keypair to secret bytes in subxt-signer

[silicology1]

How can I convert keypair to SecretKeyBytes or [u8; 32] using subxt-signer?

[jsdw]

Currently this isn't possible, I think to make it harder to accidentally misuse. Out of interest, what do you need it for?

We could add an APi to hand it back if need be (or perhaps just to turn a SecretUri into a secret key so that you can keep it somewhere and also use it to generate a Keypair)

[silicology1]

I wanted to create Iroh accounts using the same seed as blockchain accounts so that I can send P2P messages using the blockchain accounts. I'm not sure if this is the right approach. One can also store the iroh accounts in smart contract itself. Or sign Iroh messages with your Polkadot key and receiver verifies the signature using your Polkadot public key

[jsdw]

I can't really speak to whether it makes sense to reuse the secret keys in this way or not; not sure offhand what the benefits are to this!

One issue I realised is that we take in a 32 byte "mini secret key" to generate our sr25519 keypairs in a way compatible with Substrate. The mini secret key is then expanded into a "full" key when used. I can't see a way to extract the mini secret key again once expanded, so offhand it's not clear that I can hand back a secret key here (which is probably actually why it wasn't done, as I see we have secret_key methods for ecdsa/eth)!

It's a little ugly but in theory I could add a secret_key_from_phrase method which turns a seed phrase into a key that can be later passed into from_secret_key to instantiate our signer. Perhaps there's a way to recover the "mini secret key" from the Keypair though which would be preferable but I have not seen how yet!