Contest ran 1 August 20226 August 2022

5 day contest

Rigor Protocol contest

Community lending and instant payments for new home construction.

$50,000 USDC

Total Awards

Rigor Protocol contest details

BuilderOne who contracts for and supervises the construction of real estate. Builders are the one to create projects
ProjectEntity defined by a sum of tasks, a budget. It represents a real estate construction and is linked to a builder, contractor and subcontractor.
ContractorOne that agrees to furnish materials or perform services at a specified price, especially for construction work. He is invited by a builder on a project. He can assign a subcontractor on project tasks. Builder can act as a contractor.
SubcontractorOne who agrees to perform the work specified in a project task. He is assigned to the task by the project's contractor. Contractor can act as a subcontractor.
CommunityEntity with an owner and members aiming at providing loans to projects. Members can publish their projects to the community. A project can only be published to one community at a time.
Community owneronly member able to provide loans to published projects
TaskEntity defined by a cost, a subcontractor, and a status. a task can be Inactive, Active or Complete. Tasks can be flagged as Allocated when budget for this task has bee provisioned. When subcontractor confirms the assignment on a task it is being flagged as SCConfirmed
Debt tokenERC20 token mint and burn capable but with disabled transfer. Only the community contract is able to mint and burn these tokens. They represent the debt owned by the builder to the community owner when a loan has been supplied to the builder for a project
HomeFiacronym for Home Finance it is the module where all the protocol modules are linked. Addresses of allowed currencies, project factory, community, treasury and dispute contracts are registered there.
Token CurrencyCrypto currencies used for payment by the protocol. For native currencies like ETH or XDAI we use the wrapped version only.

Areas of specific concern in reviewing the code

The focus is to try and find any logic errors or ways to drain funds from the protocol in a way that is advantageous for an attacker at the expense of users with funds invested in the protocol.

Here are some areas that are of interest :

  • signatures order/concatenation included in sensitive calls.
  • meta transaction
  • smart contract updates and clone factory
  • debt issuance and interest calculation.
  • malicious parties teaming up against other parties. i.e can a contractor and a subcontractor freeze or drain funds without the builder agreement ?
  • funds sitting on project getting stuck.

Protocol Overview

HomeFi protocol is a generalized protocol that provides public, permission less, decentralized financial infrastructure for home finance. Our mission is to make home finance open, accessible and positive-sum for everyone on earth.

The Protocol is divided into modules with different areas of concerns.

HomeFi relationship between entities

All modules are behind proxies. HomeFi Proxy is responsible for initializing all the modules contract in the correct sequential order and generate upgradable proxy for them.

To improve the user experience of construction professionals using the protocol, we implemented eip-2771 meta transactions thanks to OpenZeppelin base contracts.


Here are some sequence diagrams for the main rigor flows.
Home builder will create a project and add tasks to the project. A per task budget is defined. The builder can publish the project to communities he is a member of. Community provide fix APR loans to builders .
Thanks to the loan tasks will be funded and each time a subcontractor completes them he will receive the assigned budget. Finally after selling the real estate the builder is able to repay the loan with interest.
Of course depending on the step different signatures will be required to execute the transaction onchain. The repayment can be mark as done off chain through an escrow and directly between the community owner (aka lender) and the builder.

From project creation to community lending to the project

  1. First a builder creates a project by calling the createProject() function on HomeFi.
    It will trigger the deployment of a new project thanks to the project factory.

  2. Builder invites a general contractor. It requires signing data that includes the contractor address and the project address by both the contractor and the builder. The signatures and data are used to call inviteContractor(bytes _data, bytes _signature)

  3. Builder add tasks to the project. It requires signing data that includes tasks costs, a hash (task metadata), tasks count and the project address. Both builder and contractor have to sign the data. The signatures and data are used to call addTasks(bytes _data, bytes _signature)

  4. Community Owner creates a community by calling createCommunity(bytes _hash, address _currency) on the community contract where all the communities are registered. It requires the address of the currency used by the community for lending. The currency must be register in HomeFi to be valid. It also requires a hash (community metadata).

  5. Builder is invited to be a member of that new community by the community owner. They both have to sign data including the community ID, the new member address and a message hash (the message can be anything). The data and the signatures in the right order is required to call addMember(bytes _data, bytes _signatures) on the community contract. It will add the builder as a community member allowing its projects to be published in the community.

  6. Builder publishes his project to the community. It requires signing data that
    includes community ID, APR, publishing fee and nonce . Both builder and community owner have to sign the data. The signatures and data are used to call publishProject(bytes _data, bytes _signature) .
    Note that you cannot submit a project with no total budget. Therefore it requires at least one task with a budget > 0.

  7. Optional the builder can adjust the amount of the loan requested to a community by calling toggleLendingNeeded(uint256 _communityID, address _project, uint256 _lendingNeeded)

  8. Community owner lends fund to the published project by calling lendToProject(uint256 _cost). This call will update accrued interest, mint debt token for the community owner and transfer tokens to the project contract address.

Community lend to project

Tasks completion and payment

  1. Builder add tasks to the project. It requires signing data that includes tasks costs, a hash (task metadata), tasks count and the project address. Both builder and contractor have to sign the data. The signatures and data are used to call addTasks(bytes _data, bytes _signature)

  2. Contractor assign tasks to subcontractor by calling inviteSC(uint256[] _index, address[] _to) providing tasks ID and subcontractor address. Subcontractor accepts by calling acceptInviteSC(uint256[] _taskList).

  3. Tasks need to be funded to be marked as completed. Although it can be funded through the community, the builder can also fund its project by calling directly lendToProject(uint256 _cost) on the project contract address.

  4. Task is completed by calling setComplete(bytes _data, bytes _signature). It requires signing data that includes task ID and the project address. builder, contractor and subcontractor have to sign the data. If there is no ongoing dispute about that project, task status is updated and payment is made. Indeed tokens are transferred from the project to the subcontractor's address.

Task creation and completion

Lending repayment

  • Builder repays the loan by calling repayLender(uint256 _communityID, address _project, int256 _repayAmount) on community. It will calculate the owned interest and update the remaining debt. This will trigger the burnt of lender's debt and will transfer tokens from builder to community owner.

  • If for instance an offchain repayment occurred, community owner can trigger reduceDebt(uint256 _communityID, address _project, uint256 _repayAmount, bytes _details). It will also calculate the owned interest update the remaining debt and burn community owner's debt token. Note that no token transfer between builder and lender will happen in that case.

Builder repays Community

Getting started

  • Clone this repository
git clone
cd 2022-08-rigor
  • Install dependencies with yarn
  • Create .env file (you can copy ".sample.env")
cp .sample.env .env

Build contracts

  • to compile run

yarn compile

Run tests

  • to run tests

yarn test

Run test coverage

  • to test coverage

yarn coverage

Smart Contracts

All the contracts in this section are to be reviewed. A further breakdown of contracts and their dependencies can be found here

Files in scope

Contracts (7)
contracts/HomeFiProxy.sol 🌀7093231
contracts/Disputes.sol 🧮112144273
contracts/Project.sol 🧮406474911
contracts/Community.sol 🧮422569919
Libraries (2)
contracts/libraries/SignatureDecoder.sol 🖥🧮🔖345086
Total (over 9 files):130117243153

Direct parent contracts of in-scope contracts (not in scope)

Interfaces (6)
Total (over 6 files):2744211245

HomeFiProxy.sol (93 sloc each)

HomeFi.sol (197 sloc each)

The main entry point for the HomeFi Smart Contract ecosystem. Administrative actions are executed through this contract; new project contracts are created from this contract with accompanying ERC721 for each project.

Project.sol (474 sloc each)

Child contract deployed from HomeFi.sol, Project.sol contains the primary logic around construction project management. Onboarding contractors, fund escrow, and completion tracking are all managed here. Significant multi-signature and meta-transaction functionality is included here.

ProjectFactory.sol (56 sloc each)

Technically separate from HomeFi.sol but can only be accessed by HomeFi.sol.

Community.sol (569 sloc each)

Contains all project publication and lender funding logic. Lenders fund project contracts through Community.sol, and Builders repay lenders through Community.sol as well.

Disputes.sol (144 sloc each)

In the event that a contractor (general or sub) does not get their funds and should have received them, or if there is negligence or malfeasance in the relationship between a builder and lender, participants permissioned in the project have the ability to raise a dispute that HomeFi's admins (in our case Rigor) are able to arbitrate to make sure funds arrive in the correct user's wallet.

DebtToken.sol (55 sloc each)

Used to wrap Ether, USDC, or Dai and collateralize a given project. hTokens are given to lenders in the Community.sol contract as a receipt to track their lending into the project. On an builder's repayment of a project, hTokens are instantly destroyed, and the underlying collateral is returned + interest for the loan duration.

  • It inherits OpenZeppelin ERC20 base class. Note that transfer are disabled and mint and burn are only available to the community contract.

Tasks.sol (86 sloc each)

Internal library used in Project. Contains functions specific to a task actions and lifecycle.

SignatureDecoder.sol (50 sloc each)

Decodes signatures that are encoded as bytes.

External imports

Interest calculation

Interest on a loan are calculated on the principal only and doesn't include interest on the accrued interest.

When a repayment occurs we first repay the interest and if their is money left the principal is repaid. Afterwards the interest will be calculated on the remaining principal.

Here is some examples on a spreadsheet.

Gas reports

REPORT_GAS=true yarn test

Deployment Steps

  • Run the following command to deploy smart contracts (for local)

yarn deploy-local

  • Run the following command to deploy smart contracts (for rinkeby)

yarn deploy-rinkeby



HomeFiProxy contract stores the proxies for HomeFi, Community, Disputes,
ProjectFactory, and all the three DebtTokens. These proxies' implementation can be upgraded individually. Only the admin can upgrade implementations.
All proxies are stored in an array inside HomeFiProxy with a bytes2 name associated to them.

Contract ProxyBytes2 Name
Native Currency Debt TokenDA
Token Currency 1 Debt TokenUS
Token Currency 2 Debt TokenNT

Steps to upgrade Proxy

This is valid for all HomeFi proxies- HomeFi, Community, Disputes, ProjectFactory, and DeptTokens.

  1. Add virtual modifier to all the functions of old implementation(V1) that are needed to be upgraded.
  2. Make the new implementation(V2) inherit V1.
  3. Rules:
    • Add new variable and functions normally
    • Use override modifier when overriding a V1 function or modifier
    • Cannot override or modify an event
  4. Test the V2 contracts plus regression the V2 implementation with V1 tests. To make this process easier, paste V2 implementation in ./contract/mocks/ContractNameV2Mock.sol and its tests inside ./test/utils/contractNameUpgradabilityTests.ts and simply run the Upgradability.ts test.
  5. Before upgrading on production(xDai), deploy upgrades development testnets(rinkeby) and test.
  6. Deploy upgrades on production(xDai) and test.

Upgrade Proxy Using script

  1. Save the new proxy implementation according to the step above.
  2. Run yarn compile to compile all contracts, including the new implementation.
  3. Deploy the new implementation, possibly by creating a new script, and save its address.
  4. In the ./scripts/upgrade.ts file, update the following variable accordingly to your deployment:
    • homeFiProxyAddress: address of homeFiProxy
    • proxyBytes2Name: name of the proxy to upgrade. For ex: PF for ProjectFactor. Refer ./contracts/HomeFiProxy.sol for proxies and there name.
    • newImplementationName: address of the underlying implementation. For ex: address of new ProjectFactory contract.
    • taskLibraryAddress: only required when upgrading ProjectFactory proxy. Address of TaskLibrary that is linked to Project contract.
  5. Run the upgrade script,
    yarn hardhat run scripts/upgrade.ts --network <your preferred network>
  6. The upgrade script will automatically run the tests if using the hardhat network.

    Look at various tested V2 mocks inside ./contract/mocks

ProjectFactory and Project

ProjectFactory proxy upgrade is mostly required to upgrade the underlying Project contract implementation. To make this upgrade, the new implementation of ProjectFactory must add a function to change the underlying address with new Project implementation. Potentially also updating the interface for Project contract. Check ./contracts/mock/ProjectFactoryV2Mock.sol and contracts/mock/ProjectV2Mock.sol for reference.


Latest contract addresses can be found under "deployments/<network>.json"

Scoping details answers

- Do you have a link to the repo that the contest will cover?

- How many (non-library) contracts are in the scope?

- Total sLoC in these contracts?

- How many library dependencies?

- How many separate interfaces and struct definitions are there for the contracts within scope?
7 interfaces 4 structs

- Does most of your code generally use composition or inheritance?
We are mostly using Inheritance for storing the basic schema of our contracts. Storing external functions params, returns, events, structs, and enums, without any implementation.

- How many external calls?
Two. Calling transfer() and transferFrom() on supported tokens. As of now, we are supporting USDC, WXDAI, and WETH.

- Is there a need to understand a separate part of the codebase / get context in order to audit this part of the protocol?

- Does it use an oracle?

- Does the token conform to the ERC20 standard?
We have a debt token that is a modified ERC20

- Are there any novel or unique curve logic or mathematical models?

- Does it use a timelock function?

- Is it an NFT?
We use NFTs

- Does it have an AMM?

- Is it a fork of a popular project?

- Does it use rollups?

- Is it multi-chain?

- Does it use a side-chain?