Setting Up a Decentralized Identity System for Trial Participants

Decentralized identity (DID) systems, built on self-sovereign identity (SSI) principles, offer a paradigm shift for clinical trial management. Instead of creating isolated accounts on each research portal, participants can use a single, cryptographically secure digital wallet to hold their identity credentials. This wallet, often a mobile app, stores verifiable credentials (VCs) issued by trusted entities like hospitals or regulatory bodies. These credentials can prove attributes—such as age, diagnosis, or location—without revealing the underlying personal data, enabling selective disclosure and reducing redundant data collection across studies.

The core technical components are defined by W3C standards. A Decentralized Identifier (DID) is a unique URI that points to a DID document on a distributed ledger (e.g., Ethereum, Hyperledger Indy). This document contains public keys and service endpoints for authentication. When a trial sponsor needs to verify a participant's eligibility, they request a verifiable presentation. The participant's wallet uses the private key associated with their DID to cryptographically sign and present only the required credentials from issuers, proving their validity without contacting the issuer in real-time.

Setting up this system begins with selecting a DID method and ledger. For clinical trials prioritizing permissioned control, Hyperledger Indy with the did:indy method is common. For interoperability with public Web3 ecosystems, did:ethr (Ethereum) or did:polygonid (Polygon) are strong choices. The participant's first step is wallet creation, which generates a DID and a master seed. This is often done via a mobile SDK like Trinsic's or Microsoft's ION. Code for generating a did:ethr identifier using the ethr-did library looks like this:

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const { EthrDID } = require('ethr-did');
const keypair = EthrDID.createKeyPair();
const participantDID = new EthrDID({...keypair, chainNameOrId: 'mainnet'});
console.log('DID:', participantDID.did);

The next phase is credential issuance. A research institution, acting as an issuer, must also have a DID. They create a verifiable credential schema defining the attributes (e.g., "diagnosisCode": "E11.9"). Using their issuer DID to sign, they issue the credential to the participant's DID. The participant stores this signed credential in their wallet. The JSON-LD format ensures credentials are machine-readable and linked-data compatible. Crucially, the credential's cryptographic proof allows any verifier (like a trial sponsor) to check its authenticity and that it hasn't been revoked, typically by checking a revocation registry on the ledger.

For the clinical trial application, the sponsor defines the presentation request. This is a query specifying the required credentials (e.g., "Proof of diagnosis X from an accredited hospital, and age > 18"). The participant's wallet receives this request, locates the matching credentials, and creates a verifiable presentation. This bundles the credentials with a proof signed by the participant's DID, demonstrating consent. The sponsor's backend verifies the presentation's signatures and checks revocation status. This flow enables compliant, automated eligibility checks while minimizing data exposure and central points of failure.

Key considerations for implementation include GDPR/ HIPAA compliance through data minimization, selecting ledger scalability solutions for high-volume trials, and ensuring wallet usability for non-technical participants. Projects like EBSI (European Blockchain Services Infrastructure) and IDunion provide governance frameworks and test networks for healthcare DIDs. By adopting this architecture, research organizations can reduce onboarding friction, enhance auditability, and empower participants with true control over their clinical data across multiple studies.

Building a decentralized identity (DID) system for clinical trials requires a foundational understanding of core Web3 technologies. The primary prerequisites include a working knowledge of public-key cryptography for participant key management, familiarity with decentralized identifiers (DIDs) and verifiable credentials (VCs) as defined by the W3C standards, and experience with a smart contract platform like Ethereum, Polygon, or a dedicated appchain. You'll need development tools such as Node.js, a code editor, and a wallet like MetaMask for testing. This guide assumes you are comfortable with concepts like blockchain transactions, gas fees, and interacting with JSON-RPC endpoints.

The system architecture for a trial participant DID system is multi-layered. At its core is the blockchain layer, which serves as the decentralized root of trust. This is where participant DIDs are anchored, typically as smart contracts or on-chain registries, and where critical attestations from authorized issuers (like trial sponsors or regulatory bodies) are immutably recorded. The off-chain storage layer, often using solutions like IPFS or Ceramic Network, holds the bulk of the credential data (e.g., medical history, consent forms) to maintain privacy and scalability, with only content-addressed hashes stored on-chain.

The application logic layer consists of the smart contracts that govern the system's rules. Key contracts include a DID Registry for creating and resolving participant identifiers, a Credential Schema Registry to define the structure of verifiable credentials (e.g., "Trial Eligibility Credential"), and an Attestation Registry where authorized issuers post proofs of issued credentials. These contracts enforce permissions, ensuring only accredited institutions can issue credentials related to trial participation or medical data.

Finally, the user-facing layer involves the wallets and agents that participants and verifiers use. Participants need a self-sovereign identity wallet (e.g., based on MetaMask Snaps or WalletConnect) to store their private keys, manage their DIDs, and hold received VCs. Verifiers, such as trial site administrators, use a verification service or SDK to cryptographically check the validity of a participant's credentials against the on-chain registries without accessing the underlying private data, enabling privacy-preserving eligibility checks.

We will build a system where a Trial Sponsor issues verifiable credentials to Participants, who can then store them in a personal Identity Wallet and present selective proofs to Verifiers (e.g., research sites). The core components are: an Ethereum smart contract for managing decentralized identifiers (DIDs), IPFS for credential storage, and the W3C Verifiable Credentials standard for data modeling. We'll use Hardhat for development, ethers.js for blockchain interaction, and @veramo/core for credential handling. The goal is to create a tamper-proof, privacy-preserving record of trial eligibility and participation.

First, set up the project and define the DID Registry smart contract. This contract will map a participant's Ethereum address to their DID document URI, which points to metadata stored on IPFS. Run npx hardhat init to create a project. In contracts/DIDRegistry.sol, implement a simple registry with a registerDID function that stores a bytes32 hash of the DID document content. Use OpenZeppelin's Ownable for access control so only the sponsor can register DIDs. Deploy the contract to a testnet like Sepolia using a Hardhat script, and verify the source code on Etherscan for transparency.

Next, create the credential issuance logic. The sponsor's backend will use the Veramo framework. Install @veramo/core, @veramo/credential-w3c, and @veramo/data-store. Configure Veramo with a DID provider (like did:ethr) and a key management system. To issue a credential, the sponsor creates a Verifiable Credential JSON object following the W3C model, with claims like trialId, participantDID, eligibilityStatus, and issuanceDate. Sign the credential using the sponsor's private key, resulting in a Verifiable Presentation ready for the participant. Store the signed credential JSON on IPFS via a service like Pinata or nft.storage, and record the resulting Content Identifier (CID) on-chain.

The participant's wallet application must be able to receive and store credentials. Build a simple React frontend with wagmi and viem for wallet connection. Use the @veramo/credential-w3c package to create a CredentialPlugin instance in the wallet. When a participant connects their wallet (e.g., MetaMask), the app listens for CredentialOffer events from the smart contract. Upon receiving a credential payload (the IPFS CID), the wallet fetches the JSON from IPFS, verifies the sponsor's cryptographic signature, and stores the credential securely in the user's local IndexedDB via Veramo's data store. The private key for the participant's did:ethr DID is managed securely within the wallet.

Finally, implement selective disclosure for verification. A research site (verifier) needs to confirm a participant's eligibility without seeing their full identity or other credentials. Using Zero-Knowledge Proofs (ZKPs) is ideal, but for simplicity, we can use JSON-LD signature suites with selective disclosure. The participant's wallet can generate a Verifiable Presentation that reveals only specific fields, like a proof of eligibility for Trial NCT-0458 without revealing their birth date. The verifier's backend uses Veramo's verifyCredential() method to check the signature and the credential's status (ensuring it hasn't been revoked on-chain). This completes a functional, privacy-focused loop for decentralized identity in clinical trials.

Decentralized identity (DID) systems provide a privacy-preserving framework for managing participant credentials in clinical trials. Unlike centralized databases, a DID system allows participants to own and control their identity data, sharing only verifiable claims with trial sponsors or regulators. This is achieved through a combination of on-chain registries for public keys and off-chain verifiable credentials (VCs) signed by issuers like accredited research institutions. The core smart contract functions as a permissioned registry, mapping a participant's unique DID (e.g., did:ethr:0x123...) to their public key and a list of authorized issuers, establishing a trust anchor without storing personal health information on-chain.

To set up the system, you first deploy a TrialIdentityRegistry smart contract. This contract manages the lifecycle of participant DIDs and controls which entities (e.g., PrincipalInvestigator or RegulatoryBody) are authorized to issue credentials. A participant's identity is created by calling a function like createIdentity(address participant, bytes32 didDocumentHash), which registers their Ethereum address and a hash of their initial DID document. The contract should implement role-based access control using a library like OpenZeppelin's AccessControl to ensure only authorized admins can register new issuers or revoke compromised identities, maintaining the system's integrity.

Participants interact with the system using a wallet that supports the did:ethr method, such as MetaMask with identity extensions. When a participant joins a trial, an issuer (like a trial site) creates a Verifiable Credential off-chain. This JSON-LD document contains claims (e.g., "isEnrolled": true, "trialId": "NCT12345678") and is cryptographically signed using the issuer's private key. The participant stores this VC in their digital wallet. To prove eligibility for an on-chain action—like claiming a participation reward—the participant presents the VC and generates a zero-knowledge proof or a simple signature that the smart contract can verify against the issuer's registered public key in the TrialIdentityRegistry.

A critical integration point is linking the DID system to the main trial management smart contract, which handles randomization, drug supply, and data logging. This contract, let's call it TrialManager, must check participant eligibility before recording key events. It does this by calling a verification function on the TrialIdentityRegistry. For example, a function to log a participant visit might include a modifier:

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modifier onlyEnrolledParticipant(bytes32 did, bytes memory signature) {
    require(identityRegistry.verifyCredential(did, "isEnrolled", true, signature), "Not enrolled");
    _;
}

This pattern ensures that only identities with valid, unrevoked enrollment credentials can interact with sensitive trial functions.

For developers, key considerations include selecting the appropriate DID method (like did:ethr for Ethereum or did:polygonid for Polygon), managing gas costs for registry updates, and designing a secure credential revocation process. The TrialIdentityRegistry should emit events for all major actions (IdentityCreated, IssuerAdded, CredentialRevoked) to enable off-chain monitoring and auditing. By implementing this architecture, you create a foundational layer of trust and compliance for decentralized clinical trials, enabling participant privacy, regulatory auditability, and seamless integration with other on-chain trial modules for consent management and data provenance.

This guide demonstrated a core workflow: issuing a ParticipantCredential as a Verifiable Credential (VC) to a participant's Decentralized Identifier (DID). The credential, signed with the issuer's private key, contains attested claims like participantId and trialPhase. The participant can store this credential in a secure digital wallet and present it to verifiers, such as a trial site portal, which can cryptographically verify its authenticity and integrity without contacting the original issuer. This creates a trust layer based on cryptography rather than centralized databases.

To move from a prototype to a production-ready system, several critical next steps are required. First, you must decide on a DID method and associated Verifiable Data Registry, such as the Ethereum mainnet for did:ethr, ION for did:ion, or a private Sidetree network. This determines where your DID Documents are anchored. Second, implement proper key management for your issuer DID, considering hardware security modules (HSMs) or cloud KMS solutions for production private keys. Third, design the participant's wallet experience, which could be a mobile app using React Native or a web-based wallet, ensuring it securely stores private keys and credentials.

Further development should focus on advanced credential features. Implement selective disclosure using technologies like BBS+ signatures to allow participants to reveal only specific claims (e.g., their eligibility status but not their full ID). Establish a revocation mechanism, such as a credential status list published to a registry, to handle cases where a participant withdraws consent or becomes ineligible. Finally, ensure your system complies with relevant regulations like GDPR and HIPAA by designing data minimization into credential schemas and providing clear participant consent flows.

For continued learning, explore the official specifications from the W3C Verifiable Credentials Working Group and the Decentralized Identity Foundation (DIF). Frameworks like Veramo (TypeScript/Node.js) and Aries Framework JavaScript provide robust, open-source toolkits for building agent-based identity systems. Experimenting with these tools on a test network is the best way to understand the full architecture of decentralized identity and its application to clinical trials and beyond.