Knowledge-based authentication (KBA) checks an identity claim by asking questions about information associated with the person, such as a previous address or a first pet’s name. These are commonly called security questions. Current NIST digital identity guidance does not accept KBA as an authenticator for signing in or resetting an account password: answers may be discoverable, and many questions offer attackers only a small set of plausible choices.
What knowledge-based authentication means
KBA is a check in which a person is asked to supply personal-history information to support a claim about their identity. In familiar online forms, the questions may ask for a childhood address, a school, or the name of a first pet.
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NIST’s older glossary described KBA as using knowledge about information in public databases. It also made an important distinction: such information may be private without being secret. That definition reflects a superseded NIST publication, not current approval of security questions for digital authentication. NIST CSRC Glossary: Knowledge-Based Authentication
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Are security questions an acceptable authenticator?
No. NIST SP 800-63B-4, the current NIST guideline for digital authentication, says: “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.” NIST SP 800-63B-4
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NIST’s FAQ similarly says KBA, sometimes called security questions, is no longer recognized as an acceptable authenticator under SP 800-63. Answers may be found by an attacker, and questions often have relatively few possible answers, making guessing more feasible than the wording of a question might suggest. NIST Digital Identity Guidelines FAQ
SP 800-63B-4 was published as a final guideline on July 31, 2025, superseding SP 800-63B. It sets requirements for remote digital authentication and assurance levels, particularly for government information systems; it should not be described as a universal law governing every private organization. NIST SP 800-63B-4 publication record
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Why KBA is weak for account security
- Answers can be discovered. Personal facts may appear in public records, online profiles, or other accessible sources; a question’s framing does not make its answer secret.
- Answer choices can be limited. Many questions have a relatively small range of likely responses, which makes guessing more practical.
- People may reuse answers. If the same answer is used across services, compromise of one service can put other accounts at risk.
- Answers can be awkward to store securely. NIST implementation material notes that users may enter approximate variants—such as abbreviated or expanded school names—so systems may store answers in a way that creates additional security risk. NIST implementation resources: Authenticators
Can security questions be used for password reset?
NIST says a self-service password reset must authenticate the account owner; answering stored knowledge questions is not an acceptable substitute. A service should use a recovery method that meets its authentication requirements rather than treating personal-history answers as proof of account control. NIST points to look-up secrets and out-of-band device authentication as possible approaches, subject to their own requirements. NIST Digital Identity Guidelines FAQ
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KBA, identity verification, and passwords are not the same thing
Knowledge-based verification
NIST distinguishes KBA used to authenticate a returning account user from knowledge-based verification used in identity resolution or, under restrictions, remote identity proofing. The distinction matters: the guidance does not categorically prohibit every use of personal-knowledge checks in every identity-proofing process. Those uses are addressed separately in NIST SP 800-63A. NIST Digital Identity Guidelines FAQ
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Memorized secrets
A memorized secret, such as a password, is selected and remembered for authentication. It is different from a system prompting someone to answer questions about personal facts. NIST implementation guidance cautions against prompting users for specific personal information as an authentication method. NIST implementation resources: Authenticators
Out-of-band device authentication
An out-of-band authenticator uses a physical device controlled by the claimant and a secondary channel. It is not simply any message sent through a second channel: NIST SP 800-63B-4 says email must not be used for out-of-band authentication. NIST SP 800-63B-4
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What to do if an account still asks security questions
- Prefer a recovery option that verifies control of an approved device or a recovery secret, when the service offers one.
- Do not reuse the same answer across accounts; a personal fact may be easy to discover and can be exposed through another service.
- If the service requires questions, use unique answers that are difficult to infer, and store them securely so you can reproduce them exactly.
- For an organization designing authentication, follow the applicable standard and jurisdictional requirements; NIST guidance is specifically for digital identity systems and is not itself a universal legal rule for all organizations.
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