evm-kms-signer

A TypeScript library that integrates AWS/GCP KMS (Key Management Service) with viem to create secure Ethereum signers. This allows you to sign Ethereum transactions and messages using keys stored in AWS or GCP KMS, providing enterprise-grade security for your Ethereum operations.

Features

• AWS KMS Integration: Sign Ethereum transactions using keys securely stored in AWS KMS
• GCP KMS Support: Also supports Google Cloud Platform KMS for multi-cloud deployments
• Full EIP Compliance: Supports EIP-191 (personal messages), EIP-712 (typed data), EIP-155 (replay protection), EIP-2 (signature normalization)
• Type-Safe: Built with TypeScript in strict mode with comprehensive type definitions
• viem Compatible: Seamlessly integrates with viem's Account system via toAccount
• DER Signature Parsing: Automatically converts AWS/GCP KMS DER-encoded signatures to Ethereum format
• Comprehensive Error Handling: Custom error classes for better debugging
• Well-Tested: 169 tests covering all functionality with 100% type safety

Installation

pnpm add evm-kms-signer

Or with npm:

npm install evm-kms-signer

Or with yarn:

yarn add evm-kms-signer

Usage

AWS KMS

Prerequisites

1. Create an ECC Key in AWS KMS:

   • Go to AWS KMS Console
   • Click "Create key"
   • Choose "Asymmetric" key type
   • Select "Sign and verify" key usage
   • Choose ECC_SECG_P256K1 as the key spec (this is secp256k1, Ethereum's curve)
   • Complete the key creation process

2. Grant Permissions: Ensure your AWS credentials have the following permissions:

   • kms:GetPublicKey
   • kms:Sign

3. Note Your Key ID: Copy the Key ARN or Key ID for use in your application.

Environment Variables

Create a .env file in your project root:

AWS_REGION=us-east-1
KMS_KEY_ID=arn:aws:kms:us-east-1:123456789012:key/12345678-1234-1234-1234-123456789012

# Optional: If not using IAM roles or default credentials
AWS_ACCESS_KEY_ID=your_access_key
AWS_SECRET_ACCESS_KEY=your_secret_key

Basic Usage

import 'dotenv/config'
import { KmsSigner, toKmsAccount } from 'evm-kms-signer'

async function main() {
  // Initialize the KMS signer
  const signer = new KmsSigner({
    region: process.env.AWS_REGION!,
    keyId: process.env.KMS_KEY_ID!,
  })

  // Convert to viem account
  const account = await toKmsAccount(signer)

  console.log('Account address:', account.address)

  // Sign a message
  const message = 'Hello from AWS KMS!'
  const signature = await account.signMessage({ message })

  console.log('Signature:', signature)
}

main().catch(console.error)

Use with viem

import 'dotenv/config'
import { createWalletClient, http } from 'viem'
import { sepolia } from 'viem/chains'
import { KmsSigner, toKmsAccount } from 'evm-kms-signer'

async function main() {
  // Initialize the KMS signer
  const signer = new KmsSigner({
    region: process.env.AWS_REGION!,
    keyId: process.env.KMS_KEY_ID!,
  })

  // Convert to viem account
  const account = await toKmsAccount(signer)

  // Create a wallet client
  const client = createWalletClient({
    account,
    chain: sepolia,
    transport: http()
  })

  // Send a transaction
  const hash = await client.sendTransaction({
    to: '0xa5D3241A1591061F2a4bB69CA0215F66520E67cf',
    value: 1000000000000000n, // 0.001 ETH
  })

  console.log('Transaction hash:', hash)
}

main().catch(console.error)

GCP KMS

Prerequisites

1. Create a KMS key ring and crypto key in GCP Console:

   • Go to Google Cloud Console → Security → Key Management
   • Create a new key ring in your desired location
   • Create a crypto key with purpose "Asymmetric sign"
   • Choose Elliptic Curve P-256 - SHA256 Digest algorithm (secp256k1 for Ethereum)

2. Grant Permissions: Grant roles/cloudkms.cryptoKeySignerVerifier permission to your service account:

   gcloud kms keys add-iam-policy-binding KEY_ID \
     --location=LOCATION \
     --keyring=KEYRING_ID \
     --member=serviceAccount:SERVICE_ACCOUNT_EMAIL \
     --role=roles/cloudkms.cryptoKeySignerVerifier

3. Set up authentication:

   • Set GOOGLE_APPLICATION_CREDENTIALS environment variable pointing to your service account key file, or
   • Pass keyFilename in config

Basic Usage

import { GcpSigner } from 'evm-kms-signer';

const signer = new GcpSigner({
  projectId: 'your-project-id',
  locationId: 'global',
  keyRingId: 'your-keyring-id',
  keyId: 'your-key-id',
  keyVersion: '1',
  keyFilename: '/path/to/service-account-key.json', // optional
});

const address = await signer.getAddress();
const signature = await signer.signMessage({ message: 'Hello!' });

Use with viem

import { createWalletClient, http } from 'viem';
import { mainnet } from 'viem/chains';
import { toGcpKmsAccount } from 'evm-kms-signer';

const account = await toGcpKmsAccount(signer);
const client = createWalletClient({
  account,
  chain: mainnet,
  transport: http(),
});

API Documentation

KmsSigner

The main class for signing operations using AWS KMS.

Constructor

new KmsSigner(config: KmsConfig)

Parameters:

• config.region: AWS region where your KMS key is located
• config.keyId: AWS KMS key ID or ARN
• config.credentials (optional): AWS credentials object with accessKeyId and secretAccessKey

Methods

getAddress(): Promise<Address>

Returns the Ethereum address derived from the KMS public key.

const address = await signer.getAddress()

getPublicKey(): Promise<Uint8Array>

Returns the uncompressed public key (65 bytes) from AWS KMS.

const publicKey = await signer.getPublicKey()

signMessage({ message }): Promise<Hex>

Signs a personal message (EIP-191).

const signature = await signer.signMessage({ message: 'Hello World' })

signTransaction(transaction, options?): Promise<Hex>

Signs an Ethereum transaction with EIP-155 replay protection.

const signedTx = await signer.signTransaction({
  to: '0x...',
  value: 1000000000000000n,
  chainId: 11155111,
  nonce: 0,
  maxFeePerGas: 20000000000n,
  maxPriorityFeePerGas: 1000000000n,
})

signTypedData(typedData): Promise<Hex>

Signs structured data (EIP-712).

const signature = await signer.signTypedData({
  domain: {
    name: 'Ether Mail',
    version: '1',
    chainId: 1,
    verifyingContract: '0x...'
  },
  types: {
    Person: [
      { name: 'name', type: 'string' },
      { name: 'wallet', type: 'address' }
    ]
  },
  primaryType: 'Person',
  message: {
    name: 'Bob',
    wallet: '0x...'
  }
})

toKmsAccount(signer: KmsSigner): Promise<LocalAccount>

Converts a KmsSigner instance to a viem LocalAccount that can be used with viem's wallet clients.

const account = await toKmsAccount(signer)

const client = createWalletClient({
  account,
  chain: mainnet,
  transport: http()
})

Error Classes

The library provides custom error classes for better error handling:

• KmsSignerError: Base error class
• DerParsingError: Thrown when DER signature parsing fails
• KmsClientError: Thrown when AWS KMS operations fail
• SignatureNormalizationError: Thrown when signature normalization fails
• RecoveryIdCalculationError: Thrown when recovery ID calculation fails

Security Considerations

Key Management

• Private keys never leave AWS KMS: All signing operations happen within AWS KMS
• IAM Permissions: Use least-privilege IAM policies for KMS access
• Key Rotation: Consider AWS KMS key rotation policies for your use case

Signature Security

• EIP-2 Compliance: All signatures are normalized to prevent malleability attacks
• Replay Protection: Transaction signatures include EIP-155 chainId by default
• Recovery ID: Automatically calculated and verified for all signatures

Best Practices

1. Use IAM Roles: Prefer IAM roles over hardcoded credentials in production
2. Environment Variables: Never commit .env files with credentials
3. Key Policies: Restrict KMS key usage to specific AWS principals
4. Audit Logging: Enable AWS CloudTrail to monitor KMS key usage
5. Network Security: Use VPC endpoints for KMS in production environments

Development

Running Tests

pnpm test:run

Type Checking

pnpm type-check

Building

pnpm build

Running Examples

# Sign a message
pnpm example:sign

# Send a transaction
pnpm example:tx

License

MIT

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Acknowledgments

• Built with viem - Modern TypeScript Ethereum library
• Uses AWS SDK for JavaScript v3
• Uses Google Cloud KMS Client Library
• Inspired by the need for secure key management in Ethereum applications