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Control Institute
Category: Access and Identity Management

Secret Authentication Information

Also known as: Authentication Secret, Secret Authenticator
Simply put

Secret authentication information is confidential data, such as passwords, PINs, cryptographic keys, or shared secrets, that a person or system keeps private and uses to prove their identity when logging in or accessing a system. Because its security depends on remaining confidential, it must be protected from disclosure. Not all authentication information qualifies as secret; for example, biometric data used to verify identity is generally not treated as a secret value.

Formal definition

Secret authentication information refers to any confidential value used to verify a claimant or subscriber within an authentication protocol, where the security property relies on the value being known only to the authorized party (and, where applicable, the verifier). Common examples include passwords, passphrases, PINs, symmetric keys, and other shared secrets. In ISO/IEC 27001:2022 Annex A, control 5.17 addresses the allocation, management, and protection of authentication information, which is selected via the Statement of Applicability and informed by risk assessment; the term 'authentication information' is broader than 'secret authentication information' and can encompass non-secret factors. Notably, biometric data, while used for authentication, is typically not classified as secret because it cannot be reliably kept confidential in the way a password or key can. The specific handling, storage, and lifecycle requirements for such information depend on the applicable controls, scope, and organizational risk decisions.

Why it matters

Secret authentication information sits at the core of nearly every access control decision an organization makes. When a person or system presents a password, PIN, cryptographic key, or shared secret, the entire trust model depends on that value having remained confidential. If it is disclosed, guessed, or leaked, an attacker can impersonate a legitimate user or system, and the surrounding controls that assume the secret is private are undermined. This is why the confidentiality of these values, during allocation, transmission, storage, and use, is treated as a distinct security concern rather than an afterthought.

A crucial distinction is that not all authentication information is secret. Authentication information is the broader category and can include factors that are used to prove identity but cannot be reliably kept confidential. Biometric data is the most important example: while it is used for authentication, it is generally not classified as a secret value because it cannot be kept confidential the way a password or cryptographic key can. Conflating the two categories can lead organizations to apply protection expectations that do not match the actual security properties of the factor, so precise classification matters for both design and audit purposes.

For organizations pursuing ISO/IEC 27001:2022, the handling of authentication information is addressed through Annex A control 5.17, which is selected via the Statement of Applicability and informed by risk assessment. Because Annex A controls are reference controls rather than universal mandates, the specific storage, allocation, and lifecycle requirements an organization applies depend on its scope, applicable controls, and risk decisions rather than a single fixed rule.

Who it's relevant to

Security Engineers and IT Administrators
Those who design and operate authentication systems need to distinguish secret values, passwords, PINs, symmetric keys, and shared secrets, from non-secret authentication factors such as biometrics. This distinction shapes how each factor is allocated, transmitted, stored, and protected, since only secrets rely on remaining confidential for their security.
GRC and Compliance Professionals
For teams implementing ISO/IEC 27001:2022, authentication information is addressed by Annex A control 5.17, which is selected through the Statement of Applicability and informed by risk assessment. Compliance professionals must document how secret authentication information is managed within the defined ISMS scope and recognize that the applicable requirements depend on organizational risk decisions rather than a single universal rule.
Auditors and Assessors
Auditors evaluating access control need to verify that secret authentication information is protected consistent with its confidentiality-dependent nature, and that the organization correctly separates secret values from non-secret factors like biometrics. Assessment findings should reflect the scope, applicable controls, and risk-based selections the organization has made rather than assumed mandatory practices.

Inside Secret Authentication Information

Passwords and passphrases
The most common form of secret authentication information, consisting of a memorized secret known only to the individual user and used to verify identity during authentication.
PINs
Personal identification numbers used as a memorized secret, typically shorter than passwords and often used in combination with another factor such as a card or token.
Cryptographic keys and secret values
Private keys, shared secrets, or seed values used by authentication mechanisms, which must be protected from disclosure to preserve their confidentiality.
One-time passcodes and authenticator secrets
Time-based or event-based codes, and the underlying seed secrets that generate them, which serve as authentication information that must remain confidential.

Common questions

Answers to the questions practitioners most commonly ask about Secret Authentication Information.

Is biometric data considered a form of secret authentication information?
Not in the same sense as passwords or private keys. Biometric characteristics are generally not treated as secret values, since they can be observed, captured, or otherwise obtained and cannot be changed if compromised. Secret authentication information typically refers to knowledge-based or cryptographic secrets, such as passwords, PINs, private keys, or shared secrets, that are intended to remain confidential to the authenticating party. Biometrics are more accurately described as an authentication factor based on something you are, and they should be protected as sensitive data, but classifying them as a shared secret is inaccurate.
Does managing secret authentication information mean the same thing under SOC 2 and ISO 27001?
The concept overlaps, but the two frameworks address it differently. Under ISO/IEC 27001, control expectations for authentication information appear in Annex A (with the specific reference control and its numbering depending on whether you are using the 2013 or 2022 edition), and applicability is determined through the Statement of Applicability and risk assessment. Under SOC 2, related expectations are evaluated against the relevant Trust Services Criteria, primarily the Security (Common Criteria) category, as part of a CPA firm's attestation examination. Satisfying one framework's treatment of authentication information does not automatically satisfy the other, and mapping between them is typically partial rather than one-to-one.
How should secret authentication information be handled during initial allocation to a user?
In most implementations, secrets are allocated through a controlled process that verifies the identity of the recipient, uses a secure delivery channel, and often requires the recipient to change any temporary or default value on first use. The specific mechanism depends on scope, risk assessment, and the organization's policies. Auditors and certification bodies generally look for evidence that the allocation process reduces the risk of interception and that temporary secrets are time-limited or single-use where feasible.
What is expected for the storage of secret authentication information?
Secrets are typically protected in storage using measures appropriate to their sensitivity, such as hashing of passwords rather than reversible storage, and protection of cryptographic keys through key management practices. The exact controls depend on the technology in use and the organization's risk decisions. Reviewers generally expect that stored secrets are not held in plaintext where avoidable and that access to any stored secret material is restricted and logged, though specific requirements vary by scope and applicable criteria.
How can an organization demonstrate proper management of authentication information to an assessor?
Evidence commonly includes documented policies governing the lifecycle of authentication information, records of allocation and revocation, configuration settings showing how secrets are stored and transmitted, and logs demonstrating that controls operate as described. For a SOC 2 Type II examination, the assessor evaluates operating effectiveness over the defined review period, so evidence spanning that period is typically needed; for a Type I, the focus is on suitability of design at a point in time. For ISO 27001, evidence supports both the ISMS requirements in clauses 4 through 10 and the selected Annex A controls.
What should happen to secret authentication information when a user leaves or changes roles?
In most engagements, organizations are expected to revoke or reset authentication information promptly when access is no longer required, as part of a broader joiner-mover-leaver or access management process. This may include disabling credentials, rotating shared secrets that the individual knew, and reclaiming any tokens or keys. The timing and specifics depend on the organization's policies and risk assessment, and reviewers generally look for evidence that revocation occurs in a timely and consistent manner rather than confirming a single mandated interval.

Common misconceptions

Biometric data (such as fingerprints or facial recognition) is a form of secret authentication information.
Biometrics are not secret values. Guidance such as NIST SP 800-63B implementation resources explicitly notes that biometrics are not secret; they function as a means of identifying or unlocking an authenticator rather than as confidential secret authentication information, and should be handled distinctly.
Protecting secret authentication information is solely a technical control handled by systems.
In most engagements, safeguarding secret authentication information also depends on user behavior, policy, and process controls (for example, secure distribution, storage, and revocation), so it typically requires a combination of technical and administrative measures rather than technology alone.
Implementing controls over secret authentication information for one framework automatically satisfies the requirements of another.
Mapping between frameworks such as SOC 2 and ISO 27001 is possible but partial. Controls over secret authentication information may be evidenced differently depending on the applicable criteria, scope, auditor, or certification body, so satisfying one framework does not automatically satisfy another.

Best practices

Distribute secret authentication information through secure channels and require users to change any default or initially assigned secrets promptly upon first use.
Store secret authentication information using protective measures such as hashing or encryption rather than in plaintext, and restrict access to those values.
Establish and enforce policies for the confidentiality, handling, and periodic review of secret authentication information, and communicate user responsibilities clearly.
Implement processes to promptly revoke or reset secret authentication information when compromise is suspected or when access is no longer required.
Do not treat biometric data as a confidential secret value; handle it separately from secret authentication information consistent with recognized guidance.
Retain evidence of these controls appropriate to the applicable framework, recognizing that acceptable evidence typically varies depending on scope, auditor, or certification body.