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EIP-712 Signing for Cosmos Transactions

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Overview

This chain implements a novel approach to transaction signing that enables Cosmos transactions to be signed using the Ethereum Ledger app via EIP-712 typed data. This provides unified key management for chains that support both EVM and Cosmos transaction types.

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The Problem

Traditional Cosmos chains use:
  • Key Type: secp256k1
  • Ledger App: Cosmos app
  • Address Format: Bech32 (derived from SHA256 + RIPEMD160)
EVM-compatible chains need:
  • Key Type: eth_secp256k1
  • Address Format: Ethereum hex (derived from Keccak256)
The Cosmos Ledger app cannot derive Ethereum-style addresses because it only supports compressed public keys and different hashing algorithms.

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The Solution: EIP-712

EIP-712 is a standard for typed structured data hashing and signing. Originally designed for Ethereum dApps, it can be used to sign any structured data, including Cosmos transactions.

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How It Works

┌─────────────────────┐
│ Cosmos Transaction  │
│  (MsgSend, etc.)    │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ Convert to EIP-712  │
│   Typed Data        │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│  Ethereum Ledger    │
│  App Signs with     │
│  eth_secp256k1      │
└──────────┬──────────┘
           │
           ▼
┌─────────────────────┐
│ Valid Cosmos TX     │
│   Signature         │
└─────────────────────┘

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EIP-712 Structure

A Cosmos transaction is converted to: 
{
  types: {
    EIP712Domain: [
      { name: "name", type: "string" },
      { name: "version", type: "string" },
      { name: "chainId", type: "uint256" },
      { name: "verifyingContract", type: "string" },
      { name: "salt", type: "string" }
    ],
    Tx: [
      { name: "account_number", type: "string" },
      { name: "chain_id", type: "string" },
      { name: "fee", type: "Fee" },
      { name: "memo", type: "string" },
      { name: "msgs", type: "Msg[]" },
      { name: "sequence", type: "string" }
    ],
    // ... additional types for Fee, Msg, etc.
  },
  primaryType: "Tx",
  domain: {
    name: "Cosmos Web3",
    version: "1.0.0",
    chainId: 7001,
    verifyingContract: "cosmos",
    salt: "0"
  },
  message: {
    account_number: "0",
    chain_id: "evm_7001-1",
    fee: { ... },
    memo: "",
    msgs: [ ... ],
    sequence: "0"
  }
}

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Implementation

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CLI Usage (evmd)

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Key Generation

Open the Ethereum app on your Ledger device and run: 
evmd keys add mykey --ledger
The key will use eth_secp256k1 by default.

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Transaction Signing

# Example: Bank send
evmd tx bank send mykey cosmos1... 1000aevmd --ledger --chain-id evm_7001-1
Your Ledger will display the EIP-712 domain and message hashes for verification.

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Browser Wallet Integration (Keplr)

Wallet developers can integrate EIP-712 signing using the @evmos/transactions library: 
import {
  createTxRawEIP712,
  signatureToWeb3Extension,
} from "@evmos/transactions";

// 1. Create EIP-712 payload from Cosmos transaction
const txRaw = createTxRawEIP712(messages, fee, {
  accountNumber,
  sequence,
  chainId: "evm_7001-1",
});

// 2. Sign with Ethereum provider (MetaMask, Ledger via Ethereum app, etc.)
const signature = await window.ethereum.request({
  method: "eth_signTypedData_v4",
  params: [signerAddress, JSON.stringify(txRaw.eipToSign)],
});

// 3. Convert signature to Cosmos format
const web3Extension = signatureToWeb3Extension(signature);

// 4. Broadcast to chain
const txBytes = txRaw.message.serializeBinary();
await client.broadcastTx(txBytes);
See the test web app in the evm repository for a complete working example.

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Why This Approach?

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Cosmos Leger App Limitations

  • Cosmos app cannot derive eth_secp256k1 addresses
  • Cosmos app uses different hashing (SHA256+RIPEMD160 vs Keccak256)
  • Ethereum app supports uncompressed public keys needed for EVM

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Technical Details

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Key Derivation

  • Algorithm: eth_secp256k1
  • HD Path: m/44'/60'/0'/0/0 (Ethereum standard, BIP-44)
  • Public Key Format: Uncompressed 65-byte ECDSA public key
  • Address Derivation: Keccak256(pubkey)[12:] → Bech32

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Signature Format

  • Input: EIP-712 typed data (structured Cosmos transaction)
  • Output: ECDSA signature (65 bytes: r + s + v)
  • Verification: Standard ECDSA verification against eth_secp256k1 pubkey

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EIP-712 Domain Separator

{
  name: "Cosmos Web3",
  version: "1.0.0",
  chainId: 7001, // Numeric EVM chain ID
  verifyingContract: "cosmos",
  salt: "0"
}

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Reference Implementation

  • CLI Tool: See scripts/test_ledger_manual.sh in the evm repo
  • Web App: See test-webapp in the evm repository for browser integration

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Further Reading