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 linking

The association of multiple federated identifiers with a single RP subscriber account, or the management of those associations.

account resolution

The association of an RP subscriber account with information already held by the RP prior to the federation transaction and outside of a trust agreement.

activation factor

An additional authentication factor that is used to enable successful authentication with a multi-factor authenticator.

allowlist

A documented list of specific elements that are allowed, per policy decision. In federation contexts, this is most commonly used to refer to the list of RPs allowed to connect to an IdP without subscriber intervention. This concept has historically been known as a whitelist.

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.

assertion reference

A data object, created in conjunction with an assertion, that is used by the RP to retrieve an assertion over an authenticated protected channel.

assertion presentation

The method by which an assertion is transmitted to the RP.

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.

attribute

A quality or characteristic ascribed to someone or something. An identity attribute is an attribute about the identity of a subscriber.

attribute bundle

A package of attribute values and derived attribute values from a CSP. The package has necessary cryptographic protection to allow validation of the bundle independent from interaction with the CSP or IdP. Attribute bundles are often used with subscriber-controlled wallets.

attribute provider

The provider of an identity API that provides access to a subscriber’s attributes without necessarily asserting that the subscriber is present to the RP.

attribute value

A complete statement that asserts an identity attribute of a subscriber, independent of format. For example, for the attribute “birthday,” a value could be “12/1/1980” or “December 1, 1980.”

audience restriction

The restriction of a message to a specific target audience to prevent a receiver from unknowingly processing a message intended for another recipient. In federation protocols, assertions are audience restricted to specific RPs to prevent an RP from accepting an assertion generated for a different RP.

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 describing the strength of the authentication process.

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.

authorize

A decision to grant access, typically automated by evaluating a subject’s attributes.

authorized party

In federation, the organization, person, or entity that is responsible for making decisions regarding the release of information within the federation transaction, most notably subscriber attributes. This is often the subscriber (when runtime decisions are used) or the party operating the IdP (when allowlists are used).

back-channel communication

Communication between two systems that relies on a direct connection without using redirects through an intermediary such as a browser.

bearer assertion

An assertion that can be presented on its own as proof of the identity of the presenter.

blocklist

A documented list of specific elements that are blocked, per policy decision. This concept has historically been known as a blacklist.

challenge-response protocol

An authentication protocol in which the verifier sends the claimant a challenge (e.g., a random value or nonce) that the claimant combines with a secret (e.g., by hashing the challenge and a shared secret together or by applying a private-key operation to the challenge) to generate a response that is sent to the verifier. The verifier can independently verify the response generated by the claimant (e.g., by re-computing the hash of the challenge and the shared secret and comparing to the response or performing a public-key operation on the response) and establish that the claimant possesses and controls the secret.

core attributes

The set of identity attributes that the CSP has determined and documented to be required for identity proofing.

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.

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.

derived attribute value

A statement that asserts a limited identity attribute of a subscriber without containing the attribute value from which it is derived, independent of format. For example, instead of requesting the attribute “birthday,” a derived value could be “older than 18”. Instead of requesting the attribute for “physical address,” a derived value could be “currently residing in this district.” Previous versions of these guidelines referred to this construct as an “attribute reference.”

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.

disassociability

Enabling the processing of PII or events without association to individuals or devices beyond the operational requirements of the system. [NISTIR8062]

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]

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

federated identifier

The combination of a subject identifier within an assertion and an identifier for the IdP that issued that assertion. When combined, these pieces of information uniquely identify the subscriber in the context of a federation transaction.

federation

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

Federation Assurance Level (FAL)

A category that describes the process used in a federation transaction to communicate authentication events and subscriber attributes to an RP.

federation protocol

A technical protocol that is used in a federation transaction between networked systems.

federation proxy

A component that acts as a logical RP to a set of IdPs and a logical IdP to a set of RPs, bridging the two systems with a single component. These are sometimes referred to as “brokers.”

federation transaction

A specific instance of processing an authentication using a federation process for a specific subscriber by conveying an assertion from an IdP to an RP.

front-channel communication

Communication between two systems that relies on passing messages through an intermediary, such as using redirects through the subscriber’s browser.

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:

1. One-way — It is computationally infeasible to find any input that maps to any pre-specified output.

2. 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 API

A protected API accessed by an RP to access the attributes of a specific subscriber.

Identity Assurance Level (IAL)

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

identity provider (IdP)

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

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.

login

Establishment of an authenticated session between a person and a system. Also known as “sign in”, “log on”, and “sign on.”

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.

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.

pairwise pseudonymous identifier

A pseudonymous identifier generated by an IdP for use at a specific RP.

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]

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.

processing

Operation or set of operations performed upon PII that can include, but is not limited to, the collection, retention, logging, generation, transformation, use, disclosure, transfer, and disposal of PII. [NISTIR8062]

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.

Provisioning API

A protected API that allows an RP to access identity attributes for multiple subscribers for the purposes of provisioning and managing RP subscriber accounts.

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.

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.

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.

RP subscriber account

An account established and managed by the RP in a federated system based on the RP’s view of the subscriber account from the IdP. An RP subscriber account is associated with one or more federated identifiers and allows the subscriber to access the account through a federation transaction with the IdP.

security domain

A set of systems under a common administrative and access control.

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.

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.

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).

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.

trust agreement

A set of conditions under which a CSP, IdP, and RP are allowed to participate in a federation transaction for the purposes of establishing an authentication session between the subscriber and the RP.

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.