TwentyOne

Description: the function `TwentyOne:startGame, requires that the user sends at least 1 ether to start the game, but the function just checks if the user send more than 1 ether but there is not a function to withdraw or get back these extra ether that you sent.

Impact: if the user sends more than 1 ether, these ether Will be lost, because there isn't a function to withdraw these extra ether.

Proof of Concept:

1. A user sends 2 ether.

2. The user play

3. the user Won't get back the extra ether.

Recommended Mitigation:

check that the user sent exactly 1 ether

````diff

+require(msg.value >= 1 ether, "not enough ether sent");

-require(msg.value == 1 ether, "not enough ether sent");

```