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Expand tests for ethereum-schnorr-contract

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Luke Parker
2024-10-28 18:08:31 -04:00
parent 0b61a75afc
commit ce1689b325
9 changed files with 205 additions and 51 deletions
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50
networks/ethereum/schnorr/contracts/Schnorr.sol
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@@ -1,7 +1,13 @@
// SPDX-License-Identifier: AGPL-3.0-only
pragma solidity ^0.8.26;
// See https://github.com/noot/schnorr-verify for implementation details
/// @title A library for verifying Schnorr signatures
/// @author Luke Parker <lukeparker5132@gmail.com>
/// @author Elizabeth Binks <elizabethjbinks@gmail.com>
/// @notice Verifies a Schnorr signature for a specified public key
/// @dev This contract is not complete. Only certain public keys are compatible
/// @dev See https://github.com/serai-dex/serai/blob/next/networks/ethereum/schnorr/src/tests/premise.rs for implementation details
// TODO: Pin to a specific branch/commit once `next` is merged into `develop`
library Schnorr {
// secp256k1 group order
uint256 private constant Q = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141;
@@ -11,31 +17,39 @@ library Schnorr {
// 2) An x-coordinate < Q
uint8 private constant KEY_PARITY = 27;
// px := public key x-coordinate, where the public key has an even y-coordinate
// message := the message signed
// c := Schnorr signature challenge
// s := Schnorr signature solution
function verify(bytes32 px, bytes32 message, bytes32 c, bytes32 s) internal pure returns (bool) {
/// @notice Verifies a Schnorr signature for the specified public key
/// @dev The y-coordinate of the public key is assumed to be even
/// @dev The x-coordinate of the public key is assumed to be less than the order of secp256k1
/// @dev The challenge is calculated as `keccak256(abi.encodePacked(address(R), public_key, message))` where `R` is the commitment to the Schnorr signature's nonce
/// @param public_key The x-coordinate of the public key
/// @param message The (hash of the) message signed
/// @param c The challenge for the Schnorr signature
/// @param s The response to the challenge for the Schnorr signature
/// @return If the signature is valid
function verify(bytes32 public_key, bytes32 message, bytes32 c, bytes32 s)
internal
pure
returns (bool)
{
// ecrecover = (m, v, r, s) -> key
// We instead pass the following to obtain the nonce (not the key)
// Then we hash it and verify it matches the challenge
bytes32 sa = bytes32(Q - mulmod(uint256(s), uint256(px), Q));
bytes32 ca = bytes32(Q - mulmod(uint256(c), uint256(px), Q));
// We instead pass the following to recover the Schnorr signature's nonce (not a public key)
bytes32 sa = bytes32(Q - mulmod(uint256(s), uint256(public_key), Q));
bytes32 ca = bytes32(Q - mulmod(uint256(c), uint256(public_key), Q));
/*
The ecrecover precompile checks `r` and `s` (`px` and `ca`) are non-zero,
banning the two keys with zero for their x-coordinate and zero challenge.
Each has negligible probability of occuring (assuming zero x-coordinates
are even on-curve in the first place).
The ecrecover precompile checks `r` and `s` (`public_key` and `ca`) are non-zero, banning the
two keys with zero for their x-coordinate and zero challenges. Each already only had a
negligible probability of occuring (assuming zero x-coordinates are even on-curve in the first
place).
`sa` is not checked to be non-zero yet it does not need to be. The inverse
of it is never taken.
`sa` is not checked to be non-zero yet it does not need to be. The inverse of it is never
taken.
*/
address R = ecrecover(sa, KEY_PARITY, px, ca);
address R = ecrecover(sa, KEY_PARITY, public_key, ca);
// The ecrecover failed
if (R == address(0)) return false;
// Check the signature is correct by rebuilding the challenge
return c == keccak256(abi.encodePacked(R, px, message));
return c == keccak256(abi.encodePacked(R, public_key, message));
}
}

12
networks/ethereum/schnorr/contracts/tests/Schnorr.sol
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@@ -3,7 +3,19 @@ pragma solidity ^0.8.26;
import "../Schnorr.sol";
/// @title A thin wrapper around the library for verifying Schnorr signatures to test it with
/// @author Luke Parker <lukeparker5132@gmail.com>
/// @author Elizabeth Binks <elizabethjbinks@gmail.com>
contract TestSchnorr {
/// @notice Verifies a Schnorr signature for the specified public key
/// @dev The y-coordinate of the public key is assumed to be even
/// @dev The x-coordinate of the public key is assumed to be less than the order of secp256k1
/// @dev The challenge is calculated as `keccak256(abi.encodePacked(address(R), public_key, message))` where `R` is the commitment to the Schnorr signature's nonce
/// @param public_key The x-coordinate of the public key
/// @param message The (hash of the) message signed
/// @param c The challenge for the Schnorr signature
/// @param s The response to the challenge for the Schnorr signature
/// @return If the signature is valid
function verify(bytes32 public_key, bytes calldata message, bytes32 c, bytes32 s)
external
pure