Password cracking

Password cracking is the process of recovering passwords from data that has been stored in or transmitted by a computer system. A common approach is to repeatedly try guesses for the password. The purpose of password cracking might be to help a user recover a forgotten password (though installing an entirely new password is less of a security risk, but 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.
Contents
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1 Prevention
2 Software
3 References
4 External links


Prevention
Main article: Shadow password

The best method of preventing password cracking is to ensure that attackers cannot get access even to the encrypted password. For example, on the Unix operating system, encrypted 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 (ie, 'system' privileges). This makes it harder for a malicious user to obtain the encrypted passwords in the first instance. Unfortunately, many common network protocols transmit passwords in cleartext or use weak challenge/response schemes.[1][2]

Modern Unix systems have replaced traditional DES-based password hashing with stronger methods based on MD5 and Blowfish.[3] Other systems have also begun to adopt these methods. For instance, the Cisco IOS originally used a reversible Vigenère cipher to encrypt passwords, but now uses md5-crypt with a 24-bit salt when the "enable secret" command is used.[4] These newer methods use large salt values which prevent attackers from efficiently mounting offline attacks against multiple user accounts simultaneously. The algorithms are also much slower to execute which drastically increases the time required to mount a successful offline attack.[5]

Solutions like a security token give a formal proof answer by constantly shifting password. Those solutions abruptly reduce the timeframe for brute forcing (attacker needs to break and use the password within a single shift) and they reduce the value of the stolen passwords because of its short time validity.

Software
Main category: Password cracking software

There are many password cracking software tools, but the most popular[6] are Cain and Abel, John the Ripper, Hydra, ElcomSoft and Lastbit. 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.