Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

ERC20 Token Standard #610

Merged
merged 13 commits into from
Sep 11, 2017
183 changes: 183 additions & 0 deletions EIPS/eip-20-token-standard.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,183 @@
## Preamble

EIP: 20
Title: ERC-20 Token Standard
Author: Fabian Vogelsteller <fabian@ethereum.org>, Vitalik Buterin <vitalik.buterin@ethereum.org>
Type: Standard
Category: ERC
Status: Accepted
Created: 2015-11-19


## Simple Summary

A standard interface for tokens.


## Abstract

The following standard allows for the implementation of a standard API for tokens within smart contracts.
This standard provides basic functionality to transfer tokens, as well as allow tokens to be approved so they can be spent by another on-chain third party.


## Motivation

A standard interface allows any tokens on Ethereum to be re-used by other applications: from wallets to decentralized exchanges.


## Specification

## Token
### Methods

**NOTE**: Callers MUST handle `false` from `returns (bool success)`. Callers MUST NOT assume that `false` is never returned!


#### name

Returns the name of the token - e.g. `"MyToken"`.

OPTIONAL - This method can be used to improve useability,
but interfaces and other contracts MUST NOT expect these values to be present.


``` js
function name() constant returns (string name)
```


#### symbol

Returns the symbol of the token. E.g. "HIX".

OPTIONAL - This method can be used to improve useability,

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

useability> usability

but interfaces and other contracts MUST NOT expect these values to be present.

``` js
function symbol() constant returns (string symbol)
```



#### decimals

Returns the number of decimals the token uses - e.g. `8`, means to divide the token amount by `100000000` to get its user representation.

OPTIONAL - This method can be used to improve useability,
but interfaces and other contracts MUST NOT expect these values to be present.

``` js
function decimals() constant returns (uint8 decimals)
```


#### totalSupply

Returns the total token supply.

``` js
function totalSupply() constant returns (uint256 totalSupply)
```



#### balanceOf

Returns the account balance of another account with address `_owner`.

``` js
function balanceOf(address _owner) constant returns (uint256 balance)
```



#### transfer

Transfers `_value` amount of tokens to address `_to`, and MUST fire the `Transfer` event.
The function SHOULD `throw` if the `_from` account balance has not enough tokens to spend.
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

nit: "has not" replace with "does not have"


An token contract which creates new tokens SHOULD trigger a Transfer event with the `_from` address set to `0x0` when tokens are created.

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

An token contract

*A token contract

:)


*Note* Transfers of 0 values MUST be treated as normal transfers and fire the `Transfer` event.

``` js
function transfer(address _to, uint256 _value) returns (bool success)
```



#### transferFrom

Transfers `_value` amount of tokens from address `_from` to address `_to`, and MUST fire the `Transfer` event.

The `transferFrom` method is used for a withdraw workflow, allowing contracts to transfer tokens on your behalf.
This can be used for example to allow a contract to transfer tokens on your behalf and/or to charge fees in sub-currencies.
The function SHOULD `throw` unless the `_from` account has deliberately authorized the sender of the message via some mechanism.

*Note* Transfers of 0 values MUST be treated as normal transfers and fire the `Transfer` event.

``` js
function transferFrom(address _from, address _to, uint256 _value) returns (bool success)
```



#### approve

Allows `_spender` to withdraw from your account multiple times, up to the `_value` amount. If this function is called again it overwrites the current allowance with `_value`.

**NOTE**: To prevent attack vectors like the one [described here](https://docs.google.com/document/d/1YLPtQxZu1UAvO9cZ1O2RPXBbT0mooh4DYKjA_jp-RLM/) and discussed [here](https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729),

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

it's a pity that approve sets the approval amount and doesn't add or remove to it, it was implemented without much thought but now became a standard already.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We can change that in another standard, but this one needs to be formalised

make sure to force users to set the allowance to `0` before setting it to another value for the same spender.
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggest adding "clients SHOULD" before this line.


``` js
function approve(address _spender, uint256 _value) returns (bool success)
```


#### allowance

Returns the amount which `_spender` is still allowed to withdraw from `_owner`.

``` js
function allowance(address _owner, address _spender) constant returns (uint256 remaining)
```



### Events


#### Transfer

MUST trigger when tokens are transferred, including zero value transfers.

``` js
event Transfer(address indexed _from, address indexed _to, uint256 _value)
```



#### Approval

MUST trigger on any successful call to `approve(address _spender, uint256 _value)`.

``` js
event Approval(address indexed _owner, address indexed _spender, uint256 _value)
```



## Implementation

There are already plenty of ERC20-compliant tokens deployed on the Ethereum network.
Different implementations have been written by various teams that have different trade-offs: from gas saving to improved security.

#### Example implementations are available at
- https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/token/StandardToken.sol
- https://github.com/ConsenSys/Tokens/blob/master/Token_Contracts/contracts/StandardToken.sol

#### Implementation of adding the force to 0 before calling "approve" again:
- https://github.com/Giveth/minime/blob/master/contracts/MiniMeToken.sol

## Copyright
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).