openzeppelin-contracts/README.md

# Zeppelin Solidity
Zeppelin is a library for writing secure Smart Contracts on Ethereum.

With Zeppelin, you can build distributed applications, protocols and organizations:
- using common contract security patterns (See [Onward with Ethereum Smart Contract Security](https://medium.com/bitcorps-blog/onward-with-ethereum-smart-contract-security-97a827e47702#.y3kvdetbz))
- in the Solidity language.

## Getting Started

Zeppelin integrates with [Truffle](https://github.com/ConsenSys/truffle), an Ethereum development environment. Please [install Truffle](https://github.com/ConsenSys/truffle#install) and initialize your project with `truffle init`.
```sh
sudo npm install -g truffle
mkdir myproject && cd myproject
truffle init
```

To install the Zeppelin library, run:
```sh
npm i zeppelin-solidity
```

After that, you'll get all the library's contracts in the `contracts/zeppelin` folder. You can use the contracts in the library like so:

```js
import "./zeppelin/Ownable.sol";

contract MyContract is Ownable {
  ...
}
```

> NOTE: The current distribution channel is npm, which is not ideal. [We're looking into providing a better tool for code distribution](https://github.com/OpenZeppelin/zeppelin-solidity/issues/13), and ideas are welcome.

## Add your own bounty contract

To create a bounty for your contract, inherit from the base Bounty contract and provide an implementation for `deployContract()` returning the new contract address.

```
import "./zeppelin/Bounty.sol";
import "./YourContract.sol";

contract YourBounty is Bounty {
  function deployContract() internal returns(address) {
    return new YourContract()
  }
}
```

### Implement invariant logic into your smart contract

At contracts/YourContract.sol

```
contract YourContract {
  function checkInvariant() returns(bool) {
    // Implement your logic to make sure that none of the state is broken.
  }
}
```

### Deploy your bounty contract as usual

At `migrations/2_deploy_contracts.js`

```
module.exports = function(deployer) {
  deployer.deploy(YourContract);
  deployer.deploy(YourBounty);
};
```

### Add a reward to the bounty contract

After deploying the contract, send rewards money into the bounty contract.

From `truffle console`

```
address = 'your account address'
reward = 'reward to pay to a researcher'

web3.eth.sendTransaction({
  from:address,
  to:bounty.address,
  value: web3.toWei(reward, "ether")
}

```

### Researchers hack the contract and claim their reward.

For each researcher who wants to hack the contract and claims the reward, refer to our [test](./test/Bounty.js) for the detail.

### Ends the contract

If you manage to protect your contract from security researchers and wants to end the bounty, kill the contract so that all the rewards go back to the owner of the bounty contract.

```
bounty.kill()
```

#### Truffle Beta Support
We also support Truffle Beta npm integration. If you're using Truffle Beta, the contracts in `node_modules` will be enough, so feel free to delete the copies at your `contracts` folder. If you're using Truffle Beta, you can use Zeppelin contracts like so:

```js
import "zeppelin-solidity/contracts/Ownable.sol";

contract MyContract is Ownable {
  ...
}
```

For more info see [the Truffle Beta package management tutorial](http://truffleframework.com/tutorials/package-management).

## Security
Zeppelin is meant to provide secure, tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problem you might experience.

If you find a security issue, please email [security@openzeppelin.org](mailto:security@openzeppelin.org).

## Developer Resources

Building a distributed application, protocol or organization with Zeppelin?

- Ask for help and follow progress at: https://zeppelin-slackin.herokuapp.com/

Interested in contributing to Zeppelin?

- Framework proposal and roadmap: https://medium.com/zeppelin-blog/zeppelin-framework-proposal-and-development-roadmap-fdfa9a3a32ab#.iain47pak
- Issue tracker: https://github.com/OpenZeppelin/zeppelin-solidity/issues
- Contribution guidelines: https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/CONTRIBUTING.md

## Collaborating organizations and audits by Zeppelin
- [Golem](https://golem.network/)
- [Mediachain](https://golem.network/)
- [Truffle](http://truffleframework.com/)
- [Firstblood](http://firstblood.io/)
- [Rootstock](http://www.rsk.co/)
- [Consensys](https://consensys.net/)
- [DigixGlobal](https://www.dgx.io/)
- [Coinfund](https://coinfund.io/)
- [DemocracyEarth](http://democracy.earth/)
- [Signatura](https://signatura.co/)
- [Ether.camp](http://www.ether.camp/)

among others...

## Contracts

### Ownable
Base contract with an owner.

#### Ownable( )
Sets the address of the creator of the contract as the owner.

#### modifier onlyOwner( )
Prevents function from running if it is called by anyone other than the owner.

#### transfer(address newOwner) onlyOwner
Transfers ownership of the contract to the passed address.

---
### Stoppable
Base contract that provides an emergency stop mechanism.

Inherits from contract Ownable.

#### emergencyStop( ) external onlyOwner
Triggers the stop mechanism on the contract. After this function is called (by the owner of the contract), any function with modifier stopInEmergency will not run.

#### modifier stopInEmergency
Prevents function from running if stop mechanism is activated.

#### modifier onlyInEmergency
Only runs if stop mechanism is activated.

#### release( ) external onlyOwner onlyInEmergency
Deactivates the stop mechanism.

---
### Killable
Base contract that can be killed by owner.

Inherits from contract Ownable.

#### kill( ) onlyOwner
Destroys the contract and sends funds back to the owner.
___
### Claimable
Extension for the Ownable contract, where the ownership needs to be claimed

#### transfer(address newOwner) onlyOwner
Sets the passed address as the pending owner.

#### modifier onlyPendingOwner
Function only runs if called by pending owner.

#### claimOwnership( ) onlyPendingOwner
Completes transfer of ownership by setting pending owner as the new owner.
___
### Migrations
Base contract that allows for a new instance of itself to be created at a different address.

Inherits from contract Ownable.

#### upgrade(address new_address) onlyOwner
Creates a new instance of the contract at the passed address.

#### setCompleted(uint completed) onlyOwner
Sets the last time that a migration was completed.

___
### SafeMath
Provides functions of mathematical operations with safety checks.

#### assert(bool assertion) internal
Throws an error if the passed result is false. Used in this contract by checking mathematical expressions.

#### safeMul(uint a, uint b) internal returns (uint)
Multiplies two unisgned integers. Asserts that dividing the product by the non-zero multiplicand results in the multiplier.

#### safeSub(uint a, unit b) internal returns (uint)
Checks that b is not greater than a before subtracting.

#### safeAdd(unit a, unit b) internal returns (uint)
Checks that the result is greater than both a and b.

___
### LimitBalance

Base contract that provides mechanism for limiting the amount of funds a contract can hold.

#### LimitBalance(unit _limit)
Constructor takes an unisgned integer and sets it as the limit of funds this contract can hold.

#### modifier limitedPayable()
Throws an error if this contract's balance is already above the limit.

___
### PullPayment
Base contract supporting async send for pull payments.
Inherit from this contract and use asyncSend instead of send.

#### asyncSend(address dest, uint amount) internal
Adds sent amount to available balance that payee can pull from this contract, called by payer.

#### withdrawPayments( )
Sends designated balance to payee calling the contract. Throws error if designated balance is 0, if contract does not hold enough funds ot pay the payee, or if the send transaction is not successful.

___
### StandardToken
Based on code by FirstBlood: [FirstBloodToken.sol]

Inherits from contract SafeMath. Implementation of abstract contract ERC20 (see [https://github.com/ethereum/EIPs/issues/20])

[FirstBloodToken.sol]: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
[https://github.com/ethereum/EIPs/issues/20]: see https://github.com/ethereum/EIPs/issues/20

#### approve(address _spender, uint _value) returns (bool success)
Sets the amount of the sender's token balance that the passed address is approved to use.

###allowance(address _owner, address _spender) constant returns (uint remaining)
Returns the approved amount of the owner's balance that the spender can use.

###balanceOf(address _owner) constant returns (uint balance)
Returns the token balance of the passed address.

###transferFrom(address _from, address _to, uint _value) returns (bool success)
Transfers tokens from an account that the sender is approved to transfer from. Amount must not be greater than the approved amount or the account's balance.

###function transfer(address _to, uint _value) returns (bool success)
Transfers tokens from sender's account. Amount must not be greater than sender's balance.

___
### BasicToken
Simpler version of StandardToken, with no allowances

#### balanceOf(address _owner) constant returns (uint balance)
Returns the token balance of the passed address.

###function transfer(address _to, uint _value) returns (bool success)
Transfers tokens from sender's account. Amount must not be greater than sender's balance.

___
### CrowdsaleToken
Simple ERC20 Token example, with crowdsale token creation.

Inherits from contract StandardToken.

#### createTokens(address recipient) payable
Creates tokens based on message value and credits to the recipient.

#### getPrice() constant returns (uint result)
Returns the amount of tokens per 1 ether.

## License
Code released under the [MIT License](https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/LICENSE).