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66-453: Many (but not all) AE schemes allow the message to contain "associated data" (AD) which is not made confidential, but its integrity is protected (i.e., it is readable, but tampering with it will be detected). A typical example is the header of a network packet that contains its destination address. To properly route the packet, all intermediate nodes in the message path need to know the destination, but for security reasons they cannot possess

132-410: A cryptographic salt , along with the hash. The salt is combined with the password when computing the hash, so an attacker precomputing a rainbow table would have to store for each password its hash with every possible salt value. This becomes infeasible if the salt has a big enough range, say a 32-bit number. Many authentication systems in common use do not employ salts and rainbow tables are available on

198-501: A MySpace phishing scheme in 2006 revealed 34,000 passwords, of which only 8.3% used mixed case, numbers, and symbols. The full strength associated with using the entire ASCII character set (numerals, mixed case letters, and special characters) is only achieved if each possible password is equally likely. This seems to suggest that all passwords must contain characters from each of several character classes, perhaps upper and lower-case letters, numbers, and non-alphanumeric characters. Such

264-649: A character set (e.g., the ASCII character set), syllables designed to form pronounceable passwords or even words from a word list (thus forming a passphrase ). The strength of random passwords depends on the actual entropy of the underlying number generator; however, these are often not truly random, but pseudorandom. Many publicly available password generators use random number generators found in programming libraries that offer limited entropy. However, most modern operating systems offer cryptographically strong random number generators that are suitable for password generation. It

330-442: A cracking rate of 7 billion attempts per second. A 13-character password was estimated to withstand GPU-computed attempts for over 900,000 years. In the context of 2023 hardware technology, the 2012 standard of an eight-character alpha-numeric password has become vulnerable, succumbing in a few hours. The time needed to crack a 13-character password is reduced to a few years. The current emphasis, thus, has shifted. Password strength

396-402: A game. NIST Special Publication 800-63 of June 2004 (revision two) suggested a scheme to approximate the entropy of human-generated passwords: Using this scheme, an eight-character human-selected password without uppercase characters and non-alphabetic characters OR with either but of the two character sets is estimated to have eighteen bits of entropy. The NIST publication concedes that at

462-411: A letter, adding one or two numbers, and a special character. This predictability means that the increase in password strength is minor when compared to random passwords. Password Safety Awareness Projects Google developed Interland teach the kid internet audience safety on internet. On the chapter called Tower Of Tresure it is advised to use unusual names paired with characters like (₺&@#%) with

528-518: A message and subsequently applying a MAC to the ciphertext (the Encrypt-then-MAC approach) implies security against an adaptive chosen ciphertext attack , provided that both functions meet minimum required properties. Katz and Yung investigated the notion under the name "unforgeable encryption" and proved it implies security against chosen ciphertext attacks. In 2013, the CAESAR competition

594-463: A monitor or in an unlocked desk drawer. Use of a password manager is recommended by the NCSC. The possible character set for a password can be constrained by different websites or by the range of keyboards on which the password must be entered. As with any security measure, passwords vary in strength; some are weaker than others. For example, the difference in strength between a dictionary word and

660-427: A password can be weak, corresponding to the strengths of various attack schemes; the core principle is that a password should have high entropy (usually taken to be equivalent to randomness) and not be readily derivable by any "clever" pattern, nor should passwords be mixed with information identifying the user. Online services often provide a restore password function that a hacker can figure out and by doing so bypass

726-413: A password system only stores the hash of the password, an attacker can pre-compute hash values for common password variants and all passwords shorter than a certain length, allowing very rapid recovery of the password once its hash is obtained. Very long lists of pre-computed password hashes can be efficiently stored using rainbow tables . This method of attack can be foiled by storing a random value, called

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792-424: A password, sometimes guided by suggestions or restricted by a set of rules, when creating a new account for a computer system or internet website. Only rough estimates of strength are possible since humans tend to follow patterns in such tasks, and those patterns can usually assist an attacker. In addition, lists of commonly chosen passwords are widely available for use by password-guessing programs. Such lists include

858-429: A password. In the landscape of 2012, as delineated by William Cheswick in an article for ACM magazine, password security predominantly emphasized an alpha-numeric password of eight characters or more. Such a password, it was deduced, could resist ten million attempts per second for a duration of 252 days. However, with the assistance of contemporary GPUs at the time, this period was truncated to just about 9 hours, given

924-469: A poor protocol design or implementation turning Alice's side into an oracle . Naturally, this attack cannot be mounted at all when the keys are generated randomly. Key commitment was originally studied in the 2010s by Abdalla et al. and Farshim et al. under the name "robust encryption". To mitigate the attack described above without removing the "oracle", a key-committing AEAD that does not allow this type of crafted messages to exist can be used. AEGIS

990-455: A problem to an international traveler who wished to log into a remote system using a keyboard on a local computer (see article concerned with keyboard layouts ) . Many handheld devices, such as tablet computers and smart phones , require complex shift sequences or keyboard app swapping to enter special characters. Authentication programs can vary as to the list of allowable password characters. Some do not recognize case differences (e.g.,

1056-649: A requirement is a pattern in password choice and can be expected to reduce an attacker's "work factor" (in Claude Shannon's terms). This is a reduction in password "strength". A better requirement would be to require a password not to contain any word in an online dictionary, or list of names, or any license plate pattern from any state (in the US) or country (as in the EU). If patterned choices are required, humans are likely to use them in predictable ways, such as capitalizing

1122-417: A second (wrong) key K M will be incorrect, the authentication tag would still match. Since crafting a message with such property requires Mallory to already possess both K A and K M , the issue might appear to be one of a purely academic interest. However, under special circumstances, practical attacks can be mounted against vulnerable implementations. For example, if an identity authentication protocol

1188-399: A set of N possible symbols, the number of possible passwords can be found by raising the number of symbols to the power L , i.e. N . Increasing either L or N will strengthen the generated password. The strength of a random password as measured by the information entropy is just the base-2 logarithm or log 2 of the number of possible passwords, assuming each symbol in the password

1254-452: A standard desktop computer, using a high-end graphics processor for that time. Such a device will crack a six-letter single-case password in one day. The work can be distributed over many computers for an additional speedup proportional to the number of available computers with comparable GPUs. Special key stretching hashes are available that take a relatively long time to compute, reducing the rate at which guessing can take place. Although it

1320-438: A word with obfuscation (e.g. letters in the password are substituted by, say, numbers — a common approach) may cost a password-cracking device a few more seconds; this adds little strength. The examples below illustrate various ways weak passwords might be constructed, all of which are based on simple patterns which result in extremely low entropy, allowing them to be tested automatically at high speeds.: There are many other ways

1386-608: Is a "great place" to store a written password. The minimum number of bits of entropy needed for a password depends on the threat model for the given application. If key stretching is not used, passwords with more entropy are needed. RFC 4086, "Randomness Requirements for Security", published June 2005, presents some example threat models and how to calculate the entropy desired for each one. Their answers vary between 29 bits of entropy needed if only online attacks are expected, and up to 96 bits of entropy needed for important cryptographic keys used in applications like encryption where

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1452-580: Is a guide to choosing satisfactory passwords. It is intended to: Previous password policies used to prescribe the characters which passwords must contain, such as numbers, symbols, or upper/lower case. While this is still in use, it has been debunked as less secure by university research, by the original instigator of this policy, and by the cyber security departments (and other related government security bodies ) of USA and UK. Password complexity rules of enforced symbols were previously used by major platforms such as Google and Facebook, but these have removed

1518-430: Is also possible to use ordinary dice to generate random passwords (see Random password generator § Stronger methods ) . Random password programs often can ensure that the resulting password complies with a local password policy ; for instance, by always producing a mix of letters, numbers, and special characters. For passwords generated by a process that randomly selects a string of symbols of length, L , from

1584-558: Is an example fast (if the AES instruction set is present), key-committing AEAD. It is possible to add key-commitment to an existing AEAD scheme. The plaintext is first encrypted, then a MAC is produced based on the resulting ciphertext. The ciphertext and its MAC are sent together. ETM is the standard method according to ISO/IEC 19772:2009. It is the only method which can reach the highest definition of security in AE, but this can only be achieved when

1650-483: Is based on successful decryption of a message that uses a password-based key, Mallory's ability to craft a single message that would be successfully decrypted using 1000 different keys associated with weak , and thus known to her, potential passwords, can speed up her search for passwords by a factor of almost 1000. For this dictionary attack to succeed, Mallory also needs an ability to distinguish successful decryption by Alice from an unsuccessful one, due, for example, to

1716-403: Is commonly referred to as the "bits of entropy". A password with 42 bits of entropy would be as strong as a string of 42 bits chosen randomly, for example by a fair coin toss. Put another way, a password with 42 bits of entropy would require 2 (4,398,046,511,104) attempts to exhaust all possibilities during a brute force search . Thus, increasing the entropy of the password by one bit doubles

1782-399: Is considered best practice to use key stretching, many common systems do not. Another situation where quick guessing is possible is when the password is used to form a cryptographic key . In such cases, an attacker can quickly check to see if a guessed password successfully decodes encrypted data. For example, one commercial product claims to test 103,000 WPA PSK passwords per second. If

1848-402: Is inherently insecure because the person's lifestyle, entertainment preferences, and other key individualistic qualities usually come into play to influence the choice of password, while the prevalence of online social media has made obtaining information about people much easier. Systems that use passwords for authentication must have some way to check any password entered to gain access. If

1914-580: Is no expectation that any digital computer (or combination) will be capable of breaking 256-bit encryption via a brute-force attack. Whether or not quantum computers will be able to do so in practice is still unknown, though theoretical analysis suggests such possibilities. ‹The template How-to is being considered for merging .›   Guidelines for choosing good passwords are typically designed to make passwords harder to discover by intelligent guessing. Common guidelines advocated by proponents of software system security have included: Forcing

1980-417: Is now gauged not just by its complexity but its length, with recommendations leaning towards passwords comprising at least 13-16 characters. This era has also seen the rise of Multi-Factor Authentication (MFA) as a crucial fortification measure. The advent and widespread adoption of password managers have further aided users in cultivating and maintaining an array of strong, unique passwords. A password policy

2046-433: Is produced independently. Thus a random password's information entropy, H , is given by the formula: H = log 2 ⁡ N L = L log 2 ⁡ N = L log ⁡ N log ⁡ 2 {\displaystyle H=\log _{2}N^{L}=L\log _{2}N=L{\log N \over \log 2}} where N is the number of possible symbols and L

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2112-521: Is related to the stringent requirements of choosing keys used in encryption. In 1999, an Electronic Frontier Foundation project broke 56-bit DES encryption in less than a day using specially designed hardware. In 2002, distributed.net cracked a 64-bit key in 4 years, 9 months, and 23 days. As of October 12, 2011, distributed.net estimates that cracking a 72-bit key using current hardware will take about 45,579 days or 124.8 years. Due to currently understood limitations from fundamental physics, there

2178-650: Is the number of symbols in the password. H is measured in bits . In the last expression, log can be to any base . A binary byte is usually expressed using two hexadecimal characters. To find the length, L, needed to achieve a desired strength H, with a password drawn randomly from a set of N symbols, one computes: L = ⌈ H log 2 ⁡ N ⌉ {\displaystyle L={\left\lceil {\frac {H}{\log _{2}N}}\right\rceil }} where ⌈   ⌉ {\displaystyle \left\lceil \ \right\rceil } denotes

2244-503: The Secure Hash Algorithm (SHA) series, are very hard to reverse, so an attacker who gets hold of the hash value cannot directly recover the password. However, knowledge of the hash value lets the attacker quickly test guesses offline. Password cracking programs are widely available that will test a large number of trial passwords against a purloined cryptographic hash. Improvements in computing technology keep increasing

2310-483: The authentication factors (knowledge, ownership, inherence). The first factor is the main focus of this article. The rate at which an attacker can submit guessed passwords to the system is a key factor in determining system security. Some systems impose a time-out of several seconds after a small number (e.g. three) of failed password entry attempts. In the absence of other vulnerabilities , such systems can be effectively secured with relatively simple passwords. However,

2376-699: The E&;M approach has not been proved to be strongly unforgeable in itself, it is possible to apply some minor modifications to SSH to make it strongly unforgeable despite the approach. A MAC is produced based on the plaintext, then the plaintext and MAC are together encrypted to produce a ciphertext based on both. The ciphertext (containing an encrypted MAC) is sent. Until TLS 1.2, all available SSL/TLS cipher suites were MtE. MtE has not been proven to be strongly unforgeable in itself. The SSL/TLS implementation has been proven to be strongly unforgeable by Krawczyk who showed that SSL/TLS was, in fact, secure because of

2442-483: The Internet for several such systems. Password strength is specified by the amount of information entropy , which is measured in shannon (Sh) and is a concept from information theory . It can be regarded as the minimum number of bits necessary to hold the information in a password of a given type. A related measure is the base-2 logarithm of the number of guesses needed to find the password with certainty, which

2508-475: The MAC used is "strongly unforgeable". IPSec adopted EtM in 2005. In November 2014, TLS and DTLS received extensions for EtM with RFC   7366 . Various EtM ciphersuites exist for SSHv2 as well (e.g., hmac-sha1-etm@openssh.com ). A MAC is produced based on the plaintext, and the plaintext is encrypted without the MAC. The plaintext's MAC and the ciphertext are sent together. Used in, e.g., SSH . Even though

2574-520: The average password entropy was estimated at 40.54 bits. Thus, in one analysis of over 3 million eight-character passwords, the letter "e" was used over 1.5 million times, while the letter "f" was used only 250,000 times. A uniform distribution would have had each character being used about 900,000 times. The most common number used is "1", whereas the most common letters are a, e, o, and r. Users rarely make full use of larger character sets in forming passwords. For example, hacking results obtained from

2640-408: The block size of the encryption function. Padding errors often result in the detectable errors on the recipient's side, which in turn lead to padding oracle attacks, such as Lucky Thirteen . Header (computing) In information technology , header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission , the data following

2706-447: The dozens of accounts they access. For example, in 2005, security expert Bruce Schneier recommended writing down one's password: Simply, people can no longer remember passwords good enough to reliably defend against dictionary attacks, and are much more secure if they choose a password too complicated to remember and then write it down. We're all good at securing small pieces of paper. I recommend that people write their passwords down on

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2772-498: The encoding used alongside the MtE mechanism. However, Krawczyk's proof contains flawed assumptions about the randomness of the initialization vector (IV). The 2011 BEAST attack exploited the non-random chained IV and broke all CBC algorithms in TLS 1.0 and under. In addition, deeper analysis of SSL/TLS modeled the protection as MAC-then-pad-then-encrypt, i.e. the plaintext is first padded to

2838-414: The hardest to remember. The imposition of a requirement for such passwords in a password policy may encourage users to write them down, store them in mobile devices , or share them with others as a safeguard against memory failure. While some people consider each of these user resorts to increase security risks, others suggest the absurdity of expecting users to remember distinct complex passwords for each of

2904-418: The header is sometimes called the payload or body . It is vital that header composition follows a clear and unambiguous specification or format, to allow for parsing . Weak password Password strength is a measure of the effectiveness of a password against guessing or brute-force attacks . In its usual form, it estimates how many trials an attacker who does not have direct access to

2970-741: The inclusion of lowercase letters, uppercase letters, numbers, and symbols in passwords was a common policy but has been found to decrease security, by making it easier to crack. Research has shown how predictable the common use of such symbols are, and the US and UK government cyber security departments advise against forcing their inclusion in password policy. Complex symbols also make remembering passwords much harder, which increases writing down, password resets, and password reuse – all of which lower rather than improve password security. The original author of password complexity rules, Bill Burr, has apologized and admits they decrease security, as research has found; this

3036-511: The integrity of both the associated data and the confidential information in a message. AD is useful, for example, in network packets where the header should be visible for routing , but the payload needs to be confidential, and both need integrity and authenticity . The notion of AEAD was formalized by Rogaway (2002). AE was originally designed primarily to provide the ciphertext integrity: successful validation of an authentication tag by Alice using her symmetric key K A indicates that

3102-426: The intended purpose. Passwords that are too difficult to remember may be forgotten and so are more likely to be written on paper, which some consider a security risk. In contrast, others argue that forcing users to remember passwords without assistance can only accommodate weak passwords, and thus poses a greater security risk. According to Bruce Schneier , most people are good at securing their wallets or purses, which

3168-412: The mathematical ceiling function , i.e. rounding up to the next largest whole number . The following table uses this formula to show the required lengths of truly randomly generated passwords to achieve desired password entropies for common symbol sets: People are notoriously poor at achieving sufficient entropy to produce satisfactory passwords. According to one study involving half a million users,

3234-415: The message was not tampered with by an adversary Mallory that does not possess the K A . The AE schemes usually do not provide the key commitment , a guarantee that the decryption would fail for any other key. As of 2021, most existing AE schemes (including the very popular GCM) allow some messages to be decoded without an error using more than just the (correct) K A ; while their plaintext decoded using

3300-424: The number of guesses required, making an attacker's task twice as difficult. On average, an attacker will have to try half the possible number of passwords before finding the correct one. Random passwords consist of a string of symbols of specified length taken from some set of symbols using a random selection process in which each symbol is equally likely to be selected. The symbols can be individual characters from

3366-539: The numerous online dictionaries for various human languages, breached databases of plaintext and hashed passwords from various online business and social accounts, along with other common passwords. All items in such lists are considered weak, as are passwords that are simple modifications of them. Although random password generation programs are available nowadays which are meant to be easy to use, they usually generate random, hard-to-remember passwords, often resulting in people preferring to choose their own. However, this

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3432-500: The observation that securely combining separate confidentiality and authentication block cipher operation modes could be error prone and difficult. This was confirmed by a number of practical attacks introduced into production protocols and applications by incorrect implementation, or lack of authentication. Around the year 2000, a number of efforts evolved around the notion of standardizing modes that ensured correct implementation. In particular, strong interest in possibly secure modes

3498-428: The password or key needs to be secure for a long period and stretching isn't applicable. A 2010 Georgia Tech Research Institute study based on unstretched keys recommended a 12-character random password but as a minimum length requirement. It pays to bear in mind that since computing power continually grows, to prevent offline attacks the required number of bits of entropy should also increase over time. The upper end

3564-417: The password would need, on average, to guess it correctly. The strength of a password is a function of length, complexity, and unpredictability. Using strong passwords lowers the overall risk of a security breach, but strong passwords do not replace the need for other effective security controls . The effectiveness of a password of a given strength is strongly determined by the design and implementation of

3630-583: The rate at which guessed passwords can be tested. For example, in 2010, the Georgia Tech Research Institute developed a method of using GPGPU to crack passwords much faster. Elcomsoft invented the usage of common graphic cards for quicker password recovery in August 2007 and soon filed a corresponding patent in the US. By 2011, commercial products were available that claimed the ability to test up to 112,000 passwords per second on

3696-515: The requirement following the discovery that they actually reduced security. This is because the human element is a far greater risk than cracking, and enforced complexity leads most users to highly predictable patterns (number at the end, swap 3 for E, etc.) which helps crack passwords. So password simplicity and length (passphrases) are the new best practice and complexity is discouraged. Forced complexity rules also increase support costs, and user friction and discourage user signups. Password expiration

3762-453: The secret key. Schemes that allow associated data provide authenticated encryption with associated data , or AEAD . A typical programming interface for an AE implementation provides the following functions: The header part is intended to provide authenticity and integrity protection for networking or storage metadata for which confidentiality is unnecessary, but authenticity is desired. The need for authenticated encryption emerged from

3828-516: The system store information about the user's passwords in some form and if that information is stolen, say by breaching system security, the user's passwords can be at risk. In 2019, the United Kingdom's NCSC analyzed public databases of breached accounts to see which words, phrases, and strings people used. The most popular password on the list was 123456, appearing in more than 23 million passwords. The second-most popular string, 123456789,

3894-569: The time of development, little information was available on the real-world selection of passwords. Later research into human-selected password entropy using newly available real-world data has demonstrated that the NIST scheme does not provide a valid metric for entropy estimation of human-selected passwords. The June 2017 revision of SP 800-63 (Revision three) drops this approach. Because national keyboard implementations vary, not all 94 ASCII printable characters can be used everywhere. This can present

3960-406: The upper-case "E" is considered equivalent to the lower-case "e"), and others prohibit some of the other symbols. In the past few decades, systems have permitted more characters in passwords, but limitations still exist. Systems also vary as to the maximum length of passwords allowed. As a practical matter, passwords must be both reasonable and functional for the end user as well as strong enough for

4026-452: The valid passwords are simply stored in a system file or database, an attacker who gains sufficient access to the system will obtain all user passwords, giving the attacker access to all accounts on the attacked system and possibly other systems where users employ the same or similar passwords. One way to reduce this risk is to store only a cryptographic hash of each password instead of the password itself. Standard cryptographic hashes, such as

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4092-463: Was announced to encourage design of authenticated encryption modes. In 2015, ChaCha20-Poly1305 is added as an alternative AE construction to GCM in IETF protocols. Authenticated encryption with associated data (AEAD) is a variant of AE that allows the message to include "associated data" (AD, additional non-confidential information, a.k.a. "additional authenticated data", AAD). A recipient can check

4158-564: Was in some older password policies but has been debunked as best practice and is not supported by USA or UK governments, or Microsoft which removed the password expiry feature. Password expiration was previously trying to serve two purposes: However, password expiration has its drawbacks: The hardest passwords to crack, for a given length and character set, are random character strings; if long enough they resist brute force attacks (because there are many characters) and guessing attacks (due to high entropy). However, such passwords are typically

4224-438: Was not much harder to crack, while the top five included " qwerty ", "password", and 1111111. Passwords are created either automatically (using randomizing equipment) or by a human; the latter case is more common. While the strength of randomly chosen passwords against a brute-force attack can be calculated with precision, determining the strength of human-generated passwords is difficult. Typically, humans are asked to choose

4290-803: Was sparked by the publication of Charanjit Jutla 's integrity-aware CBC and integrity-aware parallelizable , IAPM, modes in 2000 (see OCB and chronology). Six different authenticated encryption modes (namely offset codebook mode 2.0 , OCB   2.0; Key Wrap ; counter with CBC-MAC , CCM; encrypt then authenticate then translate , EAX; encrypt-then-MAC , EtM; and Galois/counter mode , GCM) have been standardized in ISO/IEC 19772:2009. More authenticated encryption methods were developed in response to NIST solicitation. Sponge functions can be used in duplex mode to provide authenticated encryption. Bellare and Namprempre (2000) analyzed three compositions of encryption and MAC primitives, and demonstrated that encrypting

4356-418: Was widely reported in the media in 2017. Online security researchers and consultants are also supportive of the change in best practice advice on passwords. Some guidelines advise against writing passwords down, while others, noting the large numbers of password-protected systems users must access, encourage writing down passwords as long as the written password lists are kept in a safe place, not attached to

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