[ZKS-05] Caller Is Not Fixed Throughout Function Execution

[vicsn]

Motivation

We should ensure the self.signer is the same throughout a call graph in a single Execution.

As recommended, this PR adds binding and hiding commitments to the signer in each transition, which needs a secret which is constant for the entire execution. We propose the following, which will leak the signer to everyone holding the root_tvk:

• signer_commitment = hash(signer address || root_tvk)

Notes:

• performance improvement: each request in an execution has the same signer and scm now, in the future we could refactor and perhaps store a single signer and scm in the Execution
• we could hypothetically check if all signer commitments in an entire transaction are the same, but perhaps this doesn't leave open the door for more flexible or multi-execute transactions.
• we cannot use the account view_key as secret because we'd leak it to the party we delegate to. It is also expensive to derive the address from the view_key within the circuit.

Test Plan

• Requires resampling, including ./resources/block.genesis