xOTP: Multi-Channel Split OTP

The Problem

SIM-swap attacks make SMS-only OTP dangerous. SS7 network interception can capture any text message. Phishing relay attacks forward OTPs in real-time. Every single-channel OTP is a single point of failure.

The FBI's IC3 reported SIM-swap losses exceeding $68 million in 2023 alone. Attackers social-engineer carriers, port victim numbers, and intercept every SMS OTP sent to that number.

Even push-based MFA is not immune — push fatigue bombing attacks overwhelm users until they approve a fraudulent request. The fundamental problem is that any single channel can be compromised independently.

The Old Way

The Solution

xOTP generates a single OTP and splits it into K-of-N shares distributed across independent channels — SMS, push notification, and email. An attacker must compromise 2-of-3 channels simultaneously to reconstruct the OTP. SIM-swap alone gets one share: noise.

The OTP is generated server-side, split via XorIDA, and each share is delivered through a different channel. The user's device collects shares and reconstructs the OTP locally. The server never sends the complete OTP through any single channel.

Channel diversity is the key: SMS travels through carrier networks, push through Apple/Google infrastructure, email through SMTP. Compromising any two simultaneously requires attacking fundamentally different systems.

The New Way

Architecture

xOTP integrates with existing authentication flows. The server generates and splits; channels deliver shares; the client reconstructs and submits.

Use Cases

Integration

import { generateSplitOTP, verifySplitOTP } from '@private.me/otpsplit';

// Server: Generate and split OTP across 3 channels
const { shares, verifier } = await generateSplitOTP({
  channels: ['sms', 'push', 'email'],
  threshold: 2,
  ttl: 300 // 5-minute expiry
});
// shares[0] → SMS gateway, shares[1] → push, shares[2] → email

// Client: Reconstruct from 2 received shares
const otp = await verifySplitOTP(
  [shares[0], shares[1]], // SMS + push shares
  verifier
);
// otp.ok === true → submit to server

Security Properties

Verifiable Data Protection

Every operation in this ACI produces a verifiable audit trail via xProve. HMAC-chained integrity proofs let auditors confirm that data was split, stored, and reconstructed correctly — without accessing the data itself.

Ready to deploy xOTP?

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Ship Proofs, Not Source

xOtp generates cryptographic proofs of correct execution without exposing proprietary algorithms. Verify integrity using zero-knowledge proofs — no source code required.

Use Cases