LOTTEREUM

[yograterol]

Audit request

LOTTEREUM - planned reduction in the number of tokens in turnover.

Source code

https://github.com/LottereumDev/Lottereum/blob/master/smart%20contract

Disclosure policy

lottereum@hotmail.com

Platform

ETH/ETC/CLO

[LottereumDev]

+

[alexo18]

Auditing time : 6 days

[yuriy77k]

@alexo18 assigned

[RideSolo]

Auditing time: 3 days.

[yuriy77k]

@RideSolo assigned

[gorbunovperm]

Estimated auditing time is 3 days.

[yuriy77k]

@gorbunovperm assigned

[gorbunovperm]

@yuriy77k My report is finished.

[yuriy77k]

You could follow the audit queue there: https://github.com/EthereumCommonwealth/Auditing/blob/master/queue.md

[yuriy77k]

Contract contain high security issues. Report was send to developer.

[yuriy77k]

LOTTEREUM security audit report performed by Callisto Security Audit Department

1. Conclusion:

This contract is not safe and cannot be deployed, it contains high severity security issues and high severity operability issues.

2. High severity issues:

2.1. Result Prediction and Manipulation

Description

Two possible scenarios can guarantee or increase the chance of an attacker to win the lottery:

• Malicious miner manipulation of the transactions orderings can allow the attacker to increase his chances of winning.
• using a simple attack contract an attacker can check the value of amountOfTicketsForEthereumLotteryPurchased if using the ethereum lottery or amountOfTicketsForTokenLotteryPurchased when using the token lottery. Setting simple condition to guarantee that he wins by checking if the value of the state variables satisfy the condition present in playLotteryByToken or playLotteryByEthereum functions.

Code snippet

buyTicketForEthereumLottery and playLotteryByEthereum

buyTicketForTokenLottery and playLotteryByToken

Recommendation

Look at here.

2.2. Anyone can add themselves as a participant without paying a commission.

Code snippet

• Line 156-169

function addParticipiant(address partAddress, LotteryType typeLot) {
  if(typeLot == LotteryType.Token) {
    if(numPartToken == participientsTokenLottery.length) {
      participientsTokenLottery.length += 1;
    }
    participientsTokenLottery[numPartToken++] = partAddress;
  }

  if(typeLot == LotteryType.Ethereum) {
    if(numPartEthereum == participientsEthereumLottery.length) {
      participientsEthereumLottery.length += 1;
    }
    participientsEthereumLottery[numPartEthereum++] = partAddress;
  }
}

Description

addParticipiant function is called from participateInTokenLottery with preliminary checks and commission paying. But also this function may be called by anyone.

Recommendation

Mark addParticipiant function as internal.

2.3. Missing function visibility specifier.

Description

The clearParticipiants() function has no visibility specifier, that may be maliciously exploited to destroy the whole lottery process.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/master/smart%20contract#L171#L156

Recommendation

Mark this functions as internal.

2.4. Missing restriction modifier.

Description

The importAddresses() function is callable externally without a restriction.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/master/smart%20contract#L179

3. Medium severity issues:

3.1. Internal Call to Restricted Function

Description

Internal call to playLotteryByEthereum and playLotteryByToken is made inside buyTicketForEthereumLottery and buyTicketForTokenLottery, however this two functions are restricted by the onlyAdministrator modifier. when amountOfTicketsForTokenLotteryPurchased or amountOfTicketsForEthereumLotteryPurchased will reach 1000 the transactions wil fail.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L227-L228

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L239-L240

Recommendation

Mark this functions as internal. And make another functions like startLotteryByTokenManually with onlyAdministrator rights.

3.2.Logical contradiction between 'buyTicketForTokenLottery()' and 'playLotteryByToken()' functions.

Description

The 'Token' and 'Ethereum' lotteries are triggered separately one from another by the 'buyTicket..' functions , but the 'playLottery...' functions implement the 'onlyAdministrator' modifier.

In case if there is intention to call the 'buyTicketForTokenLottery()' function as a contract administrator and held both lotteries at the same time, the 'allowance' mechanism needs to be used to withdraw tokens from the user account.

In case if the lotteries do may held asynchronously, the tokens of 'tokensOfLosers ' variable may be lost ,because the variable is non cumulative and reinitiated every time when the lottery is held, so there is a situation when multiple 'Token' and no 'Ethereum' lotteries will be held.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/master/smart%20contract#L228#L263#L265

3.3. Lost winning tickets.

Description

Some winning tickets may be lost, being replaced by another, purchased later, ticket .

Code snippet

https://github.com/LottereumDev/Lottereum/blob/master/smart%20contract#L226

4. Low severity issues:

4.1. Buy Ticket For Ethereum

Description

A user can send more ether than the ticket price when calling buyTicketForEthereumLottery the extra ether will be lost in the contract.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L234

4.2. Lottery Winners distribution

Description

The following description assumes that the devs didn't take into account the high severity issue mentioned in 2.1.

80% of totalFundInTokenLottery is distributed to the lottery winners, however after starting distribution only 96% of the original 80% is distributed (check the computation bellow).

(1000÷100)×(2÷100+4÷1000+2÷1000)+(1000÷20)×(4÷1000+2÷1000)+(1000÷10)×(2÷1000)+2÷10 = 0.96

Same issue with the 70% of totalFundInEthereumLottery, 96% of the original 70% will be distributed and the other 4% will be lost in the contract.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L264

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L269-L280

4.3. Identical Functions

Description

participateInEthereumLottery and participateInTokenLotterycontain the exact same code. one function should handle ether to buy tickets and the other one should handle tokens.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L197

https://github.com/LottereumDev/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L209

4.4. Known vulnerabilities of ERC-20 token

Code snippet

• Line 52

Description

It is possible to re-approve attack. More details here

Recommendation

The approval of a new amount must be made only when allowance is 0.

4.5. It is possible to lose owner rights occasionally.

Code snippet

• Line 17

Description

transferOwnership function doesn't have zero address check. And if the parameters of this function will not be added then owners rights will be transfered to 0x0 address.

Recommendation

Use require(newOwner != address(0)).

5. Minor observation:

5.1. Play & Withdraw Pattern

Description

This description assumes that the high severity security issues are solved. A play and withdrawal pattern should be used instead of playLotteryByEthereum and playLotteryByToken that will consume a highly excessive amount of gas.

Recommendation

The dev should set an opening and closing time where in between players can buy tickets and after closing time players will withdraw their reward by themselves.

5.2. Useless State Variables

Description

ticketsForTokenLottery and ticketsForEthereumLottery map players addresses to their ticket number and own address, adding useless extra data.

Code snippet

https://github.com/RideSolo/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L107

https://github.com/RideSolo/Lottereum/blob/8485c34a0364f8aad53ff6e719604d7d7aa32e12/smart%20contract#L108

5.3. Opening and Closing Time

Description

An opening time is set and checked, but no closing time is set which means that users can play the lottery even after that it closes.

5.4. The TotalSupply variable not updating.

Description

The 'TotalSupply' not updating in the 'playLotteryByEthereum()' function when distributing tokens to the investors.

Code snippet

https://github.com/LottereumDev/Lottereum/blob/master/smart%20contract#L339

Revealing audit reports:

https://gist.github.com/yuriy77k/8dc77c7a2ed7433f234b5cf1b95d59b8

https://gist.github.com/yuriy77k/8918a74d8cd0f8bf0309867d25a2a632

https://gist.github.com/yuriy77k/31f0349de39989b2c88eb5be33359fbe