. You can easily downloaded rainbow tables off the internet. The reason these rainbow tables are pre-computed is because it would a ridiculously long amount of time to generate these hashes.
So ophcrack uses these rainbow tables and compares the hashes stored in these tables to the ones generated by Windows. It may take some time to crack the password depending on the strength of the password.
How to use Ophcrack-
- First download the ophcrack LiveCD from here
- Burn the image file into an usb stick.
- Ophcrack usually contains a few rainbow tables but you should download additional ones off the internet if the password you aim to crack is strong.
- If you have downloaded additional rainbow tables then paste that rainbow table in the usb stick.
- Connect the usb stick to the target PC.
- Restart the PC and go into BIOS and change the Boot order, so that the OS boots off the usb stick first.
- After changing the boot order save the changes and boot from the usb stick.
- Select the “Ophcrack graphic mode – automatic” from the list of options presented to you on the screen.
- You will a whole bunch of text popping on your screen, don’t worry, it just means you have done everything right so far.
- Once ophcrack has booted completely, a window will automatically pop up which will start comparing hashes. Depending on the strength of the password it may take a few minutes for ophcrack to find the right password.
Ophcrack can come in handy if you have forgotten your login password but do not use ophcrack on someone else’s computer without their consent, it’s illegal.