EIP155 Namespace, aka EVM Chains - Addresses

CAIP-10

For context, see the CAIP-10 specification.

Rationale

While Ethereum “accounts” were the unstated norm in the definition of CAIP-10, there are still some particularities of the syntax that should be specified for the unfamiliar.

Special case of EOA

To express Ethereum account without reference to any specific EIP-155 chain ID, CAIP-10 identifiers can use the special chainId segment 0.

In the Ethereum account system, “externally owned accounts” (i.e. “offchain” wallets) are controlled by user agents and not by on-chain entities (i.e. deployed or deployable smart contract code). The special chainId 0 SHOULD only be used for accounts that can be used in off-chain contexts, i.e. without the use of an Ethereum node.

Note that a given address cannot be assumed to work on all current and future networks with an EIP-155 chainId, which may express or derive addresses differently for a given private key; a user account expressed with chainId segment of 0 is assumed to control the same account on chainId 1 and most ethereum chains, but MAY control a different account or additional accounts on networks that extend the account or addressing model of Ethereum, assume different key or hash derivations, etc.

Syntax

Ethereum addresses were, historically, case-insensitive and normalized to use all-lowercase letters (abcdef) like most hexadecimal numeric types. With the ratification of EIP-55, however, a particular normalization of lowercase- and uppercase- abcdefABCDEF characters was invented as an efficient form of checksum. Most implementations will still accept lowercase addresses but produce only checksum-case addresses, as many transaction-builders will validate not just against a regular expression but also against an EIP-55 checksum. Anywhere “Postel’s Law” can apply, implementers SHOULD produce checksum-case secure addresses (whether in CAIP-10 or native format), and SHOULD accept both checksum case and legacy lowercase addresses, except where the security concerns of the particular usecase outweigh interoperability. See EIP-55 for specification.

The chain ID will be used to represent blockchain except special case of 0 as chainID to represent EOA.

The chain_id string will be ammended as follows:

chain_id:    namespace + ":" + network_id + ":" + reference
namespace:   [-a-z0-9]{3,8}
network_id:    [0-9]{1,64}
reference:   0x[a-fA-F0-9]{40}

Backwards Compatibility

An earlier version of the CAIP-10 schema was defined by appending as suffix the CAIP-2 chainId delimited by the at sign (@), i.e. 0x22227A31dd842196A246d8f3b775998560eAa61d@eip155:1 in the above example. This was changed Aug 11, 2021 and some systems built against the earlier drafts may present accounts in this manner.

Test Cases

# EOA
eip155:0:0x839395e20bbB182fa440d08F850E6c7A8f6F0780

# Ethereum mainnet (valid/checksummed)
eip155:1:0x22227A31dd842196A246d8f3b775998560eAa61d

# Ethereum mainnet (will not validate in EIP155-conformant systems)
eip155:1:0x22227a31dd842196a246d8f3b775998560eaa61d

# Polygon mainnet (valid/checksummed)
eip155:137:0x0495766cD136138Fc492Dd499B8DC87A92D6685b

# Polygon mainnet (will not validate in EIP155-conformant systems)
eip155:137:0x0495766CD136138FC492DD499B8DC87A92D6685B

Security Considerations

As the Ethereum namespace evolved, user-agents that connect to dapps through an EIP-1193 interface started to accrue “off-chain” use-cases such as authenticating control of an onchain account with an “off-chain” signature (i.e. a transaction signed by the wallet and verified by a dapp or website without either party submitting it to a node or running any on-chain functions). It is RECOMMENDED that wallets using the chainId of 0 be authenticated in a standardized and secure manner which produces verifiable receipts of the authenticaiton event, such as that documented in ERC-4361 and extended by CAIP-122.

References

• EIP-155: Ethereum Improvement Proposal specifying generation and validation of ChainIDs
• ethereum-lists/chains: An open registry for eip155 network operators to claim a unique chainID and self-publish RPC/node information for them.
• ERC-20: Basic [aka Fungible] Token Standard
• ERC-721: Non-Fungible Token Standard

Rights

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Simon Warta, ligi, Pedro Gomes, Antoine Herzog, Joel Thorstensson, "namespaces/eip155-caip10: EIP155 Namespace, aka EVM Chains - Addresses [DRAFT]," Chain Agnostic Namespaces, eip155-caip10, December 2019 / March 2022. [Online serial]. Available: https://github.com/ChainAgnostic/namespaces/eip155-caip10.md