Fully integrate Qurrency

[jimthematrix]

This is for tracking the work to fully integrate the new Qurrency protocol (add link here once the paper is published) to Zeto with a new token implementation.

The name of the new token is zeto_anon_nullifier_qurrency. It's based on zeto_anon_nullifier, enhanced with a post-quantum encryption using the public key of the audit authority.

Remaining work items:

• work out the onboarding process of the audit authority, that may look like the following
  • generate the Kyber key pair
  • put the public key inside the circuit, hardcoded to avoid extra cost of using public input signals
  • register the public key
• implement the AES-256 encryption portion of the ML-KEM scheme on the message, which is defined as having the following parts:
  • input owner public key (x, y): 2
  • input secrets (value, salt) for each input UTXOs: 2 * nInputs
  • output owner public keys (x, y) for each output: 2 * nOutputs
  • output secrets (value, salt) for each output UTXOs: 2 * nOutputs
• add test code to perform end to end transaction flows
  • sender:
    • generate a random AES encryption key and use the auditor's public key to generate its encapsulation
    • encrypt the secrets in AES, and output ciphertext ct-1
    • feed the AES key to the circuit to generate the ciphertext ct-2
    • add ct-1 and ct-2 to the transaction payload
  • auditor:
    • get the ct-2 from the transaction input, and use the Kyber secret key to decrypt to recover the AES key
    • get the ct-1 from the transaction input, and decrypt using the recovered AES key
• add Qurrency to the remaining token operations (mint, deposit, withdraw, transferLocked)

[jimthematrix]

One of the thoughts from discussing with @guruvamsi-policharla is how much percentage of saving we will get if we consolidate all public signals to a single hash. This would be a trade-off between (longer) proving time and (cheaper) proof verification gas cost. Here are some comparison runs between the two approaches:

Approach	# of Circuit Constraints	Proof Verification Gas Cost
Separate inputs (9 in total)	1,958,033	226,799
Single input (Poseidon hash)	1,959,703	284,188
Single input (sha256 hash)	2,054,806	233,754

The above results are based on the following test:

$ npx hardhat test test/test/qurrency.ts 

  Test Qurrency verifier
Qurrency test contract deployed at 0x5FbDB2315678afecb367f032d93F642f64180aa3
Proof generation time: 43013ms.
Qurrency test tx gas cost: 284176
    ✔ test prepared inputs (50590ms)


  1 passing (51s)

Between the branches qurrency-separate-inputs, qurrency-single-pub-signal-poseidon and qurrency-single-pub-signal-sha256