AI Arena - honey-k12's results

Lines of code

https://github.com/code-423n4/2024-02-ai-arena/blob/cd1a0e6d1b40168657d1aaee8223dc050e15f8cc/src/FighterFarm.sol#L214 https://github.com/code-423n4/2024-02-ai-arena/blob/cd1a0e6d1b40168657d1aaee8223dc050e15f8cc/src/FighterFarm.sol#L254 https://github.com/code-423n4/2024-02-ai-arena/blob/cd1a0e6d1b40168657d1aaee8223dc050e15f8cc/src/FighterFarm.sol#L324

Vulnerability details

Description

The dna parameter in the _createNewFighter function is a crucial part of the fighter creation process.

Currently dna is calculated like this:

https://github.com/code-423n4/2024-02-ai-arena/blob/cd1a0e6d1b40168657d1aaee8223dc050e15f8cc/src/FighterFarm.sol#L214

uint256(keccak256(abi.encode(msg.sender, fighters.length)))

While the keccak256 hash function produces an output that appears random, it’s completely deterministic. This means that given the same input, it will always produce the same output. In this case, the inputs are msg.sender and fighters.length (the current number of fighters). If an attacker knows these two values, they can predict the DNA that will be generated.

Impact

This could potentially be exploited by an attacker to create fighters with specific, possibly advantageous attributes and have an unfair advantage in the game.

Tools Used

Manual Review

Recommended Mitigation Steps

To mitigate this, you could introduce additional sources of randomness into the DNA generation process. This would make it much harder for an attacker to predict the DNA.

Assessed type

Other