Natuurlijk! Hier is een overzicht en een basisontwerp voor een Solidity smart contract voor een gedecentraliseerd identiteitsverificatiesysteem. Vervolgens beschrijf ik de belangrijkste functies, beveiligingsmaatregelen en beste praktijken. --- ### Kernfuncties van het systeem 1. **Registratie**: Gebruikers kunnen hun identiteit registreren door een unieke identiteit (bijvoorbeeld een cryptografische hash van hun gegevens) toe te voegen. 2. **Verificatie**: Verificatieinstanties kunnen identiteiten valideren en een verificatiestatus toekennen zonder privégegevens bloot te geven. 3. **Gegevensbescherming**: Privégegevens worden niet opgeslagen op de blockchain, maar als hashes of pointers naar off-chain opslag. 4. **Toestemmingbeheer**: Gebruikers kunnen bepalen wie hun gegevens mag bekijken/verifiëren. --- ### Basis Solidity-implementatie ```solidity // SPDX-License-Identifier: MIT pragma solidity ^0.8.0; contract DecentralizedIdentity { // Struct voor gebruikers struct User { address owner; bytes32 identityHash; // Hash van privégegevens bool verified; mapping(address => bool) permissions; // Toestemming voor verificatie } mapping(address => User) private users; // Gebruiker registreert zichzelf met een hash van hun privégegevens function register(bytes32 identityHash) external { require(users[msg.sender].owner == address(0), "Gebruiker al geregistreerd"); User storage newUser = users[msg.sender]; newUser.owner = msg.sender; newUser.identityHash = identityHash; newUser.verified = false; } // Verificatie-instantie geeft verificatie function verify(address userAddress) external onlyVerifier { require(users[userAddress].owner != address(0), "Gebruiker niet geregistreerd"); users[userAddress].verified = true; } // Gebruiker geeft toestemming aan een verificatie-instantie function grantPermission(address verifier) external { require(users[msg.sender].owner == msg.sender, "Niet de eigenaar"); users[msg.sender].permissions[verifier] = true; } // Verificatie-instantie kan de verificatiestatus opvragen function checkVerification(address userAddress) external view returns (bool) { require(users[userAddress].permissions[msg.sender], "Geen toestemming"); return users[userAddress].verified; } // Beperkt toegang tot gevoelige functies address public verifier; // Verificatietrust modifier onlyVerifier() { require(msg.sender == verifier, "Geen verificator"); _; } // Instellen verificator function setVerifier(address _verifier) external { // Beheer alleen door eigenaar (niet geïllustreerd voor eenvoud) verifier = _verifier; } } ``` --- ### Belangrijkste functies en beveiligingsmaatregelen - **Registratie zonder opslag van privégegevens**: Alleen een hash wordt opgeslagen, niet de werkelijke gegevens. - **Toestemming en controle**: Gebruikers bepalen wie hun verificatiestatus kan opvragen. - **Beveiliging tegen reentrancy en overflow**: Gebruik van Solidity 0.8+ die ingebouwde overflowcontrole bevat. - **Access control**: Alleen geautoriseerde verificatie-instanties kunnen de verificatiestatus aanpassen. - **Gebruik van `require`-statement**: Voorkomt ongeldige operaties. --- ### Beste praktijken voor gegevensbescherming 1. **Gebruik hashes**: Sla geen gevoelige gegevens op; sla alleen hashes die off-chain kunnen worden gevalideerd. 2. **Off-chain opslag**: Bewaar privégegevens veilig buiten de blockchain, bijvoorbeeld in een IPFS of een beveiligde database. 3. **Pseudonimiteit**: Gebruik pseudoniemen of cryptografische identificaties. 4. **Toestemming en controle**: Laat gebruikers expliciet toestemming geven voor elke toegang. 5. **Encryptie**: Overweeg encryptie van off-chain gegevens en deel decryptiesleutels alleen onder strikte voorwaarden. --- ### Voorbeeld: Gebruikersvalideren zonder privégegevens bloot te geven - Gebruiker genereert een hash van hun privégegevens (bijvoorbeeld een hash van een rijbewijs). - Ze registreren deze hash op de blockchain. - Verificatie-instanties controleren de gegevens off-chain en geven de verificatie status door. - Iedereen kan de verificatie-status opvragen, maar niet de privégegevens zelf. **Voorbeeld workflow:** 1. Gebruiker maakt een hash van hun rijbewijs: `keccak256(abi.encodePacked("Gebruikersgegevens"))`. 2. Ze registreren deze hash via `register()`. 3. Een verificatie-instantie valideert de gegevens off-chain. 4. Ze roepen `verify()` aan om de gebruiker te verifiëren. 5. Andere partijen kunnen `checkVerification()` gebruiken om te zien of de gebruiker bevestigd is. --- ### Conclusie Dit ontwerp biedt een basis voor een veilig, schaalbaar en privacybewust gedecentraliseerd identiteitsverificatiesysteem. Door hashes te gebruiken, off-chain opslag te combineren met on-chain verificatie en strikte toestemming, bescherm je privacy en verbeter je de controle voor gebruikers. --- Heeft u verdere wensen of specifieke functies die u wilt toevoegen?

Of course. Here is a comprehensive design and implementation for a decentralized identity verification system in Solidity, focusing on security, privacy, and scalability. ### System Overview: "VeriDID" (Verifiable Decentralized Identity) This system allows users to create a self-sovereign identity (a DID - Decentralized Identifier) on the blockchain. Third-party verifiers (e.g., a bank, a rental service) can request proof of certain claims (e.g., "is over 18", "is a accredited investor") without the user revealing the underlying data. This is achieved using **cryptographic zero-knowledge proofs (ZKPs)** in a two-step process: off-chain proof generation and on-chain verification. --- ### 1. Key Features & Contract Design #### a) Registration Users register a unique Decentralized Identifier (DID). This acts as their identity anchor on the chain. It does not store personal data; it only points to where verifiable credentials are held (off-chain). #### b) Verification & Attestations Trusted entities (e.g., government agencies, known institutions), called **Issuers**, can create attestations for a user's DID. An attestation is a cryptographic signature on a piece of data (a "claim"), like a hash of a passport number plus a validity expiration date. #### c) Data Privacy (The Core Principle) **No private data is ever stored on the public blockchain.** The blockchain only stores: * Public DIDs. * The public addresses of trusted Issuers. * **Hashes** of claims (which are useless on their own). * **ZK-SNARK verifier contracts** or the public keys used to verify off-chain signatures. The actual credentials (passport data, age, etc.) are stored encrypted by the user on their own device or in a private storage solution (like IPFS or a personal cloud). #### d) Permission Management The contract uses an **access control pattern** to manage who can perform certain actions: * **DEFAULT_ADMIN_ROLE:** Can add/remove Issuers. * **ISSUER_ROLE:** Trusted entities allowed to issue attestations. * The user themselves are the ultimate owners of their DID and control which verifiers can see their attestations. --- ### 2. Solidity Smart Contract Code This example uses the OpenZeppelin contracts library for security and standard implementations. ```solidity // SPDX-License-Identifier: MIT pragma solidity ^0.8.19; import "@openzeppelin/contracts/access/AccessControl.sol"; import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol"; import "@openzeppelin/contracts/utils/cryptography/EIP712.sol"; contract VeriDID is AccessControl, EIP712 { using ECDSA for bytes32; // Define roles for access control bytes32 public constant ISSUER_ROLE = keccak256("ISSUER_ROLE"); // EIP-712 typehash for structured data signing (for attestations) bytes32 private constant _ATTESTATION_TYPEHASH = keccak256("Attestation(address subject,bytes32 claimHash,uint256 expiresAt)"); // Struct to hold a signed attestation from an Issuer struct Attestation { bytes32 claimHash; // hash of the claim (e.g., keccak256(abi.encodePacked(passportNumber, "isOver18:true"))) uint256 expiresAt; // Unix timestamp when this attestation becomes invalid bytes signature; // Signature from the Issuer } // Mapping from user address => Issuer address => attestation mapping(address => mapping(address => Attestation)) public attestations; // Events for off-chain clients to listen to event DIDRegistered(address indexed user); event AttestationIssued(address indexed issuer, address indexed subject, bytes32 claimHash, uint256 expiresAt); event AttestationRevoked(address indexed issuer, address indexed subject); // Constructor sets up the admin and EIP-712 domain separator constructor() EIP712("VeriDID", "1") { _grantRole(DEFAULT_ADMIN_ROLE, msg.sender); _grantRole(ISSUER_ROLE, msg.sender); // Admin is also an issuer for demo } // Users can register their DID (which is just their address) function registerDID() external { // In a real system, you might check if it's already registered emit DIDRegistered(msg.sender); } // **ISSUER FUNCTION**: Issue an attestation for a user (subject) function issueAttestation(address subject, bytes32 claimHash, uint256 expiresAt, bytes calldata signature) external onlyRole(ISSUER_ROLE) { // Reconstruct the signed message hash according to EIP-712 bytes32 digest = _hashTypedDataV4( keccak256(abi.encode(_ATTESTATION_TYPEHASH, subject, claimHash, expiresAt)) ); // Recover the signer from the signature and digest address signer = ECDSA.recover(digest, signature); // Ensure the signature is from a valid issuer (could be any issuer, not necessarily msg.sender) require(hasRole(ISSUER_ROLE, signer), "VeriDID: Invalid signer"); // Store the attestation attestations[subject][signer] = Attestation(claimHash, expiresAt, signature); emit AttestationIssued(signer, subject, claimHash, expiresAt); } // **ISSUER FUNCTION**: Revoke an attestation they previously issued function revokeAttestation(address subject) external onlyRole(ISSUER_ROLE) { delete attestations[subject][msg.sender]; emit AttestationRevoked(msg.sender, subject); } // **VERIFIER FUNCTION**: Validate a user's attestation function validateAttestation( address issuer, address subject, bytes32 claimHash, uint256 expiresAt, bytes calldata signature ) external view returns (bool) { // 1. Check if the issuer is trusted if (!hasRole(ISSUER_ROLE, issuer)) { return false; } // 2. Check if the attestation is not expired if (expiresAt < block.timestamp) { return false; } // 3. Check the stored attestation matches the provided claim Attestation memory storedAttestation = attestations[subject][issuer]; if (storedAttestation.claimHash != claimHash) { return false; } // 4. Re-verify the signature on-chain for ultimate trust bytes32 digest = _hashTypedDataV4( keccak256(abi.encode(_ATTESTATION_TYPEHASH, subject, claimHash, expiresAt)) ); address signer = ECDSA.recover(digest, signature); return (signer == issuer); } } ``` --- ### 3. Best Practices for Protecting Private Data 1. **Hashing:** Never store raw data. Only store the `keccak256` hash of the data. Without the original data, the hash is cryptographically impossible to reverse. 2. **Zero-Knowledge Proofs (ZKPs):** For complex claims (e.g., "age > 18"), use ZK-SNARKs or ZK-STARKs. The user generates a proof off-chain that they have a valid attestation for a claim *without revealing the attestation itself*. The contract only needs to run a verifier function. This is the gold standard for privacy. 3. **Encryption Off-Chain:** All sensitive data should be encrypted by the user and stored off-chain (e.g., on their device, IPFS). The blockchain should only be used as a verification layer, not a storage layer. 4. **EIP-712 Structured Signing:** Used in the contract above, it allows users to sign human-readable messages in their wallets, preventing signature replay attacks across different contracts and providing a better user experience. 5. **Minimal On-Chain Data:** Strictly audit what is written to the blockchain. If a piece of data doesn't need to be public for verification, it shouldn't be on-chain. --- ### 4. Example: Validation Without Exposing Information **Scenario:** A user wants to prove to a liquor store's website (the Verifier) that they are over 21 without revealing their exact birthdate. 1. **Issuance (One-time):** * The user goes to the DMV (the trusted **Issuer**). * The DMV verifies their driver's license, confirming their age. * The DMV's app creates a claim: `"ageThreshold:21"`. * It hashes this claim: `claimHash = keccak256(abi.encodePacked("ageThreshold:21"))`. * The DMV signs a message (using EIP-712) containing the user's DID, the `claimHash`, and an expiration date (e.g., 1 year from now). * This signature (the **attestation**) is sent to the user and also published to the `VeriDID` contract via `issueAttestation`. 2. **Verification (At the liquor store website):** * The website asks the user, "Prove you are over 21." * The user's wallet holds the original signed attestation from the DMV. * The user's wallet software generates a **Zero-Knowledge Proof**. This proof cryptographically demonstrates: * "I possess a valid signature from the DMV (a trusted Issuer)." * "That signature is for a `claimHash` that matches `keccak256(abi.encodePacked("ageThreshold:21"))`." * "The attestation has not expired." * **Critically, the proof does not reveal the signature itself, the issuer's identity, or any other attestations the user might have.** * The user sends this proof to the liquor store's website. 3. **On-Chain Check:** * The website (or its smart contract) takes the ZKP and submits it to a specialized **Verifier Contract** on-chain that is pre-programmed to validate that specific ZKP. * The Verifier Contract runs a computation and returns `true` if the proof is valid, or `false` if it's not. * The website sees a `true` result and grants access, all without ever seeing the user's birthdate or even knowing which Issuer provided the attestation. This flow provides maximum privacy and security, making it the recommended architecture for a production-grade decentralized identity system. The `VeriDID` contract above provides the foundational on-chain registry and attestation anchor that makes this advanced flow possible.