feat: ecdsa example (#6)

Cargo.toml

@@ -2,6 +2,7 @@
 members = [
     "examples/uniswap/host",
     "examples/multiplexer/host",
+    "examples/verify-quorum/host",
     "crates/client-executor",
     "crates/host-executor",
 ]

README.md

@@ -158,6 +158,8 @@ where `[example]` is one of the following
     * Calls a contract that fetches the prices of many different collateral assets.
     * The source code of this contract is found [here](./examples/multiplexer/ZkOracleHelper.sol).
     * Due to the size of this program, it's recommended to use the [SP1 Prover network](https://docs.succinct.xyz/generating-proofs/prover-network.html) to generate proofs for this example.
+* `verify-quorum`
+    * Calls a contract that verifies several ECDSA signatures on chain, and sums the stake for the addresses corresponding to valid signatures.
 
 
 ## Acknowledgments

crates/host-executor/src/lib.rs

@@ -31,7 +31,7 @@ pub struct HostExecutor<T: Transport + Clone, P: Provider<T, AnyNetwork> + Clone
     pub provider: P,
 }
 
-impl<'a, T: Transport + Clone, P: Provider<T, AnyNetwork> + Clone> HostExecutor<T, P> {
+impl<T: Transport + Clone, P: Provider<T, AnyNetwork> + Clone> HostExecutor<T, P> {
     /// Create a new [`HostExecutor`] with a specific [`Provider`] and [`BlockNumberOrTag`].
     pub async fn new(provider: P, block_number: BlockNumberOrTag) -> eyre::Result<Self> {
         let block = provider

examples/verify-quorum/SimpleStaking.sol

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
+
+/// @title SimpleStaking
+/// @notice This contract models a voting scheme, where each address has some stake. 
+///         Eventually, when a vote is called, signatures are collected and the total stake 
+///         corresponding to those signatures is returned.
+contract SimpleStaking {
+    using ECDSA for bytes32;
+
+    mapping(address => uint256) public stakeWeight;
+
+    /// @notice Returns the total stake of an address.
+    function getStake(address addr) public view returns (uint256) {
+        return stakeWeight[addr];
+    }
+
+    /// @notice Updates the stake of an address.
+    function update(address addr, uint256 weight) public {
+        stakeWeight[addr] = weight;
+    }
+
+    /// @notice Collects signatures over many messages, and returns the total stake corresponding
+    ///         to those signatures. 
+    ///
+    ///         Calling this function onchain could be expensive with a large
+    ///         number of signatures -- in that case, it would be better to prove its execution
+    ///         with SP1.
+    function verifySigned(
+        bytes32[] memory messageHashes,
+        bytes[] memory signatures
+    ) public view returns (uint256) {
+        require(
+            messageHashes.length == signatures.length,
+            "Input arrays must have the same length"
+        );
+
+        uint256 totalStake = 0;
+
+        for (uint i = 0; i < messageHashes.length; i++) {
+            address recoveredSigner = messageHashes[i].recover(signatures[i]);
+            totalStake += stakeWeight[recoveredSigner];
+        }
+
+        return totalStake;
+    }
+}