Brute - force attack - wikipedia Brute - force attack This article is about the cryptanalytic method. For similarly named methods in other disciplines, see Brute force. The EFF 's US $250,000 DES cracking machine contained over 1,800 custom chips and could brute - force a DES key in a matter of days. The photograph shows a DES Cracker circuit board fitted on both sides with 64 Deep Crack chips. In cryptography, a brute - force attack consists of an attacker trying many passwords or passphrases with the hope of eventually guessing correctly. The attacker systematically checks all possible passwords and passphrases until the correct one is found. Alternatively, the attacker can attempt to guess the key which is typically created from the password using a key derivation function. This is known as an exhaustive key search. A brute - force attack is a cryptanalytic attack that can, in theory, be used to attempt to decrypt any encrypted data ( except for data encrypted in an information - theoretically secure manner ). Such an attack might be used when it is not possible to take advantage of other weaknesses in an encryption system ( if any exist ) that would make the task easier. When password - guessing, this method is very fast when used to check all short passwords, but for longer passwords other methods such as the dictionary attack are used because a brute - force search takes too long. Longer passwords, passphrases and keys have more possible values, making them exponentially more difficult to crack than shorter ones. Brute - force attacks can be made less effective by obfuscating the data to be encoded making it more difficult for an attacker to recognize when the code has been cracked or by making the attacker do more work to test each guess. One of the measures of the strength of an encryption system is how long it would theoretically take an attacker to mount a successful brute - force attack against it. Brute - force attacks are an application of brute - force search, the general problem - solving technique of enumerating all candidates and checking each one. Contents 1 Basic concept 2 Theoretical limits 3 Credential recycling 4 Unbreakable codes 5 Countermeasures 6 Reverse brute - force attack 7 Software that performs brute - force attacks 8 See also 9 Notes 10 References 11 External links Basic concept Brute - force attacks work by calculating every possible combination that could make up a password and testing it to see if it is the correct password. As the password 's length increases, the amount of time, on average, to find the correct password increases exponentially. Theoretical limits The resources required for a brute - force attack grow exponentially with increasing key size, not linearly. Although U.S. export regulations historically restricted key lengths to 56 - bit symmetric keys ( e.g. Data Encryption Standard ), these restrictions are no longer in place, so modern symmetric algorithms typically use computationally stronger 128 - to 256 - bit keys. There is a physical argument that a 128 - bit symmetric key is computationally secure against brute - force attack. The so - called Landauer limit implied by the laws of physics sets a lower limit on the energy required to perform a computation of kT ln 2 per bit erased in a computation, where T is the temperature of the computing device in kelvins, k is the Boltzmann constant, and the natural logarithm of 2 is about 0.693. No irreversible computing device can use less energy than this, even in principle. Thus, in order to simply flip through the possible values for a 128 - bit symmetric key ( ignoring doing the actual computing to check it ) would theoretically require 2 − 1 bit flips on a conventional processor. If it is assumed that the calculation occurs near room temperature ( ~ 300 K ) the Von Neumann - Landauer Limit can be applied to estimate the energy required as ~ 10 joules, which is equivalent to consuming 30 gigawatts of power for one year. This is equal to 30 × 10 W × 365 × 24 × 3600 s = 9.46 × 10 J or 262.7 TWh ( more than 1 / 100th of the world energy production ). The full actual computation -- checking each key to see if a solution has been found -- would consume many times this amount. Furthermore, this is simply the energy requirement for cycling through the key space ; the actual time it takes to flip each bit is not considered, which is certainly greater than 0. However, this argument assumes that the register values are changed using conventional set and clear operations which inevitably generate entropy. It has been shown that computational hardware can be designed not to encounter this theoretical obstruction ( see reversible computing ), though no such computers are known to have been constructed. Modern GPUs are well - suited to the repetitive tasks associated with hardware - based password cracking As commercial successors of governmental ASIC solutions have become available, also known as custom hardware attacks, two emerging technologies have proven their capability in the brute - force attack of certain ciphers. One is modern graphics processing unit ( GPU ) technology, the other is the field - programmable gate array ( FPGA ) technology. GPUs benefit from their wide availability and price - performance benefit, FPGAs from their energy efficiency per cryptographic operation. Both technologies try to transport the benefits of parallel processing to brute - force attacks. In case of GPUs some hundreds, in the case of FPGA some thousand processing units making them much better suited to cracking passwords than conventional processors. Various publications in the fields of cryptographic analysis have proved the energy efficiency of today 's FPGA technology, for example, the COPACOBANA FPGA Cluster computer consumes the same energy as a single PC ( 600 W ), but performs like 2,500 PCs for certain algorithms. A number of firms provide hardware - based FPGA cryptographic analysis solutions from a single FPGA PCI Express card up to dedicated FPGA computers. WPA and WPA2 encryption have successfully been brute - force attacked by reducing the workload by a factor of 50 in comparison to conventional CPUs and some hundred in case of FPGAs. A single COPACOBANA board boasting 6 Xilinx Spartans -- a cluster is made up of 20 of these AES permits the use of 256 - bit keys. Breaking a symmetric 256 - bit key by brute force requires 2 times more computational power than a 128 - bit key. Fifty supercomputers that could check a billion billion ( 10 ) AES keys per second ( if such a device could ever be made ) would, in theory, require about 3 × 10 years to exhaust the 256 - bit key space. An underlying assumption of a brute - force attack is that the complete keyspace was used to generate keys, something that relies on an effective random number generator, and that there are no defects in the algorithm or its implementation. For example, a number of systems that were originally thought to be impossible to crack by brute force have nevertheless been cracked because the key space to search through was found to be much smaller than originally thought, because of a lack of entropy in their pseudorandom number generators. These include Netscape 's implementation of SSL ( famously cracked by Ian Goldberg and David Wagner in 1995 ) and a Debian / Ubuntu edition of OpenSSL discovered in 2008 to be flawed. A similar lack of implemented entropy led to the breaking of Enigma 's code. Credential recycling Credential recycling refers to the hacking practice of re-using username and password combinations gathered in previous brute - force attacks. A special form of credential recycling is pass the hash, where unsalted hashed credentials are stolen and re-used without first being brute forced. Unbreakable codes Certain types of encryption, by their mathematical properties, can not be defeated by brute force. An example of this is one - time pad cryptography, where every cleartext bit has a corresponding key from a truly random sequence of key bits. A 140 character one - time - pad - encoded string subjected to a brute - force attack would eventually reveal every 140 character string possible, including the correct answer -- but of all the answers given, there would be no way of knowing which was the correct one. Defeating such a system, as was done by the Venona project, generally relies not on pure cryptography, but upon mistakes in its implementation : the key pads not being truly random, intercepted keypads, operators making mistakes -- or other errors. Countermeasures In case of an offline attack where the attacker has access to the encrypted material, one can try key combinations without the risk of discovery or interference. However database and directory administrators can take countermeasures against online attacks, for example by limiting the number of attempts that a password can be tried, by introducing time delays between successive attempts, increasing the answer 's complexity ( e.g. requiring a CAPTCHA answer or verification code sent via cellphone ), and / or locking accounts out after unsuccessful logon attempts. Website administrators may prevent a particular IP address from trying more than a predetermined number of password attempts against any account on the site. Reverse brute - force attack In a reverse brute - force attack, a single ( usually common ) password is tested against multiple usernames or encrypted files. The process may be repeated for a select few passwords. In such a strategy, the attacker is generally not targeting a specific user. Reverse brute - force attacks can be mitigated by establishing a password policy that disallows common passwords. Software that performs brute - force attacks Aircrack - ng Cain and Abel Crack DaveGrohl Hashcat John the Ripper L0phtCrack Ophcrack RainbowCrack See also Bitcoin mining Cryptographic key length Distributed.net Key derivation function MD5CRK Metasploit Express Side - channel attack TWINKLE and TWIRL Unicity distance RSA Factoring Challenge Notes Jump up ^ Paar 2010, p. 7. Jump up ^ Landauer 1961, p. 183 - 191. Jump up ^ Graham 2011. Jump up ^ Kingsley - Hughes 2008. Jump up ^ Kamerling 2007. Jump up ^ Viega 2002, p. 18. Jump up ^ CERT - 2008. Jump up ^ Ellis. Jump up ^ NSA - 2009. Jump up ^ Reynard 1997, p. 86. Jump up ^ Burnett 2004. Jump up ^ Ristic 2010, p. 136. Jump up ^ http://www.infosecpro.com/applicationsecurity/a11.htm References Adleman, Leonard M. ; Rothemund, Paul W.K. ; Roweis, Sam ; Winfree, Erik ( June 10 -- 12, 1996 ). On Applying Molecular Computation To The Data Encryption Standard. Proceedings of the Second Annual Meeting on DNA Based Computers. Princeton University. Cracking DES -- Secrets of Encryption Research, Wiretap Politics & Chip Design. Electronic Frontier Foundation. ISBN 1 - 56592 - 520 - 3. Burnett, Mark ; Foster, James C. ( 2004 ). Hacking the Code : ASP.NET Web Application Security. Syngress. ISBN 1 - 932266 - 65 - 8. Diffie, W. ; Hellman, M.E. ( 1977 ). `` Exhaustive Cryptanalysis of the NBS Data Encryption Standard ''. Computer. 10 : 74 -- 84. doi : 10.1109 / c-m. 1977.217750. Graham, Robert David ( 22 June 2011 ). `` Password cracking, mining, and GPUs ''. erratasec.com. Retrieved 17 August 2011. Ellis, Claire. `` Exploring the Enigma ''. Plus Magazine. Kamerling, Erik ( 2007 - 11 - 12 ). `` Elcomsoft Debuts Graphics Processing Unit ( GPU ) Password Recovery Advancement ''. Symantec. Kingsley - Hughes, Adrian ( 2008 - 10 - 12 ). `` ElcomSoft uses NVIDIA GPUs to Speed up WPA / WPA2 Brute - force Attack ''. ZDNet. Landauer, L ( 1961 ). `` Irreversibility and Heat Generation in the Computing Process ''. IBM Journal of Research and Development. 5. doi : 10.1147 / rd. 53.0183. Paar, Christof ; Pelzl, Jan ; Preneel, Bart ( 2010 ). Understanding Cryptography : A Textbook for Students and Practitioners. Springer. ISBN 3 - 642 - 04100 - 0. Reynard, Robert ( 1997 ). Secret Code Breaker II : A Cryptanalyst 's Handbook. Jacksonville, FL : Smith & Daniel Marketing. ISBN 1 - 889668 - 06 - 0. Retrieved 2008 - 09 - 21. Ristic, Ivan ( 2010 ). Modsecurity Handbook. Feisty Duck. ISBN 1 - 907117 - 02 - 4. Viega, John ; Messier, Matt ; Chandra, Pravir ( 2002 ). Network Security with OpenSSL. O'Reilly. ISBN 0 - 596 - 00270 - X. Retrieved 2008 - 11 - 25. Wiener, Michael J. ( 1996 ). `` Efficient DES Key Search ''. Practical Cryptography for Data Internetworks. W. Stallings, editor, IEEE Computer Society Press. `` Technical Cyber Security Alert TA08 - 137A : Debian / Ubuntu OpenSSL Random Number Generator Vulnerability ''. United States Computer Emergency Readiness Team ( CERT ). 2008 - 05 - 16. Retrieved 2008 - 08 - 10. `` NSA 's How Mathematicians Helped Win WWII ''. National Security Agency. 15 Jan 2009. External links Basic idea on How Password Bruteforce Tool is Created RSA - sponsored DES - III cracking contest Demonstration of a brute - force device designed to guess the passcode of locked iPhones running iOS 10.3. 3 How We Cracked the Code Book Ciphers -- Essay by the winning team of the challenge in The Code Book Why not use larger cipher keys ? Cryptography History of cryptography Cryptanalysis Outline of cryptography Symmetric - key algorithm Block cipher Stream cipher Public - key cryptography Cryptographic hash function Message authentication code Random numbers Steganography Crypto - shredding Category Portal WikiProject Block ciphers ( security summary ) Common algorithms AES Blowfish DES ( internal mechanics, Triple DES ) Serpent Twofish Less common algorithms Camellia CAST - 128 IDEA RC2 RC5 RC6 SEED ARIA Skipjack TEA XTEA Other algorithms 3 - Way Akelarre Anubis BaseKing BassOmatic BATON BEAR and LION CAST - 256 Chiasmus CIKS - 1 CIPHERUNICORN - A CIPHERUNICORN - E CLEFIA CMEA Cobra COCONUT98 Crab Cryptomeria / C2 CRYPTON CS - Cipher DEAL DES - X DFC E2 FEAL FEA - M FROG G - DES GOST Grand Cru Hasty Pudding cipher Hierocrypt ICE IDEA NXT Intel Cascade Cipher Iraqi Kalyna KASUMI KeeLoq KHAZAD Khufu and Khafre KN - Cipher Kuznyechik Ladder - DES Libelle LOKI ( 97, 89 / 91 ) Lucifer M6 M8 MacGuffin Madryga MAGENTA MARS Mercy MESH MISTY1 MMB MULTI2 MultiSwap New Data Seal NewDES Nimbus NOEKEON NUSH PRESENT Prince Q RC6 REDOC Red Pike S - 1 SAFER SAVILLE SC2000 SHACAL SHARK Simon SM4 Speck Spectr - H64 Square SXAL / MBAL Threefish Treyfer UES Xenon xmx XXTEA Zodiac Design Feistel network Key schedule Lai -- Massey scheme Product cipher S - box P - box SPN Avalanche effect Block size Key size Key whitening ( Whitening transformation ) Attack ( cryptanalysis ) Brute - force ( EFF DES cracker ) MITM Biclique attack 3 - subset MITM attack Linear ( Piling - up lemma ) Differential Impossible Truncated Higher - order Differential - linear Distinguishing ( Known - key ) Integral / Square Boomerang Mod n Related - key Slide Rotational Side - channel Timing Power - monitoring Electromagnetic Acoustic Differential - fault XSL Interpolation Partitioning Rubber - hose Black - bag Davies Rebound Weak key Tau Chi - square Time / memory / data tradeoff Standardization AES process CRYPTREC NESSIE Utilization Initialization vector Mode of operation Padding Cryptography History of cryptography Cryptanalysis Outline of cryptography Symmetric - key algorithm Block cipher Stream cipher Public - key cryptography Cryptographic hash function Message authentication code Random numbers Steganography Crypto - shredding Category Portal WikiProject Retrieved from `` https://en.wikipedia.org/w/index.php?title=Brute-force_attack&oldid=820742312 '' Categories : Cryptographic attacks Hidden categories : All articles with unsourced statements Articles with unsourced statements from December 2012 Articles with unsourced statements from September 2010 Wikipedia articles needing page number citations from March 2012 Articles with unsourced statements from November 2010 Articles with unsourced statements from August 2012 Talk Contents About Wikipedia বাংলা Català Čeština Dansk Ελληνικά Español فارسی Français 한국어 Bahasa Indonesia Lietuvių Magyar Македонски മലയാളം မြန်မာဘာသာ Nederlands 日本 語 Polski Português Română Simple English Slovenščina Svenska Українська Tiếng Việt 中文 Edit links This page was last edited on 16 January 2018, at 10 : 09. 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Question: what is an attack where every possible password is attempted using a random or logical algorithm
Answer: brute-force attack