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docs/devdocs/Encryption and Privacy/Exposed-Encrypted-Variables.md
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| # 🔎 Encrypted Variables - Preventing Exposure | ||
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| Ensuring that encrypted data and variables are not leaked is important when working with Fhenix. A common oversight when working with encrypted variables is revealing them to other contracts. Lets take a look at a scenario that leaks encrypted data: | ||
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| ```solidity | ||
| contract UserBalanceVulnerable { | ||
| mapping(address => euint64) public eUserBalances; | ||
| function addBalance(inEuint64 calldata _inBalance) public { | ||
| eUserBalances[msg.sender] = eUserBalances[msg.sender].add( | ||
| FHE.asEuint64(_inBalance) | ||
| ); | ||
| } | ||
| } | ||
| ``` | ||
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| This seems secure enough and no decrypted data is directly exposed, however the `public` access to `eUserBalances` leaks sensitive data. A malicious contract is able to fetch this data and then decrypt it: | ||
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| ```solidity | ||
| contract UserBalanceAttack { | ||
| address private vulnerableContract; | ||
| function revealUserBalance(address _user) public view returns (uint64) { | ||
| return UserBalanceVulnerable(vulnerableContract) | ||
| .eUserBalances(_user) | ||
| .decrypt(); | ||
| } | ||
| } | ||
| ``` | ||
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| All contracts on the Fhenix network share an encryption key, therefore an encrypted variable in `ContractA` could be decrypted in `ContractB`. | ||
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| This is not inherently wrong, and many operations will require encrypted variables to be shared between contracts, but care must be taken to prevent open access to encrypted variables. | ||
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| ### Hardhat Task | ||
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| The `fhenix-hardhat-plugin` package contains a task that checks your contracts for any exposed encrypted variables. This task is run automatically when your contracts are compiled, but can also be run manually. | ||
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| #### Task Example | ||
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| The following contract exposes encrypted variables in 3 ways. | ||
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| ```solidity | ||
| pragma solidity >=0.8.13 <0.9.0; | ||
| import "@fhenixprotocol/contracts/FHE.sol"; | ||
| contract ContractWithExposedVariables { | ||
| // Example 1 | ||
| mapping(address => euint8) public eUserBalances; | ||
| // Example 2 | ||
| mapping(address => euint8) private _eUserBalances; | ||
| function getUserBalance(address _user) public view returns (euint8) { | ||
| return _eUserBalances[_user]; | ||
| } | ||
| // Example 3 | ||
| struct Player { | ||
| address player; | ||
| euint8[] eCards; | ||
| uint256 chips; | ||
| uint256 bet; | ||
| } | ||
| struct Dealer { | ||
| uint256 pot; | ||
| euint8[] eFlopCards; | ||
| } | ||
| struct HoldEmGameState { | ||
| Player[] players; | ||
| Dealer dealer; | ||
| } | ||
| HoldEmGameState private gameState; | ||
| // Encrypted card values is the Player and Dealer structs are leaked and can be exploited | ||
| function getGameState() public view returns (HoldEmGameState memory) { | ||
| return gameState; | ||
| } | ||
| } | ||
| ``` | ||
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| #### Output | ||
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| Below is the output of the task when analyzing the above `ContractWithExposedVariables.sol` | ||
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| <pre> | ||
| <b>fhenix-hardhat-plugin:CheckExposedEncryptedVars</b> checking for exposed encrypted variables.... | ||
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| <b style={{color:"orangered"}}>contracts/ContractWithExposedVariables.sol:ContractWithExposedVariables</b> | ||
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| <b>eUserBalances(address)</b> exposes 1 encrypted variables: | ||
| pos-0 - <b style={{color:"orangered"}}>euint8</b> | ||
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| <b>getUserBalance(address)</b> exposes 1 encrypted variables: | ||
| pos-0 - <b style={{color:"orangered"}}>euint8</b> | ||
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| <b>getGameState()</b> exposes 1 encrypted variables: | ||
| pos-0 - struct ContractWithExposedVariables.HoldEmGameState | ||
| players - struct ContractWithExposedVariables.Player[] | ||
| eCards - <b style={{color:"orangered"}}>euint8[]</b> | ||
| dealer - struct ContractWithExposedVariables.Dealer | ||
| eFlopCards - <b style={{color:"orangered"}}>euint8[]</b> | ||
| </pre> | ||
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| #### Manual Task Execution | ||
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| The task can be run manually with the command: | ||
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| ``` | ||
| npx hardhat task:fhenix:checkExposedEncryptedVars | ||
| ``` | ||
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| Or as a part of a hardhat compilation: | ||
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| ``` | ||
| npx hardhat compile | ||
| ``` |
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| { | ||
| "label": "Fhenix Helium Testnet", | ||
| "label": "Fhenix Nitrogen Testnet", | ||
| "position": 2, | ||
| "link": { | ||
| "type": "generated-index", | ||
| "description": "Fhenix Helium Testnet Specific Information" | ||
| "description": "Fhenix Nitrogen Testnet Specific Information" | ||
| } | ||
| } |
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