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Multi-factor authentication (MFA;two-factor authentication, or2FA) is anelectronic authentication method in which a user is granted access to awebsite orapplication only after successfully presenting two or more pieces of evidence (orfactors) to anauthentication mechanism. MFA protectspersonal data—which may include personal identification orfinancial assets—from being accessed by an unauthorized third party that may have been able to discover, for example, a single password.
Usage of MFA has increased in recent years. Security issues which can cause the bypass of MFA arefatigue attacks,phishing andSIM swapping.[1]
Authentication takes place when someone tries tolog into a computer resource (such as acomputer network, device, or application). The resource requires the user to supply the identity by which the user is known to the resource, along with evidence of the authenticity of the user's claim to that identity. Simple authentication requires only one such piece of evidence (factor), typically a password. For additional security, the resource may require more than one factor—multi-factor authentication, or two-factor authentication in cases where exactly two pieces of evidence are to be supplied.[2]
The use of multiple authentication factors to prove one's identity is based on the premise that an unauthorized actor is unlikely to be able to supply the factors required for access. If, in an authentication attempt, at least one of the components is missing or supplied incorrectly, the user's identity is not established with sufficient certainty and access to the asset (e.g., a building, or data) being protected by multi-factor authentication then remains blocked. The authentication factors of a multi-factor authentication scheme may include:[3]
An example of two-factor authentication is the withdrawing of money from anATM; only the correct combination of abank card (something the user possesses) and a PIN (something the user knows) allows the transaction to be carried out. Two other examples are to supplement a user-controlled password with aone-time password (OTP) or code generated or received by anauthenticator (e.g. a security token or smartphone) that only the user possesses.[4]
Anauthenticator app enables two-factor authentication in a different way, by showing a randomly generated and constantly refreshing code, rather than sending anSMS or using another method.[5] This code is aTime-based one-time password (aTOTP)), and the authenticator app contains the key material that allows the generation of these codes.
Knowledge factors ("something only the user knows") are a form of authentication. In this form, the user is required to prove knowledge of a secret in order to authenticate.
A password is a secret word or string of characters that is used for user authentication. This is the most commonly used mechanism of authentication.[3] Many multi-factor authentication techniques rely on passwords as one factor of authentication. Variations include both longer ones formed from multiple words (apassphrase) and the shorter, purely numeric, PIN commonly used forATM access. Traditionally, passwords are expected to bememorized, but can also be written down on a hidden paper or text file.
Possession factors ("something only the user has") have been used for authentication for centuries, in the form of a key to a lock. The basic principle is that the key embodies a secret that is shared between the lock and the key, and the same principle underlies possession factor authentication in computer systems. Asecurity token is an example of a possession factor.
Disconnected tokens have no connections to the client computer. They typically use a built-in screen to display the generated authentication data, which is manually typed in by the user. This type of token mostly uses aOTP that can only be used for that specific session.[6]
Connected tokens aredevices that arephysically connected to the computer to be used. Those devices transmit data automatically.[7] There are a number of different types, including USB tokens,smart cards andwireless tags.[7] Increasingly,FIDO2 capable tokens, supported by theFIDO Alliance and theWorld Wide Web Consortium (W3C), have become popular with mainstream browser support beginning in 2015.
Asoftware token (a.k.a.soft token) is a type of two-factor authentication security device that may be used to authorize the use of computer services. Software tokens are stored on a general-purpose electronic device such as adesktop computer,laptop,PDA, ormobile phone and can be duplicated. (Contrasthardware tokens, where the credentials are stored on a dedicated hardware device and therefore cannot be duplicated, absent physical invasion of the device). A soft token may not be a device the user interacts with. Typically an X.509v3 certificate is loaded onto the device and stored securely to serve this purpose.[citation needed]
Multi-factor authentication can also be applied in physical security systems. These physical security systems are known and commonly referred to as access control. Multi-factor authentication is typically deployed in access control systems through the use, firstly, of a physical possession (such as a fob,keycard, orQR-code displayed on a device) which acts as the identification credential, and secondly, a validation of one's identity such as facial biometrics or retinal scan. This form of multi-factor authentication is commonly referred to as facial verification or facial authentication.
Inherent factors ("something the user is"), are factors associated with the user, and are usuallybiometric methods, includingfingerprint,face,[8]voice, oriris recognition. Behavioral biometrics such askeystroke dynamics can also be used.
Increasingly, a fourth factor is coming into play involving the physical location of the user. While hard wired to the corporate network, a user could be allowed to login using only a pin code. Whereas if the user was off the network or working remotely, a more secure MFA method such as entering a code from a soft token as well could be required. Adapting the type of MFA method and frequency to a users' location will enable you to avoid risks common to remote working.[9]
Systems for network admission control work in similar ways where the level of network access can be contingent on the specific network a device is connected to, such asWi-Fi vs wired connectivity. This also allows a user to move between offices and dynamically receivethe same level of network access[clarification needed] in each.[citation needed]
Two-factor authentication over text message was developed as early as 1996, when AT&T described a system for authorizing transactions based on an exchange of codes over two-way pagers.[10][11]
Many multi-factor authentication vendors offer mobile phone-based authentication. Some methods include push-based authentication, QR code-based authentication, one-time password authentication (event-based and time-based), and SMS-based verification. SMS-based verification suffers from some security concerns. Phones can be cloned, apps can run on several phones and cell-phone maintenance personnel can read SMS texts. Not least, cell phones can be compromised in general, meaning the phone is no longer something only the user has.
The major drawback of authentication including something the user possesses is that the user must carry around the physical token (the USB stick, the bank card, the key or similar), practically at all times. Loss and theft are risks. Many organizations forbid carrying USB and electronic devices in or out of premises owing tomalware and data theft risks, and most important machines do not have USB ports for the same reason. Physical tokens usually do not scale, typically requiring a new token for each new account and system. Procuring and subsequently replacing tokens of this kind involves costs. In addition, there are inherent conflicts and unavoidable trade-offs between usability and security.[12]
Two-step authentication involvingmobile phones andsmartphones provides an alternative to dedicated physical devices. To authenticate, people can use their personal access codes to the device (i.e. something that only the individual user knows) plus a one-time-valid, dynamic passcode, typically consisting of 4 to 6 digits. The passcode can be sent to their mobile device[2] bySMS or can be generated by a one-time passcode-generator app. In both cases, the advantage of using a mobile phone is that there is no need for an additional dedicated token, as users tend to carry theirmobile devices around at all times.
Notwithstanding the popularity of SMS verification, security advocates have publicly criticized SMS verification,[13] and in July 2016, a United StatesNIST draft guideline proposed deprecating it as a form of authentication.[14] A year later NIST reinstated SMS verification as a valid authentication channel in the finalized guideline.[15]
In 2016 and 2017 respectively, both Google and Apple started offering user two-step authentication withpush notifications[3] as an alternative method.[16][17]
Security of mobile-delivered security tokens fully depends on the mobile operator's operational security and can be easily breached by wiretapping orSIM cloning by national security agencies.[18]
Advantages:
Disadvantages:
ThePayment Card Industry (PCI) Data Security Standard, requirement 8.3, requires the use of MFA for all remote network access that originates from outside the network to a Card Data Environment (CDE).[22] Beginning with PCI-DSS version 3.2, the use of MFA is required for all administrative access to the CDE, even if the user is within a trusted network.
The secondPayment Services Directive requires "strong customer authentication" on most electronic payments in theEuropean Economic Area since September 14, 2019.[23]
In India, theReserve Bank of India mandated two-factor authentication for all online transactions made using a debit or credit card using either a password or a one-time password sent overSMS. This requirement was removed in 2016 for transactions up to ₹2,000 after opting-in with the issuing bank.[24] Vendors such asUber have been mandated by the bank to amend their payment processing systems in compliance with this two-factor authentication rollout.[25][26][27]
Details for authentication for federal employees and contractors in the U.S. are defined in Homeland Security Presidential Directive 12 (HSPD-12).[28]
IT regulatory standards for access to federal government systems require the use of multi-factor authentication to access sensitive IT resources, for example when logging on to network devices to perform administrative tasks[29] and when accessing any computer using a privileged login.[30]
NIST Special Publication 800-63-3 discusses various forms of two-factor authentication and provides guidance on using them in business processes requiring different levels of assurance.[31]
In 2005, the United States'Federal Financial Institutions Examination Council issued guidance for financial institutions recommending financial institutions conduct risk-based assessments, evaluate customer awareness programs, and develop security measures to reliably authenticate customers remotely accessingonline financial services, officially recommending the use of authentication methods that depend on more than one factor (specifically, what a user knows, has, and is) to determine the user's identity.[32] In response to the publication, numerous authentication vendors began improperly promoting challenge-questions, secret images, and other knowledge-based methods as "multi-factor" authentication. Due to the resulting confusion and widespread adoption of such methods, on August 15, 2006, the FFIEC published supplemental guidelines—which state that by definition, a "true" multi-factor authentication system must use distinct instances of the three factors of authentication it had defined, and not just use multiple instances of a single factor.[33]
According to proponents, multi-factor authentication could drastically reduce the incidence of onlineidentity theft and other onlinefraud, because the victim's password would no longer be enough to give a thief permanent access to their information. However, many multi-factor authentication approaches remain vulnerable tophishing,[34]man-in-the-browser, andman-in-the-middle attacks.[35] Two-factor authentication in web applications are especially susceptible to phishing attacks, particularly in SMS and e-mails, and, as a response, many experts advise users not to share their verification codes with anyone,[36] and many web application providers will place an advisory in an e-mail or SMS containing a code.[37]
Multi-factor authentication may be ineffective[38] against modern threats, like ATM skimming, phishing, and malware.[39]
In May 2017,O2 Telefónica, a German mobile service provider, confirmed that cybercriminals had exploitedSS7 vulnerabilities to bypass SMS based two-step authentication to do unauthorized withdrawals from users' bank accounts. The criminals firstinfected the account holder's computers in an attempt to steal their bank account credentials and phone numbers. Then the attackers purchased access to a fake telecom provider and set up a redirect for the victim's phone number to a handset controlled by them. Finally, the attackers logged into victims' online bank accounts and requested for the money on the accounts to be withdrawn to accounts owned by the criminals. SMS passcodes were routed to phone numbers controlled by the attackers and the criminals transferred the money out.[40]
An increasingly common approach to defeating MFA is to bombard the user with many requests to accept a log-in, until the user eventually succumbs to the volume of requests and accepts one.[41] This is called a multi-factor authentication fatigue attack (also MFA fatigue attack or MFA bombing) makes use ofsocial engineering.[42][43][44] When MFA applications are configured to send push notifications to end users, an attacker can send a flood of login attempts in the hope that a user will click on accept at least once.[42]
In 2022,Microsoft has deployed a mitigation against MFA fatigue attacks with their authenticator app.[45]
In September 2022Uber security was breached by a member ofLapsus$ using a multi-factor fatigue attack.[46][47] On March 24, 2023, YouTuberLinus Sebastian declared on theLinus Tech Tips channel on theYouTube platform that he had suffered an Multi-factor authentication fatigue attack.[48] In early 2024, a small percentage ofApple consumers experienced a MFA fatigue attack that was caused by a hacker that bypassed the rate limit andCaptcha on Apple’s “Forgot Password” page.
Manymulti-factor authentication products require users to deployclientsoftware to make multi-factor authentication systems work. Some vendors have created separate installation packages fornetwork login,Web accesscredentials, andVPN connectioncredentials. For such products, there may be four or five differentsoftware packages to push down to theclient PC in order to make use of thetoken orsmart card. This translates to four or five packages on which version control has to be performed, and four or five packages to check for conflicts with business applications. If access can be operated usingweb pages, it is possible to limit the overheads outlined above to a single application. With other multi-factor authentication technology such as hardware token products, no software must be installed by end-users.[citation needed]
There are drawbacks to multi-factor authentication that are keeping many approaches from becoming widespread. Some users have difficulty keeping track of a hardware token or USB plug. Many users do not have the technical skills needed to install a client-side software certificate by themselves. Generally, multi-factor solutions require additional investment for implementation and costs for maintenance. Most hardware token-based systems are proprietary, and some vendors charge an annual fee per user. Deployment ofhardware tokens is logistically challenging. Hardwaretokens may get damaged or lost, and issuance oftokens in large industries such as banking or even within large enterprises needs to be managed. In addition to deployment costs, multi-factor authentication often carries significant additional support costs.[citation needed] A 2008 survey[49] of over 120U.S. credit unions by theCredit Union Journal reported on the support costs associated with two-factor authentication. In their report,software certificates and software toolbar approaches[clarification needed] were reported to have the highest support costs.
Research into deployments of multi-factor authentication schemes[50] has shown that one of the elements that tend to impact the adoption of such systems is the line of business of the organization that deploys the multi-factor authentication system. Examples cited include the U.S. government, which employs an elaborate system of physical tokens (which themselves are backed by robustPublic Key Infrastructure), as well as private banks, which tend to prefer multi-factor authentication schemes for their customers that involve more accessible, less expensive means of identity verification, such as an app installed onto a customer-owned smartphone. Despite the variations that exist among available systems that organizations may have to choose from, once a multi-factor authentication system is deployed within an organization, it tends to remain in place, as users invariably acclimate to the presence and use of the system and embrace it over time as a normalized element of their daily process of interaction with their relevant information system.
While the perception is that multi-factor authentication is within the realm of perfect security, Roger Grimes writes[51] that if not properly implemented and configured, multi-factor authentication can in fact be easily defeated.
In 2013,Kim Dotcom claimed to have invented two-factor authentication in a 2000 patent,[52] and briefly threatened to sue all the major web services. However, the European Patent Office revoked his patent[53] in light of an earlier 1998 U.S. patent held by AT&T.[54]
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