Password

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A password, sometimes called a passcode, is secret data, typically a string of characters, usually used to confirm a user's identity.^[1] Traditionally, passwords were expected to be memorized,^[2] but the large number of password-protected services that a typical individual accesses can make memorization of unique passwords for each service impractical.^[3] Using the terminology of the NIST Digital Identity Guidelines,^[4] the secret is held by a party called the claimant while the party verifying the identity of the claimant is called the verifier. When the claimant successfully demonstrates knowledge of the password to the verifier through an established authentication protocol,^[5] the verifier can infer the claimant's identity.

In general, a password is a sequence of characters including letters, digits, or other symbols. If the permissible characters are constrained to be numeric, the corresponding secret is sometimes called a personal identification number (PIN).

Despite its name, a password does not need to be an actual word; indeed, a non-word (in the dictionary sense) may be harder to guess, which is a desirable property of passwords. A memorized secret consisting of a sequence of words or other text separated by spaces is sometimes called a passphrase. A passphrase is similar to a password in usage, but the former is generally longer for added security.^[6]

History

Passwords 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. Polybius describes the system for the distribution of watchwords in the Roman military 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 tribune, 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.^[7]

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 Battle of Normandy, 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 D-Day 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.^[8]

Passwords have been used with computers since the earliest days of computing. The Compatible Time-Sharing System (CTSS), an operating system introduced at MIT in 1961, was the first computer system to implement password login.^[9][10] 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."^[11] In the early 1970s, Robert Morris developed a system of storing login passwords in a hashed form as part of the Unix 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 salt and invoked a modified form of the DES algorithm 25 times to reduce the risk of pre-computed dictionary attacks.^[12]

In modern times, user names and passwords are commonly used by people during a log in process that controls access to protected computer operating systems, mobile phones, cable TV decoders, automated teller machines (ATMs), etc. A typical computer user has passwords for multiple purposes: logging into accounts, retrieving e-mail, accessing applications, databases, networks, websites, and even reading the morning newspaper online.^[13]

Choosing a secure and memorable password

Generally, the easier a password is for the owner to remember, the easier it is for an attacker to guess.^[14] However, passwords that are difficult to remember may also reduce the security of a system because (a) users might need to write down or electronically store the password, (b) users will need frequent password resets and (c) users are more likely to re-use the same password across different accounts. Similarly, the more stringent the password requirements, such as "have a mix of uppercase and lowercase letters and digits" or "change it monthly", the greater the degree to which users will subvert the system.^[15] Others argue longer passwords provide more security (e.g., entropy) than shorter passwords with a wide variety of characters.^[16]

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.^[17]

Combining two or more unrelated words and altering some of the letters to special characters or numbers is another good method,^[18] but a single dictionary word is not. Having a personally designed algorithm for generating obscure passwords is another good method.^[19]

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.^[20]

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), which includes:^[21]

• 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 memorization

Traditional 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.^[3] 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 password managers, single sign-on systems and simply keeping paper lists of less critical passwords.^[22] 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 system

The security of a password-protected system depends on several factors. The overall system must be designed for sound security, with protection against computer viruses, man-in-the-middle attacks 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.^[23]

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.^[23]

Effective access control provisions may force extreme measures on criminals seeking to acquire a password or biometric token.^[24] Less extreme measures include extortion, rubber hose cryptanalysis, and side channel attack.

Some specific password management issues that must be considered when thinking about, choosing, and handling a password follow.

Password rules

Most organizations specify a password policy 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), and prohibited elements (e.g., use of one's own name, date of birth, address, telephone number). Some governments have national authentication frameworks^[61] 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 National Institute of Standards and Technology (NIST), authored by Bill Burr.^[62] It originally proposed the practice of using numbers, obscure characters and capital letters and updating regularly. In a 2017 article in The Wall Street Journal, Burr reported he regrets these proposals and made a mistake when he recommended them.^[63]

According to a 2017 rewrite of this NIST report, a number of websites have rules that actually have the opposite effect on the security of their users. This includes complex composition rules as well as forced password changes after certain periods of time. While these rules have long been widespread, they have also long been seen as annoying and ineffective by both users and cybersecurity experts.^[64] The NIST recommends people use longer phrases as passwords (and advises websites to raise the maximum password length) instead of hard-to-remember passwords with "illusory complexity" such as "pA55w+rd".^[65] A user prevented from using the password "password" may, if required to include a number and uppercase letter, simply choose "Password1". Combined with forced periodic password changes, this can lead to passwords that are difficult to remember but easy to crack.^[62]

Paul Grassi, one of the 2017 NIST report's authors, further elaborated: "Everyone knows that an exclamation point is a 1, or an I, or the last character of a password. $ is an S or a 5. If we use these well-known tricks, we aren't fooling any adversary. We are simply fooling the database that stores passwords into thinking the user did something good."^[64]

Pieris Tsokkis and Eliana Stavrou were able to identify some bad password construction strategies through their research and development of a password generator tool. They came up with eight categories of password construction strategies based on exposed password lists, password cracking tools, and online reports citing the most used passwords. These categories include user-related information, keyboard combinations and patterns, placement strategy, word processing, substitution, capitalization, append dates, and a combination of the previous categories.^[66]

Password cracking

Attempting to crack passwords by trying as many possibilities as time and money permit is a brute-force attack. A related method, rather more efficient in most cases, is a dictionary attack. In a dictionary attack, all words in one or more dictionaries are tested. Lists of common passwords are also typically tested.

Password strength 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 entropy.^[16]

Passwords easily discovered are termed weak or vulnerable; passwords 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 L0phtCrack, John the Ripper, and Cain; 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.^[12] For example, Columbia University found 22% of user passwords could be recovered with little effort.^[67] According to Bruce Schneier, 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.^[68] 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.^[69])

Alternatives to passwords for authentication

The multiple ways in which permanent or semi-permanent passwords can be compromised has prompted the development of other techniques. Some are inadequate in practice, and in any case few have become universally available for users seeking a more secure alternative.^[77] A 2012 paper^[78][79] examines why passwords have proved so hard to supplant (despite multiple predictions that they would soon be a thing of the past^[80]); 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."

• Single-use passwords. Having passwords that are only valid once makes a number of 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 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.
• Passwordless authentication in which a user can log in to a computer system without entering (and having to remember) a password or any other knowledge-based secret. In most common implementations users are asked to enter their public identifier (username, phone number, email address etc.) and then complete the authentication process by providing a secure proof of identity through a registered device or token. Most of implementations rely on public-key cryptography infrastructure where the public key is provided during registration to the authenticating service (remote server, application or website) while the private key is kept on a user's device (PC, smartphone or an external security token) and can be accessed only by providing a biometric signature or another authentication factor which is not knowledge-based.^[81]
• 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. ssh. The necessary keys are usually too large to memorize (but see proposal Passmaze)^[82] 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 as of 2008^[update] have high error rates and require additional hardware to scan,^{[needs update]} for example, fingerprints, irises, etc. They have proven easy to spoof in some famous incidents testing commercially available systems, for example, the gummie fingerprint spoof demonstration,^[83] 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.^[84] 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 letters, digits or special characters. One system requires users to select a series of faces as a password, utilizing the human brain's ability to recall faces easily.^[85] In some implementations the user is required to pick from a series of images in the correct sequence to gain access.^[86] 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.^[87][88] So far, graphical passwords are promising, but are not widely used. Studies on this subject have been made to determine their usability in the real world. While some believe that graphical passwords would be harder to crack, others suggest that people will be just as likely to pick common images or sequences as they are to pick common passwords.^{[citation needed]}
• 2D Key (2-Dimensional Key)^[89] 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)^[90] 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.

Obsolescence

"The password is dead" is a recurring idea in computer security. 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 a number of people at least since 2004.^{[91][92][93][94][95]} Alternatives to passwords include biometrics, two-factor authentication or single sign-on, Microsoft's Cardspace, the Higgins project, the Liberty Alliance, NSTIC, the FIDO Alliance and various Identity 2.0 proposals.^[96][97]

Bonneau et al. systematically compared web passwords to other technical solutions that were alternatives. They reviewed these in respect of usability, deployability, and security. Their analysis showed that most alternatives do better than passwords on security, some do better and some worse with respect to usability, while every alternative does worse than passwords on deployability.^[98]

This may be why over 20 years after this recurring idea started, passwords are still being used, despite attempts by technology businesses to change this. Some that highlight this, suggest that the problem is generally not with the system of using passwords and is instead an issue with how humans use and manage their passwords and that "in the age of disparate workforces, home WiFi networks and multiple devices, password use has continued to increase".^[99]

See also

References

External links

• Graphical Passwords: A Survey
• Large list of commonly used passwords
• Large collection of statistics about passwords
• Research Papers on Password-based Cryptography
• The international passwords conference
• Procedural Advice for Organisations and Administrators (PDF)
• Centre for Security, Communications and Network Research, University of Plymouth (PDF)
• 2017 draft update to NIST password standards for the U.S. federal government