Sign-In with Ethereum

This package provides a pure Go implementation of EIP-4361: Sign In With Ethereum.

Installation

SIWE can be easily installed in any Go project by running:

go get -u github.com/spruceid/siwe-go

Usage

SIWE exposes a Message struct which implements EIP-4361.

Parsing a SIWE Message

Parsing is done via the siwe.ParseMessage function:

var message *siwe.Message
var err error

message, err = siwe.ParseMessage(messageStr)

The function will return a nil pointer and an error if there was an issue while parsing.

Verifying and Authenticating a SIWE Message

Verification and Authentication is performed via EIP-191, using the address field of the Message as the expected signer. This returns the Ethereum public key of the signer:

var publicKey *ecdsa.PublicKey
var err error

publicKey, err = message.VerifyEIP191(signature)

The time constraints (expiry and not-before) can also be validated, at current or particular times:

var message *siwe.Message

if message.ValidNow() {
  // ...
}

// equivalent to

if message.ValidAt(time.Now().UTC()) {
  // ...
}

Combined verification of time constraints and authentication can be done in a single call with verify:

var publicKey *ecdsa.PublicKey
var err error

// Optional domain and nonce variable to be matched against the
// built message struct being verified
var optionalDomain *string
var optionalNonce *string

// Optional timestamp variable to verify at any point
// in time, by default it will use `time.Now()`
var optionalTimestamp *time.Time

publicKey, err = message.Verify(signature, optionalDomain, optionalNonce, optionalTimestamp)

// If you won't be using domain and nonce matching and want
// to verify the message at current time, it's
// safe to pass `nil` in these arguments
publicKey, err = message.Verify(signature, nil, nil, nil)

Serialization of a SIWE Message

Message instances can also be serialized as their EIP-4361 string representations via the String method:

fmt.Printf("%s", message.String())

Signing Messages from Go code

To sign messages directly from Go code, you will need to do it like shown below to correctly follow the personal_sign format.

func signHash(data []byte) common.Hash {
	msg := fmt.Sprintf("\x19Ethereum Signed Message:\n%d%s", len(data), data)
	return crypto.Keccak256Hash([]byte(msg))
}

func signMessage(message string, privateKey *ecdsa.PrivateKey) ([]byte, error) {
	sign := signHash([]byte(message))
	signature, err := crypto.Sign(sign.Bytes(), privateKey)

	if err != nil {
		return nil, err
	}

	signature[64] += 27
	return signature, nil
}

Disclaimer

Our Go library for Sign-In with Ethereum has not yet undergone a formal security audit. We welcome continued feedback on the usability, architecture, and security of this implementation.

See Also

• Sign-In with Ethereum: TypeScript
• Example SIWE application: login.xyz
• EIP-4361 Specification Draft
• EIP-191 Specification