# Miden prover
This crate contains the Miden VM prover, which proves correct execution of Miden VM. Internally, the prover uses [Miden processor](../processor/) to execute the programs, and then relies on the [Winterfell](https://github.com/novifinancial/winterfell) prover to generate STARK proofs.

## Usage
This crate exposes a `prove()` function which can be used to execute Miden VM programs and generate proofs of their execution. The function takes the following parameters:

* `program: &Program` - a reference to a Miden program to be executed.
* `stack_inputs: StackInputs` - a set of public inputs with which to execute the program.
* `host: Host` - an instance of a `Host` which can be used to supply non-deterministic inputs to the VM and receive messages from the VM.
* `options: &ProvingOptions` - config parameters for proof generation. The default options target 96-bit security level.

If the program is executed successfully, the function returns a tuple with 2 elements:

* `outputs: StackOutputs` - the outputs generated by the program.
* `proof: ExecutionProof` - proof of program execution. `ExecutionProof` can be easily serialized and deserialized using `to_bytes()` and `from_bytes()` functions respectively.

### Proof generation example
Here is a simple example of executing a program which pushes two numbers onto the stack and computes their sum:
```Rust
use miden_assembly::Assembler;
use miden_prover::{prove, ProvingOptions, StackInputs, DefaultHost};

// instantiate the assembler
let assembler = Assembler::default();

// this is our program, we compile it from assembly code
let program = assembler.compile("begin push.3 push.5 add end").unwrap();

// let's execute it and generate a STARK proof
let (outputs, proof) = prove(
    &program,
    StackInputs::default(),       // we won't provide any stack inputs
    DefaultHost::default(),       // we'll be using a default host
    &ProvingOptions::default(),   // we'll be using default options
)
.unwrap();

// the output should be 8
assert_eq!(8, outputs.stack().first().unwrap().as_int());
```

## Crate features
Miden prover can be compiled with the following features:

* `std` - enabled by default and relies on the Rust standard library.
* `concurrent` - implies `std` and also enables multi-threaded proof generation.
* `metal` - enables [Metal](https://en.wikipedia.org/wiki/Metal_(API))-based acceleration of proof generation (for recursive proofs) on supported platforms (e.g., Apple silicon).
* `no_std` does not rely on the Rust standard library and enables compilation to WebAssembly.
    * Only the `wasm32-unknown-unknown` and `wasm32-wasip1` targets are officially supported.

To compile with `no_std`, disable default features via `--no-default-features` flag.

### Concurrent proof generation
When compiled with `concurrent` feature enabled, the prover will generate STARK proofs using multiple threads. For benefits of concurrent proof generation check out these [benchmarks](../README.md#Performance).

Internally, we use [rayon](https://github.com/rayon-rs/rayon) for parallel computations. To control the number of threads used to generate a STARK proof, you can use `RAYON_NUM_THREADS` environment variable.

## License
This project is [MIT licensed](../LICENSE).