Solution to borda

lesson3_violations/Borda/BordaMissingRule.spec

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+/*
+ * Borda Missing Rule by Perito Flores
+ * -------------
+ *
+ * Verification of a simple voting contract which uses a Borda election.
+ * See https://en.wikipedia.org/wiki/Borda_count
+ */
+
+
+
+methods {
+    function points(address) external returns uint256  envfree;
+    function vote(address,address,address) external;
+    function voted(address) external returns bool  envfree;
+    function winner() external returns address  envfree;
+}
+
+
+
+rule BordaMissingRule(env e,method m){
+
+    require m.selector != sig:vote(address,address,address).selector;
+    address winnerBefore = winner();
+    calldataarg args; 
+    m(e,args);
+    address winnerAfter = winner();
+    assert winnerAfter == winnerBefore ,  "The winner can be changed only after voting";
+}

lesson3_violations/Borda/BordaNewBug.sol

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+pragma solidity ^0.8.0;
+import "./IBorda.sol";
+
+contract BordaNewBug is IBorda{
+
+    // The current winner
+    address public _winner;
+
+    // A map storing whether an address has already voted. Initialized to false.
+    mapping (address => bool)  _voted;
+
+    // Points each candidate has recieved, initialized to zero.
+    mapping (address => uint256) _points;
+
+    // current maximum points of all candidates.
+    uint256 public pointsOfWinner;
+
+
+    function vote(address f, address s, address t) public override {
+        require(!_voted[msg.sender], "this voter has already cast its vote");
+        require( f != s && f != t && s != t, "candidates are not different");
+        _voted[msg.sender] = true;
+        voteTo(f, 3);
+        voteTo(s, 2);
+        voteTo(t, 1);
+    }
+
+    function voteTo(address c, uint256 p) private {
+        //update points:w
+        _points[c] = _points[c]+ p;
+        // update winner if needed
+        if (_points[c]  > _points[_winner]  ) {
+            _winner = c;
+        }
+    }
+    function switchWinner(address newWinner) external {
+         require (points(newWinner)>=points(_winner));
+         _winner = newWinner;
+    }
+
+    function winner() external view override returns (address) {
+        return _winner;
+    }
+
+    function points(address c) public view override returns (uint256) {
+        return _points[c];
+    }
+
+    function voted(address x) public view override returns(bool) {
+        return _voted[x];
+    }
+}

lesson3_violations/Borda/BordaNewBugRuns.sh

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+echo Runing the specs...
+
+certoraRun Borda.sol --verify Borda:BordaMissingRule.spec --msg 'Missing rule also pass in the original'
+
+certoraRun BordaNewBug.sol --verify BordaNewBug:Borda.spec --msg 'Original rules passes in the buggy file'
+
+certoraRun BordaNewBug.sol --verify BordaNewBug:BordaMissingRule.spec --msg 'New rule catches the bug'