Sign in with Ethereum

This package provides a Python implementation of EIP-4361: Sign in with Ethereum.

Installation

SIWE can be easily installed in any Python project with pip:

pip install signinwithethereum

The distribution is published as signinwithethereum; the import name is siwe:

from siwe import SiweMessage

Usage

SIWE provides a SiweMessage class which implements EIP-4361.

Parsing a SIWE Message

Parsing is done by initializing a SiweMessage object with an EIP-4361 formatted string:

from siwe import SiweMessage
message = SiweMessage.from_message(message=eip_4361_string)

Or to initialize a SiweMessage as a pydantic.BaseModel right away:

message = SiweMessage(domain="login.xyz", address="0x1234...", ...)

Verifying and Authenticating a SIWE Message

Verification and authentication is performed via EIP-191, using the address field of the SiweMessage as the expected signer. The verify method checks message structural integrity, signature address validity, and time-based validity attributes.

Replay protection relies on a single-use nonce that your server issues, stores alongside the pending session, passes to verify, and consumes on success. Always pass the nonce you issued — a signature verified without a nonce check can be replayed.

try:
    message.verify(
        signature="0x...",
        domain="example.com",
        nonce=expected_nonce,  # the nonce your server issued for this session
        uri="https://example.com/login",
        chain_id=1,
        strict=True,
    )
    # Consume the nonce now so it cannot be replayed.
except siwe.VerificationError:
    # Invalid

Passing strict=True enforces that domain, uri, chain_id, and nonce are all supplied. Prefer it for authentication flows.

Smart-contract wallet signatures (EIP-1271 / EIP-6492)

For signatures produced by contract wallets (Safe, Argent, etc.) rather than externally owned accounts, pass a web3 provider to verify. The authentication arguments (strict, domain, nonce, uri, chain_id) still apply — the provider only changes how the signature itself is verified:

from web3 import HTTPProvider

message.verify(
    signature="0x...",
    domain="example.com",
    nonce=expected_nonce,
    uri="https://example.com/login",
    chain_id=1,
    strict=True,
    provider=HTTPProvider("https://mainnet.infura.io/v3/..."),
)

EOA recovery is tried first; if it fails, the signature is checked on-chain via isValidSignature(bytes32,bytes) per EIP-1271. Signatures carrying the EIP-6492 magic suffix are handed to the universal off-chain validator bytecode via eth_call, which covers counterfactual (undeployed) wallets as well as already-deployed ones. The provider's chain id is checked against the message's chain_id before any on-chain call.

Note: this is verification only. EIP-6492 allows a verifier to optionally submit the factory transaction after a successful check to finalize on-chain deployment ("side-effectful" verification). This library does not do that — if you need the wallet actually deployed, submit the factory call yourself.

Serialization of a SIWE Message

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

print(message.prepare_message())

Example

Parsing and verifying a SiweMessage is easy:

try:
    message = SiweMessage.from_message(eip_4361_string)
    message.verify(
        signature,
        domain="example.com",
        nonce=expected_nonce,
        uri="https://example.com/login",
        chain_id=1,
        strict=True,
    )
except ValueError:
    # Invalid message format
    print("Authentication attempt rejected.")
except siwe.ExpiredMessage:
    print("Authentication attempt rejected.")
except siwe.DomainMismatch:
    print("Authentication attempt rejected.")
except siwe.NonceMismatch:
    print("Authentication attempt rejected.")
except siwe.InvalidSignature:
    print("Authentication attempt rejected.")

# Message has been verified. Invalidate the stored nonce, then continue with authorization/other.

Testing

git submodule update --init
uv sync
uv run pytest

See Also

• Sign in with Ethereum: TypeScript
• SIWE website: siwe.xyz
• EIP-4361 Specification Draft
• EIP-191 Specification

Disclaimer

Our Python 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.