Sign a Message

FSCO provides a secure way to sign messages using your wallet’s private key. This is useful for proving ownership of a wallet or signing off-chain messages.

Prerequisites

Before you begin, ensure you have:

• A valid FSCO API key
• Your application’s environment configured with the API key
• A wallet ID for the wallet you want to use for signing
• The message data in hex format

Endpoint

POST /v2/wallet/{walletId}/sign/msg

Request Parameters

{
  "walletId": "8c1d496f-2827-4750-a11f-74b48c11108d",
  "data": "0xdeadbeef"
}

The request requires:

• walletId: The unique ID of the wallet to use for signing
• data: The message to sign in hex format (must start with ‘0x’)

Example Request

cURL

sign-message.sh

curl -X POST "https://api.fsco.io/v2/wallet/8c1d496f-2827-4750-a11f-74b48c11108d/sign/msg" \
  -H "Authorization: Bearer $FSCO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "walletId": "8c1d496f-2827-4750-a11f-74b48c11108d",
    "data": "0xdeadbeef"
  }'

TypeScript

sign-message.ts

import axios from 'axios';

const FSCO_API_KEY = process.env.FSCO_API_KEY;
const FSCO_API_SECRET = process.env.FSCO_API_SECRET;
const walletId = '8c1d496f-2827-4750-a11f-74b48c11108d';

const signMessage = async () => {
  const response = await axios.post(
    `https://api.fsco.io/v2/wallet/${walletId}/sign/msg`,
    {
      walletId,
      data: '0xdeadbeef',
    },
    {
      headers: {
        'x-api-key': FSCO_API_KEY,
        'x-api-secret': FSCO_API_SECRET,
        'Content-Type': 'application/json',
      },
    }
  );

  console.log('Signed Message:', response.data);
};

signMessage();

Python

sign-message.py

import requests
import os

FSCO_API_KEY = os.environ.get("FSCO_API_KEY")
FSCO_API_SECRET = os.environ.get("FSCO_API_SECRET")
wallet_id = "8c1d496f-2827-4750-a11f-74b48c11108d"


def sign_message():
    response = requests.post(
        f"https://api.fsco.io/v2/wallet/{wallet_id}/sign/msg",
        json={"walletId": wallet_id, "data": "0xdeadbeef"},
        headers={
            "x-api-key": FSCO_API_KEY,
            "x-api-secret": FSCO_API_SECRET,
            "Content-Type": "application/json",
        },
    )

    print("Signed Message:", response.json())


sign_message()

.NET

sign-message.cs

using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;

class MessageSigner
{
    static async Task Main()
    {
        var apiKey = Environment.GetEnvironmentVariable("FSCO_API_KEY");
        var client = new HttpClient();
        var walletId = "8c1d496f-2827-4750-a11f-74b48c11108d";

        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", apiKey);
        client.DefaultRequestHeaders.Add("Content-Type", "application/json");

        var requestBody = JsonSerializer.Serialize(new {
            walletId = walletId,
            data = "0xdeadbeef"
        });
        var content = new StringContent(requestBody, Encoding.UTF8, "application/json");

        var response = await client.PostAsync($"https://api.fsco.io/v2/wallet/{walletId}/sign/msg", content);
        var responseString = await response.Content.ReadAsStringAsync();

        Console.WriteLine("Signed Message: " + responseString);
    }
}

Response

Response

sign-message-response.json

{
  "walletId": "8c1d496f-2827-4750-a11f-74b48c11108d",
  "signedData": "0x4a882e6a0d41b0832a1d3c38d1c2d8a3a4a34a5e6f7c8d9e0f1a2b3c4d5e6f7"
}

Important Notes

• The message must be in hex format and start with ‘0x’
• The wallet must exist and be active
• The signed message can be used for verification on-chain or off-chain
• The signature follows the standard Ethereum message signing format
• The walletId in the path must match the walletId in the request body

Next Steps

• Sign a Transaction
• Create a Wallet
• Wallet Module Overview
• Wallet API Reference