PoC non-membership implementation

[mrain]

Proof of concept non-membership proof implementation

• Sparse Merkle tree
• Interval Merkle tree

[chancharles92]

• Implementation of Sparse Merkle Tree (SMT). (Jellyfish)
• Circuit gadget for SMT non-membership proof. (Jellyfish)
• Integrate the non-membership proof circuit into CAP circuit (CAP/blacklist-poc branch)

cc @alxiong @mrain and feel free to edit.

[alxiong]

integrate the non-membership proof circuit into CAP circuit

my understanding from @ben-a-fisch is that, we should separate them. In a new CAP transaction (specifically a transfer), you will have to provide the original transfer validity proof, then additionally, and optionally a non-blacklisted proof.
(^ this is what I understand as "user opt out to be marked as high risk")

In my mind, we just write a new non-membership gadget and a thin circuit around that, and result in an additional field: TransferNote.non_blacklist_proof: Option<Proof>.