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Knowledge-based authentication (KBA) checks an identity claim by asking questions about personal information associated with the person, such as a previous address. It is often called “security questions.” For digital account authentication, current NIST guidance does not accept KBA: answers may be discoverable or guessable, so they do not reliably prove that the person controlling the account is its owner.
How knowledge-based authentication works
A service presents a question based on information linked to a claimed identity and asks the person to supply the answer. Traditionally, these questions have been used when creating an account, signing in, or trying to recover access. The service compares the response with an answer associated with the account or identity record.
NIST’s older glossary described KBA as using information from public databases and characterized that information as private rather than secret. That is a historical definition, not current approval of security questions as a digital authenticator. NIST CSRC Glossary: Knowledge-Based Authentication
Why NIST no longer accepts KBA for digital authentication
NIST’s current digital identity guidance states: “Knowledge-based authentication, where the claimant is prompted to answer questions that are presumably known only by the claimant, does not constitute an acceptable secret for digital authentication.” The guideline explains that answers may be discoverable and that many questions offer only a small set of likely choices, making guessing a significant risk. NIST SP 800-63B-4
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Personal information can be private without being secret. A former address or other personal detail may be available from records, social media, or people who know the account holder. A question can therefore feel personal without providing strong evidence that the person answering controls the account.
NIST’s implementation guidance also identifies practical weaknesses: people may reuse answers across services, and answers can be difficult to store safely if a system accepts approximate variants such as shortened or expanded names. NIST 800-63-3 Implementation Resources: Authenticators
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Can security questions be used for password resets?
No—not as a substitute for authenticating the account owner under NIST guidance. A stored answer to a personal question does not establish that the person requesting a reset controls the account. NIST identifies look-up secrets and out-of-band device authentication as possible approaches, subject to their own requirements. NIST SP 800-63 FAQ
An out-of-band authenticator uses a physical device controlled by the claimant and a secondary channel. That does not mean any second channel is secure: SP 800-63B-4 says email must not be used for out-of-band authentication. NIST SP 800-63B-4
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KBA, knowledge-based verification, and passwords are different
- KBA or security questions: Questions about personal or identity-associated facts, historically used as an authentication method. NIST no longer recognizes them as an acceptable authenticator for digital authentication.
- Knowledge-based verification (KBV): A related practice that NIST says may be used for identity resolution and, with restrictions, remote identity proofing. It is not the same as authenticating a returning user to an account; the detailed boundaries are in SP 800-63A. NIST SP 800-63 FAQ
- Memorized secret: A secret a person chooses and remembers for authentication, such as a password. It is not equivalent to answering prompts about personal facts. NIST’s implementation guidance cautions against prompts for specific personal information. NIST 800-63-3 Implementation Resources: Authenticators
What NIST’s guidance applies to
NIST SP 800-63B-4, titled Digital Identity Guidelines: Authentication and Authenticator Management, was published as a final publication on July 31, 2025, superseding SP 800-63B. It sets requirements for digital identity services, including government information systems, and is organized around three authenticator assurance levels. It should not be described as a universal law governing every private organization. NIST SP 800-63B-4 publication record
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