3.1.4.2 Single-Factor OTP Verifiers

Before · SP 800-63B

After · SP 800-63B-4

Single-Factor OTP Verifiers

Before · SP 800-63B

After · SP 800-63B-4

Single-factor OTP verifiers effectively duplicate the process of generating the OTP used by the authenticator. As such, the symmetric keys used by authenticators are also present in the verifier and SHALL be strongly protected against unauthorized disclosure by access controls that limit access to the keys to only those software components that require access.

When binding a single-factor OTP authenticator to a subscriber account, the verifier or associated CSP SHALL use approved cryptography for key establishment to generate and exchange keys or to obtain the secrets required to duplicate the authenticator output.

The verifier SHALL use approved encryption and an authenticated protected channel when collecting the OTP. Verifiers SHALL accept a given OTP only once while it is valid to provide replay resistance, as described in Sec. 3.2.7 . If a claimant’s authentication is denied due to the duplicate use of an OTP, verifiers MAY warn the claimant if an attacker has been able to authenticate in advance. Verifiers MAY also warn a subscriber in an existing session of the attempted duplicate use of an OTP.

Time-based OTPs [TOTP] SHALL have a defined lifetime that is determined by the expected clock drift in either direction of the authenticator over its lifetime plus an allowance for network delay and claimant entry of the OTP.

The verifier SHOULD implement or, if the authenticator output is less than 64 bits in length, SHALL implement a rate-limiting mechanism that effectively limits the number of failed authentication attempts that can be made on the subscriber account, as described in Sec. 3.2.2 .