Add a notary service

[doubiliu]

close #2646

[ZhangTao1596]

Suggestions about constant values by @roman-khimov #2425 (comment)

[AnnaShaleva]

The Notary contract logic looks good to me except the #2661 (comment).

@doubiliu, could you, please, take a look at neo-project/neo-modules#691 (comment), I think that this PR is also affected and changes are needed.

After that we'll need to adjust a part of NotaryRequest verification code.

[ZhangTao1596]

@erikzhang @shargon @Liaojinghui Can you review this one? Especially the enum values we choose.

[Jim8y]

what if teh Signers size is 1 here?

[ZhangTao1596]

Fallback tx MUST have 2 signers. The check is here https://github.com/neo-ngd/neo/blob/4b10f64835eade8edb2005d9171cd2b839639f9a/src/neo/Network/P2P/Payloads/NotaryRequest.cs#L108

[Jim8y]

Suggested change

	var balance = NativeContract.Notary.BalanceOf(snapshot, fallbackTransaction.Signers[1].Account);
	if (fallbackTransaction.Signers.Length != 2) return false;
	var balance = NativeContract.Notary.BalanceOf(snapshot, fallbackTransaction.Signers[1].Account);

[ZhangTao1596]

This is checked in VerifyStateIndependent.

[Jim8y]

Aren't they belong to different functionalities? Or they are supposed to be used together all the time?

[ZhangTao1596]

Like transaction verification
Transaction.VerifyStateDependent is supposed to call after Tansaction.VerifyStateIndependent. So we don't verify signature in state dependent.

[erikzhang]

Use Extensible payload?

[ZhangTao1596]

Not everyone can send extansible paylaod. Users need this request to send their signature so that node with notary plugin can collect them.

[doubiliu]

Use Extensible payload?

Maybe difficult. Because RequestPayload has a more complex verification logic, extansible paylaod is not enough to support
public bool Verify(ProtocolSettings settings) { var nKeysMain = MainTransaction.GetAttributes<NotaryAssisted>(); if (!nKeysMain.Any()) return false; if (nKeysMain.ToArray()[0].NKeys == 0) return false; if (!fallbackTransaction.Script.SequenceEqual(FallbackFixedScript)) return false; if (FallbackTransaction.Signers.Length != 2) return false; if (fallbackTransaction.Signers[1].Scopes != WitnessScope.None) return false; if (FallbackTransaction.Witnesses[0].InvocationScript.Length != 66 || FallbackTransaction.Witnesses[0].VerificationScript.Length != 0 || (FallbackTransaction.Witnesses[0].InvocationScript[0] != (byte)OpCode.PUSHDATA1 && FallbackTransaction.Witnesses[0].InvocationScript[1] != 64)) return false; if (FallbackTransaction.GetAttribute<NotValidBefore>() is null) return false; var conflicts = FallbackTransaction.GetAttributes<ConflictAttribute>(); if (conflicts.Count() != 1) return false; if (conflicts.ToArray()[0].Hash != MainTransaction.Hash) return false; var nKeysFallback = FallbackTransaction.GetAttributes<NotaryAssisted>(); if (!nKeysFallback.Any()) return false; if (nKeysFallback.ToArray()[0].NKeys != 0) return false; if (MainTransaction.ValidUntilBlock != FallbackTransaction.ValidUntilBlock) return false; if (!fallbackTransaction.VerifyWitness(settings, null, fallbackTransaction.Signers[1].Account, fallbackTransaction.Witnesses[1], 0_02000000, out _)) return false; return this.VerifyWitnesses(settings, null, 0_02000000); }

[Jim8y]

though i saw this before, but still, this logic is increadblly complex~~~

[roman-khimov]

Why don't we move #1991 and #1992 implementations out of this PR and merge them into master? Both have some use even without notary subsystem, merging them will allow to properly review these parts and simplify this PR. #1992 is rather trivial and can be merged in a day probably, #1991 is a bit more involved, but we'll take a look at the specifics of it and it'll be done, allowing to concentrate on other notary details then. Just as a reminder, T5 NeoFS sidechain runs with notary enabled already, so I think we should move on with it and doing that in smaller steps is easier.

[Jim8y]

This pr is too long and contains too many changes that is not actually part of this pr, is that possible to clean them up? @doubiliu

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[AnnaShaleva]

@Jim8y, @shargon and everyone interested: this PR has a large amount of code, and some of this code is out-of-date. It is hard to review and track changes in this PR, and thus we propose to go step-by-step on the path of Notary-related issues implementation (#2895, #2896 and #2897 are a must have).

Based on this PR in the nearest future I'll create a set of PRs that solve mentioned issues. Some parts of the current PR don't work as expected, there is still the set of unresolved conversations, so I'll update the code and make it work properly. We propose to close this PR and start with a tiny fresh #3172.

What do you think?