B.3 Implementation Requirements

Many syncable authenticators are built on W3C’s [WebAuthn] specification, which provides a common data structure, a challenge-response cryptographic protocol, and an API for leveraging public-key credentials. The specification is flexible and adaptive, meaning that not all deployments of WebAuthn credentials will meet the requirements of federal agencies for implementation.

The specification has a series of flags that the RP application can request from the authenticator to provide additional context for the authentication event and determine whether it meets the RP’s access policies. This section describes certain flags in the WebAuthn specification that federal agencies acting as RPs should understand and interrogate when building their syncable authenticator implementations to align with AAL2 guidelines.

The following requirements apply to WebAuthn Level 3 flags:

User Present (UP)

The User Present flag indicates that a “presence” test confirmed that the user has interacted with the authenticator (e.g., tapping a hardware token inserted into a USB port). This supports authentication intent, as described in Sec. 3.2.8. Verifiers SHOULD confirm that the User Present flag has been set.

User Verified (UV)

The User Verified flag indicates that the authenticator has locally authenticated the user using one of the available “user verification” methods. Verifiers SHALL indicate that UV is preferred and SHALL inspect responses to confirm the value of the UV flag. This indicates whether the authenticator can be treated as a multi-factor cryptographic authenticator. If the user is not verified, agencies SHALL treat the authenticator as a single-factor cryptographic authenticator. A further extension to the WebAuthn Level 3 specification (see Sec. 10.3 of [WebAuthn]) provides additional data on verification methods if agencies seek to gain context on the local authentication event.

Backup Eligible

The Backup Eligible flag indicates whether the authenticator can be synced to a different device (i.e., whether the key can be stored elsewhere). It is important to note that just because an authenticator can be synced does not mean that it has been synced. Verifiers MAY use this flag to establish policies that restrict the use of syncable authenticators. This flag is necessary to distinguish authenticators that are device-bound from those that may be cloned to more than one device.

Backup State

The Backup State flag indicates whether an authenticator has been synced to a different device. Verifiers MAY use this flag to establish restrictions on authenticators that are synced to other devices. Agencies SHOULD NOT condition acceptance based on this flag for public-facing applications due to user experience concerns.

In addition to the flags specified above, agencies may wish to gain additional information on the origins and capabilities of the syncable authenticators that they choose to implement and accept. Within the context of WebAuthn, some authenticators support attestation features that can be used to determine the capabilities and manufacturers of specific authenticators. For federal enterprise use cases, agencies SHOULD implement attestation capabilities based on the functionality offered by their platform providers. This would take the form of a manufacturer attestation in which the RP requests identifying information about the authenticator.

The unavailability of attestations SHOULD NOT block the use of syncable authenticators for broad public-facing applications. Due to the limited availability of attestations in consumer products, requiring their use is likely to divert users to less secure authentication options that are vulnerable to phishing (e.g., PSTN-based out-of-band authentication). While authentication transaction metadata (e.g., the User Verified flag indicating the use of a local activation factor) is available in WebAuthn responses, attestation can provide stronger assurance of the characteristics of the authenticator used in a transaction. RPs SHOULD use attestation to determine the level of confidence they have in a syncable authenticator when attestations are available.

When the RP receives flag and attestation data, the authenticator may provide information that is incomplete or inconsistent with access to a resource. Agencies SHALL evaluate the use cases for syncable authenticators and determine the appropriate access policy decisions that they intend to make based on the returned information.

1. Ülevaade

1.1 Viited

1.2 Tuvastatud nõuded

1.3 Seotud regulatsioonid

2. Tuvastatud nõuded

3. Seotud regulatsioonid

• NIST -

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