Adding Typed Structured Data Hashing and Signing Protocol

[Jim8y]

Summary or problem description
People need to know what they are signing in readable and verifiable plaintext, instead of hex string.

Do you have any solution you want to propose?
Typed Structured Data Hasing and Signing Protocol is a good one.

Neo Version

• Neo 3

Where in the software does this update applies to?

• Other: Neo Proposals

[roman-khimov]

This is a very good thing to have, but in Neo context there is a huge barrier to that: transaction's NeoVM script. The fact that we can have Turing-complete code in each and every transaction is a huge and underrated feature of Neo, while at the same time it's a problem for this kind of protocol since you have to deal with VM code and not just (typed) data.

Maybe it can be handled for simple cases like only calling exactly one method of one contract, though. We have invokefunction JSON-RPC and somehow it deals with its (typed, btw) input producing some bytecode to run. Now you need to ensure that there is only one way to turn this input into bytecode (there are lots of ways to PUSH 1 onto the stack) and that can be some base for the thing. But the process itself looks like
https://github.com/neo-project/neo/blob/535aa2057b6ddddb90b2009ef47f8ba16fd3d036/src/Neo/VM/Helper.cs#LL105C11-L105C11
or
https://github.com/nspcc-dev/neo-go/blob/a0117042e8fc1b88b33b854b82e83e42ca6b286b/pkg/services/rpcsrv/params/txBuilder.go#L115
and we're not even considering the inverse VM->structure process for now.

[roman-khimov]

But we may consider moving to neo-project/proposals#68 for this discussion.