> ## Documentation Index
> Fetch the complete documentation index at: https://docs.phantom.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Sign a message
> Request message signatures from Bitcoin users through Phantom to verify address ownership without fees.
**The `window.phantom.bitcoin` provider has been deprecated.**
When a dapp is connected to Phantom, it can also request that the user signs a given message. Applications are free to write their own messages which will be displayed to users from within Phantom's signature prompt. Message signatures do not involve network fees and are a convenient way for apps to verify ownership of an address.
Phantom’s `signMessage` function accepts two parameters: an encoded `message` and an `address` that should be used to sign the message. It returns a Promise that resolves if the user approves the signature request. Once resolved, it contains the resulting `signature`.
```typescript theme={null}
// function signature
function signMessage(
address: string,
message: Uint8Array,
): Promise<{
signature: Uint8Array;
}>;
```
The following is an example of how to construct and sign a message with Phantom:
```typescript theme={null}
const message = new TextEncoder().encode('hello world');
const address = "bc1phajtersv55fwud5xr0t70p5234swy396a6avqhuny0qf83zssvrsm7tl4q"; // see "Establishing a Connection"
const { signature } = await phantomProvider.signMessage(address, message);
```
To verify that a message was signed by a given address, we recommend using the [bip322-js](https://github.com/ACken2/bip322-js) library like so:
```typescript theme={null}
import { Verifier } from "bip322-js";
// helper method
function bytesToBase64(bytes) {
const binString = String.fromCodePoint(...bytes);
return btoa(binString);
}
const isValidSignature = Verifier.verifySignature(
address,
new TextDecoder().decode(message),
bytesToBase64(signature),
);
console.log(isValidSignature);
// true
```