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ERC-735.md

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EIP: 735
Title: Claim Holder
Author: Fabian Vogelsteller (@frozeman)
Type: Standard
Category: ERC
Status: Discussion
Created: 2017-10-09

Abstract

The following describes standard functions for adding, removing and holding of claims. These claims can attested from third parties (issuers) or self attested.

Motivation

This standardised claim holder interface will allow Dapps and smart contracts to check the claims about a claim holder. Trust is here transfered to the issuers of claims.

Definitions

  • claim issuer: is another smart contract or external account, which issues claims about this identity. The claim issuer can be an identity contract itself.
  • claim: A claim is an information an issuer has about the identity holder. This contains the following:
    • topic: A uint256 number which represents the topic of the claim. (e.g. 1 biometric, 2 residence (ToBeDefined: number schemes, sub topics based on number ranges??))
    • scheme : The scheme with which this claim SHOULD be verified or how it should be processed. Its a uint256 for different schemes. E.g. could 3 mean contract verification, where the data will be call data, and the issuer a contract address to call (ToBeDefined). Those can also mean different key types e.g. 1 = ECDSA, 2 = RSA, etc. (ToBeDefined)
    • issuer: The issuers identity contract address, or the address used to sign the above signature. If an identity contract, it should hold the key with which the above message was signed, if the key is not present anymore, the claim SHOULD be treated as invalid. The issuer can also be a contract address itself, at which the claim can be verified using the call data.
    • signature: Signature which is the proof that the claim issuer issued a claim of topic for this identity. it MUST be a signed message of the following structure: keccak256(address identityHolder_address, uint256 _ topic, bytes data) // or keccak256(abi.encode(identityHolder_address, topic, data)) ?
    • data: The hash of the claim data, sitting in another location, a bit-mask, call data, or actual data based on the claim scheme.
    • uri: The location of the claim, this can be HTTP links, swarm hashes, IPFS hashes, and such.

Specification

Claim Holder

claim structure

The claims issued to the identity. Returns the claim properties.

struct Claim {
    uint256 topic;
    uint256 scheme;
    address issuer; // msg.sender
    bytes signature; // this.address + topic + data
    bytes data;
    string uri;
}

getClaim

Returns a claim by ID.

function getClaim(bytes32 _claimId) constant returns(uint256 topic, uint256 scheme, address issuer, bytes signature, bytes data, string uri);

getClaimIdsByTopic

Returns an array of claim IDs by topic.

function getClaimIdsByTopic(uint256 _topic) constant returns(bytes32[] claimIds);

addClaim

Requests the ADDITION or the CHANGE of a claim from an issuer. Claims can requested to be added by anybody, including the claim holder itself (self issued).

_signature is a signed message of the following structure: keccak256(address identityHolder_address, uint256 topic, bytes data).

Claim IDs are generated using keccak256(address issuer_address + uint256 topic).

This COULD implement an approval process for pending claims, or add them right away.

Possible claim topics:

  • 1: Biometric data
  • 2: Permanent address

(TODO: add more in the initial standard? 3: Claim registry?)

Returns claimRequestId: COULD be send to the approve function, to approve or reject this claim.

Triggers if the claim is new Event and approval process exists: ClaimRequested Triggers if the claim is new Event and is added: ClaimAdded Triggers if the claim index existed Event: ClaimChanged

function addClaim(uint256 _topic, uint256 _scheme, address _issuer, bytes _signature, bytes _data, string _uri) returns (uint256 claimRequestId)

removeClaim

Removes a claim. Can only be removed by the claim issuer, or the claim holder itself.

Triggers Event: ClaimRemoved

function removeClaim(bytes32 _claimId) returns (bool success)

Events

ClaimRequested

COULD be triggered when addClaim was successfully called.

event ClaimRequested(uint256 indexed claimRequestId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri)

ClaimAdded

MUST be triggered when a claim was successfully added.

event ClaimAdded(bytes32 indexed claimId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri))

ClaimRemoved

MUST be triggered when removeClaim was successfully called.

event ClaimRemoved(bytes32 indexed claimId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri))

ClaimChanged

MUST be triggered when changeClaim was successfully called.

event ClaimChanged(bytes32 indexed claimId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri)

Solidity Interface

pragma solidity ^0.4.18;

contract ERC735 {

    event ClaimRequested(uint256 indexed claimRequestId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri);
    event ClaimAdded(bytes32 indexed claimId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri);
    event ClaimRemoved(bytes32 indexed claimId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri);
    event ClaimChanged(bytes32 indexed claimId, uint256 indexed topic, uint256 scheme, address indexed issuer, bytes signature, bytes data, string uri);

    struct Claim {
        uint256 topic;
        uint256 scheme;
        address issuer; // msg.sender
        bytes signature; // this.address + topic + data
        bytes data;
        string uri;
    }

    function getClaim(bytes32 _claimId) public constant returns(uint256 topic, uint256 scheme, address issuer, bytes signature, bytes data, string uri);
    function getClaimIdsByTopic(uint256 _ topic) public constant returns(bytes32[] claimIds);
    function addClaim(uint256 _topic, uint256 _scheme, address _issuer, bytes _signature, bytes _data, string _uri) public returns (uint256 claimRequestId);
    changeClaim(bytes32 _claimId, uint256 _topic, uint256 _scheme, address _issuer, bytes _signature, bytes _data, string _uri) returns (bool success);
    function removeClaim(bytes32 _claimId) public returns (bool success);
}

Constraints

  • A claim can only be one per topic per issuer.

Additional References