CIP 90: A Space that Fully EVM Compatible

#1
cip title author status type created replaces
90 A Space Fully EVM compatible Fan Long [email protected] Chenxing Li [email protected] Draft Spec Breaking 2022-01-10 72, 80

Simple Summary

Introduce a new space that is fully EVM compatible.

Abstract

This CIP aims to introduce a new fully EVM-compatible space. The new space is called EVM Space, and the current space is called Native Space. The EVM Space follows the same rule as EVM and supports eth rpc like eth_getBalance, so the tools from ethereum economics can be used on Conflux directly.

The accounts in two spaces are separated. A native space account can only interact with the other accounts in native space with the original conflux transaction type. An EVM space account can only interact with the other accounts in EVM space with Ethereum transaction type EIP-155. A new internal contract will be deployed for assets and data cross-space. Unlike cross-chain operations, the cross-space operations are atomic and with layer 1 security.

Motivation

Conflux has a virtual machine that is similar to EVM. However, there are still some differences between Conflux VM and Ethereum VM. Conflux has a different transaction format and a different rule for generating addresses from public keys. This impedes the EVM compatible dApps porting to Conflux. The previous CIP-72 and CIP-80 try to solve these obstacles. But that will influence the current applications. So this CIP introduces a new space to construct a space that is fully EVM-compatible without changing the existing accounts and transactions.

Specification

Addresses

At the user level, the native space still uses base32 format address like cfx:aa... and the EVM space uses hex checksum address like 0xaAD8... . At the system level, both the native space and the EVM space are in the format of 160 bits. One address in two spaces is two different accounts. Their balances and nonces will be counted separately.

Storage Key

The Conflux uses Delta MPT as the underlying authenticated data structure for the ledger state. Delta MPT provides a key-value interface to the virtual machine.

In computing the storage key for accounts in EVM space, we calculate the storage key for the account with the same address in the native space and insert byte 0x81 at position 20 (index started at 0).

In computing the delta set storage key (see section 3.2.2 for details) for accounts in EVM space, we compute the storage key for the account with the same address in the native space and insert byte 0x81 at position 32 (index started at 0).

Virtual Machine

  • Support the precompiled contracts on Ethereum from address 0x00..01 to address 0x00..08.
  • The NUMBER opcode will return the epoch number.
  • The BLOCKHASH opcode can only take NUMBER-1 as input. (Unlike Ethereum, which takes any integer in NUMBER-256 to NUMBER-1 as input)
  • No gas refund in SSTORE opcode and SUICIDE opcode.
  • The operations which occupy storage have a different gas cost.
    • SSTORE costs 40000 gas (instead of 20000 gas in Ethereum) when changing a storage entry from zero to non-zero.
    • When deploying a new contract, each byte costs 400 gas (instead of 200 gas in Ethereum).
    • When creating a new account by CALL or SUICIDE, it consumes 50000 gas (instead of 25000 gas in Ethereum).

Cross Space Operations

Mapped Account

Each the native space account has a mapped account in the EVM space. The address of the mapped account is the last 160 bits of the keccak hash value of the original account. With the assumption for the security of the keccak hash function, the mapped address will never collide with the addresses generated by Ethereum tools. The native space account can withdraw the balance from the mapped account.

Internal Contract

A new internal contract called the CrossSpace contract will be deployed at the address 0x0888000000000000000000000000000000000006 with the following interfaces. The native space user/contract can interact with the accounts in the EVM space and process the return value in the same transaction. So the cross-space operations can be atomic.

When making a cross-space call, only 1/10 of available gas can be passed in the EVM space. This is aimed to limit gas usage in a cross-space call.

pragma solidity >=0.5.0;

interface CrossSpace {

    event Call(bytes20 indexed sender, bytes20 indexed receiver, uint256 value, uint256 nonce, bytes data);

    event Create(bytes20 indexed sender, bytes20 indexed contract_address, uint256 value, uint256 nonce, bytes init);

    event Withdraw(bytes20 indexed sender, address indexed receiver, uint256 value);

    function createEVM(bytes calldata init) external payable returns (bytes20);

    function transferEVM(bytes20 to) external payable returns (bytes memory output);

    function callEVM(bytes20 to, bytes calldata data) external payable returns (bytes memory output);

    function staticCallEVM(bytes20 to, bytes calldata data) external view returns (bytes memory output);

    function withdrawFromMapped(uint256 value) external;

    function mappedBalance(address addr) external view returns (uint256);

    function mappedNonce(address addr) external view returns (uint256);
}

Block gas limit

Only the block whose block height is a multiple of 5 can pack Ethereum type transaction. The total gas limit of these transaction cannot exceed half of the block gas limit.

Rationale

About the storage key

In the current implementation, the 21-th byte of encoded storage key is a valid ascii charachter. So set the highest bit of the 21-th byte can distinguish new storage keys from the existing keys.

About the interface of the internal contracts

The internal contracts use type bytes20 to indicate an address in the EVM space. Because an EVM space address may be invalid in Conflux Space and rejected by some interfaces in RPC.

Backwards Compatibility

This CIP is spec breaking.

Test Cases

TBA.

Implementation

TBA.

Security Considerations

TBA.

Copyright

Copyright and related rights waived via CC0.

For more information, please refer to CIP 90: A Space that Fully EVM Compatible: https://github.com/Conflux-Chain/CIPs/blob/master/CIPs/cip-90.md

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