Add MillionaireComparison contract implementing Yao's Millionaires' Problem

contracts/MillionaireComparison.sol

@@ -0,0 +1,205 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.19;
+
+import "@coti-io/coti-contracts/contracts/utils/mpc/MpcCore.sol";
+
+/**
+ * @title MillionaireComparison
+ * @notice Implements Yao's Millionaires' Problem using COTI's MPC (Multi-Party Computation)
+ * @dev Two parties (Alice and Bob) can compare their wealth without revealing the actual amounts
+ */
+contract MillionaireComparison {
+    // Store encrypted wealth values
+    utUint64 private _aliceWealth;
+    utUint64 private _bobWealth;
+
+    // Track who has submitted their wealth
+    bool private _aliceSet;
+    bool private _bobSet;
+
+    // Store comparison results for each party
+    utUint8 private _aliceResult;  // Result encrypted for Alice
+    utUint8 private _bobResult;    // Result encrypted for Bob
+
+    // Store addresses for consistent encryption
+    address private _alice;
+    address private _bob;
+
+    // Events for tracking operations
+    event WealthSubmitted(address indexed user, string role);
+    event ComparisonCompleted(address indexed requester);
+
+    /**
+     * @notice Initialize the contract with Alice and Bob addresses
+     * @param alice Address of the first party (Alice)
+     * @param bob Address of the second party (Bob)
+     */
+    constructor(address alice, address bob) {
+        require(alice != address(0) && bob != address(0), "Invalid addresses");
+        require(alice != bob, "Alice and Bob must be different");
+
+        _alice = alice;
+        _bob = bob;
+        _aliceSet = false;
+        _bobSet = false;
+    }
+
+    /**
+     * @notice Check if Alice has submitted her wealth
+     */
+    function isAliceWealthSet() external view returns (bool) {
+        return _aliceSet;
+    }
+
+    /**
+     * @notice Check if Bob has submitted his wealth
+     */
+    function isBobWealthSet() external view returns (bool) {
+        return _bobSet;
+    }
+
+    /**
+     * @notice Check if both parties have submitted their wealth
+     */
+    function areBothWealthsSet() external view returns (bool) {
+        return _aliceSet && _bobSet;
+    }
+
+    /**
+     * @notice Alice submits her encrypted wealth
+     * @param wealth Encrypted input (itUint64) representing Alice's wealth
+     */
+    function setAliceWealth(itUint64 calldata wealth) external {
+        require(msg.sender == _alice, "Only Alice can set her wealth");
+        require(!_aliceSet, "Alice's wealth already set");
+
+        gtUint64 gtWealth = MpcCore.validateCiphertext(wealth);
+        _aliceWealth = MpcCore.offBoardCombined(gtWealth, _alice);
+        _aliceSet = true;
+
+        emit WealthSubmitted(msg.sender, "Alice");
+    }
+
+    /**
+     * @notice Bob submits his encrypted wealth
+     * @param wealth Encrypted input (itUint64) representing Bob's wealth
+     */
+    function setBobWealth(itUint64 calldata wealth) external {
+        require(msg.sender == _bob, "Only Bob can set his wealth");
+        require(!_bobSet, "Bob's wealth already set");
+
+        gtUint64 gtWealth = MpcCore.validateCiphertext(wealth);
+        _bobWealth = MpcCore.offBoardCombined(gtWealth, _bob);
+        _bobSet = true;
+
+        emit WealthSubmitted(msg.sender, "Bob");
+    }
+
+    /**
+     * @notice Perform the comparison and store encrypted results for both parties
+     * @dev Can be called by either Alice or Bob once both have submitted their wealth
+     * @dev Result encoding: 0 = Alice is richer, 1 = Bob is richer, 2 = Equal
+     */
+    function compareWealth() external {
+        require(_aliceSet && _bobSet, "Both parties must submit their wealth first");
+        require(msg.sender == _alice || msg.sender == _bob, "Only Alice or Bob can trigger comparison");
+
+        // Load the stored encrypted wealth values
+        gtUint64 aliceWealth = MpcCore.onBoard(_aliceWealth.ciphertext);
+        gtUint64 bobWealth = MpcCore.onBoard(_bobWealth.ciphertext);
+
+        // Perform comparisons
+        gtBool aliceGreater = MpcCore.gt(aliceWealth, bobWealth);  // Alice > Bob
+        gtBool bobGreater = MpcCore.gt(bobWealth, aliceWealth);     // Bob > Alice
+
+        // Create result values: 0 = Alice richer, 1 = Bob richer, 2 = Equal
+        gtUint8 zero = MpcCore.setPublic8(0);
+        gtUint8 one = MpcCore.setPublic8(1);
+        gtUint8 two = MpcCore.setPublic8(2);
+
+        // Determine result:
+        // If Alice > Bob: result = 0
+        // If Bob > Alice: result = 1
+        // Otherwise (equal): result = 2
+
+        // First check if Alice is greater
+        gtUint8 tempResult = MpcCore.mux(aliceGreater, one, zero);  // If Alice > Bob, set 0, else 1
+
+        // Then check if Bob is greater
+        gtUint8 finalResult = MpcCore.mux(bobGreater, tempResult, one);  // If Bob > Alice, set 1, else keep tempResult
+
+        // If neither is greater, they are equal
+        gtBool neitherGreater = MpcCore.and(
+            MpcCore.not(aliceGreater),
+            MpcCore.not(bobGreater)
+        );
+        finalResult = MpcCore.mux(neitherGreater, finalResult, two);  // If equal, set 2, else keep result
+
+        // Store encrypted results for each party
+        _aliceResult = MpcCore.offBoardCombined(finalResult, _alice);
+        _bobResult = MpcCore.offBoardCombined(finalResult, _bob);
+
+        emit ComparisonCompleted(msg.sender);
+    }
+
+    /**
+     * @notice Returns the encrypted comparison result for Alice
+     * @return The encrypted result as ctUint8 (0 = Alice richer, 1 = Bob richer, 2 = Equal)
+     */
+    function getAliceResult() public view returns (ctUint8) {
+        require(msg.sender == _alice, "Only Alice can view her result");
+        return _aliceResult.userCiphertext;
+    }
+
+    /**
+     * @notice Returns the encrypted comparison result for Bob
+     * @return The encrypted result as ctUint8 (0 = Alice richer, 1 = Bob richer, 2 = Equal)
+     */
+    function getBobResult() public view returns (ctUint8) {
+        require(msg.sender == _bob, "Only Bob can view his result");
+        return _bobResult.userCiphertext;
+    }
+
+    /**
+     * @notice Returns Alice's address
+     */
+    function getAliceAddress() external view returns (address) {
+        return _alice;
+    }
+
+    /**
+     * @notice Returns Bob's address
+     */
+    function getBobAddress() external view returns (address) {
+        return _bob;
+    }
+
+    /**
+     * @notice Returns Alice's stored encrypted wealth value
+     * @return The encrypted wealth ciphertext
+     */
+    function getAliceWealth() public view returns (ctUint64) {
+        require(_aliceSet, "Alice's wealth not set yet");
+        return _aliceWealth.ciphertext;
+    }
+
+    /**
+     * @notice Returns Bob's stored encrypted wealth value
+     * @return The encrypted wealth ciphertext
+     */
+    function getBobWealth() public view returns (ctUint64) {
+        require(_bobSet, "Bob's wealth not set yet");
+        return _bobWealth.ciphertext;
+    }
+
+    /**
+     * @notice Reset the contract state (for testing purposes)
+     * @dev Can only be called by Alice (contract initiator)
+     */
+    function reset() external {
+        require(msg.sender == _alice, "Only Alice can reset the contract");
+        _aliceSet = false;
+        _bobSet = false;
+    }
+}