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Identity Authority
Category: Passwords & Hashing

Passphrase

Simply put

A passphrase is a memorized secret made up of a sequence of words or other text that a person uses to prove their identity when logging in. It works much like a password but is typically longer, often composed of multiple words and sometimes including spaces between them. Because of its greater length, a passphrase can be easier to remember while still being harder to guess.

Formal definition

A passphrase is a knowledge-factor authenticator: a memorized secret consisting of a sequence of words or other text that a claimant supplies to authenticate their identity. Functionally it is a longer variant of a password, commonly at least 14 characters and frequently structured as four or more words, sometimes separated by spaces. As a knowledge factor it may serve as a standalone credential or as one factor within an MFA arrangement; the specific storage, hashing, complexity, and length requirements applied to a passphrase depend on the deployment and applicable policy and are out of scope for this definition.

Why it matters

Passphrases matter because they address a persistent tension in knowledge-factor authentication: secrets that are hard for an attacker to guess are often hard for a legitimate user to remember, while secrets that are easy to remember tend to be weak. By structuring a memorized secret as a sequence of words, often four or more, sometimes separated by spaces, a passphrase can achieve substantial length, typically at least 14 characters, while remaining memorable. This makes the passphrase a practical way to raise the strength of a knowledge factor without forcing users toward the fragile coping behaviors (reuse, predictable substitutions, written-down secrets) that short complex passwords tend to encourage.

From an IAM design perspective, it is important to keep the passphrase's role in scope. A passphrase is still a knowledge factor, so it is subject to the same categories of risk as any other memorized secret: phishing, credential stuffing where a passphrase has been reused, server-side compromise of the stored credential, and interception. Greater length raises the cost of brute-force and guessing attacks, but it does not by itself protect against these other threat classes. Treating a passphrase as inherently secure rather than as one strengthened variant of a memorized secret can lead to overconfidence in single-factor deployments.

For that reason, a passphrase is most valuable when its role is understood clearly relative to the rest of the authentication design. It can serve as a standalone credential or as one factor within a multi-factor arrangement, and the storage, hashing, complexity, and length requirements applied to it depend on the deployment and applicable policy. The passphrase improves one dimension, resistance to guessing through length and memorability, and should be evaluated alongside the other controls that address the risks length alone cannot cover.

Who it's relevant to

IAM engineers and system administrators
Those configuring authentication policies decide whether users can or must set word-based secrets, and what length and complexity rules apply. Understanding a passphrase as a longer variant of a password, rather than a distinct mechanism, helps in setting length requirements and validation logic that support memorable but strong secrets without introducing brittle constraints.
Security architects
Architects deciding where a passphrase fits in an authentication design need to treat it as one knowledge factor whose main benefit is resistance to guessing through length. Because it does not by itself mitigate phishing, reuse, or server-side compromise, architects should evaluate whether it is used standalone or as one factor within an MFA arrangement, and what storage and hashing protections back it.
Compliance officers
Those mapping authentication controls to policy should note that passphrase length, complexity, hashing, and storage requirements are set by deployment and applicable policy rather than by the passphrase concept itself. Assessing an implementation means examining those configured choices, not assuming that word-based secrets meet any particular standard by virtue of their form.

Inside Passphrase

Knowledge factor
A passphrase is a knowledge-based authentication factor, meaning it verifies identity based on something the principal knows rather than something they possess or an inherent characteristic. It is used during the authentication step, not authorization.
Sequence of words or extended string
Unlike a traditional password, a passphrase is typically composed of multiple words or a longer character sequence, increasing overall length and, in most cases, entropy while remaining more memorable to the user.
Length and entropy characteristics
The security value of a passphrase generally derives from its length and unpredictability. Depending on how words are chosen (for example, randomly selected versus common phrases), effective entropy can vary significantly.
Storage representation
In most deployments a passphrase is not stored in plaintext; it is typically transformed via a one-way hashing function, often with a salt and a work factor, before storage in a directory or credential store.
Role within a factor set
A passphrase can serve as a single factor or as the knowledge component within an MFA or 2FA configuration when combined with a possession or inherence factor. On its own it does not constitute multi-factor authentication.

Common questions

Answers to the questions practitioners most commonly ask about Passphrase.

Is a passphrase just a longer password, or is it a fundamentally different credential type?
A passphrase is not a different credential type; it remains a knowledge factor and is validated the same way any password is. The distinction is one of composition and length rather than category: a passphrase typically uses a sequence of words or a longer string of characters, but it is still a shared secret authenticating a principal based on something they know. It does not, by itself, constitute multi-factor authentication, and combining a passphrase with another passphrase does not add a second factor.
Does using a passphrase instead of a password make authentication passwordless?
No. Passwordless authentication removes reliance on a memorized knowledge-factor secret altogether, typically favoring possession and inherence factors such as those used with FIDO2/WebAuthn credentials. A passphrase is still a knowledge factor and a memorized secret, so systems that authenticate with passphrases are not passwordless regardless of how long or complex the passphrase is.
How should passphrases be stored so they can be verified without keeping the plaintext?
In most deployments, passphrases are verified against a stored hash produced by a password-hashing function designed to be computationally expensive, rather than stored in plaintext or under fast general-purpose hashes. The exact algorithm and parameters depend on your platform and policy. Note that hashing protects the stored secret at rest and is distinct from transport protection, which is handled separately by the connection layer.
Should length or complexity requirements be prioritized when setting a passphrase policy?
This depends on your policy framework and applicable guidance, and practice varies. Many modern approaches emphasize length and encourage longer memorized secrets while relaxing arbitrary composition rules, but the specifics should follow the standard or regulatory guidance your organization is bound by. Because behavior and requirements vary by deployment context, validate any policy against the framework you are actually subject to rather than assuming a universal rule.
Does adopting passphrases reduce the need for multi-factor authentication?
No. A passphrase remains a single knowledge factor, so it does not provide the independent second factor that MFA requires. In most deployments, a passphrase can serve as the knowledge component while a separate possession or inherence factor supplies the additional factor. Step-up authentication may also be layered on top for higher-risk operations, but that is an authorization-time decision distinct from the passphrase itself.
Can passphrases be provisioned and managed through directory and provisioning standards like LDAP or SCIM?
The account and attribute lifecycle can be managed through directory and provisioning mechanisms, but the handling of the secret itself depends on the system and protocol involved. SCIM defines a password attribute for provisioning, and directories such as those accessed over LDAP typically store a hashed representation rather than the plaintext. How the secret is transmitted, hashed, and verified varies by implementation, so confirm the specific behavior of your directory and provisioning tooling rather than assuming uniform handling.

Common misconceptions

A passphrase is fundamentally different in kind from a password and therefore inherently more secure.
A passphrase is still a knowledge factor and is subject to the same categories of risk (phishing, reuse, credential theft). Its advantage is typically greater length and memorability, but its actual strength depends on how it is chosen and how it is stored.
Using a passphrase counts as multi-factor authentication.
A passphrase alone is a single knowledge factor. MFA or 2FA requires combining it with a factor of a different category, such as possession or inherence. Length does not change the number of factors.
A longer passphrase is always secure regardless of composition.
Length helps, but a passphrase built from a well-known quotation or predictable phrase may have far lower effective entropy than its character count suggests. Unpredictability of selection matters, and behavior varies by policy and deployment.

Best practices

Treat a passphrase as a single knowledge factor and pair it with a possession or inherence factor to achieve genuine MFA where the risk profile warrants it.
Store passphrases using a salted, one-way hash with an appropriate work factor rather than in plaintext or reversibly encrypted form, noting that hashing and encryption are distinct protections.
Favor length and unpredictability over composition complexity rules, and discourage well-known phrases that reduce effective entropy despite appearing long.
Screen candidate passphrases against known-breached credential lists and common-phrase dictionaries during enrollment and reset, depending on your platform's capabilities.
Consider step-up authentication for sensitive operations rather than relying on the passphrase alone for all access decisions.
Where feasible, offer phishing-resistant alternatives such as passkeys or WebAuthn-based authentication, since a passphrase remains vulnerable to phishing and reuse regardless of its strength.
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