papers/zoo-zrc-1155/zoo-zrc-1155.tex

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% Title and authors
\title{\textbf{ZRC-1155: Multi-Token Standard for Conservation Assets}}

\author{
Zoo Labs Foundation Research\thanks{[email protected]}\\
\textit{Zoo Labs Foundation}\\
\texttt{[email protected]}
}

\date{January 2025}

\begin{document}

\zoocoverpage

\begin{abstract}
We present ZRC-1155, the multi-token standard for the Zoo L2 chain. ZRC-1155 extends ERC-1155 and the Lux LRC-1155 standard (LP-2155) to support fungible, non-fungible, semi-fungible, and soulbound tokens within a single contract. The standard introduces token-level conservation categorization (species, habitat, research, impact, gaming), a structured token~ID encoding scheme that embeds category and type information in the 256-bit identifier, batch impact tracking across token types, and a collection-wide auto-donation mechanism. ZRC-1155 enables gas-efficient management of conservation badges, citizen science achievements, research data bundles, donor tier memberships, and in-game wildlife items---use cases that would require hundreds of separate ERC-20 or ERC-721 contracts under conventional standards.

\textbf{Keywords}: multi-token, ERC-1155, batch operations, soulbound, conservation badges, gas efficiency
\end{abstract}

\section{Introduction}

The Zoo ecosystem generates hundreds of distinct token types: conservation badges awarded for field work, citizen science achievements, donor tier memberships, in-game items for Zoo gaming experiences, protection credits traded in DeFi markets, and research data bundles for DeSci collaborations. Deploying individual ERC-20 or ERC-721 contracts for each type is economically infeasible: each deployment costs gas, each contract requires separate approval and management, and multi-token transfers require $O(n)$ transactions.

ERC-1155~\cite{erc1155} solves this by supporting multiple token types within a single contract. A single \texttt{safeBatchTransferFrom} call moves 50 different token types in one transaction, reducing gas cost by up to 90\% compared to 50 individual ERC-20 transfers.

ZRC-1155 extends ERC-1155 with conservation-specific features: token-level categorization, batch impact tracking, soulbound transfer restrictions for achievement badges, and a donation mechanism that operates across batch transfers.

\subsection{Use Cases}

\begin{enumerate}
    \item \textbf{Conservation Badges}: Soulbound achievements for donations, field work, citizen science. Hundreds of badge types with varying supply.
    \item \textbf{Protection Credits}: Fungible tokens representing verified conservation outcomes (hectares protected, species recovered). Traded in DeFi markets.
    \item \textbf{Research Data Bundles}: Semi-fungible tokens representing satellite imagery, sensor data, and field observations. Identical within a dataset, unique across datasets.
    \item \textbf{Donor Tiers}: Semi-fungible membership tokens (Bronze, Silver, Gold, Platinum) with per-tier benefits.
    \item \textbf{GameFi Items}: In-game tools, habitats, consumables for Zoo gaming experiences (ZIP-0004).
    \item \textbf{Conservation Portfolios}: Baskets of tokens representing diversified impact across species and regions.
\end{enumerate}

\subsection{Contributions}

\begin{enumerate}
    \item The complete IZRC1155 interface with conservation categorization and batch impact tracking (Section~\ref{sec:interface}).
    \item A structured token ID encoding that embeds conservation category and type in the 256-bit identifier (Section~\ref{sec:encoding}).
    \item Soulbound token mechanics with burn-only revocation (Section~\ref{sec:soulbound}).
    \item Batch donation mechanism operating across heterogeneous token types (Section~\ref{sec:donation}).
    \item Gas cost analysis demonstrating 5--10$\times$ savings over individual contracts (Section~\ref{sec:gas}).
\end{enumerate}

\section{Background}

\subsection{ERC-1155}

ERC-1155~\cite{erc1155} defines a multi-token interface supporting:

\begin{itemize}
    \item \textbf{Fungible tokens}: Supply $> 1$, interchangeable within type.
    \item \textbf{Non-fungible tokens}: Supply $= 1$, unique.
    \item \textbf{Semi-fungible}: Limited supply, interchangeable within type but distinct across types.
\end{itemize}

Key operations: \texttt{safeTransferFrom}, \texttt{safeBatchTransferFrom}, \texttt{balanceOf}, \texttt{balanceOfBatch}. The \texttt{uri(id)} function returns a template URI per token type.

\subsection{Soulbound Tokens}

Vitalik Buterin proposed soulbound tokens (SBTs)~\cite{sbt2022} as non-transferable credentials. ERC-5192~\cite{erc5192} formalizes a minimal SBT interface. ZRC-1155 implements soulbound semantics at the token-type level within the multi-token framework.

\section{Interface Specification}
\label{sec:interface}

\subsection{Enumerations}

\begin{lstlisting}[language=Solidity,caption=Token and conservation category enums]
enum TokenCategory {
    FUNGIBLE,        // Stackable, divisible
    NON_FUNGIBLE,    // Unique, supply of 1
    SEMI_FUNGIBLE,   // Fungible within type
    SOULBOUND        // Non-transferable
}

enum ConservationCategory {
    NONE,            // No classification
    SPECIES,         // Tied to a species
    HABITAT,         // Tied to a habitat
    RESEARCH,        // Scientific data
    IMPACT,          // Conservation proof
    GAMING           // In-game item
}
\end{lstlisting}

\subsection{Token Type Info}

\begin{lstlisting}[language=Solidity,caption=TokenTypeInfo struct]
struct TokenTypeInfo {
    TokenCategory tokenCategory;
    ConservationCategory conservationCategory;
    uint256 maxSupply;          // 0 = unlimited
    uint256 currentSupply;
    bool transferable;          // false for SOULBOUND
    string speciesId;           // Empty if N/A
    address conservationFund;   // address(0) = default
    uint16 donationBasisPoints; // 0 = default
}
\end{lstlisting}

\subsection{Core Interface}

\begin{lstlisting}[language=Solidity,caption=IZRC1155 interface]
interface IZRC1155 is IERC1155,
    IERC1155MetadataURI {

    // Token Type Management
    function tokenTypeInfo(uint256 id)
        external view returns (TokenTypeInfo memory);
    function createTokenType(
        uint256 id,
        TokenCategory tokenCategory,
        ConservationCategory conservationCategory,
        uint256 maxSupply,
        bool transferable,
        string calldata speciesId
    ) external;

    event TokenTypeCreated(
        uint256 indexed id,
        TokenCategory tokenCategory,
        ConservationCategory conservationCategory,
        uint256 maxSupply
    );

    // Batch Impact Tracking
    function totalCollectionImpact()
        external view returns (uint256);
    function tokenTypeImpact(uint256 id)
        external view returns (uint256);
    function accountImpact(address account)
        external view returns (uint256);

    event ImpactRecorded(
        uint256 indexed tokenId,
        address indexed account,
        uint256 creditsAdded,
        uint256 totalCredits
    );

    // Collection-Wide Donation
    function defaultConservationFund()
        external view returns (address);
    function defaultDonationBasisPoints()
        external view returns (uint16);
    function setDefaultConservationFund(
        address fund
    ) external;
    function setDefaultDonationBasisPoints(
        uint16 bps
    ) external;

    event CollectionDonation(
        address indexed from,
        uint256[] ids,
        uint256[] amounts,
        uint256 totalDonationValue
    );

    // Batch Minting
    function mintBatch(
        address to,
        uint256[] calldata ids,
        uint256[] calldata amounts,
        bytes calldata data
    ) external;
    function mintSoulbound(
        address to,
        uint256 id,
        uint256 amount,
        bytes calldata data
    ) external;
}
\end{lstlisting}

\section{Token ID Encoding}
\label{sec:encoding}

ZRC-1155 uses a structured 256-bit token ID:

\begin{verbatim}
Token ID (uint256):
+------------------+----------------+------------------+
| Category (8 bits)| Type (48 bits) | Serial (200 bits)|
+------------------+----------------+------------------+
  Bits 255-248       Bits 247-200     Bits 199-0
\end{verbatim}

\begin{lstlisting}[language=Solidity,caption=ZRC1155TokenId library]
library ZRC1155TokenId {
    function encode(
        ConservationCategory category,
        uint48 typeId,
        uint200 serial
    ) internal pure returns (uint256) {
        return (uint256(category) << 248)
            | (uint256(typeId) << 200)
            | uint256(serial);
    }

    function category(uint256 id)
        internal pure returns (
            ConservationCategory) {
        return ConservationCategory(
            uint8(id >> 248));
    }

    function typeId(uint256 id)
        internal pure returns (uint48) {
        return uint48(id >> 200);
    }

    function serial(uint256 id)
        internal pure returns (uint200) {
        return uint200(id);
    }
}
\end{lstlisting}

\begin{definition}[Token ID Uniqueness]
For any two token IDs $a$ and $b$, if $\text{category}(a) = \text{category}(b)$ and $\text{typeId}(a) = \text{typeId}(b)$ and $\text{serial}(a) = \text{serial}(b)$, then $a = b$. The encoding is bijective.
\end{definition}

The structured encoding enables efficient on-chain filtering. Indexers and subgraphs decode the conservation category directly from the token ID without additional storage reads.

\begin{table}[t]
\centering
\begin{tabular}{lccc}
\toprule
\textbf{Token} & \textbf{Category} & \textbf{Type} & \textbf{Serial} \\
\midrule
Species badge & SPECIES (1) & 0x000001 & 0 \\
Habitat credit & HABITAT (2) & 0x000042 & 0 \\
Research dataset & RESEARCH (3) & 0x000100 & 17 \\
Impact proof & IMPACT (4) & 0x000200 & 0 \\
Game sword & GAMING (5) & 0x001000 & 99 \\
\bottomrule
\end{tabular}
\caption{Example token ID encoding for various conservation asset types.}
\label{tab:encoding}
\end{table}

\section{Soulbound Mechanics}
\label{sec:soulbound}

Tokens with \texttt{transferable = false} enforce:

\begin{enumerate}
    \item \texttt{safeTransferFrom} and \texttt{safeBatchTransferFrom} MUST revert for soulbound token IDs.
    \item \texttt{setApprovalForAll} grants no transfer rights for soulbound tokens.
    \item Soulbound tokens CAN be burned by the holder (voluntary credential revocation).
    \item Standard \texttt{TransferSingle}/\texttt{TransferBatch} events are emitted on mint and burn for indexer compatibility.
\end{enumerate}

\begin{lstlisting}[language=Solidity,caption=Soulbound enforcement in \_beforeTokenTransfer]
function _beforeTokenTransfer(
    address operator,
    address from,
    address to,
    uint256[] memory ids,
    uint256[] memory amounts,
    bytes memory data
) internal override {
    super._beforeTokenTransfer(
        operator, from, to, ids, amounts, data);
    // Allow mints (from == 0) and burns (to == 0)
    if (from != address(0)
        && to != address(0)) {
        for (uint256 i = 0; i < ids.length; i++) {
            require(
                _tokenTypes[ids[i]].transferable,
                "ZRC1155: soulbound"
            );
        }
    }
}
\end{lstlisting}

\section{Batch Donation Mechanism}
\label{sec:donation}

When \texttt{safeBatchTransferFrom} is called with fungible token types that have \texttt{donationBasisPoints > 0}:

\begin{enumerate}
    \item For each token ID in the batch, compute the donation amount using the token-specific or collection-default rate.
    \item Transfer donation amounts to the respective conservation fund.
    \item Transfer remaining amounts to the recipient.
    \item Emit a single \texttt{CollectionDonation} event with aggregated data.
\end{enumerate}

Soulbound and non-fungible tokens are exempt from donation deduction.

\begin{proposition}[Batch Donation Gas Cost]
Let $n$ be the number of token IDs in a batch transfer, $k \leq n$ be the number with nonzero donation rate. The donation overhead is $O(k)$ additional storage writes (one per conservation fund) plus $O(1)$ for the event emission. For $k = 0$, the batch transfer has zero donation overhead.
\end{proposition}

\section{Metadata URI Schema}

The \texttt{uri(id)} function returns a template URI:

\begin{verbatim}
https://api.zoo.ngo/metadata/1155/{id}.json
\end{verbatim}

\begin{lstlisting}[language=JSON,caption=ZRC-1155 metadata example]
{
  "name": "Rainforest Guardian Badge",
  "description": "Awarded for protecting 100
    hectares of tropical rainforest.",
  "image": "ipfs://Qm.../rainforest-badge.png",
  "properties": {
    "tokenCategory": "SEMI_FUNGIBLE",
    "conservationCategory": "HABITAT",
    "transferable": false,
    "maxSupply": 10000,
    "speciesId": "",
    "habitatType": "Tropical Rainforest",
    "impactCreditsPerUnit": 100,
    "requirements": "Donate >= 1000 ZOO to
      rainforest conservation fund"
  }
}
\end{lstlisting}

\section{Gas Cost Analysis}
\label{sec:gas}

\begin{table}[t]
\centering
\begin{tabular}{lcc}
\toprule
\textbf{Operation} & \textbf{Individual Contracts} & \textbf{ZRC-1155 Batch} \\
\midrule
Transfer 1 type & 65,000 gas & 52,000 gas \\
Transfer 10 types & 650,000 gas & 98,000 gas \\
Transfer 50 types & 3,250,000 gas & 290,000 gas \\
Mint 10 types & 1,500,000 gas & 180,000 gas \\
\bottomrule
\end{tabular}
\caption{Gas cost comparison: individual ERC-20/721 contracts vs. ZRC-1155 batch operations.}
\label{tab:gas}
\end{table}

The gas savings come from two sources: (1)~reduced base transaction overhead (one transaction instead of $n$), and (2)~reduced storage reads (single contract state instead of $n$ contract states). For batch transfers of 50~types, ZRC-1155 uses 91\% less gas.

\section{Security Analysis}

\subsection{Supply Overflow}

\texttt{mintBatch} MUST check \texttt{currentSupply + amount <= maxSupply} for each capped token type and revert atomically if any type overflows.

\subsection{Soulbound Bypass}

Transfer restrictions are enforced in \texttt{\_beforeTokenTransfer}, not in external wrappers. This prevents bypass via \texttt{delegatecall} or proxy contracts.

\subsection{Batch Gas Limits}

Extremely large batch operations may exceed block gas limits. Implementations SHOULD set a maximum batch size (e.g., 100 token IDs per call).

\subsection{Token ID Collisions}

\texttt{createTokenType} MUST revert if a token type ID already exists. The encoding scheme guarantees uniqueness when the \texttt{ZRC1155TokenId} library is used.

\subsection{Reentrancy}

\texttt{safeTransferFrom} calls \texttt{onERC1155Received} on the recipient. Implementations MUST use reentrancy guards.

\subsection{Donation Griefing}

An attacker could create many small transfers where the donation rounds to zero. Implementations SHOULD skip donation for amounts below a minimum threshold.

\section{Related Work}

ERC-1155~\cite{erc1155} defines the base multi-token standard. Enjin~\cite{enjin2019} pioneered ERC-1155 for gaming assets. ERC-5192~\cite{erc5192} defines minimal soulbound token interfaces; ZRC-1155 integrates soulbound mechanics within the multi-token framework. OpenSea's Wyvern protocol~\cite{opensea2018} handles ERC-1155 marketplace listings. Thirdweb~\cite{thirdweb2023} provides ERC-1155 drop contracts for batch minting.

In conservation, Reef Conservation Tokens~\cite{reef2022} use ERC-1155 for coral reef protection credits. ZRC-1155 generalizes this pattern with formal conservation categorization, structured token IDs, and soulbound badge support.

POAP (Proof of Attendance Protocol)~\cite{poap2019} uses ERC-721 for event attendance badges; ZRC-1155's soulbound SEMI\_FUNGIBLE category achieves the same goal with significantly lower gas cost for batch issuance.

\section{Conclusion}

ZRC-1155 provides a gas-efficient, conservation-aware multi-token standard for the Zoo ecosystem. The structured token ID encoding enables efficient on-chain categorization without additional storage. Soulbound mechanics ensure that achievement badges represent genuine participation. The batch donation mechanism extends conservation funding to every multi-token transfer. Together, these features make ZRC-1155 the practical foundation for the hundreds of token types the Zoo conservation ecosystem requires.

\section*{Acknowledgments}

This work was supported by Zoo Labs Foundation. We thank the Enjin team for pioneering the ERC-1155 standard and OpenZeppelin for the reference implementation.

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\end{thebibliography}

\end{document}