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//! # Zero Knowledge SNARKs
//!
//! This crate provides functionality for creating and using zero knowledge
//! proofs. The implementation is based on
//! [groth16](https://eprint.iacr.org/2016/260.pdf).
//!
//! # Usage
//!
//! The main functions of the alrotihm are the `setup`, `prove` and `verify`
//! functions in the `groth16` module. Intermediate representations can be
//! generated from .zk files, which are written in a DSL that represents an
//! arithmetic circuit.
//!
//! ## Language
//!
//! The language for representing arithmetic circuits is quite basic and is
//! written in a lisp-esque style that uses parenthesised prefix notation. The
//! following is an example program for a circuit that computes a quadratic
//! polynomial `y = ax^2 + bx + c`:
//! ```text
//! (in x a b c)
//! (out y)
//! (verify x y)
//!
//! (program
//! (= t1
//! (* x a))
//! (= t2
//! (* x (+ t1 b)))
//! (= y
//! (* 1 (+ t2 c))))
//! ```
//! The order must always follow `in`, `out`, `verify` and then `program`.
//! Currently parentheses are 'sticky' in that there must not be any whitespace
//! between them and their interior tokens. The keywords are as follows:
//! * `in` precedes the list of input wires to the circuit, excluding the
//! constant unity wire.
//! * `out` precedes the list of output wires from the circuit.
//! * `verify` precedes the list of wires that the verifier will check by
//! providing them as input in the verification process.
//! * `program` precedes the list of multiplication subcircuits that constitute
//! the entire arithmetic circuit. The multiplication subcircuits model a
//! single multiplication gate that has fan in two, where the two inputs can
//! be a linear combination of any number of circuit inputs and previous
//! internal wires. They use the following keywords.
//! * `=` is the assignment operator, which takes two arguments. The first is
//! the variable that is being assigned to, and represents the output wire of
//! the multiplication gate. The second is the expression being assigned, and
//! represents the linear combination of input wires.
//! * `*` is the multiplication operator, which is used both for the
//! multiplication gate and also to represent the constant scaling in the
//! linear combination inputs to the multiplication gate. It takes only two
//! arguments; when used for a multiplication gate the order does not matter,
//! but for constant scaling the constant must be the first argument.
//! * `+` is the addition operator, and as stated before can have an arbitrary
//! number of arguments. Each argument can either be a variable, or a scaled
//! variable (i.e. it can either look like `x`, or, for example, like `(* 5
//! x)`).
//!
//! # Examples
//!
//! As an example, consider the simple arithmetic expression `x = 4ab + c + 6`.
//! We want to verify the wires `x` and `b`. The program file can look like the
//! following:
//! ```text
//! (in a b c)
//! (out x)
//! (verify b x)
//!
//! (program
//! (= temp
//! (* a b))
//! (= x
//! (* 1 (+ (* 4 temp) c 6))))
//! ```
//! Suppose that the prover wants to prove that they know values `a` and `c` for
//! which the circuit is satisfied when the verifier inputs `b = 2` and `x =
//! 34`. For our example we will use the satisfying assignments `a = 3` and `c =
//! 4`. The following code is an example of the setup, prove and verify process.
//! ```
//! extern crate zksnark;
//!
//! use zksnark::groth16;
//! use zksnark::groth16::{Proof, SigmaG1, SigmaG2, QAP};
//! use zksnark::groth16::circuit::{ASTParser, TryParse};
//! use zksnark::groth16::fr::FrLocal;
//! use zksnark::groth16::coefficient_poly::CoefficientPoly;
//!
//! // x = 4ab + c + 6
//! let code = &*::std::fs::read_to_string("test_programs/simple.zk").unwrap();
//! let qap: QAP<CoefficientPoly<FrLocal>> =
//! ASTParser::try_parse(code)
//! .unwrap()
//! .into();
//!
//! // The assignments are the inputs to the circuit in the order they
//! // appear in the file
//! let assignments = &[
//! 3.into(), // a
//! 2.into(), // b
//! 4.into(), // c
//! ];
//! let weights = groth16::weights(code, assignments).unwrap();
//!
//! let (sigmag1, sigmag2) = groth16::setup(&qap);
//!
//! let proof = groth16::prove(&qap, (&sigmag1, &sigmag2), &weights);
//!
//! assert!(groth16::verify(
//! &qap,
//! (sigmag1, sigmag2),
//! &vec![FrLocal::from(2), FrLocal::from(34)],
//! proof
//! ));
//! ```
#![doc(
html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk.png",
html_favicon_url = "https://www.rust-lang.org/favicon.ico",
html_root_url = "https://docs.rs/rand/0.5.4",
html_playground_url = "https://play.rust-lang.org/"
)]
mod encryption;
pub mod field;
pub mod groth16;
#[doc(hidden)]
pub use groth16::circuit::dummy_rep::DummyRep;
#[doc(hidden)]
pub use groth16::circuit::{ASTParser, TryParse};
#[doc(hidden)]
pub use groth16::circuit::{Circuit, CircuitInstance, WireId};
#[doc(hidden)]
pub use groth16::coefficient_poly::CoefficientPoly;
#[doc(hidden)]
pub use groth16::fr::FrLocal;
#[doc(hidden)]
pub use groth16::{Proof, SigmaG1, SigmaG2, QAP};
#[cfg(test)]
mod tests {
use super::field::z251::Z251;
use super::groth16::Random;
use super::*;
#[test]
fn simple_circuit_test() {
// x = 4ab + c + 6
let code = &*::std::fs::read_to_string("test_programs/simple.zk").unwrap();
let qap: QAP<CoefficientPoly<FrLocal>> = ASTParser::try_parse(code).unwrap().into();
// The assignments are the inputs to the circuit in the order they
// appear in the file
let assignments = &[
3.into(), // a
2.into(), // b
4.into(), // c
];
let weights = groth16::weights(code, assignments).unwrap();
let (sigmag1, sigmag2) = groth16::setup(&qap);
let proof = groth16::prove(&qap, (&sigmag1, &sigmag2), &weights);
assert!(groth16::verify(
&qap,
(sigmag1, sigmag2),
&vec![FrLocal::from(2), FrLocal::from(34)],
proof
));
let (sigmag1, sigmag2) = groth16::setup(&qap);
let proof = groth16::prove(&qap, (&sigmag1, &sigmag2), &weights);
assert!(!groth16::verify(
&qap,
(sigmag1, sigmag2),
&vec![FrLocal::from(2), FrLocal::from(25)],
proof
));
}
fn to_bits(mut n: u8) -> [u8; 8] {
let mut bits: [u8; 8] = [0; 8];
for i in 0..8 {
bits[i] = n % 2;
n = n >> 1;
}
bits
}
#[test]
fn comparator_8bit_test() {
// Circuit for checking if a > b
let code = &*::std::fs::read_to_string("test_programs/8bit_comparator.zk").unwrap();
let qap: QAP<CoefficientPoly<Z251>> = ASTParser::try_parse(code).unwrap().into();
for _ in 0..1000 {
let (a, b) = (Z251::random_elem(), Z251::random_elem());
let (abits, bbits) = (to_bits(a.inner), to_bits(b.inner));
let assignments = abits
.iter()
.chain(bbits.iter())
.map(|&bit| Z251::from(bit as usize))
.collect::<Vec<_>>();
let weights = groth16::weights(code, &assignments).unwrap();
let (sigmag1, sigmag2) = groth16::setup(&qap);
let proof = groth16::prove(&qap, (&sigmag1, &sigmag2), &weights);
if a.inner > b.inner {
let mut inputs = vec![Z251::from(1)];
inputs.append(
&mut bbits
.iter()
.map(|&bit| Z251::from(bit as usize))
.collect::<Vec<_>>(),
);
assert!(groth16::verify(&qap, (sigmag1, sigmag2), &inputs, proof));
} else {
let mut inputs = vec![Z251::from(0)];
inputs.append(
&mut bbits
.iter()
.map(|&bit| Z251::from(bit as usize))
.collect::<Vec<_>>(),
);
assert!(groth16::verify(&qap, (sigmag1, sigmag2), &inputs, proof));
}
}
}
#[test]
fn circuit_builder_test() {
// Build the circuit
let mut circuit = Circuit::<FrLocal>::new();
let x = circuit.new_wire();
let x_checker = circuit.new_bit_checker(x);
let y = circuit.new_wire();
let y_checker = circuit.new_bit_checker(y);
let or = circuit.new_or(x, y);
let mut instance =
CircuitInstance::new(circuit, vec![x_checker, y_checker, or], vec![x, y], |w| {
FrLocal::from(w.inner_id() + 1)
});
let qap: QAP<CoefficientPoly<FrLocal>> = QAP::from(DummyRep::from(&instance));
let assignments = vec![FrLocal::from(0), FrLocal::from(1)];
let weights = instance.weights(assignments);
let (sigmag1, sigmag2) = groth16::setup(&qap);
let proof = groth16::prove(&qap, (&sigmag1, &sigmag2), &weights);
assert!(groth16::verify(
&qap,
(sigmag1, sigmag2),
&[FrLocal::from(0), FrLocal::from(0), FrLocal::from(1)],
proof
));
}
}