Examples of circuits for bellman, a Rust zk-SNARKs library.
Bellman provides a
Circuit trait which you can use to synthesize the constraints in your program.
multiply.rs contains a circuit for the statement "I know
y such that
x * y = public_input".
cube.rs contains a circuit for the statement "I know
x such that
x^3 + x + 5 == 35"
Constructing a circuit
To construct a circuit, first flatten your program into its constituent steps.
Allocate the variables, then enforce the constraints.
Enforcing the constraint takes the form of
A * B = C. (is a linear combination, vectors of all your variables)
lc in the
cs.enforce function stands for "linear combination", and is an inner product of all the variables with some vector of coefficients.
These examples use the function
generate_random_parameters to generate a random set of parameters for testing. For real use cases, these parameters would have to be generated securely, through a multi-party computation.
Creating a proof
To create a proof, instantiate a version of the struct that is passed into the circuit, with the inputs to the circuit.
In these examples, the function
create_random_proof is used to create a random groth16 proof.
Verifying a proof
To verify a proof, prepare the verifying key by passing in
prepare_verifying_key. This gives you the prepared viewing key,
verify_proof takes the prepared viewing key
proof, and the output as an array.
cargo test runs test proofs using both example circuits. Tests are located at the bottom of their source files.
cargo run runs the
cube.rs example proof in the main file.