EOTS Sign PoC

A Proof of Concept implementation of an Ephemeral One-Time Signature (EOTS) scheme using Schnorr signatures, designed to prevent claim reuse by enforcing single-use signatures through public nonce exposure.

Overview

This project demonstrates how EOTS can protect against signature/claim reuse by making it impossible for a signer to reuse their signature without exposing their private key:

1. EOTS Implementation: A secure Schnorr signing procedure that deliberately exposes the public nonce, making it publicly visible. Each signature contains:

   • publicKey: the x‑coordinate of the signer's public key (32‑byte hex, with even y assumed)
   • publicNonce: the x‑coordinate of the ephemeral nonce point R (32‑byte hex, with even y)
   • s: the signature scalar (32‑byte hex)

2. Protection Mechanism: By making the nonce public, any attempt to reuse it for a second claim would expose the signer's private key. This creates a strong deterrent against signature reuse, effectively making each signature single-use only.

Installation

npm install

Security Mechanism Demonstration

To understand how EOTS protects against claim reuse, run:

yarn demo:vulnerability

This demonstrates:

1. How a signature is bound to a single claim through its public nonce
2. Why attempting to reuse the signature for a different claim would expose the signer's private key
3. The mathematical proof that makes this protection possible

Understanding the Protection

The security relies on the fact that if someone tries to reuse a nonce to sign two different claims, they create two equations:

s1 = a + e1*d  (mod n)
s2 = a + e2*d  (mod n)

where:

• s1, s2 are the signature scalars
• a is the exposed nonce
• e1, e2 are the challenge values
• d is the private key
• n is the curve order

Any attempt to sign a second claim would allow others to solve:

s1 - s2 = d * (e1 - e2)  (mod n)

This would reveal the private key d, making it financially catastrophic to attempt claim reuse.

Usage

Basic Example

import { signEOTS, verifyEOTSSignature } from 'eots-sign-poc';

const claim = "I am selling this asset for 1 BTC";
const privateKey = Buffer.from("your-private-key-hex", "hex");
const nonce = Buffer.from("your-nonce-hex", "hex");

// Sign claim - this will expose the public nonce
const signature = signEOTS(privateKey, claim, nonce);

// Anyone can verify the claim
const isValid = verifyEOTSSignature(
  signature.publicKey,
  signature.publicNonce,
  claim,
  signature.s
);

Running Examples

npm run demo:vulnerability  # Claim reuse protection demo

Development

Build

npm run build

Test

npm test

Lint

npm run lint

Format Code

npm run format

License

MIT

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.