Security Software Technologies' L0phtCrack 2.5 uses three methods to crack Windows NT password hashes: dictionary, hybrid, and brute force. By default, L0phtCrack runs all three methods on every hash: first dictionary, then hybrid, then brute force. To enable or disable any of the crack methods, choose Options from the Tools menu and set the options in the Tools Options dialog box, which Figure A shows.

In a dictionary crack, L0phtCrack encrypts (i.e., hashes) all the passwords in a dictionary file you specify and compares every result with the password hash. If L0phtCrack finds any matches, it knows the password is the dictionary word. L0phtCrack comes with a default dictionary file, words-english. You can download additional files from the Internet or create a custom file. In the Tools Options dialog box, you can choose to run the dictionary attack against the LANMAN password hash, the NT LAN Manager (NTLM) password hash, or both (which is the default).

In a hybrid crack, L0phtCrack extends the dictionary crack by appending numbers or symbols to each word in the dictionary file. For example, in addition to trying "Galileo," L0phtCrack also tries "Galileo24," "13Galileo," "?Galileo," "Galileo!," and so on. The default number of characters L0phtCrack tries is two, and you can change this number in the Tools Options dialog box.

In a brute-force crack, L0phtCrack tries every possible combination of characters in a character set. L0phtCrack offers four character sets, ranging from alpha only to all alphanumeric plus all symbol characters. You can choose a character set from the Character Set drop-down box in the Tools Options dialog box or type a custom character set in the Character Set drop-down box. L0phtCrack saves custom sets in files with an .lc extension. You can also specify a character set in the password file, as the example in Figure 2 shows.