What identity proofing method is a refinement of the Hashed Message Authentication Code One-Time Password (HOTP)?

The correct answer is TOTP (Time-Based One-Time Password) because it builds upon the principles established by HOTP (Hashed Message Authentication Code One-Time Password) while introducing a time-sensitive element. HOTP generates one-time passwords based on a counter, but TOTP enhances this by generating passwords that are valid for a limited period, typically 30 seconds. This means that even if a TOTP code is intercepted, it will quickly expire, thereby offering an additional layer of security against replay attacks.

By integrating time as a factor into the one-time password generation process, TOTP ensures that passwords are not only unique but also transient, making it more secure for identity proofing in various applications. The time-based approach helps in ensuring that authentication codes are continually changing, providing a dynamic response rather than a static one, which can be a target for attackers.

This refined method maintains the foundational concepts of HOTP while addressing some of its limitations, making TOTP a widely adopted technique for secure authentication across numerous platforms and services.