Attestation Contract Template B

pragma solidity ^0.4.24;

contract registry{
    struct Certificate {
        mapping(address => bool) attested;
        mapping(address => string) ipfsRootHash;
    }

    mapping(string => Certificate) certificates;

    function attest(string _hash, string _ipfsRootHash) public {
        Certificate storage currentCertificate = certificates[_hash];
        currentCertificate.attested[msg.sender] = true;
        currentCertificate.ipfsRootHash[msg.sender] = _ipfsRootHash;
    }

    function verify(string _hash) public view returns (bool) {
        return certificates[_hash].attested[msg.sender];
    }
    
    function getMetaData(string _hash) public view returns (string) {
        require(certificates[_hash].attested[msg.sender]);
        return certificates[_hash].ipfsRootHash[msg.sender];
    }
}