forked from DecentralizedClimateFoundation/DCIPs
72 lines
3.3 KiB
Markdown
72 lines
3.3 KiB
Markdown
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---
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eip: 5192
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title: Minimal Soulbound NFTs
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description: Minimal interface for soulbinding EIP-721 NFTs
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author: Tim Daubenschütz (@TimDaub), Anders (@0xanders)
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discussions-to: https://ethereum-magicians.org/t/eip-5192-minimal-soulbound-nfts/9814
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status: Final
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type: Standards Track
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category: ERC
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created: 2022-07-01
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requires: 165, 721
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---
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## Abstract
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This standard is an extension of [EIP-721](./eip-721.md). It proposes a minimal interface to make tokens soulbound using the feature detection functionality of [EIP-165](./eip-165.md). A soulbound token is a non-fungible token bound to a single account.
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## Motivation
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The Ethereum community has expressed a need for non-transferrable, non-fungible, and socially-priced tokens similar to World of Warcraft’s soulbound items. But the lack of a token standard leads many developers to simply throw errors upon a user's invocation of transfer functionalities. Over the long term, this will lead to fragmentation and less composability.
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In this document, we outline a minimal addition to [EIP-721](./eip-721.md) that allows wallet implementers to check for a token contract's permanent (non-)transferability using [EIP-165](./eip-165.md).
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## Specification
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The keywords "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.
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### Contract Interface
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A token with a `uint256 tokenId` may be bound to a receiving account with `function locked(...)` returning `true`. In this case, all [EIP-721](./eip-721.md) functions of the contract that transfer the token from one account to another must throw.
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```solidity
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// SPDX-License-Identifier: CC0-1.0
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pragma solidity ^0.8.0;
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interface IERC5192 {
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/// @notice Emitted when the locking status is changed to locked.
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/// @dev If a token is minted and the status is locked, this event should be emitted.
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/// @param tokenId The identifier for a token.
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event Locked(uint256 tokenId);
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/// @notice Emitted when the locking status is changed to unlocked.
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/// @dev If a token is minted and the status is unlocked, this event should be emitted.
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/// @param tokenId The identifier for a token.
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event Unlocked(uint256 tokenId);
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/// @notice Returns the locking status of an Soulbound Token
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/// @dev SBTs assigned to zero address are considered invalid, and queries
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/// about them do throw.
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/// @param tokenId The identifier for an SBT.
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function locked(uint256 tokenId) external view returns (bool);
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}
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```
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To aid recognition that an [EIP-721](./eip-721.md) token implements "soulbinding" via this EIP upon calling [EIP-721](./eip-721.md)'s `function supportsInterface(bytes4 interfaceID) external view returns (bool)` with `interfaceID=0xb45a3c0e`, a contract implementing this EIP must return `true`.
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## Rationale
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The above model is the simplest possible path towards a canonical interface for Soulbound tokens. It reflects upon the numerous Soulbound token implementations that simply revert upon transfers.
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## Backwards Compatibility
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This proposal is fully backward compatible with [EIP-721](./eip-721.md).
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## Security Considerations
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There are no security considerations related directly to the implementation of this standard.
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## Copyright
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Copyright and related rights waived via [CC0](../LICENSE.md).
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