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EIP-5003

Insert Code into EOAs with AUTHUSURP

Allow migrating away from ECDSA by deploying code in place of an externally owned account.
StagnantStandards Track: Core
Created: 2022-03-26
Requires: EIP-3074, EIP-3607
Dan Finlay (@danfinlay), Sam Wilson (@SamWilsn)
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1 min read

The EIP-5003 proposal introduces a new opcode called AUTHUSURP, which allows code to be deployed at an EIP-3074 authorized address. This effectively revokes the original signing key's authority for externally owned accounts (EOAs). EOAs currently have limitations in terms of security and functionality, such as the inability to rotate keys or enable sponsored transactions. This proposal aims to provide a migration path off of EOAs by allowing code to be inserted in place of the original signing key. This would enable users to take advantage of the benefits of contract-based accounts, such as choosing their own authentication algorithm and enabling social recovery. However, contracts using ECDSA signatures outside of transactions may not be aware that the account is no longer controlled by a private key, which could pose a security risk. The proposal suggests mitigating this risk by modifying the ecrecover pre-compiled contract. The proposal is distinct from EIP-3074, which provides opcodes for delegating signing authority to a smart contract, while EIP-5003 provides a final migration path off the EOA's original signing key.

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Abstract

This EIP introduces a new opcode, AUTHUSURP, which deploys code at an EIP-3074 authorized address. For externally owned accounts (EOAs), together with EIP-3607, this effectively revokes the original signing key's authority.

Motivation

EOAs currently hold a significant amount of user-controlled value on Ethereum blockchains, but are limited by the protocol in a variety of critical ways. These accounts do not support rotating keys for security, batching to save gas, or sponsored transactions to reduce the need to hold ether yourself. There are countless other benefits that come from having a contract account or account abstraction, like choosing one's own authentication algorithm, setting spending limits, enabling social recovery, allowing key rotation, arbitrarily and transitively delegating capabilities, and just about anything else we can imagine.

New users have access to these benefits using smart contract wallets, and new contracts can adopt recent standards to enable app-layer account abstraction (like EIP-4337), but these would neglect the vast majority of existing Ethereum users' accounts. These users exist today, and they also need a path to achieving their security goals.

Those added benefits would mostly come along with EIP-3074 itself, but with one significant shortcoming: the original signing key has ultimate authority for the account. While an EOA could delegate its authority to some additional contract, the key itself would linger, continuing to provide an attack vector, and a constantly horrifying question lingering: have I been leaked? In other words, EIP-3074 can only grant authority to additional actors, but never revoke it.

Today's EOAs have no option to rotate their keys. A leaked private key (either through phishing, or accidental access) cannot be revoked. A prudent user concerned about their key security might migrate to a new secret recovery phrase but at best this requires a transaction per asset (making it extremely expensive), and at worst, some powers (like hard-coded owners in a smart contract) might not be transferable at all.

We know that EOAs cannot provide ideal user experience or safety, and there is a desire in the community to change the norm to contract-based accounts, but if that transition is designed without regard for the vast majority of users today—for whom Ethereum has always meant EOAs—we will be continually struggling against the need to support both of these userbases. This EIP provides a path not to enshrine EOAs, but to provide a migration path off of them, once and for all.

This proposal combines well with, but is distinct from, EIP-3074, which provides opcodes that could enable any externally owned account (EOA) to delegate its signing authority to an arbitrary smart contract. It allows an EOA to authorize a contract account to act on its behalf without forgoing its own powers, while this EIP provides a final migration path off the EOA's original signing key.

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.

Conventions

  • top - N - the Nth most recently pushed value on the EVM stack, where top - 0 is the most recent.
  • invalid execution - execution that is invalid and must exit the current execution frame immediately, consuming all remaining gas (in the same way as a stack underflow or invalid jump).
  • empty account - account where its balance is 0, its nonce is 0, and it has no code.

AUTHUSURP (0xf8)

A new opcode AUTHUSURP shall be created at 0xf8. It shall take two stack elements and return one stack element.

Input

StackValue
top - 0offset
top - 1length

Output

StackValue
top - 0address

Behavior

AUTHUSURP behaves identically to CREATE (0xf0), except as described below:

  • If authorized (as defined in EIP-3074) is unset, execution is invalid.
  • If authorized points to an empty account, then static_gas remains 32,000. Otherwise, static_gas shall be 7,000.
  • AUTHUSURP does not check the nonce of the authorized account.
  • The initcode runs at the address authorized.
  • If the initcode returns no bytes, its execution frame must be reverted, and AUTHUSURP returns zero.
  • After executing the initcode, but before the returned code is deployed, if the account's code is non-empty, the initcode's execution frame must be reverted, and AUTHUSURP returns zero.
  • The code is deployed into the account with the address authorized.

Rationale

AUTHUSURP does not check the nonce of the authorized account because it must work with accounts that have previously sent transactions.

When using AUTHUSURP, if the initcode were to deploy a zero-length contract, there would be no way to prevent using AUTHUSURP again later.

The account's code must be checked immediately before deploying to catch the situation where the initcode attempts to AUTHUSURP at the same address. This is unnecessary with other deployment instructions because they increment and check the account's nonce.

Backwards Compatibility

AUTHUSURP with EIP-3607 revokes the authority of the original ECDSA signature to send transactions from the account. This is completely new behavior, although it is somewhat similar to the CREATE2 opcode.

Security Considerations

Contracts using ECDSA signatures outside of transactions will not be aware that the usurped account is no longer controlled by a private key. This means that, for example, the private key will always have access to the permit function on token contracts. This can—and should—be mitigated by modifying the ecrecover pre-compiled contract.

Copyright and related rights waived via CC0.

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