HOTP
HMAC-based One-Time Password
A one-time password generated from a counter and a shared secret.
HOTP generates one time passwords from a shared secret and an incrementing counter using HMAC, so each successful use advances the counter on both sides. It supports multifactor authentication as a something you have factor on hardware tokens and authenticator apps. Because it is event based rather than clock based, a code stays valid until used, which can create resynchronization gaps if the counter drifts. The exam contrast is TOTP, which replaces the counter with the current time and expires codes after a short window.
HMAC/counter-based one-time password: changes each time you use it, no clock needed.
Looking HOTP up is step one. Getting tested on it is step two.
A free account opens all 4 Domain 1 objectives, 271 exam-style questions with a lesson and a lab on each, a placement check that skips what you already know, and a dated plan. No card.
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