Ethereum

Load it

import { useBlockchain, blockchains } from "@agntn/keys";

const ethereumChain = useBlockchain(await blockchains.ethereum()());

The address

Uncompressed public key without the 04, Keccak-256, last 20 bytes, 0x, then the EIP-55 case checksum.

const privateKey = "0000000000000000000000000000000000000000000000000000000000000001";
const publicKey = ethereumChain.getKeyPublic(privateKey);

ethereumChain.getAddress(publicKey); // 0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf

Yes, that's the address of private key 1. It shows up in a lot of test suites.

Validation

ethereumChain.validateAddress("0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf"); // true
ethereumChain.validateAddress("0x7e5f4552091a69125d5dfcb7b8c2659029395bdf"); // true, no checksum to check
ethereumChain.validateAddress("0x7e5F4552091A69125d5DfCb7b8C2659029395Bdf"); // false, bad checksum

Lowercase and uppercase pass, mixed case has to match. A rejected mixed case address is almost always a copy and paste that lost a character somewhere, so treat false as "look at it again", not as "this address doesn't exist".

Signing

signMessage prepends "\x19Ethereum Signed Message:\n" + length, hashes with Keccak-256, and signs with secp256k1. That's personal_sign, the same hash MetaMask, ethers and viem sign. Default output is 64 bytes of r||s, which verifyMessage here checks against a public key.

const signature = ethereumChain.signMessage("hello", privateKey);
ethereumChain.verifyMessage("hello", signature, publicKey); // true

Anything that recovers the signer from the signature needs v, so pass recovered:

const recoverable = ethereumChain.signMessage("hello", privateKey, { recovered: true });
// 65 bytes, r||s||v, identical to what ethers signMessage gives for the same key
ethereumChain.verifyMessage("hello", recoverable, publicKey); // true, and the v has to match

verifyMessage takes either length. On 65 bytes it also recovers from the v, so a signature carrying the other one fails instead of passing on r||s alone. The 64-byte form is what you want inside this package, the 65-byte form is what you send out. See the EVM guide for what ethers does with the short one, it's not an error and that's the problem.

Who signed this?

The 65-byte form also works backwards. recoverMessageSigner takes the message and the signature and gives you the key:

const signer = ethereumChain.recoverMessageSigner("hello", recoverable);
ethereumChain.getAddress(signer.publicKey); // 0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf

Typed data and raw ecrecover digests go through hashTypedData and recoverDigestSigner. The EVM guide has both. Same rule as always: check the address.

One driver, every EVM chain

Ethereum is AbstractEVMBlockchain with a name and coin type 60. Base is the same class with a different name. The EVM guide explains why one private key gives one address on every EVM chain and how to add another one in two lines.