In smart contracts, we will need methods to handle cryptographic attestations to a users identifier or abilities. Let’s say we have a real estate agent, KiwiRealtors, that provides an “expression of interest” function though a smart contract and requires the users to provide an attestation that they are a resident of New Zealand or Australia, as a legal requirement. This has actually happened in the New Zealand property market and it is the perfect example of a need to handle such attestations.

However, it is not practical for a smart contract to explicitly trust an attestation issuer. There are multiple issuers who can provide an attestation to a person’s residency - a local Justice of the Peace, the land title office, local police, passport authority etc. We envision a model where the effort to manage the list of qualified issuers is practically outsourced to a list.

Anyone can publish a list of issuers. Only the most trusted and carefully maintained lists gets popular use.


This ERC provides a smart contract interface for anyone to manage a list of attestation issuers. A smart contract would explicitly trust a list, and therefore all attestations issued by the issuers on the list.

Draft implementation

    /* The purpose of this contract is to manage the list of attestation
     * issuer contracts and their capacity to fulfill requirements
 contract ManagedListERC
      /* a manager is the steward of a list. Only he/she/it can change the
       * list by removing/adding attestation issuers to the list.

       * An issuer in the list is represented by their contract
       * addresses, not by the attestation signing keys managed by such a
       * contract.
      struct List
	      string name;
	      string description; // short description of what the list entails
	      string capacity; // serves as a filter for the attestation signing keys
	  /* if a smart contract specifies a list, only attestation issued
	   * by issuers on that list is accepted. Furthermore, if that
	   * list has a non-empty capacity, only attestations signed by a
	   * signing key with that capacity is accepted. */

	    address[] issuerContracts; // all these addresses are contracts, no signing capacity
	    uint expiry;

      // find which list the sender is managing, then add an issuer to it
      function addIssuer(address issuerContractAddress) public;

      //return false if the list identified by the sender doesn't have this issuer in the list
      function removeIssuer(address issuerContractAddress, List listToRemoveIssuerFrom) public returns(bool);

      /* called by services, e.g. Kiwi Properties or James Squire */
      /* loop through all issuer's contract and execute validateKey() on
       * every one of them in the hope of getting a hit, return the
       * contract address of the first hit. Note that there is an attack
       * method for one issuer to claim to own the key of another which
       * is mitigated by later design. */
       //loop through the issuers array, calling validate on the signingKeyOfAttestation
      function getIssuerCorrespondingToAttestationKey(bytes32 list_id, address signingKeyOfAttestation) public returns (address);

       /* for simplicity we use sender's address as the list ID,
	 * accepting these consequences: a) if one user wish to maintain
	 * several lists with different capacity, he or she must use a
	 * different sender address for each. b) if the user replaced the
	 * sender's key, either because he or she suspects the key is
	 * compromised or that it is lost and reset through special means,
	 * then the list is still identified by the first sender's
	 * address.

      function createList(List list) public;

      /* replace list manager's key with the new key */
      function replaceListIndex(List list, address manager) public returns(bool);


Click here to see an example implementation of this ERC

#1387 #1386