fcomm: Functional Commitments

This example is a work in progress, for demonstration purposes only, and subject to change.

The fcomm CLI exposes an interface for creating and verifying Lurk proofs, and for manipulating functional commitments.

Functional Commitments

TODO: Explanation of functional commitment interface.

Creating and Verifying Evaluation Proofs

To see how proofs work, first navigate to the fcomm/examples directory. From the lurk-rs project root,

➜  lurk-rs git:(master) ✗ cd fcomm/examples
➜  examples git:(master) ✗

To generate a very simple proof, type the following command (this will be surprisingly slow):

> make fibonacci-proof

To see the program whose evaluation was proved, see its source.

To see what the generated proof object claim's to attest, see the claim section of the generated json. This can be viewed more legibly if you have a JSON formatter like jq installed:

➜  examples ✗ cat fibonacci-proof.json| jq | more

Yielding something like:

{
  "claim": {
    "Evaluation": {
      "expr": "(LETREC ((NEXT (LAMBDA (A B N TARGET) (IF (EQ N TARGET) A (NEXT B (+ A B) (+ 1 N) TARGET)))) (FIB (NEXT 0 1 0))) (FIB 1))",
      "env": "NIL",
      "cont": "Outermost",
      "expr_out": "1",
      "env_out": "NIL",
      "cont_out": "Terminal",
      "status": "Terminal",
      "iterations": null
    }
  },
  "proof": {
    "Recursive": {
      ...
    }
  }
}


To verify the generated proof:

```bash
> make verify-fibonacci-proof

Please note the following limitations:

• Proof as serialized here are not optimized for size.
• The Groth16 and SnarkPack+ parameters used here were not the result of a trusted setup so are insecure.
• To simplify reproducibility in development and for example purposes, these parameters are deterministically generated on-demand.
• The parameters are currently uncached.
• This adds time to both proof and verification.
• For larger values of the ReductionCount option (see: lib.rs), this can be significant.
• Even for the smallest circuits used in the default examples, this leads to deceptively slow verification.

To see the commands that were used, see the Makefile.