Why do passkeys reduce replay risk more effectively than passwords plus one-time codes?

Why passkeys are harder to replay than passwords and one-time codes

Replay risk depends on whether an attacker can capture something reusable and present it later as proof of authentication. Passkeys are designed to make that much harder because the private key stays on the user’s device and the relying party gets a fresh cryptographic assertion tied to the current login ceremony, not a reusable secret.

The practical difference is that passwords and one-time codes are bearer secrets in transit or at rest: if they are phished, intercepted, logged, or coerced, they can often be reused within their validity window. Passkeys replace that with device-bound cryptographic proof, so the intercepted material is either useless or bound to the wrong context.

That is why passkeys change the attacker’s job from stealing a reusable credential to defeating the device’s local unlock and origin-bound signing process. The distinction matters most in phishing, proxy, and token relay scenarios, where the attacker’s goal is not to guess a password but to reuse an authentication artifact.

What makes passwords plus one-time codes easier to replay

Passwords and one-time codes fail for different reasons, but both can still be replayable in practice. A password can be captured once and used repeatedly until it is changed. A one-time code is time-limited, but if an attacker relays it quickly through a real-time phishing page, the victim and attacker can both complete the login flow before the code expires.

That short replay window is enough for modern phishing kits and adversary-in-the-middle techniques. The code does not need to survive long, it only needs to survive long enough for the attacker to finish the authentication transaction or convert the session into a valid token or cookie.

Passkeys remove that usability gap by making the credential non-exportable in normal operation and by binding the assertion to the genuine site or app. A stolen password or OTP can travel; a passkey assertion is meant to be produced only by the enrolled device, for the intended service, at the time of login. For background on phishing-resistant authentication, NIST SP 800-63 Digital Identity Guidelines is the clearest external reference, and NHIMG’s Passwordless and Passkeys Guide explains the same mechanism in rollout terms.

Why the replay protection is stronger in real deployments

The key security advantage is not just that passkeys are passwordless, but that they are designed to be origin-bound and resistant to reuse outside the legitimate ceremony. That means the attacker cannot simply harvest a shared secret and try it again later from a different device, network, or browser.

In real environments, this also reduces the value of common compromise paths such as phishing, credential stuffing, and OTP relay. When the authentication proof cannot be copied into a second session, the attacker has fewer opportunities to turn a captured login event into durable access. If you want a standards-based discussion of the passkey model and its assurance properties, NIST SP 800-63 Digital Identity Guidelines remains the strongest baseline.

Replay resistance is strongest when the rest of the account lifecycle supports it. Recovery flows, device replacement, and fallback factors can reintroduce replay-like exposure if they allow weak account takeover paths. That is why NHIMG’s Workforce Identity Security Guide is useful for seeing passkeys in the broader sign-in and recovery stack, not as a stand-alone feature.

Practitioner Guidance

What to verify: Treat passkeys as a replay-control improvement only if the relying party actually enforces phishing-resistant authentication, the assertion is bound to the real origin, and fallback paths do not quietly downgrade the user back to reusable secrets or weak OTP recovery.

Decision rule: If a control can be captured and reused elsewhere, it is replay-prone by design; if the secret never leaves the authenticator and the service verifies a fresh signed challenge, the attacker’s reuse options collapse sharply.

Common mistake: Teams sometimes stop at “we added MFA” and miss that SMS, TOTP, and help-desk recovery can still be relayed, intercepted, or socially engineered, which leaves the replay problem partially intact.

Practitioner takeaway: The real win is not that passkeys are simply stronger than passwords, it is that they remove the reusable artifact that makes replay practical in the first place.

Related resources from NHI Mgmt Group

• How should security teams reduce phishing, vishing, and smishing risk without relying only on passwords or one-time codes?
• Why do time-based one-time passwords reduce the risk of account compromise better than reusable login codes?
• Why do one-time passwords reduce the risk of replay attacks compared with static passwords?
• Why do FIDO2 and passkeys reduce phishing risk more effectively than OTP codes?