Password Cracking

In cryptanalysis and computer security, password cracking is the process of recovering passwords from data that have been stored in or transmitted by a computer system. A common approach (brute-force attack) is to repeatedly try guesses for the password.

The purpose of password cracking might be to help a user recover a forgotten password (installing an entirely new password is less of a security risk, but it involves System Administration privileges), to gain unauthorized access to a system, or as a preventive measure by System Administrators to check for easily crackable passwords. On a file-by-file basis, password cracking is utilized to gain access to digital evidence for which a judge has allowed access but the particular file's access is restricted.

The best method of preventing a password from being cracked is to ensure that attackers cannot get access even to the hashed password. For example, on the Unixoperating system, hashed passwords were originally stored in a publicly accessible file /etc/passwd. On modern Unix (and similar) systems, on the other hand, they are stored in the file /etc/shadow, which is accessible only to programs running with enhanced privileges (i.e., "system" privileges). This makes it harder for a malicious user to obtain the hashed passwords in the first instance. Unfortunately, many common Network Protocols transmit passwords in cleartext or use weak challenge/response schemes.

There are many password cracking software tools, but the most popular are Cain and Abel, John the Ripper, Hashcat, Hydra, DaveGrohl and ElcomSoft. Many litigation support software packages also include password cracking functionality. Most of these packages employ a mixture of cracking strategies, with brute force and dictionary attacks proving to be the most productive.