Draft ERC: Cross-Chain Event Archive

ERCs
1

Hey, I have been working on cross-blockchain migration and backup. I have figured out that a generic brick is missing to specify a generic way to archive event from one blockchain to another. I think that it could be a great fit for a new ERC.

I have drafted an ERC proposal and I would like to have insights from the community. Thank you for your help :slight_smile:!

ERC PR : Not done

ERC-XXXX: Cross-Chain Event Archive

Abstract

This ERC defines a standard interface for archiving events from any blockchain (EVM or non-EVM) to an EVM-compatible chain, enabling indexers / off-chain applications to ingest cross-chain event history through a consistent and minimal envelope.

Motivation

As the blockchain ecosystem fragments across L2s, sidechains, and non-EVM chains, protocols increasingly need historical event data to be accessible across chains. Real-world asset (RWA) protocols, for example, must maintain a complete, auditable history of all on-chain events — token transfers, compliance attestations, NAV updates — across every chain where their assets are issued or traded.

Currently, there is no standard way to archive events from a source chain to a destination chain. This standard defines a minimal, universal envelope that:

  • Preserves full provenance of the original event

  • Supports both EVM and non-EVM source chains

  • Requires no knowledge of the source ABI to ingest

Specification

Event

interface IEventArchive {
    /// @notice Emitted when an event from a source chain is archived
    /// @param sourceChainId    keccak256 of the CAIP-2 chain identifier string (e.g. keccak256("eip155:1"))
    /// @param sourceTxHash     The transaction hash on the source chain that emitted the event
    /// @param sourceAddress    The contract address on the source chain that emitted the event, zero-padded to bytes32
    /// @param sourceLogIndex   The log index of the event within the source transaction
    /// @param sourceBlockNumber The block number, ledger sequence, slot, or equivalent on the source chain
    /// @param payload          Original event data in the native encoding of the source chain
    event EventArchived(
        bytes32 indexed sourceChainId,
        bytes32 indexed sourceTxHash,
        bytes32 indexed sourceAddress,
        uint256 sourceLogIndex,
        uint256 sourceBlockNumber,
        bytes payload
    );

    /// @notice Archive an event from a source chain
    function archiveEvent(
        bytes32 sourceChainId,
        bytes32 sourceTxHash,
        bytes32 sourceAddress,
        uint256 sourceLogIndex,
        uint256 sourceBlockNumber,
        bytes calldata payload
    ) external;
}

Event ID

The canonical unique identifier for an archived event is the tuple:

eventId = (sourceChainId, sourceTxHash, sourceLogIndex)

This tuple is globally unique across all chains. Implementations MUST NOT archive the same eventId twice.

Chain Identification

sourceChainId is the keccak256 hash of the CAIP-2 chain identifier string. This allows universal chain identification without maintaining a numeric registry, while remaining efficient for on-chain indexing and filtering.

Well-known values:

Chain CAIP-2 sourceChainId
Ethereum mainnet eip155:1 keccak256("eip155:1")
Base eip155:8453 keccak256("eip155:8453")
Arbitrum One eip155:42161 keccak256("eip155:42161")
Stellar pubnet stellar:pubnet keccak256("stellar:pubnet")
Solana mainnet solana:mainnet keccak256("solana:mainnet")

Indexed Fields

The three indexed fields enable the most common indexer query patterns:

Field Purpose
sourceChainId Filter all archived events originating from a given chain
sourceTxHash Look up whether a specific transaction has been archived
sourceAddress Filter all archived events from a specific source contract

Source Address

sourceAddress is encoded as bytes32. For EVM chains, the 20-byte address is zero-padded to 32 bytes. For non-EVM chains, the native address format is used directly or encoded as a 32-byte value according to the chain’s conventions.

Source Block Number

sourceBlockNumber represents the position of the event in the source chain’s history. Its semantics depend on the source chain:

Chain type sourceBlockNumber meaning
EVM Block number
Stellar Ledger sequence
Solana Slot

Payload

payload contains the original event data in the native encoding of the source chain. Its format is fully determined by sourceChainId:

Chain type Payload encoding
EVM ABI-encoded log (topics + data)
Stellar XDR-encoded contract event
Solana Borsh-encoded program log or CPI event

The standard does not prescribe payload decoding — this is the responsibility of the indexer, which derives the appropriate decoder from sourceChainId.

Security Considerations

Implementations MUST document their trust assumptions. Indexers SHOULD verify archived events against the source chain when trust is critical.

Implementations MUST enforce uniqueness of (sourceChainId, sourceTxHash, sourceLogIndex) to prevent duplicate archiving.