Introduction :

This Audit Report highlights the overall security of BtcCredit Smart Contract. With this report, we have tried to ensure the reliability of their smart contract by complete assessment of their system’s architecture and the smart contract codebase.

Auditing Approach and Methodologies applied :

Quillhash team has performed thorough testing of the project starting with analysing the code design patterns in which we reviewed the smart contract architecture to ensure it is structured and safe use of third party smart contracts and libraries.
Our team then performed a formal line by line inspection of the Smart Contract in order to find any potential issues like race conditions, transaction-ordering dependence, timestamp dependence, and denial of service attacks.
In the Unit testing Phase we coded/conducted Custom unit tests written for each function in the contract to verify that each function works as expected. In Automated Testing, We tested the Smart Contract with our in-house developed tools to identify vulnerabilities and security flaws.

The code was tested in collaboration of our multiple team members and this included –

1. Testing the functionality of the Smart Contract to determine proper logic has been followed throughout.
2. Analyzing the complexity of the code by thorough, manual review of the code, line-by-line.
3. Deploying the code on testnet using multiple clients to run live tests
4. Analysing failure preparations to check how the Smart Contract performs in case of bugs and vulnerabilities.
5. Checking whether all the libraries used in the code are on the latest version.
6. Analyzing the security of the on-chain data.

Audit Details

Project Name: BTCCREDIT
website/Etherscan Code: Code
Languages: Solidity (Smart contract), Javascript (Unit Testing)

Summary of BTCCREDIT Smart Contract :

QuillAudits conducted a security audit of a smart contract of BTCcredit. BTCcredit contract is used to create the ERC20 utility token which is a BTCCredit token, Smart contract contains basic functionalities of ERC20 token with total supply of 300 million and Mint function to mint more Btc credit tokens.

Audit Goals

The focus of the audit was to verify that the smart contract system is secure, resilient and working according to its specifications. The audit activities can be grouped in the following three categories:

Security: Identifying security related issues within each contract and within the system of contracts.
Sound Architecture: Evaluation of the architecture of this system through the lens of established smart contract best practices and general software best practices.
Code Correctness and Quality: A full review of the contract source code. The primary areas of focus include:

• Correctness
• Readability
• Sections of code with high complexity
• Quantity and quality of test coverage

Security Level references :

Every issue in this report was assigned a severity level from the following:

High severity issues will bring problems and should be fixed.

Medium severity issues could potentially bring problems and should eventually be fixed.

Low severity issues are minor details and warnings that can remain unfixed but would be better fixed at some point in the future.

Number of issues per severity

High severity issues:-

1 distributeTokens(address _address, uint _amount);

distributeTokens function of smart contract only check whether total supply is less than or equal to distributed tokens, but doesn’t subtract from minted tokens, as minted tokens are already sent to a particular address, hence owner will be able to distribute tokens more than total supply, as shown in the pictures below.

Total supply is: 300001000
0x410 is holding: 300002000

You can use one variable that will automatically update when mint functions is called and will update the no of tokens minted while distributing tokens check whether distributed tokens is less than the total supply subtracted from minted tokens.
Status: Issues Fixed by Developer

Medium Severity Issues:-

1 Use transfer event while burning tokens, as etherscan reads transfer events. As now burn doesn’t emit transfer function now, etherscan couldn’t be able to read balance of an account that has burned all the tokens and still showing previous balance of that address.

In both burn() and burnFrom() function of token contract.
Status: Issues Fixed by Developer

Low Severity Issues:-

1 Solidity version must be fixed (Always use latest Version).
It should not pragma solidity ^0.4.25;
It should be pragma solidity 0.4.25;
Status: Issues Fixed by Developer

version should be fixed so that development phase and deployment phase should have the same solidity version.

2 SafeMath.sol contract functions access modifier can be changed to internal, as there is no use to make them public functions.

Use: access modifier internal in place of public.
Status: Issues Fixed by Developer

Issues while checking initial audit fixes

Medium Severity Issues:-

As you can see in the above picture, after minting 300 million tokens total supply was 600 million and, when 1 million tokens are burnt from account 1, transfer event was omitted from contract to address(0), but it should be from address (msg.sender/caller) to address(0) that’s why percentage of token holder is higher than 100% (total supply).

Status: Not Fixed

Unit Testing

Test Suite

Contract: BTCcredit Token Contracts

✓ Should correctly initialize constructor values of BTCCToken Token Contract (250ms)
✓ Should check the Total Supply of BTCCToken Tokens (80ms)
✓ Should check the Name of a token of BTCC Token contract (79ms)
✓ Should check the symbol of a token of BTCCToken contract (64ms)
✓ Should check the decimal of a token of BTCCToken contract (74ms)
✓ Should check the balance of an Owner (66ms)
✓ Should check the owner of a contract (57ms)
✓ Should check the New owner of a contract (57ms)
✓ Should check the balance of a contract (64ms)
✓ Should check the distributed tokens of a contract (68ms)
✓ Should check the owner account is not frozen (66ms)
✓ Should check the minted tokens (52ms)
✓ Should Not be able to distribute tokens to accounts[1] by Non Owner account (154ms)
✓ Should Not be able to distribute tokens more then total supply (170ms)
✓ Should be able to distribute tokens to accounts[1] (257ms)
✓ Should check the distributed tokens of a contract after sent to account[1] (62ms)
✓ Should Not be able to Freeze Accounts[1] by non owner account (263ms)
✓ Should Freeze Accounts[1] (210ms)
✓ Should Not be able to transfer Tokens when account is freezed (97ms)
✓ Should Not be able to UnFreeze Accounts[1] by non owner account (94ms)
✓ Should UnFreeze Accounts[1] (201ms)
✓ Should be able to transfer Tokens after Unfreeze (340ms)
✓ Should Not be able to burn tokens when account doesn't have tokens (96ms)
✓ Should be able to burn tokens (217ms)
✓ Should be able to emit transfer event while burn tokens (217ms)
✓ Should check the Total Supply of BTCCToken Tokens after token burnt
✓ Should Not be able to Mint Tokens by Non owner account (96ms)
✓ Should be able to Mint Tokens by owner only and send to accounts[3] (210ms)
✓ Should check the minted tokens after minted (44ms)
✓ Should Not be able to distribute tokens to accounts[6] less then total supply and minted tokens (127ms)
✓ Should be able to distribute tokens to accounts[6] less then total supply and minted tokens (192ms)
✓ Should check the Total Supply of BTCCToken Tokens after tokens minted (59ms)
✓ Should be able to transfer ownership of token Contract (160ms)
✓ Should check the New owner of a contract
✓ Should be able to Accept ownership of token Contract (124ms)
✓ Should check the New owner of a contract after ownership accepted
✓ should Approve address to spend specific token (155ms)
✓ Should be able to transfer Tokens approved by account[3] to account[5] (299ms)
✓ should check the allowance later
✓ Should be able to burn Tokens approved by account[3] to account[5] (162ms)
✓ Should be able to emit transfer event while burnFrom tokens (217ms)
✓ Should check the Total Supply of BTCCToken Tokens after tokens burn
✓ Should correctly initialize constructor values of sample Token Contract (110ms)
✓ Should check the balance of a sample contract Owner
✓ Should be able to transfer sample tokens to BTCCToken contract (219ms)
✓ Should be able to transfer sample tokens to owner of BTCCToken, sent to contract of BTCCToken (225ms)
✓ Should Not be able to send ethers to contract
Contract: BTCCToken Token Contract for final audit testing at maximum values
✓ Should correctly initialize constructor values of BTCCToken Token Contract (99ms)
✓ Should check the Total Supply of BTCCToken Tokens (39ms)
✓ Should check the Name of a token of BTCC Token contract
✓ Should check the symbol of a token of BTCCToken contract
✓ Should check the decimal of a token of BTCCToken contract
✓ Should check the balance of a Owner
✓ Should check the owner of a contract
✓ Should check the New owner of a contract
✓ Should check the balance of a contract (57ms)
✓ Should check the distributed tokens of a contract
✓ Should check the owner account is not frozen
✓ Should check the minted tokens (38ms)
✓ Should be able to Mint Tokens by owner only more then total supply (128ms)
✓ Should check the minted tokens after minted
✓ Should check the Total Supply of BTCCToken Tokens after tokens minted
✓ Should be able to distribute tokens to accounts[1] (192ms)
✓ Should be able to self destruct (192ms)

Final Result of Test:

✓ 64 Passing (8s) PASSED

❌ 0 Failed

Manual Transactions

Network: Rinkeby

Coverage report

Token A is a sample token contract to check transferAnyERC20Token() function of BTCCtoken contract function.

Implementation Recommendations :

• _totalSupply variable can be declared as private variable, as totalSupply() function already using _totalSupply variable.
• Use SafeMath while subtracting totalSupply with balance[address(0)].
  transferFrom() function should check allowance first.
• Use transfer event while initializing tokens in constructor, transfer event from address(0) to contract address and also update the balance of the contract.
• While distributing tokens use transfer event from contract address to beneficiary to maintain all the balance events on etherscan.

Comments:

Use case of smart contract is very well designed and Implemented. Overall, the code is clearly written and demonstrates effective use of abstraction, separation of concerns, and modularity. BTCCREDIT development team demonstrated high technical capabilities, both in the design of the architecture and in the implementation. All the severity issues have been fixed by BTCCREDIT team and we request BTCcredit team to go through recommendations as well to maintain standardisation of code.
Note: Smart contract code contain self destruct function which can be called by owner only.