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.cally varying between lower- and uppercase lettersSee Also: hashing algorithm, password, public key or appending simple numeric strings like  123 to thecryptography standards (PKCS) ends of words.Combining a dictionary andrule-based approach is often called a hybrid attack.password crackingÏ%ýÿ Brute-force attack: When dictionaries fail, bruteGuessing the password for an application or systemforce is usually the only alternative.A brute-forceuntil the right one is found.attack simply involves trying all possible combinaýÿtions of letters, numbers, and special characters toOverviewgenerate all possible passwords of every possibleSince passwords form one of the foundations of securitylength until either the correct password is found orfor most systems and networks, guessing or  crackingthe program or attacker gives up.passwords is high on the list of priorities for attackers tryýÿing to break into and compromise such systems.CrackýÿThe ease with which passwords can be cracked variesing passwords can be approached two ways:between different platforms and systems.Operatingsystems such as Microsoft Windows Server 2003 storeÏ%ýÿ Online cracking: This approach generally involvespasswords securely in encrypted form.To crack such sniffing network traffic to capture authenticationpasswords usually requires at the minimum physicalsessions and try to extract passwords from capturedaccess to the system using administrative credentials,information.This is generally slow and difficult toand even then brute force is usually the only approachaccomplish, but there are tools available that arefor extracting passwords.User applications such as Pspecifically designed for sniffing out passwordsoffice productivity tools can protect documents withfrom network traffic.passwords, and these are generally easier to crack thanÏ%ýÿ Offline cracking: This is the preferred method andpasswords for user accounts.Older platforms such asinvolves compromising a system through someWindows 95 stored password information in *.pwl filesexploit to gain access to its password file or data- that were weakly encrypted and easy to crack.base, and then running a tool called a passwordMarketplacecracker to try to guess valid passwords for userTwo popular tools used by attackers for cracking pass-accounts.Offline cracking can be performed on thewords are L0phtCrack (whose current version is namedcompromised machine or the password file can beLC4) and John the Ripper.While password crackers are grabbed and copied to a machine located outsidefrequently used for ill purposes, they also have validthe compromised network to be cracked at leisure.uses in business environments.For example, an adminýÿEven some worms such as DoubleTap and 1i0n canistrator might use a password cracker to audit theautomatically grab passwords from infected systems.strength of user passwords to ensure guidelines outlinedin the company security policy are being followed.237password grinding password recoveryCompanies like ElcomSoft (www.elcomsoft.com) and more difficult for the attacker to recover the originalPassword Crackers Inc.(www.pwcrack.com) also pro- passwords.Password hashes are used in challenge-vide legitimate tools and services to companies that need response authentication schemes such as NTLM forto recover lost passwords in order to access password- securely authenticating users without transmitting theprotected documents or an administrator account or to password over the connection.disable screen savers.See Also: hashing algorithm, password, passwordNotes crackingSome devices such as routers and switches often havedocumented procedures for recovering passwords whenpassword policypasswords have been lost or forgotten.Refer to the venýÿA policy enforced by an operating system regardingdor s Web site for more information.attributes of passwords for user accounts.See Also: brute-force attack, dictionary attack, JohnOverviewthe Ripper, L0phtCrack, password, PwdumpMost operating systems today include support for pass-word policies, a feature that allows administrators topassword grinding configure what forms of passwords are acceptable forManually trying to guess passwords for an application, accounts and how these passwords are managed.Onsystem, or network.Microsoft Windows 2000, for example, Local SecurityPolicy can be configured with the following passwordOverviewpolicy settings:Password grinding is a primitive form of passwordcracking in which the attacker simply attempts to log on Ï% Minimum allowed length for passwordsrepeatedly to the target machine, trying different pass-Ï%ýÿ Whether passwords can be simple (e.g., password)words until either the correct one is guessed or the sysýÿor complex (e.g., paSS4321)tem locks out the attacker.While this might seem like afruitless activity, it is amazing how many users employ Ï%ýÿ Whether a password history (list of old passwords)the word password as their passwords and how many will be maintained or not, and the number of pass-administrators fail to change or disable the default pass- words maintainedwords included with devices such as routers they installÏ%ýÿ Minimum password age (time until password mustPon their networks [ Pobierz caÅ‚ość w formacie PDF ]