ERC-7754: Tamperproof Web Immutable Transaction (TWIT)

Provides a mechanism for dapps to use the extension wallets API in a tamperproof way

Abstract

Introduces a new RPC method to be implemented by wallets, wallet_signedRequest, that enables dapps to interact with wallets in a tamperproof manner via “signed requests”. The dapp associates a public key with its DNS record and uses the corresponding private key to sign payloads sent to the wallet via wallet_signedRequest. Wallets can then use use the public key in the DNS record to validate the integrity of the payload.

Motivation

This standard aims to enhance the end user’s experience by granting them confidence that requests from their dapps have not been tampered with. In essence, this is similar to how HTTPS is used in the web.

Currently, the communication channel between dapps and wallets is vulnerable to man in the middle attacks. Specifically, attackers can intercept RPC requests by injecting JavaScript code in the page, via e.g. an XSS vulnerability or due to a malicious extension. Once an RPC request is intercepted, it can be modified in a number of pernicious ways, including:

• Editing the calldata in order to siphon funds or otherwise change the transaction outcome
• Modifying the parameters of an EIP-712 request
• Obtaining a replayable signature from the wallet

Even if the user realizes that requests from the dapp may be tampered with, they have little to no recourse to mitigate the problem. Overall, the lack of a chain of trust between the dapp and the wallet hurts the ecosystem as a whole:

• Users cannot simply trust otherwise honest dapps, and are at risk of losing funds
• Dapp maintainers are at risk of hurting their reputations if an attacker finds a viable MITM attack

For these reasons, we recommend that wallets implement the wallet_signedRequest RPC method. This method provides dapp developers with a way to explicitly ask the wallet to verify the integrity of a payload. This is a significant improvement over the status quo, which forces dapps to rely on implicit approaches such as argument bit packing.

Specification

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119 and RFC 8174.

Overview

We propose to use the dapp’s domain certificate of a root of trust to establish a trust chain as follow:

1. The user’s browser verifies the domain certificate and displays appropriate warnings if overtaken
2. The DNS record of the dapp hosts a TXT field pointing to a URL where a JSON manifest is hosted
   • This file SHOULD be at a well known address such as https://example.com/.well-known/twit.json
3. The config file contains an array of objects of the form { id, alg, publicKey }
4. For signed requests, the dapp first securely signs the payload with a private key, for example by submitting a request to its backend
5. The original payload, signature, and public key id are sent to the wallet via the wallet_signedRequest RPC method
6. The wallet verifies the signature before processing the request normally

Wallet integration

Key discovery

Attested public keys are necessary for the chain of trust to be established. Since this is traditionally done via DNS certificates, we propose the addition of a DNS record containing the public keys. This is similar to RFC-6636’s DKIM, but the use of a manifest file provides more flexibility for future improvements, as well as support for multiple algorithm and key pairs.

Similarly to standard RFC-7519’s JWT practices, the wallet could eagerly cache dapp keys. However, in the absence of a revocation mechanism, a compromised key could still be used until caches have expired. To mitigate this, wallets SHOULD NOT cache dapp public keys for more than 2 hours. This practice establishes a relatively short vulnerability window, and manageable overhead for both wallet and dapp maintainers.

Example DNS record for my-crypto-dapp.invalid:

...
TXT: TWIT=/.well-known/twit.json

Example TWIT manifest at https://my-crypto-dapp.invalid.com/twit.json:

{
  "publicKeys": [
    { "id": "1", "alg": "ECDSA", "publicKey": "0xaf34..." },
    { "id": "2", "alg": "RSA-PSS", "publicKey": "0x98ab..." }
  ]
}

Dapps SHOULD only rely on algorithms available via SubtleCrypto, since they are present in every browser.

Manifest schema

We propose a simple and extensible schema:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "TWIT manifest",
  "type": "object",
  "properties": {
    "publicKeys": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "id": { "type": "string" },
          "alg": { "type": "string" },
          "publicKey": { "type": "string" }
        }
      }
    }
  }
}

RPC method

The parameters of wallet_signedRequest are specified by this TypeScript interface:

type RequestPayload<Params> = { method: string; params: Params };

type SignedRequestParameters<Params> = [
  requestPayload: RequestPayload<Params>,
  signature: `0x${string}`,
  keyId: string,
];

Here’s a non-normative example of calling wallet_signedRequest using the EIP-1193 provider interface:

const keyId = '1';
const requestPayload: RequestPayload<TransactionParams> = {
  method: 'eth_sendTransaction',
  params: [
    {
      /* ... */
    },
  ],
};
const signature: `0x${string}` = await getSignature(requestPayload, keyId);

// Using the EIP-1193 provider interface
const result = await ethereum.request({
  method: 'wallet_signedRequest',
  params: [requestPayload, signature, keyId],
});

Signature verification

1. Upon receiving an EIP-1193 call, the wallet MUST check of the existence of the TWIT manifest for the sender.tab.url domain a. The wallet MUST verify that the manifest is hosted on the sender.tab.url domain b. The wallet SHOULD find the DNS TXT record to find the manifest location b. The wallet MAY first try the /.well-known/twit.json location
2. If TWIT is NOT configured for the sender.tab.url domain, then proceed as usual
3. If TWIT is configured and the request method is used, then the wallet SHOULD display a visible and actionable warning to the user a. If the user opts to ignore the warning, then proceed as usual b. If the user opts to cancel, then the wallet MUST cancel the call
4. If TWIT is configured and the wallet_signedRequest method is used with the parameters requestPayload, signature and keyId then: a. The wallet MAY display a visible cue indicating that this interaction is signed b. The wallet MUST verify that the keyId exists in the TWIT manifest and find the associated key record c. From the key record, the wallet MUST use the alg field and the publicKey field to verify requestPayload integrity by calling crypto.verify(alg, key, signature, requestPayload) d. If the signature is invalid, the wallet MUST display a visible and actionable warning to the user i. If the user opts to ignore the warning, then proceed to call request with the argument requestPayload ii. If the user opts to cancel, then the wallet MUST cancel the call e. If the signature is valid, the wallet MUST call request with the argument requestPayload

Example method implementation (wallet)

async function signedRequest(
  requestPayload: RequestPayload<unknown>,
  signature: `0x${string}`,
  keyId: string,
): Promise<unknown> {
  // 1. Get the domain of the sender.tab.url
  const domain = getDappDomain();

  // 2. Get the manifest for the current domain
  // It's possible to use RFC 8484 for the actual DNS-over-HTTPS specification, see https://datatracker.ietf.org/doc/html/rfc8484.
  // However, here we are doing it with DoHjs.
  // This step is optional, and you could go directly to the well-known address first at `domain + '/.well-known/twit.json'`
  const doh = require('dohjs');
  const resolver = new doh.DohResolver('https://1.1.1.1/dns-query');

  let manifestPath = '';
  const dnsResp = await resolver.query(domain, 'TXT');
  for (record of dnsResp.answers) {
    if (!record.data.startsWith('TWIT=')) continue;

    manifestPath = record.data.substring(5); // This should be domain + '/.well-known/twit.json'
    break;
  }

  // 3. Parse the manifest and get they key and algo based on `keyId`
  const manifestReq = await fetch(manifestPath);
  const manifest = await manifestReq.json();
  const keyData = manifest.publicKeys.filter((x) => x.id == keyId);
  if (!keyData) {
    throw new Error('Could not find the signing key');
  }

  const key = keyData.publicKey;
  const alg = keyData.alg;

  // 4. Verify the signature
  const valid = await crypto.verify(alg, key, signature, requestPayload);
  if (!valid) {
    throw new Error('The data was tampered with');
  }
  return await processRequest(requestPayload);
}

Wallet UX suggestion

Similarly to the padlock icon for HTTPS, wallets should display a visible indication when TWIT is configured on a domain. This will improve the UX of the end user who will immediately be able to tell that interactions between the dapp they are using and the wallet are secure, and this will encourage dapp developer to adopt TWIT, making the overall ecosystem more secure

When dealing with insecure request, either because the dapp (or an attacker) uses request on a domain where TWIT is configured, or because the signature does not match, wallets should warn the user but not block: an eloquently worded warning will increase the transparency enough that end user may opt to cancel the interaction or proceed with the unsafe call.

Rationale

The proposed implementation does not modify any of the existing functionalities offered by EIP-712 and EIP-1193. Its additive nature makes it inherently backward compatible. Its core design is modeled after existing solutions to existing problems (such as DKIM). As a result the proposed specification will be non disruptive, easy to implements for both wallets and dapps, with a predictable threat model.

Security Considerations

Replay prevention

While signing the requestArg payload guarantees data integrity, it does not prevent replay attacks in itself:

1. a signed payload can be replayed multiple times
2. a signed payload can be replayed across multiple chains

Effective time replay attacks as described in 1. are generally prevented by the transaction nonce. Cross chain replay can be prevented by leveraging the EIP-712 signTypedData method.

Replay attack would still be possible on any method that is not protected by either: this affects effectively all the “readonly” methods which are of very limited value for an attacker.

For these reason, we do not recommend a specific replay protection mechanism at this time. If/when the need arise, the extensibility of the manifest will provide the necessary room to enforce a replay protection envelope (eg:JWT) for affected dapp.

Copyright

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Erik Marks (@remarks), Guillaume Grosbois (@uni-guillaume), "ERC-7754: Tamperproof Web Immutable Transaction (TWIT) [DRAFT]," Ethereum Improvement Proposals, no. 7754, July 2024. [Online serial]. Available: https://eips.ethereum.org/EIPS/eip-7754.