Sign-In with Ethereum (EIP-4361): verificar en el servidor

app.example wants you to sign in with your Ethereum account:
0x701111bB8ee63D09066471B2b26E8a6eD017B521

Sign in to app.example.

URI: https://app.example/login
Version: 1
Chain ID: 31337
Nonce: 7d19b07372ad88a030c953465f770a48
Issued At: 2026-10-20T13:10:41.396Z
Expiration Time: 2026-10-20T13:20:41.396Z

import { randomBytes } from "node:crypto";
import { parseSiweMessage } from "viem/siwe";

/**
 * Server side of Sign-In with Ethereum (EIP-4361). `client` is a viem public client connected
 * to the chain the sessions are bound to: EIP-4361 requires contract accounts to be resolved
 * on the message's Chain ID.
 */
export function createSiweVerifier({ client, domain, origin, maxAgeSeconds = 300 }) {
  const pending = new Map(); // nonce -> expiry (ms); one entry per sign-in attempt

  return {
    /** Step 1: a fresh nonce for the page that is about to ask the wallet to sign. */
    issueNonce() {
      const nonce = randomBytes(16).toString("hex"); // 128 bits from the OS CSPRNG, 32 alphanumeric characters
      pending.set(nonce, Date.now() + maxAgeSeconds * 1000);
      return nonce;
    },

    /** Step 2: check the signed message, then the signature; returns the session subject. */
    async verify(message, signature) {
      const fields = parseSiweMessage(message);
      const expiry = pending.get(fields.nonce);
      pending.delete(fields.nonce); // single use, whatever the outcome
      if (expiry === undefined) throw new Error("unknown or already used nonce");
      if (Date.now() > expiry) throw new Error("nonce expired");
      if (fields.domain !== domain) throw new Error(`message is for ${fields.domain}`);
      if (!fields.uri || new URL(fields.uri).origin !== origin) throw new Error(`URI ${fields.uri} is not on ${origin}`);
      if (fields.version !== "1") throw new Error(`unsupported version ${fields.version}`);
      if (fields.chainId !== client.chain.id) throw new Error(`message is for chain ${fields.chainId}`);
      if (!fields.issuedAt || Date.now() - fields.issuedAt.getTime() > maxAgeSeconds * 1000) {
        throw new Error("issued too long ago");
      }
      // verifySiweMessage checks domain and nonce only when they are passed, plus expiration and
      // not-before, then the signature: ecrecover for plain accounts, ERC-1271 for deployed
      // contract accounts, ERC-6492 for contract accounts that are not deployed yet.
      const valid = await client.verifySiweMessage({ message, signature, domain, nonce: fields.nonce });
      if (!valid) throw new Error("signature does not verify");
      return { address: fields.address, chainId: fields.chainId }; // bind the session to the address
    },
  };
}

// Two ways a SIWE check goes wrong without any attacker skill: calling the library without the
// expected values, and changing the line endings of the message. EOA only; keys generated here.
import { createPublicClient, http } from "viem";
import { generatePrivateKey, privateKeyToAccount } from "viem/accounts";
import { foundry } from "viem/chains";
import { createSiweMessage } from "viem/siwe";

const client = createPublicClient({ chain: foundry, transport: http("http://127.0.0.1:8545") });
const alice = privateKeyToAccount(generatePrivateKey());

// A message alice signed on some other site, with that site's nonce.
const elsewhere = createSiweMessage({
  domain: "other.example", address: alice.address, uri: "https://other.example/", version: "1",
  chainId: foundry.id, nonce: "a1b2c3d4", issuedAt: new Date(),
});
const signature = await alice.signMessage({ message: elsewhere });
console.log(`verifySiweMessage({ message, signature })                 -> ${await client.verifySiweMessage({ message: elsewhere, signature })}`);
console.log(`verifySiweMessage({ message, signature, domain, nonce }) -> ${await client.verifySiweMessage({ message: elsewhere, signature, domain: "app.example", nonce: "f00dfeed" })}`);

// The same message after a transport or template turned LF into CRLF.
const crlf = elsewhere.replaceAll("\n", "\r\n");
console.log(`same message with CRLF line endings                      -> ${await client.verifySiweMessage({ message: crlf, signature })}`);

// What personal_sign receives over EIP-1193: the hex-encoded UTF-8 message first, then the address.
const params = [`0x${Buffer.from(elsewhere, "utf8").toString("hex")}`, alice.address];
console.log(`personal_sign params: ["${params[0].slice(0, 26)}...", "${params[1]}"]`);

verifySiweMessage({ message, signature })                 -> true
verifySiweMessage({ message, signature, domain, nonce }) -> false
same message with CRLF line endings                      -> false
personal_sign params: ["0x6f746865722e6578616d706c...", "0xC527ED169430Ca38aADCEb03cd04f6F390b4840F"]

// How related are two consecutive nonces from viem's generateSiweNonce()?
import { generateSiweNonce } from "viem/siwe";

const a = generateSiweNonce();
const b = generateSiweNonce();
console.log(`first   ${a}`);
console.log(`second  ${b}`);
console.log(`second equals first shifted by one character: ${b.slice(0, 95) === a.slice(1)}`);
console.log(`alphabet: ${[...new Set(a + b)].sort().join("")}`);

first   ef56353692864c3d4da72cbdea645d3aac4543c9527e869572a71cbd5bf1d340b2488493e175223f8453b8e6e4afae8b
second  f56353692864c3d4da72cbdea645d3aac4543c9527e869572a71cbd5bf1d340b2488493e175223f8453b8e6e4afae8b7
second equals first shifted by one character: true
alphabet: 0123456789abcdef

// SPDX-License-Identifier: MIT
pragma solidity 0.8.30;

/// A minimal smart-contract account for the article's lab: one owner key, ERC-1271 signature checks.
contract OwnerWallet {
    address public immutable owner;

    constructor(address owner_) {
        require(owner_ != address(0), "owner required");
        owner = owner_;
    }

    /// ERC-1271: returns 0x1626ba7e when `signature` is the owner's signature over `hash`.
    function isValidSignature(bytes32 hash, bytes calldata signature) external view returns (bytes4) {
        if (signature.length != 65) return 0xffffffff;
        bytes32 r = bytes32(signature[0:32]);
        bytes32 s = bytes32(signature[32:64]);
        uint8 v = uint8(signature[64]);
        // Reject high-s values (EIP-2), so one owner signature has exactly one valid encoding.
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) return 0xffffffff;
        return ecrecover(hash, v, r, s) == owner ? bytes4(0x1626ba7e) : bytes4(0xffffffff);
    }
}

/// Deploys OwnerWallet with CREATE2, so a wallet's address is known before it exists (ERC-6492).
contract OwnerWalletFactory {
    function deploy(address owner, bytes32 salt) external returns (address wallet) {
        wallet = predict(owner, salt);
        if (wallet.code.length == 0) new OwnerWallet{salt: salt}(owner);
    }

    function predict(address owner, bytes32 salt) public view returns (address) {
        bytes32 initCodeHash = keccak256(abi.encodePacked(type(OwnerWallet).creationCode, abi.encode(owner)));
        return address(uint160(uint256(keccak256(abi.encodePacked(bytes1(0xff), address(this), salt, initCodeHash)))));
    }
}

// Lab driver: an EOA, a deployed ERC-1271 wallet and an undeployed (ERC-6492) wallet sign in to the
// same server on a local anvil chain; then the attacks the server has to refuse. All keys are generated here.
import { readFileSync } from "node:fs";
import { createPublicClient, createTestClient, createWalletClient, encodeFunctionData, hashMessage, http, parseEther, recoverMessageAddress, serializeErc6492Signature } from "viem";
import { generatePrivateKey, privateKeyToAccount } from "viem/accounts";
import { foundry } from "viem/chains";
import { createSiweMessage } from "viem/siwe";
import { createSiweVerifier } from "./siwe-server.mjs";

const transport = http("http://127.0.0.1:8545");
const client = createPublicClient({ chain: foundry, transport });
const deployer = privateKeyToAccount(generatePrivateKey());
await createTestClient({ chain: foundry, mode: "anvil", transport }).setBalance({ address: deployer.address, value: parseEther("10") });
const wallet = createWalletClient({ account: deployer, chain: foundry, transport });

const artifact = (name) => JSON.parse(readFileSync(`/chain/out/OwnerWallet.sol/${name}.json`, "utf8"));
const { abi: factoryAbi, bytecode } = artifact("OwnerWalletFactory");
const deployTx = await wallet.deployContract({ abi: factoryAbi, bytecode: bytecode.object });
const factory = (await client.waitForTransactionReceipt({ hash: deployTx })).contractAddress;
const predict = (owner, salt) => client.readContract({ address: factory, abi: factoryAbi, functionName: "predict", args: [owner, salt] });
const deployWallet = async (owner, salt) => {
  const hash = await wallet.writeContract({ address: factory, abi: factoryAbi, functionName: "deploy", args: [owner, salt] });
  await client.waitForTransactionReceipt({ hash });
};

const server = createSiweVerifier({ client, domain: "app.example", origin: "https://app.example" });
const messageFor = (address, overrides = {}) =>
  createSiweMessage({
    domain: "app.example",
    address,
    statement: "Sign in to app.example.",
    uri: "https://app.example/login",
    version: "1",
    chainId: foundry.id,
    nonce: server.issueNonce(),
    issuedAt: new Date(),
    expirationTime: new Date(Date.now() + 10 * 60_000),
    ...overrides,
  });

// Three users. alice: a plain account. bob: a deployed smart wallet. carol: a smart wallet not deployed yet.
const alice = privateKeyToAccount(generatePrivateKey());
const bob = privateKeyToAccount(generatePrivateKey());
const carol = privateKeyToAccount(generatePrivateKey());
const salt = `0x${"00".repeat(31)}01`;
await deployWallet(bob.address, salt);
const bobWallet = await predict(bob.address, salt);
const carolWallet = await predict(carol.address, salt);

const aliceMessage = messageFor(alice.address);
console.log(`${aliceMessage}\n`);

const attempts = [];
attempts.push(["EOA, personal_sign", aliceMessage, await alice.signMessage({ message: aliceMessage })]);
const bobMessage = messageFor(bobWallet);
attempts.push(["deployed wallet, ERC-1271", bobMessage, await bob.sign({ hash: hashMessage(bobMessage) })]);
const carolMessage = messageFor(carolWallet);
attempts.push([
  "undeployed wallet, ERC-6492",
  carolMessage,
  serializeErc6492Signature({
    address: factory,
    data: encodeFunctionData({ abi: factoryAbi, functionName: "deploy", args: [carol.address, salt] }),
    signature: await carol.sign({ hash: hashMessage(carolMessage) }),
  }),
]);
console.log(`carol's wallet has code before sign-in: ${Boolean(await client.getCode({ address: carolWallet }))}`);

for (const [label, message, signature] of attempts) {
  let recovered;
  try {
    recovered = await recoverMessageAddress({ message, signature });
  } catch (e) {
    recovered = e.shortMessage ?? e.message;
  }
  const claimed = message.split("\n")[1];
  const result = await server.verify(message, signature).then((s) => `session for ${s.address.slice(0, 10)}...`, (e) => `rejected: ${e.message}`);
  console.log(`${label.padEnd(28)} ${result}; ecrecover alone gives ${recovered === claimed ? "the same address" : String(recovered).slice(0, 42)}`);
}
console.log(`carol's wallet has code after sign-in:  ${Boolean(await client.getCode({ address: carolWallet }))}`);

// What the server must refuse.
const check = async (label, message, signature) => {
  const result = await server.verify(message, signature).then(() => "ACCEPTED", (e) => `rejected: ${e.message}`);
  console.log(`${label.padEnd(36)} ${result}`);
};
const replayed = messageFor(alice.address);
const replayedSig = await alice.signMessage({ message: replayed });
await server.verify(replayed, replayedSig);
await check("same message and signature again", replayed, replayedSig);
const phish = messageFor(alice.address, { domain: "app-example.login", uri: "https://app-example.login/" });
await check("signed on a look-alike site", phish, await alice.signMessage({ message: phish }));
const otherChain = messageFor(alice.address, { chainId: 1 });
await check("message for chain 1", otherChain, await alice.signMessage({ message: otherChain }));
const stale = messageFor(alice.address, { issuedAt: new Date(Date.now() - 3600_000), expirationTime: new Date(Date.now() + 3600_000) });
await check("issued an hour ago", stale, await alice.signMessage({ message: stale }));
const original = messageFor(alice.address);
const originalSig = await alice.signMessage({ message: original });
await check("statement edited after signing", original.replace("Sign in to app.example.", "Sign in to app.example as admin."), originalSig);
const mallory = privateKeyToAccount(generatePrivateKey());
const claimsBob = messageFor(bobWallet);
await check("bob's wallet, signed by someone else", claimsBob, await mallory.sign({ hash: hashMessage(claimsBob) }));

carol's wallet has code before sign-in: false
EOA, personal_sign           session for 0x701111bB...; ecrecover alone gives the same address
deployed wallet, ERC-1271    session for 0x5d3a68A0...; ecrecover alone gives 0xE4e0d879c3a051245cc489dE8Ae281c019691864
undeployed wallet, ERC-6492  session for 0x6F47E5F9...; ecrecover alone gives invalid signature length
carol's wallet has code after sign-in:  false
same message and signature again     rejected: unknown or already used nonce
signed on a look-alike site          rejected: message is for app-example.login
message for chain 1                  rejected: message is for chain 1
issued an hour ago                   rejected: issued too long ago
statement edited after signing       rejected: signature does not verify
bob's wallet, signed by someone else rejected: signature does not verify