Simple Secret Sharing

This project implements a threshold secret sharing scheme using polynomial interpolation over a prime field in Go. It's designed to securely split and reconstruct private keys used in cryptographic operations, specifically for ECDSA signatures on the secp256k1 curve.

Features

• Secret sharing using Shamir's Secret Sharing scheme
• Implementation of prime field arithmetic
• Polynomial evaluation and interpolation
• Integration with secp256k1 curve for ECDSA signatures
• Threshold-based reconstruction of secrets

How It Works

1. Secret Splitting (Construct function):

   • Takes a private key as input
   • Creates a polynomial of degree t-1 where f(0) is the secret
   • Generates n shares, where each share is a point (x, f(x)) on the polynomial

2. Secret Reconstruction (Reconstruct function):

   • Takes t shares as input
   • Uses Lagrange interpolation to reconstruct the original polynomial
   • Recovers the secret by evaluating f(0)

Usage

The main functions provided by this library are:

func Construct(dA *big.Int, outFilesValues []io.Writer, outFilesXs []io.Writer, n, t int)
func Reconstruct(ShareHandles []io.Reader, xsHandles []io.Reader, outFile io.Writer, t int)

• Construct: Splits a secret into n shares, requiring t shares for reconstruction.
• Reconstruct: Reconstructs the secret from t shares.

Testing

The project includes a comprehensive test suite in secret_share_test.go. This test:

1. Generates an ECDSA key pair
2. Creates a signature
3. Splits the private key into shares
4. Reconstructs the private key from a subset of shares
5. Verifies the reconstructed key by checking the signature

To run the tests:

go test ./...

Dependencies

• github.com/ethereum/go-ethereum/crypto/secp256k1: For elliptic curve operations

Security Considerations

This implementation is for educational purposes and has not been audited for production use. In a real-world scenario, additional security measures should be implemented, such as:

• Secure random number generation
• Constant-time operations to prevent timing attacks
• Secure storage and transmission of shares

License

This project is licensed under the terms specified in the LICENSE file.