This is the report from a security audit performed on Heiswap Dapp by gorbunovperm.
Heiswap (黑 swap) is an Ethereum transaction mixer that ultilizes parts of CryptoNote to enable zero-knowledge transactions. It ulitilizes Ring Signatures and pseudo-stealth addresses to achieve its zero-knowledge properties. The deployed smart contract handles the signature verification, while the client is responsible for generating the pseudo-stealth address. Ring signatures was only possible on the EVM (gas-wise) due to the recent addition of EIP198.
Description: https://kndrck.co/posts/introducing_heiswap/
Dapp: https://heiswap.exchange/
Commit hash: afd1a2731bdcaea03698e29ee179b0b29b536807
In total, 4 issues were reported including:
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0 critical severity issue.
-
1 high severity issue.
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2 medium severity issues.
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0 low severity issues.
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0 owner privileges.
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1 note.
Confidentiality is based on the fact that there is no links between 5(maximum) deposits and 5 withdrawals. But the contract provides for the premature closure of the ring, even if the amount of participants is less than 5. The exposer can intentionally enter each ring together with the observed address and close the ring with two participants. Thus, he will be able to detect the withdrawing address.
To have only two participants in the ring, the exposer can track the transaction of the observed address and as soon as it appeared to make an Front-Running Attack closing the previous ring. Then the observed address will come into a new ring, which the exposer will be able to close with 2 participants.
When the deposit is not an exact value, rounding occurs. And a decimal fraction of deposit remains blocked in the contract. For example, if an amount of 2.7ETH is deposited , 0.7ETH will be lost.
Return the rest of the rounding.
The contract provides for compensation of gas during the withdrawal of funds:
// Send ETH to receiver
// Calculate fees (1.33%) + gasUsage fees
uint256 gasUsed = startGas - gasleft();
uint256 fees = (withdrawEther / 75) + gasUsed + startGas;
But gasleft()
function returns just the amount of gas(not in wei
). These calculations do not take into account the gas price. Therefore, the returned funds will be incomparably less than spent.
blocksPassed
variable is not used.
There are some dangerous vulnerabilities were discovered here.