Blockchain digital certificates system development

Development of Blockchain Digital Certificates System

Blockchain certificates solve main problem of traditional digital documents: verification. PDF diploma can be faked. Blockchain certificate is verified in seconds — anyone can check authenticity without contacting issuer.

System Architecture

Issuer (university, platform, company) issues certificate, signs and records hash on-chain.

Recipient gets certificate (PDF + JSON) and verification link.

Verifier (employer, another university) checks authenticity — document hash matches on-chain record.

On-Chain Storage: Hashes, Not Data

Storing full data on-chain is expensive and violates privacy. Correct approach: store only hash of certificate.

contract CertificateRegistry {
    mapping(bytes32 => CertificateRecord) public certificates;
    
    struct CertificateRecord {
        address issuer;
        uint256 issuedAt;
        bool revoked;
        string metadataURI;  // IPFS CID with metadata
    }
    
    event CertificateIssued(bytes32 indexed certHash, address indexed recipient, address indexed issuer);
    event CertificateRevoked(bytes32 indexed certHash);
    
    function issueCertificate(
        bytes32 certHash,
        address recipient,
        string calldata metadataURI
    ) external onlyAuthorizedIssuer {
        require(certificates[certHash].issuedAt == 0, "Already issued");
        
        certificates[certHash] = CertificateRecord({
            issuer: msg.sender,
            issuedAt: block.timestamp,
            revoked: false,
            metadataURI: metadataURI
        });
        
        emit CertificateIssued(certHash, recipient, msg.sender);
    }
    
    function verifyCertificate(bytes32 certHash) external view 
        returns (bool valid, address issuer, uint256 issuedAt) {
        CertificateRecord memory record = certificates[certHash];
        valid = record.issuedAt > 0 && !record.revoked;
        issuer = record.issuer;
        issuedAt = record.issuedAt;
    }
}

Blockcerts Standard

Blockcerts — open standard for blockchain certificates (MIT + Learning Machine). Describes JSON-LD format and verification process.

{
    "@context": ["https://www.w3.org/2018/credentials/v1", "https://w3id.org/blockcerts/v3"],
    "type": ["VerifiableCredential", "BlockcertsCredential"],
    "issuer": "did:ethr:0xIssuerAddress",
    "issuanceDate": "2024-01-15T00:00:00Z",
    "credentialSubject": {
        "id": "did:ethr:0xRecipientAddress",
        "achievement": {
            "name": "Bachelor of Computer Science"
        }
    },
    "proof": {
        "type": "MerkleProof2019",
        "merkleRoot": "0xabc123",
        "txId": "0xTransactionHash",
        "targetHash": "0xCertificateHash"
    }
}

Batch Issuance via Merkle Tree

Issue 1000 diplomas in one transaction:

Merkle tree from hashes of all certificates. Only merkle root stored on-chain. Each certificate contains merkle proof — path from leaf to root. Verification: compute certificate hash → check merkle proof → compare with on-chain root.

Savings: 1 transaction instead of 1000. Verification cost — local computations.

Development of digital certificates system — 3-6 weeks for basic system with web UI for issuance and verification.