eRLC iExec

1 Executive Summary

This report presents the results of our engagement with iExec to review the eRLC code base for KYC-enabled ERC-20 (ERC-677) tokens as well as the integration of these tokens with the iExec PoCo smart contracts.

The review was conducted by Shayan Eskandari and Nicholas Ward over the course of 10 person-days between January 4th and January 8th, 2021.

2 Scope

Our review focused on the commit hash b16266d4940f9cc695859a47c483485c48fbda66 for eRLC and the KYC additions to the PoCo delegate modules at commit hash 96a39c9d53668896321556d23351a4e79d4d46a8. Notably, the scope excluded the PoCo delegate mechanism itself and all other functionalities within the PoCo system. The complete list of files in scope for each repository can be found in the Appendix.

2.1 Objectives

Together with the iExec team, we identified the following priorities for our review:

  1. Ensure that the system is implemented consistently with the intended functionality, and without unintended edge cases.
  2. Identify known vulnerabilities particular to smart contract systems, as outlined in our Smart Contract Best Practices, and the Smart Contract Weakness Classification Registry.
  3. Assess the design and implementation of the eRLC token contract, including KYC access controls and deposit and withdrawal functionality.
  4. Review the addition of KYC-aware transfer hooks and authorization checks to the PoCo system.

3 Security Specification

This section describes, from a security perspective, the expected behavior of the system under review. It is not a substitute for documentation. The purpose of this section is to identify specific security properties that were validated by the audit team.

3.1 Actors

The relevant actors are listed below with their respective abilities:

eRLC Actors:


    • Manage KYC Admins
    • Initiate Snapshots of user balances snapshot
    • Claim any tokens sent to the eRLC contract (will be added to the admin’s balance)
    • Recover unintentional deposits of the underlying token (will be added to the admin’s balance)
  • KYC Admin (KYC_ADMIN_ROLE): kyc admin, manages kyc members

    • Grant and revoke KYC role to a set of addresses grantKYC , revokeKYC

    • Deposit, Withdraw, Receive, and Transfer tokens.
  • Anyone else:

    • Due to the verification of KYC in the ERC-677 _beforeTokenTransfer() callback, no account without the KYC_MEMBER_ROLE can perform any actions in the contract.

While it is an explicitly desired property of the system, it is important to note the ability of the KYC Admin to revoke KYC at any time, effectively freezing the funds for a given address.

3.2 Security Properties

The following is a non-exhaustive list of security properties that were verified in this audit:

  • eRLC as described in the Executive summary is mainly a KYC token, hence trusting the admins to act according to the regulations is a feature of the system. This includes but not limited to locking accounts (none-KYC members) from using the system, minting new tokens and claiming the extra tokens in the contract.
  • Only the KYC Admin can grant or revoke KYC approval
  • No address without the KYC_MEMBER_ROLE can deposit, transfer, or withdraw eRLC tokens
  • Tokens can be minted only on deposit of an equivalent amount of the underlying asset or by the Admin when claiming the excess balance of the eRLC contract via recover()
  • No amount of the underlying asset can be withdrawn from the eRLC contract without burning an equivalent amount of the eRLC token

4 Recommendations

4.1 Share status codes between ERC20KYC and IexecERC20CoreKYC

Both ERC20KYC and the PoCo system’s IexecERC20CoreKYC utilize the same status codes for ERC20KYC.detectTransferRestriction, with a status code of 0 indicating no restriction. To prevent future changes to these status codes from raising conflicts between the two definitions, it would be beneficial to define them in a single independent library or contract, perhaps as a solidity enum.


uint8 internal constant _RESTRICTION_OK               = uint8(0);
uint8 internal constant _RESTRICTION_MISSING_KYC_FROM = uint8(0x01);
uint8 internal constant _RESTRICTION_MISSING_KYC_TO   = uint8(0x02);


uint8 restrictionCode = m_baseToken.detectTransferRestriction(from, to, amount);
if (restrictionCode != uint8(0))

4.2 eRLC: Include Transfer(address,address,uint256,bytes) event  Acknowledged

The ERC-677 standard includes an event, Transfer(address,address,uint256,bytes), to be emitted from the transferAndCall() function. Including this event would prevent deviation from the token standard and make it easier to trace external calls from the token contract.

However, we believe ERC-677 to be under-specified in its current form, suggesting that deviation from the standard may not warrant a change if the event is currently excluded for other reasons. Simply making this deviation explicit in user-facing documentation may suffice.

4.3 eRLC: Require a delay period before granting KYC_ADMIN_ROLE  Acknowledged


The development team already has plans in place to use a TimelockController as the KYC_DEFAULT_ADMIN of the eRLC contract. We agree that this is a sufficient solution and has the additional benefit of avoiding unnecessary code complexity in the eRLC contract.

The KYC Admin has the ability to freeze the funds of any user at any time by revoking the KYC_MEMBER_ROLE. The trust requirements from users can be decreased slightly by implementing a delay on granting this ability to new addresses.

While the management of private keys and admin access is outside the scope of this review, the addition of a time delay can also help protect the development team and the system itself in the event of private key compromise.


Batch granting and revoking of the KYC_MEMBER_ROLE. These functions can only be called by the KYC_ADMIN_ROLE:


function grantKYC(address[] calldata accounts)
external virtual override
    for (uint256 i = 0; i < accounts.length; ++i)
        grantRole(KYC_MEMBER_ROLE, accounts[i]);

function revokeKYC(address[] calldata accounts)
external virtual override
    for (uint256 i = 0; i < accounts.length; ++i)
        revokeRole(KYC_MEMBER_ROLE, accounts[i]);

Appendix 1 - Files in Scope

This review covered the following files:

eRLC Repository:

File SHA-1 hash
ERC677.sol 9a187e76516e352fec834f2f77612b717e6d7bd1
KYC.sol e922130045a37dcd7ce791ac3566a08f6e3d1fbe
ERLC.sol da987bd06bda51a2b8a2b76d6e505a9ba61c25a7
ERLCTokenSwap.sol 20ad99f44374a4e9ed43e8cd245a83201455b5f2
ERC20KYC.sol 48b443f2127724e50b6c93e67f2b5c108a113ce2
Claimable.sol cf0ab5b6f255aa38a669032f791c6ed3089ca971
ERC20Softcap.sol d81ba880a2879360356f31ac2f117c6bdca6ea42
interfaces/IKYC.sol f8b8601a1bef3f8ee15b8697284e97c93397138e
interfaces/IERC20KYC.sol 9c2f0d2348444de354f5490ab47b4eec9e89904f
interfaces/IERC677Receiver.sol 55b4232894ca3cabb81433bf192da40fbeed54cd
interfaces/IERC677.sol 410c708e946bdaa845c8d263c2d5dbbeaf75bc86
interfaces/IERC1404.sol dad28efcd76127a3bc6a9cbcd74038e44a680ebc

PoCo Repository:

File SHA-1 hash
modules/delegates/IexecERC20CoreKYC.sol 6d516c02f71c1ff38970b8e246d133486a21804f
modules/delegates/IexecERC20DelegateKYC.sol 7b946cecff33f5bee80715103bb9f1def3c6f5c4
modules/delegates/IexecPoco1DelegateKYC.sol fa9e7ba731f11a5a58dcdf48a9a581f529ef1b72
modules/delegates/IexecEscrowTokenDelegateKYC.sol e221d94d3b248cc36c333da7a6c8c4b8a2015d41
modules/delegates/IexecPoco2KYCDelegate.sol 904a694194f47e43c3695949c45ae19c6bb82384

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