OTP Verification

What is OTP Verification?

OTP (One-Time Password) verification is an authentication method used in electronic signing to add an extra layer of identity assurance. Before a signer can access a document, the system sends a unique, time-limited code — typically 4 to 6 digits — to the signer's registered phone number via SMS or to their authentication app. The signer must enter this code to proceed with signing.

OTP verification is a form of two-factor authentication (2FA). The first factor is something the signer knows or has (their email link or account credentials), and the second factor is something they possess (their phone). This combination makes it significantly harder for an unauthorized person to sign a document, even if they have intercepted the signing link.

SMS-based OTP is the most common implementation due to its simplicity — nearly everyone has a phone capable of receiving text messages, and no special app installation is required. App-based OTP (using authenticator apps like Google Authenticator) offers better security because it's not vulnerable to SIM-swapping attacks, but requires the signer to have the app installed.

In the context of e-signature compliance, OTP verification strengthens the "sole control" requirement for advanced electronic signatures under eIDAS. By requiring a code that only the intended signer's phone can receive, the signing platform demonstrates that the signature creation data was used under the signer's exclusive control, bolstering the legal standing of the signature.