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Security Fundamentals & Crypto · Foundational

One-Time Password (OTP)

Password valid for only one login session or transaction, generated by a token, app, or service.

Definition

OTPs limit replay because each code expires after use or after a short time. They are generated with HOTP (counter-based) or TOTP (time-based) algorithms, or sent via SMS or email. OTPs can still be phished in real time by adversary-in-the-middle attacks.

Example

A bank texts a six-digit code that must be entered to approve a wire transfer.

Exam tip

Don't confuse OTP (one-time password) with one-time pad.

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