Glossary

A wide variety of terms are used in the realm of digital identity. While many definitions are consistent with earlier versions of SP 800-63, some have changed in this revision. Many of these terms lack a single, consistent definition, warranting careful attention to how the terms are defined here.

account recovery: The ability to regain ownership of a subscriber account and its associated information and privileges.
activation: The process of inputting an activation factor into a multi-factor authenticator to enable its use for authentication.
activation factor: An additional authentication factor that is used to enable successful authentication with a multi-factor authenticator.
activation secret: A password that is used locally as an activation factor for a multi-factor authenticator.
approved cryptography: An encryption algorithm, hash function, random bit generator, or similar technique that is Federal Information Processing Standard (FIPS)-approved or NIST-recommended. Approved algorithms and techniques are either specified or adopted in a FIPS or NIST recommendation.
assertion: A statement from an IdP to an RP that contains information about an authentication event for a subscriber. Assertions can also contain identity attributes for the subscriber.
asymmetric keys: Two related keys, comprised of a public key and a private key, that are used to perform complementary operations such as encryption and decryption or signature verification and generation.
attestation: Information conveyed to the CSP, generally at the time that an authenticator is bound, describing the characteristics of a connected authenticator or the endpoint involved in an authentication operation.
attribute: A quality or characteristic ascribed to someone or something. An identity attribute is an attribute about the identity of a subscriber.
authenticate: See authentication.
authenticated protected channel: An encrypted communication channel that uses approved cryptography where the connection initiator (client) has authenticated the recipient (server). Authenticated protected channels are encrypted to provide confidentiality and protection against active intermediaries and are frequently used in the user authentication process. Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) [RFC9325] are examples of authenticated protected channels in which the certificate presented by the recipient is verified by the initiator. Unless otherwise specified, authenticated protected channels do not require the server to authenticate the client. Authentication of the server is often accomplished through a certificate chain that leads to a trusted root rather than individually with each server.
authenticated session: See protected session.
authentication: The process by which a claimant proves possession and control of one or more authenticators bound to a subscriber account to demonstrate that they are the subscriber associated with that account.
Authentication Assurance Level (AAL): A category that describes the strength of the authentication process.
authentication factor: The three types of authentication factors are something you know, something you have, and something you are. Every authenticator has one or more authentication factors.
authentication intent: The process of confirming the claimant’s intent to authenticate or reauthenticate by requiring user intervention in the authentication flow. Some authenticators (e.g., OTPs) establish authentication intent as part of their operation. Others require a specific step, such as pressing a button, to establish intent. Authentication intent is a countermeasure against use by malware at the endpoint as a proxy for authenticating an attacker without the subscriber’s knowledge.
authentication protocol: A defined sequence of messages between a claimant and a verifier that demonstrates that the claimant has possession and control of one or more valid authenticators to establish their identity, and, optionally, demonstrates that the claimant is communicating with the intended verifier.
authentication secret: A generic term for any secret value that an attacker could use to impersonate the subscriber in an authentication protocol.
These are further divided into short-term authentication secrets, which are only useful to an attacker for a limited period of time, and long-term authentication secrets, which allow an attacker to impersonate the subscriber until they are manually reset. The authenticator secret is the canonical example of a long-term authentication secret, while the authenticator output — if it is different from the authenticator secret — is usually a short-term authentication secret.
authenticator: Something that the subscriber possesses and controls (e.g., a cryptographic module or password) and that is used to authenticate a claimant’s identity. See authenticator type and multi-factor authenticator.
authenticator binding: The establishment of an association between a specific authenticator and a subscriber account that allows the authenticator to be used to authenticate for that subscriber account, possibly in conjunction with other authenticators.
authenticator output: The output value generated by an authenticator. The ability to generate valid authenticator outputs on demand proves that the claimant possesses and controls the authenticator. Protocol messages sent to the verifier depend on the authenticator output, but they may or may not explicitly contain it.
authenticator secret: The secret value contained within an authenticator.
authenticator type: A category of authenticators with common characteristics, such as the types of authentication factors they provide and the mechanisms by which they operate.
authenticity: The property that data originated from its purported source.
authorize: A decision to grant access, typically automated by evaluating a subject’s attributes.
biometric sample: An analog or digital representation of biometric characteristics prior to biometric feature extraction, such as a record that contains a fingerprint image.
biometrics: Automated recognition of individuals based on their biological or behavioral characteristics. Biological characteristics include but are not limited to fingerprints, palm prints, facial features, iris and retina patterns, voiceprints, and vein patterns. Behavioral characteristics include but are not limited to keystrokes, angle of holding a smart phone, screen pressure, typing speed, mouse or mobile phone movements, and gyroscope position.
blocklist: A documented list of specific elements that are blocked, per policy decision. This concept has historically been known as a blacklist.
claimant: A subject whose identity is to be verified using one or more authentication protocols.
credential: An object or data structure that authoritatively binds an identity — via an identifier — and (optionally) additional attributes, to at least one authenticator possessed and controlled by a subscriber.
A credential is issued, stored, and maintained by the CSP. Copies of information from the credential can be possessed by the subscriber, typically in the form of one or more digital certificates that are often contained in an authenticator along with their associated private keys.
credential service provider (CSP): A trusted entity whose functions include identity proofing applicants to the identity service and registering authenticators to subscriber accounts. A CSP may be an independent third party.

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cross-site request forgery (CSRF): An attack in which a subscriber who is currently authenticated to an RP and connected through a secure session browses an attacker’s website, causing the subscriber to unknowingly invoke unwanted actions at the RP.
For example, if a bank website is vulnerable to a CSRF attack, it may be possible for a subscriber to unintentionally authorize a large money transfer by clicking on a malicious link in an email while a connection to the bank is open in another browser window.
cross-site scripting (XSS): A vulnerability that allows attackers to inject malicious code into an otherwise benign website. These scripts acquire the permissions of scripts generated by the target website to compromise the confidentiality and integrity of data transfers between the website and clients. Websites are vulnerable if they display user-supplied data from requests or forms without sanitizing the data so that it is not executable.
cryptographic authenticator: An authenticator that proves possession of an authentication secret through direct communication with a verifier through a cryptographic authentication protocol.
cryptographic key: A value used to control cryptographic operations, such as decryption, encryption, signature generation, or signature verification. For the purposes of these guidelines, key requirements shall meet the minimum requirements stated in Table 2 of [SP800-57Part1]. See asymmetric keys or symmetric keys.
cryptographic module: A set of hardware, software, or firmware that implements approved security functions including cryptographic algorithms and key generation.
digital authentication: The process of establishing confidence in user identities that are digitally presented to a system. In previous editions of SP 800-63, this was referred to as electronic authentication.
digital identity: An attribute or set of attributes that uniquely describes a subject within a given context.
digital signature: An asymmetric key operation in which the private key is used to digitally sign data and the public key is used to verify the signature. Digital signatures provide authenticity protection, integrity protection, and non-repudiation support but not confidentiality or replay attack protection.
digital transaction: A discrete digital event between a user and a system that supports a business or programmatic purpose.
electronic authentication (e-authentication): See digital authentication.
endpoint: Any device that is used to access a digital identity on a network, such as laptops, desktops, mobile phones, tablets, servers, Internet of Things devices, and virtual environments.
enrollment: The process through which a CSP/IdP provides a successfully identity-proofed applicant with a subscriber account and binds authenticators to grant persistent access.
entropy: The amount of uncertainty that an attacker faces to determine the value of a secret. Entropy is usually stated in bits. A value with n bits of entropy has the same degree of uncertainty as a uniformly distributed n-bit random value.
equity: The consistent and systematic fair, just, and impartial treatment of all individuals, including individuals who belong to underserved communities that have been denied such treatment, such as Black, Latino, and Indigenous and Native American persons, Asian Americans and Pacific Islanders, and other persons of color; members of religious minorities; lesbian, gay, bisexual, transgender, and queer (LGBTQ+) persons; persons with disabilities; persons who live in rural areas; and persons otherwise adversely affected by persistent poverty or inequality. [EO13985]
factor: See authentication factor

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Federal Information Processing Standard (FIPS)

Under the Information Technology Management Reform Act (Public Law 104-106), the Secretary of Commerce approves the standards and guidelines that the National Institute of Standards and Technology (NIST) develops for federal computer systems. NIST issues these standards and guidelines as Federal Information Processing Standards (FIPS) for government-wide use. NIST develops FIPS when there are compelling federal government requirements, such as for security and interoperability, and there are no acceptable industry standards or solutions. See background information for more details.

FIPS documents are available online on the FIPS home page: https://www.nist.gov/itl/fips.cfm

federation

A process that allows for the conveyance of identity and authentication information across a set of networked systems.

hash function

A function that maps a bit string of arbitrary length to a fixed-length bit string. Approved hash functions satisfy the following properties:

One-way — It is computationally infeasible to find any input that maps to any pre-specified output.
Collision-resistant — It is computationally infeasible to find any two distinct inputs that map to the same output.

identifier

A data object that is associated with a single, unique entity (e.g., individual, device, or session) within a given context and is never assigned to any other entity within that context.

identity

See digital identity

Identity Assurance Level (IAL)

A category that conveys the degree of confidence that the subject’s claimed identity is their real identity.

identity proofing

The processes used to collect, validate, and verify information about a subject in order to establish assurance in the subject’s claimed identity.

identity provider (IdP)

The party in a federation transaction that creates an assertion for the subscriber and transmits the assertion to the RP.

identity resolution

The process of collecting information about an applicant to uniquely distinguish an individual within the context of the population that the CSP serves.

injection attack

An attack in which an attacker supplies untrusted input to a program. In the context of federation, the attacker presents an untrusted assertion or assertion reference to the RP in order to create an authenticated session with the RP.

manageability

Providing the capability for the granular administration of personally identifiable information, including alteration, deletion, and selective disclosure. [NISTIR8062]

memorized secret

See password.

message authentication code (MAC)

A cryptographic checksum on data that uses a symmetric key to detect both accidental and intentional modifications of the data. MACs provide authenticity and integrity protection, but not non-repudiation protection.

mobile code

Executable code that is normally transferred from its source to another computer system for execution. This transfer is often through the network (e.g., JavaScript embedded in a web page) but may transfer through physical media as well.

multi-factor authentication (MFA)

An authentication system that requires more than one distinct type of authentication factor for successful authentication. MFA can be performed using a multi-factor authenticator or by combining single-factor authenticators that provide different types of factors.

multi-factor authenticator

An authenticator that provides more than one distinct authentication factor, such as a cryptographic authentication device with an integrated biometric sensor that is required to activate the device.

network

An open communications medium, typically the Internet, used to transport messages between the claimant and other parties. Unless otherwise stated, no assumptions are made about the network’s security; it is assumed to be open and subject to active (e.g., impersonation, session hijacking) and passive (e.g., eavesdropping) attacks at any point between the parties (e.g., claimant, verifier, CSP, RP).

nonce

A value used in security protocols that is never repeated with the same key. For example, nonces used as challenges in challenge-response authentication protocols must not be repeated until authentication keys are changed. Otherwise, there is a possibility of a replay attack. Using a nonce as a challenge is a different requirement than a random challenge, because a nonce is not necessarily unpredictable.

non-repudiation

The capability to protect against an individual falsely denying having performed a particular transaction.

offline attack

An attack in which the attacker obtains some data (typically by eavesdropping on an authentication transaction or by penetrating a system and stealing security files) that the attacker is able to analyze in a system of their own choosing.

online attack

An attack against an authentication protocol in which the attacker either assumes the role of a claimant with a genuine verifier or actively alters the authentication channel.

online guessing attack

An attack in which an attacker performs repeated logon trials by guessing possible values of the authenticator output.

passphrase

A password that consists of a sequence of words or other text that a claimant uses to authenticate their identity. A passphrase is similar to a password in usage but is generally longer for added security.

password

A type of authenticator consisting of a character string that is intended to be memorized or memorable by the subscriber to permit the claimant to demonstrate something they know as part of an authentication process. Passwords are referred to as memorized secrets in the initial release of SP 800-63B.

personal identification number (PIN)

A password that typically consists of only decimal digits.

personal information

See personally identifiable information.

personally identifiable information (PII)

Information that can be used to distinguish or trace an individual’s identity, either alone or when combined with other information that is linked or linkable to a specific individual. [A-130]

pharming

An attack in which an attacker corrupts an infrastructure service such as DNS (e.g., Domain Name System [DNS]) and causes the subscriber to be misdirected to a forged verifier/RP, which could cause the subscriber to reveal sensitive information, download harmful software, or contribute to a fraudulent act.

phishing

An attack in which the subscriber is lured (usually through an email) to interact with a counterfeit verifier/RP and tricked into revealing information that can be used to masquerade as that subscriber to the real verifier/RP.

phishing resistance

The ability of the authentication protocol to prevent the disclosure of authentication secrets and valid authenticator outputs to an impostor verifier without reliance on the vigilance of the claimant.

physical authenticator

An authenticator that the claimant proves possession of as part of an authentication process.

possession and control of an authenticator

The ability to activate and use the authenticator in an authentication protocol.

predictability

Enabling reliable assumptions by individuals, owners, and operators about PII and its processing by an information system. [NISTIR8062]

private key

In asymmetric key cryptography, the private key (i.e., a secret key) is a mathematical key used to create digital signatures and, depending on the algorithm, decrypt messages or files that are encrypted with the corresponding public key. In symmetric key cryptography, the same private key is used for both encryption and decryption.

presentation attack

Presentation to the biometric data capture subsystem with the goal of interfering with the operation of the biometric system.

presentation attack detection (PAD)

Automated determination of a presentation attack. A subset of presentation attack determination methods, referred to as liveness detection, involves the measurement and analysis of anatomical characteristics or voluntary or involuntary reactions, to determine if a biometric sample is being captured from a living subject that is present at the point of capture.

Privacy Impact Assessment (PIA)

A method of analyzing how personally identifiable information (PII) is collected, used, shared, and maintained. PIAs are used to identify and mitigate privacy risks throughout the development lifecycle of a program or system. They also help ensure that handling information conforms to legal, regulatory, and policy requirements regarding privacy.

protected session

A session in which messages between two participants are encrypted and integrity is protected using a set of shared secrets called “session keys.”

A protected session is said to be authenticated if — during the session — one participant proves possession of one or more authenticators in addition to the session keys, and if the other party can verify the identity associated with the authenticators. If both participants are authenticated, the protected session is said to be mutually authenticated.

pseudonym

A name other than a legal name.

pseudonymity

The use of a pseudonym to identify a subject.

pseudonymous identifier

A meaningless but unique identifier that does not allow the RP to infer anything regarding the subscriber but that does permit the RP to associate multiple interactions with a single subscriber.

public key

The public part of an asymmetric key pair that is used to verify signatures or encrypt data.

public key certificate

A digital document issued and digitally signed by the private key of a certificate authority that binds an identifier to a subscriber’s public key. The certificate indicates that the subscriber identified in the certificate has sole control of and access to the private key. See also [RFC5280].

public key infrastructure (PKI)

A set of policies, processes, server platforms, software, and workstations used to administer certificates and public-_private key_ pairs, including the ability to issue, maintain, and revoke public key certificates.

reauthentication

The process of confirming the subscriber’s continued presence and intent to be authenticated during an extended usage session.

relying party (RP)

An entity that relies upon a verifier’s assertion of a subscriber’s identity, typically to process a transaction or grant access to information or a system.

remote

A process or transaction that is conducted through connected devices over a network, rather than in person.

replay attack

An attack in which the attacker is able to replay previously captured messages (between a legitimate claimant and a verifier) to masquerade as that claimant to the verifier or vice versa.

replay resistance

The property of an authentication process to resist replay attacks, typically by the use of an authenticator output that is valid only for a specific authentication.

restricted

An authenticator type, class, or instantiation that has additional risk of false acceptance associated with its use and is therefore subject to additional requirements.

risk assessment

The process of identifying, estimating, and prioritizing risks to organizational operations (i.e., mission, functions, image, or reputation), organizational assets, individuals, and other organizations that result from the operation of a system. A risk assessment is part of risk management, incorporates threat and vulnerability analyses, and considers mitigations provided by security controls that are planned or in-place. It is synonymous with “risk analysis.”

risk management

The program and supporting processes that manage information security risk to organizational operations (including mission, functions, image, reputation), organizational assets, individuals, and other organizations and includes (i) establishing the context for risk-related activities, (ii) assessing risk, (iii) responding to risk once determined, and (iv) monitoring risk over time.

salt

A non-secret value used in a cryptographic process, usually to ensure that the results of computations for one instance cannot be reused by an attacker.

Secure Sockets Layer (SSL)

See Transport Layer Security (TLS).

Senior Agency Official for Privacy (SAOP)

Person responsible for ensuring that an agency complies with privacy requirements and manages privacy risks. The SAOP is also responsible for ensuring that the agency considers the privacy impacts of all agency actions and policies that involve PII.

session

A persistent interaction between a subscriber and an endpoint, either an RP or a CSP. A session begins with an authentication event and ends with a session termination event. A session is bound by the use of a session secret that the subscriber’s software (e.g., a browser, application, or OS) can present to the RP to prove association of the session with the authentication event.

session hijack attack

An attack in which the attacker is able to insert themselves between a claimant and a verifier subsequent to a successful authentication exchange between the latter two parties. The attacker is able to pose as a subscriber to the verifier or vice versa to control session data exchange. Sessions between the claimant and the RP can be similarly compromised.

shared secret

A secret used in authentication that is known to the subscriber and the verifier.

side-channel attack

An attack enabled by the leakage of information from a physical cryptosystem. Characteristics that could be exploited in a side-channel attack include timing, power consumption, and electromagnetic and acoustic emissions.

single-factor

A characteristic of an authentication system or an authenticator that requires only one authentication factor (i.e., something you know, something you have, or something you are) for successful authentication.

single sign-on (SSO)

An authentication process by which one account and its authenticators are used to access multiple applications in a seamless manner, generally implemented with a federation protocol.

social engineering

The act of deceiving an individual into revealing sensitive information, obtaining unauthorized access, or committing fraud by associating with the individual to gain confidence and trust.

subject

A person, organization, device, hardware, network, software, or service. In these guidelines, a subject is a natural person.

subscriber

An individual enrolled in the CSP identity service.

subscriber account

An account established by the CSP containing information and authenticators registered for each subscriber enrolled in the CSP identity service.

symmetric key

A cryptographic key used to perform both the cryptographic operation and its inverse. (e.g., to encrypt and decrypt or create a message authentication code and to verify the code).

sync fabric

Any on-premises, cloud-based, or hybrid service used to store, transmit, or manage authentication keys generated by syncable authenticators that are not local to the user’s device.

syncable authenticators

Software or hardware cryptographic authenticators that allow authentication keys to be cloned and exported to other storage to sync those keys to other authenticators (i.e., devices).

system of record (SOR)

An SOR is a collection of records that contain information about individuals and are under the control of an agency. The records can be retrieved by the individual’s name or by an identifying number, symbol, or other identifier.

System of Record Notice (SORN)

A notice that federal agencies publish in the Federal Register to describe their systems of records.

token

See authenticator.

transaction

See digital transaction

Transport Layer Security (TLS)

An authentication and security protocol widely implemented in browsers and web servers. TLS is defined by [RFC5246]. TLS is similar to the older SSL protocol, and TLS 1.0 is effectively SSL version 3.1. SP 800-52, Guidelines for the Selection and Use of Transport Layer Security (TLS) Implementations [SP800-52], specifies how TLS is to be used in government applications.

usability

The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use. [ISO/IEC9241-11]

verifier

An entity that verifies the claimant’s identity by verifying the claimant’s possession and control of one or more authenticators using an authentication protocol. To do this, the verifier needs to confirm the binding of the authenticators with the subscriber account and check that the subscriber account is active.

verifier impersonation

See phishing.

zeroize

Overwrite a memory location with data that consists entirely of bits with the value zero so that the data is destroyed and unrecoverable. This is often contrasted with deletion methods that merely destroy references to data within a file system rather than the data itself.