Add support for NRD kernels

[lehnberg]

Add support for the new NRD kernel type and signature structure in the wallet.

Context

April 14 dev meeting:

• yeastplume: Actually, reminds me I had a question on nerd kernels just in respect to the wallet, should there be a separate issue to support them in the wallet, support for the new kernel type and new signature structure?
  • antiochp: Hmm - yeah actually using them is non-trivial.
  • jaspervdm: I think regular send operations do not need to use them, so no for now.
  • antiochp: And not really much use outside multiparty outputs.
  • jaspervdm: Until we want to implement some form of payment channel.
  • yeastplume: Yes, I thought so, but I was thinking a bare minimum... Recognizing them and supporting the new sig format. With a more fully-fleshed out api to come much later. I suppose this can all come after the hf anyhow.
  • antiochp: No sig changes.
  • tromp: Wallet should just skip all kernels it doesn't recognize. E.g. when recovering.
  • antiochp: Oh I see what you mean, message being changed is specific to the kernel type.
  • yeastplume: Additional sig format? Or did I read that wrong. There should probably be some bare minimum recognition of them in the wallet, I don't think we'd want a state where some wallets in the wild know about them and others don't.
  • jaspervdm: Not sure I understand, any tx the wallet will construct will either have a plain kernel or a lock height kernel, it does not ever construct a nrd kernel.
  • antiochp: Hmm - want to open an issue on grin-wallet to track this conversation.
  • jaspervdm: Unless we explicitly want to add that feature.
  • antiochp: We can comment there offline.
  • jaspervdm: But not sure we want to.
  • yeastplume: But some other wallet might.
  • jaspervdm: Wallet could simply refuse to sign such a tx.
  • yeastplume: Anyhow, yes we can take this offline.
  • jaspervdm: Since it requires an additional fee. Yes agreed.