Add BIP0322 Proof of Funds & implement RegisterIntent

[louisinger]

update: #485 (comment)

This PR deletes the nostr notifications system and replace it by a simple GetNote API. OwnershipProof is also replaced by BIP0322 "Proof of Funds".

GetNote

GetNote RPC expects bip322_signature and the associated message. If the signature is valid, the server returns a note where amount = sum of bip322_signature outpoints. The server also mark the VTXOs as spent in DB to prevent cheating.

BIP0322 Proof of funds

common.bip322 package is standalone and follows the BIP0322 specifications ⚠️ except that it doesn't verify the inputs sequence in order to allow the proof to be used for offchain outpoints.

The message must be the current Unix timestamp. It is considered valid by the server if and only if it is close to current timestamp.

CLI and SDK

sdk.RecoverSweptVtxos or ark recover CLI command automatically fetch swept and unspent VTXOs, create a BIP0322 signature, fetch the associated note and redeem it.

it closes #484
it closes #483

@altafan @Kukks please review

[Kukks]

Couldn't one simply use the VTXO ownership proof in itself as a note? The api to exchange a proof for a vtxo is redundant:

This flow:

• VTXO expires/gets swept
• Wallet goes online, detected expired vtxo
• Wallet creates proof, send to GetNote
• Server returns note
• Wallet redeems note for new VTXO

Proposed flow:

• VTXO expires/gets swept
• Wallet goes online, detected expired vtxo
• Wallet creates proof and registers it as input for next batch

[louisinger]

Proposed flow:

• VTXO expires/gets swept
• Wallet goes online, detected expired vtxo
• Wallet creates proof and registers it as input for next batch

I agree, but if we do that, we should be able to register also the not expired VTXOs in the same proof no ? If I have 1 VTXO not swept + 1 expired VTXO, I create a proof containing both outpoints and use it as input ?

something like:

message RegisterInputsForNextRoundRequest {
  repeated TaprootTree revealed_taproot_tree = 1; // reveal tapscripts of unspent & not expired vtxos
  repeated string notes = 2;
  string bip322_signature = 3; // proof of funds for "inputs" array + swept vtxos you want to recover
}

[louisinger]

According to the latest discussion, I've removed the GetNote RPC and reworked the inputs' registration flow:

message RegisterInputsForNextRoundRequest {
  map<string, Tapscripts> tapscripts = 1; 
  Bip322Signature bip322_signature = 2;
  repeated string notes = 3;
}

To register inputs, users must provide a valid BIP322 signature signing a timestamp message. The server accepts the signature if now - timestamp < 15 seconds.

The BIP322 proof of funds tx may include:

• boarding UTXOs
• unspent VTXOs
• recoverable VTXOs (expired but unspent)

map<string, Tapscripts> tapscripts = 1; field should contain the revealed tapscripts for boarding and unspent VTXOs.

[tiero]

lets not replace it, and only add a new RPC

[Kukks]

lets not replace it, and only add a new RPC

Ideally we do remove it in the medium term, it's a redundant rpc and keeps duplicate logic around input proofs