Need to fix sign and verify messages for altcoins. I don't know how to do this.

[username1565]

I don't understand C++ syntax of the source code
in altcoins modules for signing and verify messages,
so I cann't fix this script to be compatible with altcoins wallets.

For example, we can using signing and verify the signed messages for altcoins:

1. Go here: https://username1565.github.io/brainwallet.github.io/
2. Select in the menu the Vertcoin (VTC) or another altcoin.
3. Go to "sign" tab.
4. As you can see, there is using private key and address for altcoins.
5. Sign message:
   Private key: 'KwSrQfTpAq6zodDmBvk8RzgqL9D35EFcDPg4NEprfzv77VyMr6Kc'
   Address: 'VejdSd7zrm3XSok4CC8t94rTfZVuBwUStu'
   Message: 'This is an example of a signed message.'
   Signature type: 'Inputs.IO'
6. Click "Sign Message" button.
7. Result:
   '-----BEGIN BITCOIN SIGNED MESSAGE-----
   This is an example of a signed message.
   -----BEGIN SIGNATURE-----
   VejdSd7zrm3XSok4CC8t94rTfZVuBwUStu
   H4zF7QP0kQZ3WnMYRXZNGvJy7j9pWHYD4MR2GBYFgL47ei2CIngAlN2eJzO8bw+DGDkkhvhAxUwurjjkhALaKnY=
   -----END BITCOIN SIGNED MESSAGE-----'
8. This result can be verified only by script, using permalink or copy and paste the signed message.
   Permalink:
   https://username1565.github.io/brainwallet.github.io/#verify?vrAddr=VejdSd7zrm3XSok4CC8t94rTfZVuBwUStu&vrMsg=This%20is%20an%20example%20of%20a%20signed%20message.&vrSig=H4zF7QP0kQZ3WnMYRXZNGvJy7j9pWHYD4MR2GBYFgL47ei2CIngAlN2eJzO8bw%2BDGDkkhvhAxUwurjjkhALaKnY%3D
   result: Message verified to be from VejdSd7zrm3XSok4CC8t94rTfZVuBwUStu (permalink)

But in vertcoin-qt wallet "Message verification failed".
Also, the message, which signed in vertcoin-qt wallet -
cann't be successfully verified using brainwallet "Verify" tab:
https://username1565.github.io/brainwallet.github.io/#verify

Here is the source code of module for signing and verify messages, in vertcoin-qt.exe:
https://github.com/vertcoin-project/vertcoin-core/blob/0.13.0/src/qt/signverifymessagedialog.cpp
But I don't understand anything there.

Can anyone fix this for all another altcoins?

Also, I see here https://github.com/username1565/brainwallet.github.io/blob/master/js/bitcoinsig.js
there is the prefix for message digest:

function msg_digest(message) {
    var b = msg_bytes("Bitcoin Signed Message:\n").concat(msg_bytes(message));
    return Crypto.SHA256(Crypto.SHA256(b, {asBytes:true}), {asBytes:true});
}

and here: https://github.com/vertcoin-project/vertcoin-core/blob/0.13.0/src/qt/signverifymessagedialog.cpp is using strMessageMagic
and this is defined here: https://github.com/vertcoin-project/vertcoin-core/blob/0.13.0/src/validation.cpp
as

const std::string strMessageMagic = "Vertcoin Signed Message:\n";

[username1565]

This issue - already resolved: de17257