Ophcrack is free open source utility which can be used to cracking the passwords of windows user accounts (including XP and Vista) with a GUI (Graphical User Interface). Have you ever fell in a situation where you wanted to recover your password that your nasty friend changed? Or do you want to be a geek star in front of your friends by cracking the password. Then this tool is for you.
Ophcrack cracks windows passwords by LM hashes through rainbow tables. A rainbow table is a lookup table offering time-memory tradeoff used in recovering plain text passwords from a password hash which is generated by a cryptographic hash function. Windows uses SAM file (Security Accounts Manager) which is stored as registry file to store passwords in a hashed format, either implemented using LM hash or NTLM hash. By default, Windows kernel puts a lock on the SAM file so that it may not be moved or copied while Windows is running. However, software developers have developed various techniques to dump the contents of the file in memory, so as to make password hacking feasible. Ophcrack has the ability to import SAM files using various techniques, like dumping dynamically for the local system, or of a remote system, or a pre-dumped encrypted file, etc. Once you have obtained the SAM file, the next thing that you require is the rainbow tables (which consists of the LM hashes, separately available for Windows XP and Vista), which are provided by developers (small ones which includes alphanumeric characters are free, while the big ones which includes all the printable characters like spaces, special characters are commercial). Once you have them both, cracking alpha numeric password is easy (if the length is under 14 chars). Ophcrack also supports cracking of NTLM hashes, which is used in Windows Vista, where LM hash is disabled or when passwords are greater than 14 characters. As every coin has two faces, this tool has a high probability of being misused, but nevertheless, it forces the developers to make more uncompromising techniques to impart security.