TMC Token Smart Contract Audit
# 1. Introduction
iosiro was commissioned by the [TMC Foundation](https://tmcfoundation.io/) to conduct an audit on their ERC-20 token smart contracts. The audit was performed on 04 March 2020.
This report is organized into the following sections.
* **[Section 2 - Executive Summary:](#section-2)** A high-level description of the findings of the audit.
* **[Section 3 - Audit Details:](#section-3)** A description of the scope and methodology of the audit.
* **[Section 4 - Design Specification:](#section-4)** An outline of the intended functionality of the smart contracts.
* **[Section 5 - Detailed Findings:](#section-5)** Detailed descriptions of the findings of the audit.
The information in this report should be used to understand the risk exposure of the smart contracts, and as a guide to improving the security posture of the smart contracts by remediating the issues that were identified. The results of this audit are only a reflection of the source code reviewed at the time of the audit and of the source code that was determined to be in-scope.
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# 2. Executive Summary
This report presents the findings of a smart contract audit performed by iosiro on the TMC token smart contracts. The purpose of this audit was to achieve the following.
* Ensure that the smart contracts functioned as intended.
* Identify potential security flaws.
Assessing the economics, game theory, or underlying business model of the platform were strictly beyond the scope of this audit.
Due to the unregulated nature and ease of transfer of cryptocurrencies, operations that store or interact with these assets are considered very high risk with regards to cyber attacks. As such, the highest level of security should be observed when interacting with these assets. This requires a forward-thinking approach, which takes into account the new and experimental nature of blockchain technologies. There are a number of techniques that can help to achieve this, some of which are described below.
* Security should be integrated into the development lifecycle.
* Defensive programming should be employed to account for unforeseen circumstances.
* Current best practices should be followed when possible.
Several informational issues were identified during the audit. These included best practice recommendations to improve the security, readability, and functionality of the codebase.
The code quality was found to be relatively poor, as it was not properly formatted, did not make use of comments, and did not conform to industry standards. It is recommended that the token be reimplemented using the current OpenZeppelin smart contracts to better adhere to industry standards.
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# 3. Audit Details
## 3.1 Scope
The source code considered in-scope for the assessment is described below. Code from all other files is considered to be out-of-scope. Out-of-scope code that interacts with in-scope code is assumed to function as intended and introduce no functional or security vulnerabilities for the purposes of this audit.
### 3.1.1 TMC Official Smart Contracts
**Project Name:** TMC-Official<br/>
**Files:** [b923cde](https://github.com/TMC-Official/ERC20-Contract/blob/b923cde02d2fd928760cc1e810410c2064fe1530/ERC20_Contract.sol)<br/>
## 3.2 Methodology
A variety of techniques were used while conducting the audit. These techniques are briefly described below.
### 3.2.1 Code Review
The source code was manually inspected to identify potential security flaws. Code review is a useful approach for detecting security flaws, discrepancies between the specification and implementation, design improvements, and high risk areas of the system.
### 3.2.2 Dynamic Analysis
The contracts were compiled, deployed, and tested in a Ganache test environment. Manual analysis was used to confirm that the code operated at a functional level, and to verify the exploitability of any potential security issues identified.
### 3.2.3 Automated Analysis
Tools were used to automatically detect the presence of several types of security vulnerabilities, including reentrancy, timestamp dependency bugs, and transaction-ordering dependency bugs. The static analysis results were manually analysed to remove false positive results. True positive results would be indicated in this report. Static analysis was conducted using Slither and MythX. Tools such as the Remix IDE, compilation output, and linters were also used to identify potential areas of concern.
## 3.3 Risk Ratings
Each issue identified during the audit has been assigned a risk rating. The rating is determined based on the criteria outlined below.
* **High Risk** - The issue could result in a loss of funds for the contract owner or system users.
* **Medium Risk** - The issue resulted in the code specification being implemented incorrectly.
* **Low Risk** - A best practice or design issue that could affect the security of the contract.
* **Informational** - A lapse in best practice or a suboptimal design pattern that has a minimal risk of affecting the security of the contract.
* **Closed** - The issue was identified during the audit and has since been addressed to a satisfactory level to remove the risk that it posed.
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# 4. Design Specification
The following section outlines the intended functionality of the system at a high level.
## 4.1 TMC Token Smart Contract
The TMC Token contract is described below.
#### ERC-20 Token
The token should implement the ERC-20 standard with the following values.
| Field | Value |
| ------------ | ------------- |
| Symbol | TMC |
| Name | TMC Coin |
| Decimals | 18 |
| Total Supply | 500 million |
#### Ownable
The token should have an owner address, who is able to perform special operations. It should be possible for the owner to transfer their ownership to another address.
#### Stoppable
It should be possible for the owner to stop and start all transfers in the system.
#### Blacklist
It should be possible for the owner to add and remove addresses from a blacklist. When an address is blacklisted, it should not be possible for the address to send or receive tokens.
#### Airdrop
There should be functionality built into the token that allows the owner to pass in an array of addresses and amounts to transfer tokens to.
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# 5. Detailed Findings
The following section includes in depth descriptions of the findings of the audit.
## 5.1 High Risk
No high risk issues were present at the conclusion of the audit.
## 5.2 Medium Risk
No medium risk issues were present at the conclusion of the audit.
## 5.3 Low Risk
No low risk issues were present at the conclusion of the audit.
## 5.4 Informational
### 5.4.1 Design Comments
Actions to improve the functionality and readability of the codebase are outlined below.
#### Use `bool` for Blacklist State
An `int` type was use for storing whether an address was blacklisted. A more intuitive type for this binary state would be a boolean, using `true` or `false` to indicate whether an address was blacklisted.
#### Use `require` for Blacklist
The `transfer(...)` and `transferFrom(...)` functions returned `false` if attempting to transfer from or to a blacklisted address. While this is within the ERC-20 standard, a more intuitive implementation would revert through a `require` statement. This would prevent third-parties from potentially assuming that a transfer succeeded if the return value of the function was not validated.
#### Use `require` for `onlyOwner`
The `onlyOwner` modifier returned `false` instead of reverting. It is recommended that a `require` statement be used to explicitly revert if the function is called by a non-owner address.
#### Use SafeMath
While no instances of integer overflows or underflows were identified, it is still advisable that mathematical operations be performed using [SafeMath](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol).
#### No Token Creation Transfer Event
In the ERC-20 standard it specifies that a Transfer event be emitted whenever there is movement of tokens. On ERC20_Contract.sol#L61, the total supply is allocated to the `msg.sender`, however no event is emitted. It is recommended that an event transferring the tokens from 0x0 to the address be added.
#### Interface Incorrectly Defined
On ERC20_Contract.sol#L23 `ERC20Interface` implies that the code should be an interface, however the `contract` keyword was used. It is recommended that ERC20_Contract.sol#L26 be removed and the keyword changed to `interface`.
#### No Function Visibility
The `stop(...)` and `start(...)` functions had an implied public visibility. It is recommended that a visibility is explicitly set on these functions by using the `public` keyword to improve the readability of the code.
#### Inexact Compiler Version
The pragma version was not fixed to a specific version, as it specified `^0.4.21`, which would result in using the highest non-breaking version (highest version below `0.5.0`). According to best practice, where possible, all contracts should use the same compiler version, which should be fixed to a specific version. This helps to ensure that contracts do not accidentally get deployed using an alternative compiler, which may pose the risk of unidentified bugs. An explicit version also helps with code reuse, as users would be able to see the author’s intended compiler version. It is recommended that the pragma version is changed to a fixed value, for example `0.4.25`.
