1. Why Platforms Still Demand SMS OTP at Registration
A common question among developers is: “If TOTP Authenticator apps and Passkeys are more secure than SMS, why do Google, OpenAI, Discord, and Telegram still require an SMS OTP when creating an account?”
The answer lies in resource scarcity (Anti-Sybil defense):
- Anyone can generate 100,000 TOTP secrets or WebAuthn keypairs per second in software for $0.00.
- Physical cellular phone numbers (MSISDNs) are a finite, carrier-regulated resource. Requiring a Non-VoIP SMS verification at registration acts as a rate-limiter against automated botnets.
2. Technical Comparison: SMS OTP vs. RFC 6238 TOTP vs. Passkeys
| Feature | SMS OTP | TOTP Authenticator (RFC 6238) | WebAuthn Passkeys (FIDO2) |
|---|---|---|---|
| Cryptographic Basis | Server-generated random digits | Shared Base32 secret + HMAC-SHA1(Secret, floor(Time/30)) |
Asymmetric public/private keypair |
| Requires Cellular Signal? | Yes (Carrier SMS network) | No (100% offline math) | No |
| Token Lifetime | 5 – 10 minutes | 30 seconds | Per-challenge nonce |
| Best Use Case | Initial account sign-up verification | Primary 2FA after sign-up | Phishing-resistant passwordless login |
3. Best Practice Workflow
- Rent a 10-minute Non-VoIP number on NEXUSOTP to pass initial sign-up verification.
- Immediately open your account’s 2FA / Security settings and enroll an RFC 6238 TOTP Authenticator (you can test how Base32 secrets work using our client-side TOTP Generator).
- Remove SMS as a fallback recovery factor so your account never depends on the temporary phone number again.