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EIPS/eip-xxxx.md

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+---
+eip: 5107
+title: Name-bound Tokens
+description: A standard interface for non-separable non-fungible tokens, also known as "Name-bound" or "soulbound tokens" or "badges"
+author: Tim Daubenschütz (@TimDaub), Tom Cohen (@TheWaler), Enrico Bottazzi (@enricobottazzi)
+discussions-to: https://ethereum-magicians.org/t/name-bound-tokens/9362
+status: Draft
+type: Standards Track
+category: ERC
+created: 2022-05-24
+requires: 137, 165, 721
+---
+
+## Abstract
+
+Proposes a standard API for Name-bound Tokens (NBT) within smart contracts. A NBT is a non-fungible token bound to a single ENS hashnode, and cannot be transferred between ENS names. This EIP defines basic functionality to gift, mint, and track NBTs.
+
+## Motivation
+
+The Ethereum community has expressed a need for non-transferrable, non-fungible tokens. While Account-bound tokens technically allow for a simple binding mechanism, their central mechanic discourages healthy key rotation routines.
+
+Common use cases for Name-bound tokens include tracking an individual's achievements (which can be used as credentials), or items that cannot be transferred (like certain loot in multiplayer online games).
+
+The purpose of this document is to make NBTs a reality on Ethereum by creating consensus around a **maximally backward-compatible** but otherwise **minimal** interface definition.
+
+## Specification
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
+
+`EIP-XXXX` tokens _must_ implement the interfaces:
+
+- [EIP-165](./eip-165.md)'s `ERC165` (`0x01ffc9a7`)
+- [EIP-721](./eip-721.md)'s `ERC721Metadata` (`0x5b5e139f`)
+
+`EIP-XXXX` tokens _must not_ implement the interfaces:
+
+- [EIP-721](./eip-721.md)'s `ERC721` (`0x80ac58cd`)
+
+```solidity
+// SPDX-License-Identifier: CC0-1.0
+pragma solidity ^0.8.6;
+
+/// @title Name-bound tokens
+/// @dev See https://eips.ethereum.org/EIPS/eip-XXXX
+///  Note: the ERC-165 identifier for this interface is 0x6352211e.
+interface IERCXXXX /* is ERC165, ERC721Metadata */ {
+  /// @dev This emits when ownership between ENS nodes of any NBT changes by any mechanism.
+  ///  This event emits when NBTs are created (`from` == 0x0) and destroyed
+  ///  (`to` == 0x0).
+  event Transfer(bytes32 indexed _from, bytes32 indexed _to, uint256 indexed _id);
+  /// @notice Find the owner of an NBT
+  /// @dev NBTs assigned to empty string namehash ('') are considered invalid, and queries
+  ///  about them do throw.
+  /// @param _tokenId The identifier for an NFT
+  /// @return The address of the owner of the NFT
+  function ownerOf(uint256 _tokenId) external view returns (bytes32);
+}
+```
+
+See [`EIP-721`](./eip-721.md) for a definition of its metadata JSON Schema.
+
+## Rationale
+
+### Interface
+
+`EIP-XXXX` shall be maximally backward-compatible but still only expose a minimal and simple to implement interface definition.
+
+As [`EIP-721`](./eip-721.md) tokens have seen widespread adoption with wallet providers and marketplaces, using its `ERC721Metadata` interface with [`EIP-165`](./eip-165.md) for feature-detection potentially allows implementers to support `EIP-XXXX` tokens out of the box.
+
+If an implementer of [`EIP-721`](./eip-721.md) properly built [`EIP-165`](./eip-165.md)'s `function supportsInterface(bytes4 interfaceID)` function, already by recognizing that [`EIP-721`](./eip-721.md)'s track and transfer interface component with the identifier `0x80ac58cd` is not implemented, transferring of a token should not be suggested as a user interface option.
+
+Still, however, since `EIP-XXXX` supports [`EIP-721`](./eip-721.md)'s `ERC721Metadata` extension, an account-bound token should be displayed in wallets and marketplaces with no changes needed.
+
+### Provenance Indexing
+
+NBTs can be indexed by tracking the emission of `event Transfer(bytes32 indexed _from, bytes32 indexed _to, uint256 indexed _id)`.
+
+We recommend implementers to validate `Transfer`'s `_from` field by comparing it to the transaction-level `_from` field to mitigate "sleepminting" attacks.
+
+## Backwards Compatibility
+
+We have adopted the [`EIP-165`](./eip-165.md) and `ERC721Metadata` functions purposefully to create a high degree of backward compatibility with [`EIP-721`](./eip-721.md). We have deliberately used [`EIP-721`](./eip-721.md) terminology such as `function ownerOf(...)` and `event Transfer` to minimize the effort of familiarization for `EIP-XXXX` implementers already familiar with, e.g., [`EIP-20`](./eip-20.md) or [`EIP-721`](./eip-721.md).
+
+## Copyright
+
+Copyright and related rights waived via [CC0](../LICENSE.md).