Phantom Browser Extensions can't sign non-utf8 bytes with signMessage

[jsamol]

Summary

I'm trying to sign arbitrary non-utf8 encoded bytes with Phantom using @solana/wallet-adapter. Unfortunately, the browser extensions (Chrome, Firefox) seem to be unable to do so and throw You cannot sign solana transactions using sign message on every try. Interestingly enough, the Android application doesn't share this behaviour and has no problems with signing the same messages. I haven't tested the other extensions - Brave and Edge.

I've seen other discussions reporting the same (#189, #181), but I don't find the answers sufficient to close the issue, especially that it looks like it's a problem only in a browser and not even a single non-utf8 byte can be signed - which with certainty isn't a transaction.

Example

No response

Steps to Reproduce

Sign arbitrary bytes with a browser extension using @solana/wallet-adapter:

import { useWallet } from '@solana/wallet-adapter-react';

const message = new Uint8Array([183]);

const { signMessage } = useWallet();
await signMessage(message); // fails with `You cannot sign solana transactions using sign message`

To compare behaviours, sign the same with the Android application using the MWA SDK:

val message = byteArrayOf((183).toByte())

val walletAdapter = MobileWalletAdapter(...)
// connect and get the public key
walletAdapter.transact(...) {
    signMessagesDetached(
        arrayOf(message),
        arrayOf(publicKey),
    )
} // returns TransactionResult.Success with the signature

Phantom Version

25.8.0

Is there an existing discussion for this?

• I have searched the existing discussions

[adamdelphantom]

@jsamol Can I understand your use case for signing non-utf8 byte messages?

[jsamol]

I was working on integrating Solana wallets with a Substrate-base network, allowing Solana users to seamlessly onboard and interact with the chain without needing to set up a new wallet. This required that the wallets were able to sign an encoded Substrate transaction.

Eventually, we had to come up with a workaround for Phantom's limitation and introduced a special signature type that allowed us to encode the raw transaction bytes into a utf8 string, which, of course, was still not quite human-readable - it never could, but the wallet was able to handle it.

I understand the goal of this strict signing rule, and I do agree that wallets should protect their users from malicious intent, especially when it's a transaction signing request coming in through a channel that it's not supposed to come in, but I also believe that there are ways to recognize a Solana transaction from arbitrary bytes, which could be applied in this case and allow more flexibility for the developers.