💻Παράρτημα: ο κώδικας των Έξυπνων Συμβολαίων του Bluechain SSI

Περιεχόμενα:

1. Ολόκληρος ο κώδικας του PassportManager.sol smart contract

2. Ολόκληρος ο κώδικας του Migrations.sol smart contract

Υπενθυμίζουμε ότι οι τελευταίες εκδόσεις όλων των Έξυπνων Συμβολαίων του Bluechain SSI μπορούν πάντα να βρεθούν (και να σχολιαστούν!) στο δημόσιο GitHub directory μας: 🐈 https://github.com/d-sfounis/bluechain_SSI Όλα τα τελευταία νέα του project: Bluechain Self Sovereign Identity διατηρούνται στη σελίδα μας: 🌊 https://bluechain.tech/

1. Smart Contract: PassportManager

To PassportManager contract είναι το κύριο Έξυπνο Συμβόλαιο του συστήματος BluechainSSI. Ενσωματώνει όλες τις κύριες και βοηθητικές λειτουργίες που περιγράφησαν κατά το Reference της προηγούμενης ενότητας (📕 Αναλυτική λίστα μεθόδων & μεταβλητών (Reference)). Συνάμα, περιέχει εκτενή σχολιασμό μέσα στον ίδιο τον κώδικα ώστε να ενισχύεται η ανοικτότητα και η κατανοητικότητά του προς τον προγραμματιστή-αναγνώστη.

contracts/PassportManager.sol

/* SPDX-License-Identifier: GPL-3.0-or-later
 * Author: Dimitrios Sfounis, for Bluechain Social Cooperative Enterprise, Athens (GR), February 2021
 * Website: https://bluechain.tech
 * Project: European Self-Sovereign Identity on blockchain, intended for electronic Health records,
 *      Funded under the European Cohesion Fund's "Vouchers for Innovation" programme.
 */
pragma solidity >=0.8.0 <0.9;

contract PassportManager {
    /* Basic implementation of a user's identity: a Passport! */
    struct Passport {
        string flair_name; //User nickname. It's optional.
        //The controller (owner) of this passport instance.
        //Initially, it's the first user/deployer. This can change later on.
        address controller;
        //the main workhorse of this struct. This is a hashmap of
        //key-value pairs of keccak256 hashes of the (string)sha256 checksum of any identity file (say, a PDF certificate)
        //and a trust-score stored as a simple integer. The more people have voted to trust this particular document of your passport,
        //the higher the score is. Simple, right? Probably not...
        //bytes32 because keccak256, through the web3.eth lib, always produces 32 bytes (256 bits) of output.
        mapping(bytes32 => uint) identity_files;
        //Lookup table for the previous mapping, just so we don't ever have to deal with orphaned values.
        //#NOTE: If you self-destruct this contract, be sure to iterate over `identity_files` and delete all keys using this Lookup Table.
        mapping(bytes32 => bytes32) identity_files_LUT;
        //Also this helps for easy, O(1) search of whether an address is here or not: //#NOTE: DEPRECATED in v0.2.0
        //mapping(bytes32 => bool) identity_files_LUT_Bool;
        //Delegates of this passport and its contained identity files, able to control it too.
        //Disabling this for now, we'll see if we can circumvent delegation functionality as defined in the CALYSPSO paper by Kokkoris-Kogias.
        //address[] delegates;
    }
    
    //The main database of our user IDs. This hashtable stores key-value pairs of
    //address to (struct Passport) objects belonging to this smart contract's users.
    //bytes32 because keccak256, through the web3 library, always produces 32 bytes (256 bits) of output.
    //the public attribute just gives it an automatic getter. However, the getter only returns a tuple containing all atomic fields,
    //and not the actual data structure.
    mapping(address => Passport) public user_passports;
    //And the associated lookup table, for quick O(1) lookup:
    mapping(address => address) public user_passports_LUT;
    
    /* Debugging Events! Respect these, they'll save you headache(s) */
    event PassportInitialized(address passport_id, address by);
    event AddedIDFileToPassport(address passport_id, bytes32 hashed_file);
    event Voted(address passport_id, address voter);
    
    /* Helper function to check if a user has initialized/created a Passport before */
    function hasInitializedPassport(address addr) private view returns (bool) {
        //All these checks cumulatively mean that a passport has been properly initialized
        if(user_passports_LUT[addr] != address(0)){
            Passport storage p = user_passports[addr];
            
            if(p.controller != address(0)){
                return true;
            }
        }
        return false;
    }

    function initPassport(string memory nickname) public returns (string memory, address) {
        require(!(hasInitializedPassport(msg.sender)), "Your User Passport is already initialized!");
        //As taken by the Solidity docs:
        //We cannot use "Passport[campaignID] = Passport(beneficiary, goal, 0, 0)"
        //because the RHS creates a memory-struct "Passport" that contains a mapping.
        Passport storage p = user_passports[msg.sender];
        
        p.flair_name = nickname;
        p.controller = msg.sender;
        //Mark passport as initialized, and emit the event.
        user_passports_LUT[msg.sender] = msg.sender;
        
        emit PassportInitialized(user_passports_LUT[msg.sender], msg.sender);
        return (p.flair_name, p.controller);
    }
    
    function addIDFileToPassport(address passport_id, bytes32 id_file) public returns (address, bytes32, uint) {
        Passport storage p = user_passports[passport_id];
        require(hasInitializedPassport(passport_id));
        require(p.controller == msg.sender, "Sender/controller mismatch when accessing passport");
        require(p.identity_files_LUT[id_file] == "", "ID File is already contained in this Passport!");
        
        p.identity_files_LUT[id_file] = id_file;
        //trust-score == 1 means we've self-added this file and only us do trust it. In other words, this is a new, self-trusted-only doc.
        //#TODO: There's probably a better way to do this other than using magic numbers...
        p.identity_files[id_file] = 1;
        //Return all these for debugging and testing purposes. It's a tuple of (controller_address, identity_file_byte32hash, trust_score).
        emit AddedIDFileToPassport(passport_id, id_file);
        return (p.controller, p.identity_files_LUT[id_file], p.identity_files[id_file]);
    }
    
    //This function raises the trust score of a Passport, when a user vouches for it.
    //Only users with already initiated Passports, and therefore active members of the community, can vouch for other people's Passports.
    function voteForDocInPassport(address passport_id, bytes32 doc_id) public returns (address, bytes32, uint) {
        require(PassportExists(passport_id), "Passport_id does not exist!");
        require(passport_id != msg.sender, "You can't vote on the trust score of your own Passport's documents!");
        Passport storage p = user_passports[passport_id];
        require(DocExistsInPassport(p, doc_id), "Document doesn't exist in specified Passport!");
        require(hasInitializedPassport(msg.sender), "You have to have an active Passport yourself to vote on others!");
        //Everything ok, we found it. Raise its score by 1.
        p.identity_files[doc_id] = p.identity_files[doc_id] + 1;
        return (passport_id, doc_id, p.identity_files[doc_id]);
    }
    
    function PassportExists(address passport_id) private view returns (bool) {
        if(user_passports_LUT[passport_id] == address(0)){
            return false;
        }
        return true;
    }
    
    function DocExistsInPassport(Passport storage P, bytes32 doc_id) private view returns (bool) {
        if(P.identity_files_LUT[doc_id] == bytes32(0)){
            return false;
        }
        return true;
    }
    
    /* TODO 1: We need a voting function, to play with trust_scores of stored Passport documents */
    /* DONE! */
    /* TODO 2: We need a function to export DID documents and Verifiable Claims as per specification format. Possibly a view function, so it doesn't burn up gas */
    /* TODO 3: We need some failsafe against Orphaned Passports... */
    /* TODO 4: Currently, trust_scores of documents are handled like magic numbers. This is generally an anti-pattern, let's look into a better way of doing this. */ 
    /* TODO 5: The contract should maintain a list of Arbitrator addresses, for example Gnomon's address. Votes to documents from those addresses should give +100 score instead of just +1 */
        /* This is as per the CALYPSO paper where the Trust Committee is maintained as a separate group, and votes from them are stronger */
}

2. Smart Contract: Migrations

To Migrations contract και γενικά η λογική των "migrations over redeployments" αποτελεί εσωτερική σχεδιαστική επιλογή του ίδιου του Truffle. Στην ουσία, είναι τρόπος του Truffle να "βοηθάει" το σύστημά μας με το να κρατά ιστορικό των εκδόσεων του Bluechain SSI που έχουν ενεργοποιηθεί πάνω στο blockchain, και να αποφεύγει να ξανα-ενεργοποιεί κάτι όμοιο που ήδη έχει ξαναενεργοποιηθεί στο παρελθόν (σώζοντάς μας, έτσι, deployment costs).

Βρίσκουμε ελάχιστη χρησιμότητα σε αυτήν την αρχιτεκτονική. Μάλιστα, η Ομάδα μας αντιπαραθέτει τα πλεονεκτήματα που προσφέρει η χρήση Migrations με τα μειονεκτήματα του structure & debugging clutter που δημιουργούνται στο σύστημα μας, εξ'αιτίας αυτής. Πολλές φορές κατά την υλοποίηση του συστήματος χρειάστηκε να δαπανήσουμε περισσότερο χρόνο πάνω από τα logs μας, για να καταλάβουμε τί είναι irrelevant Migrations functionality και τι πραγματικά αφορούσε το PassportManager contract μας.

Για πληρότητα, ωστόσο, παραθέτουμε το smart contract και εδώ. Το συμβόλαιο είναι άρρηκτα συνδεδεμένο με τα migrations .js files στο directory ./migrations, όπου κρατείται στην ουσία το ιστορικό των μεταβολών και των ενεργοποιήσων των έξυπνων συμβολαίων του συστήματός μας.

contracts/Migrations.sol

// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity >=0.4.22 <0.9.0;

contract Migrations {
  address public owner = msg.sender;
  uint public last_completed_migration;

  modifier restricted() {
    require(
      msg.sender == owner,
      "This function is restricted to the contract's owner"
    );
    _;
  }

  function setCompleted(uint completed) public restricted {
    last_completed_migration = completed;
  }
}