HistoryPasswords have been used since ancient times. Sentries would challenge those wishing to enter an area to supply a password or ''watchword'', and would only allow a person or group to pass if they knew the password. describes the system for the distribution of watchwords in the as follows:
The way in which they secure the passing round of the watchword for the night is as follows: from the tenth maniple of each class of infantry and cavalry, the maniple which is encamped at the lower end of the street, a man is chosen who is relieved from guard duty, and he attends every day at sunset at the tent of the , and receiving from him the watchword—that is a wooden tablet with the word inscribed on it – takes his leave, and on returning to his quarters passes on the watchword and tablet before witnesses to the commander of the next maniple, who in turn passes it to the one next to him. All do the same until it reaches the first maniples, those encamped near the tents of the tribunes. These latter are obliged to deliver the tablet to the tribunes before dark. So that if all those issued are returned, the tribune knows that the watchword has been given to all the maniples, and has passed through all on its way back to him. If any one of them is missing, he makes inquiry at once, as he knows by the marks from what quarter the tablet has not returned, and whoever is responsible for the stoppage meets with the punishment he merits.Passwords in military use evolved to include not just a password, but a password and a counterpassword; for example in the opening days of the , paratroopers of the U.S. 101st Airborne Division used a password—''flash''—which was presented as a challenge, and answered with the correct response—''thunder''. The challenge and response were changed every three days. American paratroopers also famously used a device known as a "cricket" on in place of a password system as a temporarily unique method of identification; one metallic click given by the device in lieu of a password was to be met by two clicks in reply. Passwords have been used with computers since the earliest days of computing. The (CTSS), an operating system introduced at in 1961, was the first computer system to implement password login. CTSS had a LOGIN command that requested a user password. "After typing PASSWORD, the system turns off the printing mechanism, if possible, so that the user may type in his password with privacy." In the early 1970s, developed a system of storing login passwords in a hashed form as part of the operating system. The system was based on a simulated Hagelin rotor crypto machine, and first appeared in 6th Edition Unix in 1974. A later version of his algorithm, known as crypt(3), used a 12-bit and invoked a modified form of the DES algorithm 25 times to reduce the risk of pre-computed s. In modern times, user names and passwords are commonly used by people during a process that to protected computer s, s, decoders, s (ATMs), etc. A typical has passwords for many purposes: logging into accounts, retrieving , accessing applications, databases, networks, web sites, and even reading the morning newspaper online.
Choosing a secure and memorable passwordThe easier a password is for the owner to remember generally means it will be easier for an ) than shorter passwords with a wide variety of characters. In ''The Memorability and Security of Passwords'', Jeff Yan et al. examine the effect of advice given to users about a good choice of password. They found that passwords based on thinking of a phrase and taking the first letter of each word are just as memorable as naively selected passwords, and just as hard to crack as randomly generated passwords. Combining two or more unrelated words and altering some of the letters to special characters or numbers is another good method, but a single dictionary word is not. Having a personally designed algorithm for generating obscure passwords is another good method. However, asking users to remember a password consisting of a "mix of uppercase and lowercase characters" is similar to asking them to remember a sequence of bits: hard to remember, and only a little bit harder to crack (e.g. only 128 times harder to crack for 7-letter passwords, less if the user simply capitalises one of the letters). Asking users to use "both letters and digits" will often lead to easy-to-guess substitutions such as 'E' → '3' and 'I' → '1', substitutions that are well known to attackers. Similarly typing the password one keyboard row higher is a common trick known to attackers. In 2013, Google released a list of the most common password types, all of which are considered insecure because they are too easy to guess (especially after researching an individual on social media): * The name of a pet, child, family member, or significant other * Anniversary dates and birthdays * Birthplace * Name of a favorite holiday * Something related to a favorite sports team * The word "password"
Alternatives to memorizationTraditional advice to memorize passwords and never write them down has become a challenge because of the sheer number of passwords users of computers and the internet are expected to maintain. One survey concluded that the average user has around 100 passwords. To manage the proliferation of passwords, some users employ the same password for multiple accounts, a dangerous practice since a data breach in one account could compromise the rest. Less risky alternatives include the use of s, systems and simply keeping paper lists of less critical passwords. Such practices can reduce the number of passwords that must be memorized, such as the password manager's master password, to a more manageable number.
Factors in the security of a password systemThe security of a password-protected system depends on several factors. The overall system must be designed for sound security, with protection against es, s and the like. Physical security issues are also a concern, from deterring shoulder surfing to more sophisticated physical threats such as video cameras and keyboard sniffers. Passwords should be chosen so that they are hard for an attacker to guess and hard for an attacker to discover using any of the available automatic attack schemes. See and for more information. Nowadays, it is a common practice for computer systems to hide passwords as they are typed. The purpose of this measure is to prevent bystanders from reading the password; however, some argue that this practice may lead to mistakes and stress, encouraging users to choose weak passwords. As an alternative, users should have the option to show or hide passwords as they type them.Lyquix Blog: Do We Need to Hide Passwords?
Rate at which an attacker can try guessed passwordsThe 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, also known as throttling. In the absence of other vulnerabilities, such systems can be effectively secure with relatively simple passwords if they have been well chosen and are not easily guessed. Many systems store a of the password. If an attacker gets access to the file of hashed passwords guessing can be done offline, rapidly testing candidate passwords against the true password's hash value. In the example of a web-server, an online attacker can guess only at the rate at which the server will respond, while an off-line attacker (who gains access to the file) can guess at a rate limited only by the hardware on which the attack is running. Passwords that are used to generate cryptographic keys (e.g., for or security) can also be subjected to high rate guessing. Lists of common passwords are widely available and can make password attacks very efficient. (See .) Security in such situations depends on using passwords or passphrases of adequate complexity, making such an attack computationally infeasible for the attacker. Some systems, such as PGP and Wi-Fi WPA, apply a computation-intensive hash to the password to slow such attacks. See .
Limits on the number of password guessesAn alternative to limiting the rate at which an attacker can make guesses on a password is to limit the total number of guesses that can be made. The password can be disabled, requiring a reset, after a small number of consecutive bad guesses (say 5); and the user may be required to change the password after a larger cumulative number of bad guesses (say 30), to prevent an attacker from making an arbitrarily large number of bad guesses by interspersing them between good guesses made by the legitimate password owner. Attackers may conversely use knowledge of this mitigation to implement a against the user by intentionally locking the user out of their own device; this denial of service may open other avenues for the attacker to manipulate the situation to their advantage via social engineering.
Form of stored passwordsSome computer systems store user passwords as , against which to compare user logon attempts. If an attacker gains access to such an internal password store, all passwords—and so all user accounts—will be compromised. If some users employ the same password for accounts on different systems, those will be compromised as well. More secure systems store each password in a cryptographically protected form, so access to the actual password will still be difficult for a snooper who gains internal access to the system, while validation of user access attempts remains possible. The most secure don't store passwords at all, but a one-way derivation, such as a , modulus, or an advanced . Roger Needham invented the now-common approach of storing only a "hashed" form of the plaintext password. When a user types in a password on such a system, the password handling software runs through a algorithm, and if the hash value generated from the user's entry matches the hash stored in the password database, the user is permitted access. The hash value is created by applying a to a string consisting of the submitted password and, in many implementations, another value known as a . A salt prevents attackers from easily building a list of hash values for common passwords and prevents password cracking efforts from scaling across all users. and SHA1 are frequently used cryptographic hash functions, but they are not recommended for password hashing unless they are used as part of a larger construction such as in .Alexander, Steven. (2012-06-20
Methods of verifying a password over a network
Simple transmission of the passwordPasswords are vulnerable to interception (i.e., "snooping") while being transmitted to the authenticating machine or person. If the password is carried as electrical signals on unsecured physical wiring between the user access point and the central system controlling the password database, it is subject to snooping by methods. If it is carried as packeted data over the Internet, anyone able to watch the packets containing the logon information can snoop with a very low probability of detection. Email is sometimes used to distribute passwords but this is generally an insecure method. Since most email is sent as , a message containing a password is readable without effort during transport by any eavesdropper. Further, the message will be stored as on at least two computers: the sender's and the recipient's. If it passes through intermediate systems during its travels, it will probably be stored on there as well, at least for some time, and may be copied to , or history files on any of these systems. Using client-side encryption will only protect transmission from the mail handling system server to the client machine. Previous or subsequent relays of the email will not be protected and the email will probably be stored on multiple computers, certainly on the originating and receiving computers, most often in clear text.
Transmission through encrypted channelsThe risk of interception of passwords sent over the Internet can be reduced by, among other approaches, using protection. The most widely used is the (TLS, previously called ) feature built into most current Internet . Most browsers alert the user of a TLS/SSL-protected exchange with a server by displaying a closed lock icon, or some other sign, when TLS is in use. There are several other techniques in use; see .
Hash-based challenge–response methodsUnfortunately, there is a conflict between stored hashed-passwords and hash-based ; the latter requires a client to prove to a server that they know what the (i.e., password) is, and to do this, the server must be able to obtain the shared secret from its stored form. On many systems (including -type systems) doing remote authentication, the shared secret usually becomes the hashed form and has the serious limitation of exposing passwords to offline guessing attacks. In addition, when the hash is used as a shared secret, an attacker does not need the original password to authenticate remotely; they only need the hash.
Zero-knowledge password proofsRather than transmitting a password, or transmitting the hash of the password, systems can perform a , which proves knowledge of the password without exposing it. Moving a step further, augmented systems for (e.g., AMP, B-SPEKE, PAK-Z, SRP-6) avoid both the conflict and limitation of hash-based methods. An augmented system allows a client to prove knowledge of the password to a server, where the server knows only a (not exactly) hashed password, and where the unhashed password is required to gain access.
Procedures for changing passwordsUsually, a system must provide a way to change a password, either because a user believes the current password has been (or might have been) compromised, or as a precautionary measure. If a new password is passed to the system in unencrypted form, security can be lost (e.g., via wiretapping) before the new password can even be installed in the password database and if the new password is given to a compromised employee, little is gained. Some websites include the user-selected password in an unencrypted confirmation e-mail message, with the obvious increased vulnerability. systems are increasingly used to automate the issuance of replacements for lost passwords, a feature called . The user's identity is verified by asking questions and comparing the answers to ones previously stored (i.e., when the account was opened). Some password reset questions ask for personal information that could be found on social media, such as mother's maiden name. As a result, some security experts recommend either making up one's own questions or giving false answers.
Password longevity"Password aging" is a feature of some operating systems which forces users to change passwords frequently (e.g., quarterly, monthly or even more often). Such policies usually provoke user protest and foot-dragging at best and hostility at worst. There is often an increase in the number of people who note down the password and leave it where it can easily be found, as well as help desk calls to reset a forgotten password. Users may use simpler passwords or develop variation patterns on a consistent theme to keep their passwords memorable. Because of these issues, there is some debate as to whether password aging is effective. Changing a password will not prevent abuse in most cases, since the abuse would often be immediately noticeable. However, if someone may have had access to the password through some means, such as sharing a computer or breaching a different site, changing the password limits the window for abuse.
Number of users per passwordSingle passwords are also much less convenient to change because many people need to be told at the same time, and they make removal of a particular user's access more difficult, as for instance on graduation or resignation. Separate logins are also often used for accountability, for example to know who changed a piece of data.
Password security architectureCommon techniques used to improve the security of computer systems protected by a password include: * Not displaying the password on the display screen as it is being entered or obscuring it as it is typed by using asterisks (*) or bullets (•). * Allowing passwords of adequate length. (Some operating systems, including early versions of Unix and Windows, limited passwords to an 8 character maximum,"Ten Windows Password Myths"
Password reuseIt is common practice amongst computer users to reuse the same password on multiple sites. This presents a substantial security risk, because an _needs_to_only_compromise_a_single_site_in_order_to_gain_access_to_other_sites_the_victim_uses._This_problem_is_exacerbated_by_also_reusing_User_(computing)">usernames,_and_by_websites_requiring_email_logins,_as_it_makes_it_easier_for_an_attacker_to_track_a_single_user_across_multiple_sites._Password_reuse_can_be_avoided_or_minimised_by_using_
Writing down passwords on paperHistorically, many security experts asked people to memorize their passwords: "Never write down a password". More recently, many security experts such as recommend that people use passwords that are too complicated to memorize, write them down on paper, and keep them in a wallet."Ten Windows Password Myths"
After deathAccording to a survey by the , one in ten people are now leaving their passwords in their wills to pass on this important information when they die. One-third of people, according to the poll, agree that their password-protected data is important enough to pass on in their will.
Multi-factor authenticationMulti-factor authentication schemes combine passwords (as "knowledge factors") with one or more other means of authentication, to make authentication more secure and less vulnerable to compromised passwords. For example, a simple two-factor login might send a text message, e-mail, automated phone call, or similar alert whenever a login attempt is made, possibly supplying a code that must be entered in addition to a password. More sophisticated factors include such things as hardware tokens and biometric security.
Password rulesMost organizations specify a that sets requirements for the composition and usage of passwords, typically dictating minimum length, required categories (e.g., upper and lower case, numbers, and special characters), prohibited elements (e.g., use of one's own name, date of birth, address, telephone number). Some governments have national authentication frameworks that define requirements for user authentication to government services, including requirements for passwords. Many websites enforce standard rules such as minimum and maximum length, but also frequently include composition rules such as featuring at least one capital letter and at least one number/symbol. These latter, more specific rules were largely based on a 2003 report by the (NIST), authored by Bill Burr.Hate silly password rules? So does the guy who created them
Password crackingAttempting to crack passwords by trying as many possibilities as time and money permit is a . A related method, rather more efficient in most cases, is a . In a dictionary attack, all words in one or more dictionaries are tested. Lists of common passwords are also typically tested. is the likelihood that a password cannot be guessed or discovered, and varies with the attack algorithm used. Cryptologists and computer scientists often refer to the strength or 'hardness' in terms of . Passwords easily discovered are termed ''weak'' or ''vulnerable''; passwords very difficult or impossible to discover are considered ''strong''. There are several programs available for password attack (or even auditing and recovery by systems personnel) such as , , and ; some of which use password design vulnerabilities (as found in the Microsoft LANManager system) to increase efficiency. These programs are sometimes used by system administrators to detect weak passwords proposed by users. Studies of production computer systems have consistently shown that a large fraction of all user-chosen passwords are readily guessed automatically. For example, Columbia University found 22% of user passwords could be recovered with little effort. According to , examining data from a 2006 phishing attack, 55% of MySpace passwords would be crackable in 8 hours using a commercially available Password Recovery Toolkit capable of testing 200,000 passwords per second in 2006. He also reported that the single most common password was ''password1'', confirming yet again the general lack of informed care in choosing passwords among users. (He nevertheless maintained, based on these data, that the general quality of passwords has improved over the years—for example, average length was up to eight characters from under seven in previous surveys, and less than 4% were dictionary words.)
Incidents* On July 16, 1998, CERT Coordination Center, CERT reported an incident where an attacker had found 186,126 encrypted passwords. At the time the attacker was discovered, 47,642 passwords had already been cracked. * In September, 2001, after the deaths of 960 New York employees in the September 11 attacks, financial services firm Cantor Fitzgerald through Microsoft broke the passwords of deceased employees to gain access to files needed for servicing client accounts. Technicians used brute-force attacks, and interviewers contacted families to gather personalized information that might reduce the search time for weaker passwords. * In December 2009, a major password breach of the RockYou, Rockyou.com website occurred that led to the release of 32 million passwords. The hacker then leaked the full list of the 32 million passwords (with no other identifiable information) to the Internet. Passwords were stored in cleartext in the database and were extracted through a SQL injection vulnerability. The Imperva Application Defense Center (ADC) did an analysis on the strength of the passwords. * In June 2011, NATO (North Atlantic Treaty Organization) experienced a security breach that led to the public release of first and last names, usernames, and passwords for more than 11,000 registered users of their e-bookshop. The data was leaked as part of Operation AntiSec, a movement that includes Anonymous (group), Anonymous, LulzSec, as well as other hacking groups and individuals. The aim of AntiSec is to expose personal, sensitive, and restricted information to the world, using any means necessary. * On July 11, 2011, Booz Allen Hamilton, a consulting firm that does work for the Pentagon, had their servers hacked by Anonymous (group), Anonymous and leaked the same day. "The leak, dubbed 'Military Meltdown Monday,' includes 90,000 logins of military personnel—including personnel from United States Central Command, USCENTCOM, United States Special Operations Command, SOCOM, the United States Marine Corps, Marine corps, various United States Air Force, Air Force facilities, Homeland Security, United States State Department, State Department staff, and what looks like private sector contractors." These leaked passwords wound up being hashed in SHA1, and were later decrypted and analyzed by the ADC team at Imperva, revealing that even military personnel look for shortcuts and ways around the password requirements.
Alternatives to passwords for authenticationThe numerous ways in which permanent or semi-permanent passwords can be compromised has prompted the development of other techniques. Unfortunately, some are inadequate in practice, and in any case few have become universally available for users seeking a more secure alternative. A 2012 paper examines why passwords have proved so hard to supplant (despite numerous predictions that they would soon be a thing of the past); in examining thirty representative proposed replacements with respect to security, usability and deployability they conclude "none even retains the full set of benefits that legacy passwords already provide." * One-time password, Single-use passwords. Having passwords that are only valid once makes many potential attacks ineffective. Most users find single-use passwords extremely inconvenient. They have, however, been widely implemented in personal online banking, where they are known as TAN (banking), Transaction Authentication Numbers (TANs). As most home users only perform a small number of transactions each week, the single-use issue has not led to intolerable customer dissatisfaction in this case. * Time-synchronized one-time passwords are similar in some ways to single-use passwords, but the value to be entered is displayed on a small (generally pocketable) item and changes every minute or so. * PassWindow one-time passwords are used as single-use passwords, but the dynamic characters to be entered are visible only when a user superimposes a unique printed visual key over a server-generated challenge image shown on the user's screen. * Access controls based on public-key cryptography e.g. Secure Shell, ssh. The necessary keys are usually too large to memorize (but see proposal Passmaze) and must be stored on a local computer, security token or portable memory device, such as a USB flash drive or even floppy disk. The private key may be stored on a cloud service provider, and activated by the use of a password or two-factor authentication. * Biometric methods promise authentication based on unalterable personal characteristics, but currently (2008) have high error rates and require additional hardware to scan, for example, fingerprints, iris (anatomy), irises, etc. They have proven easy to spoof in some famous incidents testing commercially available systems, for example, the gummie fingerprint spoof demonstration, and, because these characteristics are unalterable, they cannot be changed if compromised; this is a highly important consideration in access control as a compromised access token is necessarily insecure. * Single sign-on technology is claimed to eliminate the need for having multiple passwords. Such schemes do not relieve users and administrators from choosing reasonable single passwords, nor system designers or administrators from ensuring that private access control information passed among systems enabling single sign-on is secure against attack. As yet, no satisfactory standard has been developed. * Envaulting technology is a password-free way to secure data on removable storage devices such as USB flash drives. Instead of user passwords, access control is based on the user's access to a network resource. * Non-text-based passwords, such as graphical passwords or mouse-movement based passwords. Graphical passwords are an alternative means of authentication for log-in intended to be used in place of conventional password; they use images, graphics or colours instead of Letter (alphabet), letters, numerical digit, digits or special characters. One system requires users to select a series of faces as a password, utilizing the human brain's ability to face perception, recall faces easily. In some implementations the user is required to pick from a series of images in the correct sequence in order to gain access. Another graphical password solution creates a one-time password using a randomly generated grid of images. Each time the user is required to authenticate, they look for the images that fit their pre-chosen categories and enter the randomly generated alphanumeric character that appears in the image to form the one-time password. So far, graphical passwords are promising, but are not widely used. Studies on this subject have been made to determine its usability in the real world. While some believe that graphical passwords would be harder to Password cracking, crack, others suggest that people will be just as likely to pick common images or sequences as they are to pick common passwords. * 2D Key (2-Dimensional Key) is a 2D matrix-like key input method having the key styles of multiline passphrase, crossword, ASCII/Unicode art, with optional textual semantic noises, to create big password/key beyond 128 bits to realize the MePKC (Memorizable Public-Key Cryptography) using fully memorizable private key upon the current private key management technologies like encrypted private key, split private key, and roaming private key. * Cognitive passwords use question and answer cue/response pairs to verify identity.
"The password is dead"That "the password is dead" is a recurring idea in . The reasons given often include reference to the usability as well as security problems of passwords. It often accompanies arguments that the replacement of passwords by a more secure means of authentication is both necessary and imminent. This claim has been made by numerous people at least since 2004. Alternatives to passwords include biometrics, two-factor authentication or , Microsoft's Cardspace, the Higgins project, the Liberty Alliance, NSTIC, the FIDO Alliance and various Identity 2.0 proposals. However, in spite of these predictions and efforts to replace them passwords are still the dominant form of authentication on the web. In "The Persistence of Passwords," Cormac Herley and Paul van Oorschot suggest that every effort should be made to end the "spectacularly incorrect assumption" that passwords are dead. They argue that "no other single technology matches their combination of cost, immediacy and convenience" and that "passwords are themselves the best fit for many of the scenarios in which they are currently used." Following this, Bonneau et al. systematically compared web passwords to 35 competing authentication schemes in terms of their usability, deployability, and security. Their analysis shows that most schemes do better than passwords on security, some schemes do better and some worse with respect to usability, while ''every'' scheme does worse than passwords on deployability. The authors conclude with the following observation: "Marginal gains are often not sufficient to reach the activation energy necessary to overcome significant transition costs, which may provide the best explanation of why we are likely to live considerably longer before seeing the funeral procession for passwords arrive at the cemetery."
See also* Access code (disambiguation) * Authentication * CAPTCHA * Cognitive science * Diceware * Kerberos (protocol) * Keyfile * Passphrase * Secure Password Sharing * * Password fatigue * Password length parameter * * Password notification e-mail * Password policy * Password psychology * * Password synchronization * Password-authenticated key agreement * Pre-shared key * Random password generator * Rainbow table * Self-service password reset * Usability of web authentication systems