Simplify solo machine SignBytes construction

[colin-axner]

Summary

The solo machine has unnecessary layering when constructing the signature bytes the solo machine will sign over. The layers were added via a misunderstanding of the security implications. The current construction does not support the proposed changes in the spec repo to support Generic Verification functions. We should simplify the solo machine signature bytes to allow for the solo machine to verify signatures over new paths without modifying the existing code.

Problem Definition

The solo machine currently requires each path verified to have an associated DataType. Adding a type requires adding a new data type. This was added via a misunderstanding of the security implications. It was noted that the proto definitions do not provide uniqueness and we want to ensure that a signature corresponds to a specific path. What was missed is that the uniqueness is not provided by the proto definition, but by the usage of the proto definition. The path provided by core IBC will be unique and is already encoded into the signature data.

Proposal

• Remove DataType
• Remove each Verify type definition for constructing data
• Change DataType to Path in SignBytes

Backward compatibility considerations

Doing these changes will change the verification of solo machine signatures. That is, solo machines would need to correctly construct their signature data based on the version of 06-solomachine the chain they are talking to is using.

I think the practical approach is to deprecate the existing functionality and support it as legacy handling for a certain amount of time (giving chains/solo machines time to update to the newest changes). We could either try to construct the new and old sign bytes and see if one of them verifies or create a temporary requirement that the diversifier append a -06-solomachine-version-1 to indicate it will use the new functionality.

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[crodriguezvega]

Closed by #1687