Update misbehaviour handling to work with IBC 7

[sainoe]

Problem

The current implementation of the cryptographic equivocation feature utilizes an IBC-Go method to validate consumer client Misbehaviour. Specifically, in IBC-Go v4, the CheckMisbehaviourAndUpdateState method confirms that a given Misbehaviour satisfies the following three conditions:

• The headers of the misbehaviour posses different BlockIDs for the same block height.
• The trusted state in the headers is consistent with valid consensus states.
• The commit in the headers is signed by at least the TrustLevel of their trusted validator set.

Throughout the migration from IBC-Go v6 to v7, the ClientState interface has undergone some changes, including the split of the CheckMisbehaviourAndUpdateState into four distinct methods ref. IBC-Go doc.

As a result, the upgrade of the cryptographic equivocation feature from IBC-Go v4 to IBC-Go v7 necessitates adaptation to these changes. The adjustment should ensure that the same three conditions mentioned above are enforced for handling Misbehaviours.

Closing criteria

Update the Misbehaviour handling to perform the same verification that in CheckMisbehaviourAndUpdateState.

Problem details

[insumity]

What you describe sounds good to me.

The way I see this, is that CheckMisbehaviourAndUpdateState in v4.4.2 consists of the following 2 chunks:

1. Check if blockIDs are different if the headers contain bogus (i.e., wrong ordering) BFT times:

if tmMisbehaviour.Header1.GetHeight().EQ(tmMisbehaviour.Header2.GetHeight()) {
    blockID1, err := tmtypes.BlockIDFromProto(&tmMisbehaviour.Header1.SignedHeader.Commit.BlockID)
    [...]
    blockID2, err := tmtypes.BlockIDFromProto(&tmMisbehaviour.Header2.SignedHeader.Commit.BlockID)
    [...]
    if bytes.Equal(blockID1.Hash, blockID2.Hash) {
        return ...
    }
} else {
    if tmMisbehaviour.Header1.SignedHeader.Header.Time.After(tmMisbehaviour.Header2.SignedHeader.Header.Time) {
        return ...
    }
}

In IBC v7.3.1, the same functionality is provided by CheckForMisbehaviour.

2. Compare against the trusted consensus states and verify signatures using the trusted validator set:

tmConsensusState1, err := GetConsensusState(clientStore, cdc, tmMisbehaviour.Header1.TrustedHeight)
[..]

tmConsensusState2, err := GetConsensusState(clientStore, cdc, tmMisbehaviour.Header2.TrustedHeight)
[...]

if err := checkMisbehaviourHeader(
    &cs, tmConsensusState1, tmMisbehaviour.Header1, ctx.BlockTime(),
); err != nil {
    return ...
}
if err := checkMisbehaviourHeader(
    &cs, tmConsensusState2, tmMisbehaviour.Header2, ctx.BlockTime(),
); err != nil {
    return ...
}

In IBC v7.3.1, the same functionality is provided by VerifyClientMessage when called with a Misbehaviour message because VerifyClientMessage calls verifyMisbehaviour that performs the above.

Therefore, we can replace IBC v4's CheckMisbehaviourAndUpdateState with a call to CheckForMisbehaviour and a call to VerifyClientMessage in IBC v7 as follows:

clientMessage := transform MsgSubmitConsumerMisbehaviour to a clientMessage with a misbehaviour
isMisbehaviour := clientState.CheckForMisbehaviour(ctx, k.cdc, clientStore, clientMessage)
err := clientstate.VerifyClientMessage(ctx, cdc, clientStore, clientMessage)
return isMisbehaviour && err != nil

[sainoe]

Thanks @insumity! Glad to see that we came to the same conclusion for this refactoring to IBC v7.
The #1401 updates the feat/ics-misbehaviour-handling branch accordingly.