3.2.11 Connected Authenticators

Wired connections, including those with embedded authenticators, MAY be assumed to be trustworthy because their attack surface is minimal. Claimants SHOULD be advised to use trusted hardware (e.g., cables, adapters) to ensure that they have not been compromised.

Wireless authenticator connections are potentially vulnerable to threats, including eavesdropping, injection, and relay attacks. Wireless connections include technologies that function in the absence of a physical connection, such as radio frequency (e.g., Bluetooth and NFC), optical, and acoustic technologies.

The potential for such attacks on wireless connections depends on the technology’s effective range. To minimize the attack surface for threats to the authenticator-endpoint connection, the authentication process SHALL require physical proximity between the authenticator and endpoint by establishing a wireless connection with a range of no more than 240 meters.³

Wireless connections SHALL establish a key for encrypted communication between the authenticator and endpoint in one of the following ways:

When using a wireless technology with an effective range of less than 1 meter (e.g., NFC), any activation secret transmitted from the endpoint to the authenticator SHALL be encrypted using a key that is established between the devices. An authenticated connection SHOULD be used. A pairing code SHALL be used if the authenticator is configured to require authenticated pairing.

Encrypting only the activation secret and not the entire authentication transaction may expose sensitive information (e.g., the identity of the RP), although this would require the attacker to be very close to the subscriber. Special care should be taken with authenticators that contain personal information but do not require authenticated pairing. Encryption SHOULD be used to protect that information against eavesdropping attacks.

Network connections and wireless technologies with an effective range of 1 meter or more (e.g., Bluetooth Low Energy [BLE]) SHALL use an authenticated protected channel between the authenticator and endpoint. The entire authentication transaction SHALL be encrypted.

The key established by the association process may be either temporary (i.e., valid for a limited number of transactions or time-limited) or persistent. A mechanism for endpoints to remove persistent keys SHALL be provided.

An example of a wireless connection with an authenticator is the virtual contact interface specified in [SP800-73pt2].

Hybrid connections use a combination of technologies to establish a secure connection between the authenticator and endpoint via a network tunnel service. A visual representation (e.g., QR code) is used to support key establishment between the authenticator and endpoint, which is supplemented by a wireless technology (e.g., Bluetooth LE) to require physical proximity between the parties when the association is made. The requirement for physical proximity of the authenticator reduces the potential for phishing attacks that might otherwise associate the authenticator with an attacker endpoint.

Hybrid connections (e.g., hybrid transports specified by the CTAP2.2 protocol [FIDO2]) SHALL be established between authenticators and endpoints in one of the following ways:

A mechanism for endpoints to remove cached associations with authenticators SHALL be provided.