Is it available to have an application that is managed by single Entity?

Question

If For example Entity A wants to build a smart contract that manage a group of devices. But since each device uses pseudonym and he may change it later, is there any way to build the contract such that each device should have a certain address for a certain amount of Time ( month for example) and Is it available now in Etherum so that that Entity A can issue addresses for devices joining the smart contract ? Just thinking of a private application on the etherum controlled by a single entity and also also he would like to detect bad users

Answer 1

It would be better for the devices to have semi-permanent identifiers, their address, and then Entity A will have exclusive management control of a whitelist or similar access control system. The contract would reject interactions from unauthorized devices.

This is just a very quick sketch with some important concerns glossed over to illustrate the idea.

pragma solidity 0.4.25;

contract SimpleWhitelist {

    address public owner;
    mapping(address => bool) public isAuthorizedDevice;

    modifier onlyOwner {
        require(msg.sender==owner);
        _;
    }

    modifier onlyAuthorizedDevice {
        require(isAuthorizedDevice[msg.sender]);
        _;
    }

    constructor() public {
        owner = msg.sender;
    }

    function addOrRemoveDevice(address device, bool authorized) public onlyOwner {
        isAuthorizedDevice[device]=authorized;
    }

    function somethingDevicesDo() public onlyAuthorizedDevice {
        // contract rejects transaction unless the sender is whitelisted.
    }
}

Hope it helps.