Designing a Secure USDC-Based Raffle Contract

Smart Contracts
1

Hi everyone :waving_hand:

I'm working on a smart contract that implements a simple raffle system using USDC (ERC20) instead of ETH.

:bullseye: Concept Overview

  • Users enter the raffle by staking USDC.
  • The contract holds all staked tokens until the raffle cycle ends.
  • A random winner is selected (likely using Chainlink VRF).
  • The winner receives the full USDC pool.

In the next version, I plan to extend this into a yield-based lottery, where:

  • Users stake USDC, which is deposited into Aave or Compound.
  • Only the generated yield is distributed as the reward.
  • Users can stake only when the raffle is in an Open state (not during winner selection).
  • If a user withdraws before the raffle cycle ends, their principal and any yield they’ve generated are returned to their wallet.

:hammer_and_wrench: Design Questions

  1. Is the USDC staking flow (approve → transferFrom) considered the safest and most standard pattern for ERC20-based deposits?
  2. Any recommended best practices for handling ERC20 transfers securely (especially for tokens like USDC that have 6 decimals and sometimes non-standard behaviors)?
  3. When integrating with Aave or Compound, how should I handle yield extraction to ensure both safety and gas efficiency?

Any advice, design patterns, or example implementations from OpenZeppelin contracts or community projects would be greatly appreciated :folded_hands:

Thanks in advance!
Support!

2

Hi! Interesting design - a USDC-based raffle with a future yield-lottery extension is a solid approach.

Below are answers to your questions + some recommended patterns.

USDC Staking Flow (approve → transferFrom)

Yes, the standard ERC-20 deposit flow is:

  1. User calls approve(contract, amount)

  2. Contract executes transferFrom(user, contract, amount)

This is currently the safest + most widely supported pattern.
It ensures:
-No custody without explicit approval
-No blind pulling of funds
-Better UX for integrations / frontends

Depending on UX, you may consider ERC-20 Permit (EIP-2612), but note USDC does not support permit.

So approve → transferFrom remains the correct pattern.

3

i have another approach like when user calls stake with some x amount and then that x amount is transfered to contract .Now contract sends it aave pool.May be this doesn’t require approve from the user.