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Security Fundamentals & Crypto · Foundational

Time-Based One-Time Password (TOTP)

OTP algorithm (RFC 6238) that generates codes from a shared secret and the current time, typically every 30 seconds.

Definition

TOTP extends HOTP by using the time step as the counter. Codes expire quickly, limiting replay. It requires reasonably synchronized clocks and a shared secret usually provisioned via QR code into an authenticator app.

Example

Google Authenticator shows a new six-digit TOTP code every 30 seconds.

Exam tip

TOTP codes expire; they are still phishable in real time.

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