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A strong password should be long, unique to one account, and difficult to guess—not merely packed with uppercase letters, numbers, and symbols. NIST’s current guidance sets a minimum of 15 characters when a password is the only authentication factor, and permits a minimum of eight when it is used only as part of multi-factor authentication (MFA). Those are requirements for services covered by NIST’s guidance, not a guarantee that every site follows them or that a password meeting the minimum is safe from guessing.
Length matters more than forced character variety
NIST’s current guidance treats length as a primary factor in password strength. It encourages people to make passwords as long as they want within reason, and says services should allow a maximum length of at least 64 characters. A service’s actual limit may differ.
Requiring a mix of uppercase and lowercase letters, numbers, and symbols does not necessarily make a password unpredictable. People often meet such rules with familiar, foreseeable substitutions—for example, adding a capital letter or symbol to a common word. NIST therefore prohibits verifiers from imposing character-composition rules and instead requires them to block common, expected, or compromised password choices.
A long password is not automatically strong: a familiar phrase or a common password padded with a few characters may still be guessable. Length helps when the choice itself is not common or predictable. NIST does not specify a universal word count for passphrases; it notes that “The use of passphrases (i.e., passwords with multiple words) is often an effective way to create a longer password.” NIST SP 800-63B-4, Appendix A
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What NIST’s current password guidance requires
SP 800-63B-4 sets different minimums depending on whether a password is used alone or with another authentication factor. These are requirements for verifiers and credential service providers within the standard’s scope; they are not a universal guarantee about every website.
| Password use | NIST guidance | What it means for you |
|---|---|---|
| Password as the only authentication factor | At least 15 characters | A service following the standard must set this minimum. |
| Password used only as part of MFA | At least 8 characters | A verifier may allow a shorter minimum than 15, but not shorter than 8. |
| Maximum length a verifier should permit | At least 64 characters | This is a capacity recommendation, not a promise that every service accepts 64 characters. |
NIST also says verifiers should accept printable ASCII characters and spaces, and should accept Unicode. For length checks, each Unicode code point counts as one character. A particular site may handle character support or text input differently. The standard also says verifiers must not require periodic password changes, but must require a change when there is evidence that the password has been compromised. NIST SP 800-63B-4
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Make every account password unique
Do not reuse a password across accounts. If one service is compromised, reuse can put other accounts at risk. A password manager can generate and store distinct passwords, and NIST says services must allow password managers and autofill. It also says they should permit pasting when autofill is unavailable.
If you use a manager, create a unique password for every account or use its password-generation feature. Protect the manager’s master secret carefully: it is the key to the passwords stored in the vault. NIST Digital Identity Guidelines FAQ
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What a strong password cannot prevent
Password length and complexity help reduce the risk of guessing, but they do not prevent every way credentials can be stolen. NIST specifically notes that keystroke logging, phishing, and social engineering are not addressed by making a password longer or more complex. A unique password limits reuse across accounts; it cannot stop you from being tricked into entering it on a fraudulent site or having it captured by malicious software. NIST SP 800-63B-4, Appendix A
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