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A passphrase is a memorized secret made from a sequence of words or other text that you use to prove your identity. In everyday account sign-in, it is a kind of password—usually longer and often easier to remember as several words. In some security systems, the term has a narrower meaning: text used to derive a cryptographic key that protects another key. Those are different uses, not one universal login mechanism.
What is a passphrase?
The National Institute of Standards and Technology (NIST) defines a passphrase as “a memorized secret consisting of a sequence of words or other text that a claimant uses to authenticate their identity.” In ordinary account use, that means a longer password assembled as a sequence of words or other text. NIST describes it as similar to a password in use, but generally longer.
A passphrase is a “something you know” credential. The important properties are that it is hard for someone else to guess, kept secret, and entered only where it is meant to be used. It need not be a grammatical sentence, and adding spaces or symbols does not automatically make it secure.
How does a passphrase work?
Signing in to an account
For a typical website or app, you enter the passphrase into the sign-in field to demonstrate knowledge of your credential. NIST’s current digital identity standard describes centrally verified passwords as being sent to the verifier over an authenticated, protected channel. This is the ordinary password-style use of a passphrase; it is not necessarily converted into a separate encryption key by the site.
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Whether a particular service accepts spaces, punctuation, or a long passphrase depends on that service’s rules. Check its password requirements and maximum length rather than assuming every site accepts the same characters.
Protecting a cryptographic key
In a different context, a passphrase can be used as input to a mathematical key-derivation process. In NISTIR 7966, it derives a key that encrypts an identity key; the passphrase is entered again to regenerate the key when decryption is needed. This is a specific key-protection use, not how every website login works.
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What are the types of passphrases and related credentials?
These are useful practical distinctions, not an exhaustive formal taxonomy:
| Credential | What it is | Typical use or trade-off |
|---|---|---|
| Multiword passphrase | A memorized sequence of words or other text. | Can make a longer secret easier to remember, but predictable phrases can still be guessed. |
| Character-string password | A memorized secret that may combine letters, numbers, or symbols. | May be shorter or harder to remember; apparent complexity alone does not establish strength. |
| Numeric PIN | NIST defines a PIN as a password that typically consists only of decimal digits. | Related to passwords, but distinct in its numeric form and often used in device or service-specific sign-in flows. |
Is a passphrase more secure than a password?
Not automatically. A long, unpredictable passphrase can resist guessing better than a short or reused password, and multiple words can be easier to recall than a random-looking string of similar length. But a familiar quotation, personal detail, or predictable word sequence may be easier to guess than a randomly generated password. NIST notes that estimating the entropy of human-chosen secrets is difficult and emphasizes length in its guidance.
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NIST’s consumer guidance illustrates why length matters: it gives about 200 billion combinations for an eight-character lowercase password, against a stated guessing rate of 100 billion guesses per second. The same guidance says an exhaustive search of all combinations of 15 lowercase letters would take more than 500 years at that rate. These are simplified brute-force illustrations, not universal cracking forecasts; real attack speed depends on the verifier and the attacker’s method.
A longer passphrase does not prevent phishing, keylogging, or social engineering. Use a unique credential for each account, and enable multi-factor authentication (MFA) where available. A password manager can help create and keep track of distinct credentials without requiring you to memorize each one.
How should you create a passphrase?
- Make it long. NIST’s public guidance recommends passwords of at least 15 characters and notes that several real words can make a long secret easier to invent and remember. This is NIST guidance, not a guarantee that every service accepts a passphrase of that length.
- Choose something difficult to predict. Avoid familiar quotations, personal information, and obvious sequences. Multiple words are not enough if the combination is predictable.
- Use a different credential for each account. Reuse can expose multiple accounts if one credential is compromised. A password manager can help manage unique credentials.
- Check the service’s rules. Requirements for accepted characters and maximum length vary. NIST says verifiers should not require mixed character types, but an individual site may still impose its own constraints.
- Add MFA when offered. A passphrase protects the sign-in secret; MFA adds another authentication factor and can help when a password is exposed.
NIST’s consumer guidance uses “cassette lava baby” as an 18-character example of a passphrase, but explicitly warns readers not to use it because the example is public. It is an illustration, not a recommended credential.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How many words should a passphrase have?
There is no universal word count established by the cited NIST guidance. NIST recommends at least 15 characters for passwords and presents multiple real words as one way to create a longer, memorable secret. The right construction also depends on how unpredictable the words are, whether the service accepts the length and characters, and whether the credential is unique to that account.
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Do passphrases need numbers, capitals, or symbols?
NIST’s current SP 800-63-4 says verifiers shall not require composition rules such as mandatory mixtures of character types. Its public guidance likewise says it no longer recommends requiring special characters and numbers. That does not mean every website follows NIST’s guidance or accepts a phrase without symbols; follow the specific service’s stated requirements.
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