Passkeys are device-based, phishing-resistant credentials that authenticate the user locally with biometrics or a PIN. Password plus OTP methods rely on memorized secrets and separately delivered codes, which are easier to intercept, reuse, or lose. For digital signing, passkeys usually provide stronger assurance, fewer delivery failures, and a smoother user experience.
Where passkeys and password plus OTP diverge for signing trust
For digital signing, the practical difference is not just how a user logs in, but how strongly the authentication step binds the signer to a specific device, secret holder, and session. Passkeys are designed to be phishing-resistant and origin-bound, so the assertion is created locally on the user’s device. Password plus OTP still depends on a memorized secret and a second factor that can be intercepted, relayed, or socially engineered.
That difference matters when a signing workflow is treated as an approval event with real legal, financial, or operational consequence. A passkey-based flow reduces the chance that an attacker can capture reusable credentials during the approval step, while password plus OTP leaves more room for credential replay, push or code fatigue, and support-channel abuse.
The distinction is also visible in failure modes. Passkeys usually fail closed when the device is unavailable, unenrolled, or outside the trusted user context. Password plus OTP often fails in less predictable ways, because the password can be reused elsewhere and the OTP may arrive through SMS, email, or an app that is itself exposed to delivery and device compromise risk.
- Passkeys give you stronger phishing resistance because the relying party challenge is tied to the authentic website or app origin.
- Password plus OTP gives you more compatibility across legacy systems, but the assurance level depends heavily on how the OTP is delivered and protected.
- For digital signing, the best test is whether the method produces a high-confidence signer assertion that is resistant to replay and credential theft.
Assurance, usability, and operational failure modes
Passkeys usually improve both assurance and user experience because the user unlocks a device-held credential with biometrics or a PIN instead of typing a password and then waiting for a second factor. That reduces abandonment, delivery delays, and the help-desk burden created when codes never arrive, devices are out of sync, or users are locked out of an OTP channel.
Password plus OTP can still be acceptable for lower-risk signing or transitional environments, but its assurance is uneven. The weakest point is often not the OTP algorithm itself, but the surrounding process, such as recovery flows, SMS fallback, shared inboxes, or call-center resets that let an attacker step around the second factor.
For practitioners, the choice comes down to whether the signing event needs resilient, low-friction proof of the user’s presence on a controlled device, or merely a conventional login step before the signature action is accepted.
- Use passkeys when the signed action should be resistant to phishing and session relay.
- Keep password plus OTP only where compatibility or migration constraints prevent stronger methods.
- Treat recovery, device replacement, and fallback channels as part of the signing security model, not as administrative afterthoughts.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST SP 800-63, CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST SP 800-63 | AAL — Authentication Assurance Level | Digital signing hinges on assurance strength of the login method. |
| FAL — Federation Assurance Level | Passkeys reduce phishing and assertion replay risk in federated sign-in paths. | |
| Recommendation — Map signing workflows to the required assurance level before accepting an authentication method. Require phishing-resistant authenticators for federated signing access. | ||
| CIS Controls v8 | 6 — Access Control Management | The question compares stronger and weaker authentication paths for a high-value action. |
| 6.3 — Require MFA for Externally Exposed Applications | Password plus OTP is still a multi-factor path, but passkeys materially improve phishing resistance. | |
| Recommendation — Enforce stronger authentication for signing actions and remove weak fallback access paths. Prefer phishing-resistant authentication for exposed signing portals. | ||
| NIST CSF 2.0 | PR.AA — Identity Management, Authentication, and Access Control | The subject is specifically about how users are authenticated before a signing action. |
| PR.AC — Identity Management, Authentication, and Access Control | Access to sign should be tied to stronger proof of user presence and device control. | |
| Recommendation — Use phishing-resistant authentication where signer assurance matters. Limit signing access to authenticated sessions with strong proof of possession. | ||
Practitioner Guidance
What to verify: If the signature has legal or high-impact business weight, verify that the authentication method is bound to the actual user and not just to a reachable mailbox or phone number. For password plus OTP, confirm the delivery path, reset path, and fallback path are all protected to the same standard as the signing event itself.
Decision rule: If the workflow needs phishing resistance and repeatable assurance, prefer passkeys; if you must keep password plus OTP, limit it to lower-risk signing or short-lived transition use while you remove weak recovery options.
What good looks like: The user completes the signing step on a trusted device with minimal friction, the authentication event is origin-bound, and the organisation can explain why the method is suitable for the level of signer assurance required.
Practitioner takeaway: For digital signing, the key question is not which method is familiar, but which one gives the strongest defensible signer assurance with the fewest ways for an attacker to intercept, replay, or socially engineer the approval.
Related resources from NHI Mgmt Group
- What is the difference between phishing-resistant MFA and traditional password-based authentication in government identity programs?
- What is the difference between passwordless authentication and traditional password-based login for mobile apps?
- What is the difference between SMS OTP and phishing-resistant passkeys for authentication security?
- What is the difference between device fingerprinting and traditional username and password authentication?
