ARC-200: Algorand Smart Contract Token Specification

Base specification for tokens implemented as smart contracts

Algorand Smart Contract Token Specification

Abstract

This ARC (Algorand Request for Comments) specifies an interface for tokens to be implemented on Algorand as smart contracts. The interface defines a minimal interface required for tokens to be held and transferred, with the potential for further augmentation through additional standard interfaces and custom methods.

Motivation

Currently, most tokens in the Algorand ecosystem are represented by ASAs (Algorand Standard Assets). However, to provide rich extra functionality, it can be desirable to implement tokens as smart contracts instead. To foster an interoperable token ecosystem, it is necessary that the core interfaces for tokens be standardized.

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.

Core Token specification

A smart contract token that is compliant with this standard MUST implement the following interface:

{
  "name": "ARC-200",
  "desc": "Smart Contract Token Base Interface",
  "methods": [
    {
      "name": "arc200_name",
      "desc": "Returns the name of the token",
      "readonly": true,
      "args": [],
      "returns": { "type": "byte[32]", "desc": "The name of the token" }
    },
    {
      "name": "arc200_symbol",
      "desc": "Returns the symbol of the token",
      "readonly": true,
      "args": [],
      "returns": { "type": "byte[8]", "desc": "The symbol of the token" }
    },
    {
      "name": "arc200_decimals",
      "desc": "Returns the decimals of the token",
      "readonly": true,
      "args": [],
      "returns": { "type": "uint8", "desc": "The decimals of the token" }
    },
    {
      "name": "arc200_totalSupply",
      "desc": "Returns the total supply of the token",
      "readonly": true,
      "args": [],
      "returns": { "type": "uint256", "desc": "The total supply of the token" }
    },
    {
      "name": "arc200_balanceOf",
      "desc": "Returns the current balance of the owner of the token",
      "readonly": true,
      "args": [
        {
          "type": "address",
          "name": "owner",
          "desc": "The address of the owner of the token"
        }
      ],
      "returns": {
        "type": "uint256",
        "desc": "The current balance of the holder of the token"
      }
    },
    {
      "name": "arc200_transfer",
      "desc": "Transfers tokens",
      "readonly": false,
      "args": [
        {
          "type": "address",
          "name": "to",
          "desc": "The destination of the transfer"
        },
        {
          "type": "uint256",
          "name": "value",
          "desc": "Amount of tokens to transfer"
        }
      ],
      "returns": { "type": "bool", "desc": "Success" }
    },
    {
      "name": "arc200_transferFrom",
      "desc": "Transfers tokens from source to destination as approved spender",
      "readonly": false,
      "args": [
        {
          "type": "address",
          "name": "from",
          "desc": "The source  of the transfer"
        },
        {
          "type": "address",
          "name": "to",
          "desc": "The destination of the transfer"
        },
        {
          "type": "uint256",
          "name": "value",
          "desc": "Amount of tokens to transfer"
        }
      ],
      "returns": { "type": "bool", "desc": "Success" }
    },
    {
      "name": "arc200_approve",
      "desc": "Approve spender for a token",
      "readonly": false,
      "args": [
        { "type": "address", "name": "spender" },
        { "type": "uint256", "name": "value" }
      ],
      "returns": { "type": "bool", "desc": "Success" }
    },
    {
      "name": "arc200_allowance",
      "desc": "Returns the current allowance of the spender of the tokens of the owner",
      "readonly": true,
      "args": [
        { "type": "address", "name": "owner" },
        { "type": "address", "name": "spender" }
      ],
      "returns": { "type": "uint256", "desc": "The remaining allowance" }
    }
  ],
  "events": [
    {
      "name": "arc200_Transfer",
      "desc": "Transfer of tokens",
      "args": [
        {
          "type": "address",
          "name": "from",
          "desc": "The source of transfer of tokens"
        },
        {
          "type": "address",
          "name": "to",
          "desc": "The destination of transfer of tokens"
        },
        {
          "type": "uint256",
          "name": "value",
          "desc": "The amount of tokens transferred"
        }
      ]
    },
    {
      "name": "arc200_Approval",
      "desc": "Approval of tokens",
      "args": [
        {
          "type": "address",
          "name": "owner",
          "desc": "The owner of the tokens"
        },
        {
          "type": "address",
          "name": "spender",
          "desc": "The approved spender of tokens"
        },
        {
          "type": "uint256",
          "name": "value",
          "desc": "The amount of tokens approve"
        }
      ]
    }
  ]
}

Ownership of a token by a zero address indicates that a token is out of circulation indefinitely, or otherwise burned or destroyed.

The methods arc200_transfer and arc200_transferFrom method MUST error when the balance of from is insufficient. In the case of the arc200_transfer method, from is implied as the owner of the token. The arc200_transferFrom method MUST error unless called by an spender approved by an owner. The methods arc200_transfer and arc200_transferFrom MUST emit a Transfer event. A arc200_Transfer event SHOULD be emitted, with from being the zero address, when a token is minted. A arc200_Transfer event SHOULD be emitted, with to being the zero address, when a token is destroyed.

The arc200_Approval event MUST be emitted when an arc200_approve or arc200_transferFrom method is called successfully.

A value of zero for the arc200_approve method and the arc200_Approval event indicates no approval. The arc200_transferFrom method and the arc200_Approval event indicates the approval value after it is decremented.

The contract MUST allow multiple operators per owner.

All methods in this standard that are marked as readonly MUST be read-only as defined by ARC-22.

Rationale

This specification is based on ERC-20.

Core Specification

The core specification identical to ERC-20.

Backwards Compatibility

This standard introduces a new kind of token that is incompatible with tokens defined as ASAs. Applications that want to index, manage, or view tokens on Algorand will need to handle these new smart tokens as well as the already popular ASA implementation of tokens will need to add code to handle both, and existing smart contracts that handle ASA-based tokens will not work with these new smart contract tokens.

While this is a severe backward incompatibility, smart contract tokens are necessary to provide richer and more diverse functionality for tokens.

Security Considerations

The fact that anybody can create a new implementation of a smart contract tokens standard opens the door for many of those implementations to contain security bugs. Additionally, malicious token implementations could contain hidden anti-features unexpected by users. As with other smart contract domains, it is difficult for users to verify or understand the security properties of smart contract tokens. This is a tradeoff compared with ASA tokens, which share a smaller set of security properties that are easier to validate to gain the possibility of adding novel features.

Copyright

Copyright and related rights waived via CCO.

Citation

Please cite this document as:

Nicholas Shellabarger, "ARC-200: Algorand Smart Contract Token Specification," Algorand Requests for Comments, no. 200, July 2023. [Online serial]. Available: https://github.com/algorandfoundation/ARCs/blob/main/ARCs/arc-0200.md.