How to verify a signature from the Phantom wallet?

Question

I am able to sign a message on the client side using something like this:

const encodedMessage = new TextEncoder().encode("some message");
const signedMessage = await provider.signMessage(encodedMessage, "utf8");

Now I want to verify the signature on the back end side using Kotlin (or Java).

Problem:

1. I cannot find the information about the algorithm that is used for signing messages in the documentation.
2. It seems like there are no Java/Kotlin libraries that work with Phantom and Solana (found a few which are not updated for a year).

Question: How can I verify a signature from the Phantom wallet using Java? Or generally how can I do that in any language? (I will port it to Java then).

Answer 1

In JavaScript, you can use the tweetnacl library to verify signatures.

const hasSucceededVerification = nacl.sign.detached.verify(
    encodedMessage, // the message
    signedMessage, // the signature
    publicKey.toBytes() // public key
); // returns boolean

console.log(`signature verified?: ${hasSucceededVerification}`);

Ed25519 is the signature system used on Solana.

You can find a complete example here: https://solanacookbook.com/references/offline-transactions.html#sign-transaction