Attributes

We've already discussed the #[zkp_program] attribute. However, there are also attributes on program arguments.

#![allow(unused)]
fn main() {
use sunscreen::{
    types::zkp::{ConstrainEq, Field, FieldSpec}, zkp_program, zkp_var
};

#[zkp_program]
fn all_kinds<F: FieldSpec>(
    #[private] x: Field<F>,
    #[public] p: Field<F>,
) {
    // prove that our secret value x is equal to either p or 1
    let poly = (x - p) * (x - zkp_var!(1));
    poly.constrain_eq(zkp_var!(0));
}
}

Note that zkp_program arguments should appear in the order private, public, and finally constant to match prove call.

Private

The #[private] attribute is used for any arguments that are private to the prover (i.e. shouldn't be seen by anyone else). In more formal terminology, these arguments are the witnesses. For example, this might be a private key in an encryption scheme or something application specific like an account balance that you (as the prover) wish to keep hidden.

This is the default argument type; omitting an attribute is the same as specifying #[private].

Public

The #[public] attribute is used for any arguments that are public to both the prover and verifier. For example, this could be the public generator of a group in some encryption scheme or something application specific like a minimum balance threshold for issuing transactions.

Constant

We do not discuss these in the main docs; please see the advanced section if you're interested in working with constant arguments.

Linked

Lastly, there is also a #[linked] attribute available when the linkedproofs feature is enabled. This attribute is used when linking together our FHE and ZKP compilers; see the linked section for more details.