Signed bytes from Schnorrkel library throws Bad Signature error

Question

Hey I have some call data which is similar to this.

I am signing it using schnorrkel libaray function function. as secret.sign_simple(&[], msg) where secret is a Keypair and msg is in bytes.

Then I create a multisignature using

let sig_slice: &[u8] = &sig_bytes;
let sig = Signature::try_from(sig_slice).unwrap();
let multisig = MultiSignature::Sr25519(sig);

where &sig_bytes in bytes returned by signing and if I add that signature to make a extrinsic bytes e.g. here

I get error Transaction has a bad signature.

And if I send the same extrinsic using subxt and pass the signer as PairSigner<SubstrateConfig, sr25519::Pair> it works fine. But I can't use this pair sign function when signing a msg because of nature of architecture. I have to use an independent lib something more generic.

How can I solve this error?

Answer 1

Actually we need a context string for substrate signatures

let context = schnorrkel::signing_context(b"substrate");
Signature::Sr25519(secret.sign(context.bytes(msg)))

and then we can use the sign function which gives us a valid signature.