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DID Methods & Address Mapping

Overview

EXIT attestations use DID-derived Ethereum addresses as the EAS recipient field. This document explains how each supported DID method maps to an address and the implications for key management.

did:key — Synthetic Addresses

did:key identifiers (typically Ed25519 keys) have no native Ethereum address. The adapter derives a synthetic address via keccak256(did_string), taking the last 20 bytes.

Important:

  • These addresses are not real EOAs — no private key controls them
  • They cannot send transactions or hold funds
  • They exist solely as deterministic identifiers for the EAS recipient field
  • The same did:key always produces the same address
did:key:z6MkhaXgBZDvotDkL5257faiztiGiC2QtKLGpbnnEGta2doK
  → keccak256("did:key:z6Mk...") → 0x<last 40 hex chars>

did:ethr — Key Rotation

did:ethr maps directly to an Ethereum address (did:ethr:0x1234... → 0x1234...).

Key rotation behavior:

  • Attestations bind to the address at anchor time
  • If changeOwner is called on the DID registry, the old address no longer controls the DID
  • However, old attestations remain valid — they record a historical fact
  • This is forward-only rotation, consistent with W3C DID Core and KERI principles
  • New attestations should use the new owner address

Recommendation: Consumers should verify the current DID Document (via a DID resolver) before trusting attestations from a did:ethr subject. If changeOwner has been called, the consumer may want to treat pre-rotation attestations differently depending on their trust policy.

// Example: resolve did:ethr before trusting
import { Resolver } from 'did-resolver';
import { getResolver } from 'ethr-did-resolver';

const resolver = new Resolver(getResolver({ infuraProjectId: '...' }));
const doc = await resolver.resolve('did:ethr:0x1234...');

// Check if the DID document's controller matches the attester
const controller = doc.didDocument?.controller;

did:pkh — Chain ID Discarded

did:pkh:eip155:<chainId>:0x... extracts the address directly. The chain ID is intentionally discarded.

Rationale:

  • The EAS recipient is an Ethereum address, valid across all EVM chains
  • did:pkh:eip155:1:0x1234... and did:pkh:eip155:137:0x1234... produce the same recipient
  • The attestation's target chain is determined by which EAS contract it's submitted to, not the DID's chain ID
  • This is correct: the attestation is about the address, not from it

Summary

DID Method Address Source Real EOA? Key Rotation
did:ethr Direct extraction Yes changeOwner — forward-only
did:pkh Direct extraction (chain ID dropped) Yes N/A (address-based)
did:key keccak256(did) last 20 bytes No (synthetic) N/A (immutable)