add stark verification example Scout script

scripts/mimc-stark-verifier/Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+name = "phase2-stark-verifier"
+version = "0.0.0"
+authors = ["Jared Wasinger"]
+license = "Apache-2.0"
+repository = "https://github.com/ewasm/scout"
+description = "Eth 2.0 Phase 2 execution script: MIMC STARK verifier"
+publish = false
+edition = "2018"
+
+[dependencies]
+ssz = "0.1.2"
+ssz-derive = "0.1.2"
+sha3 = "^0.6"
+stark_verifier = { git = "https://github.com/jwasinger/stark-verifier", branch = "feat/lib" }
+num-bigint = { git = "https://github.com/jwasinger/num-bigint", branch = "feature/pow"}
+num-traits = "0.2.8"
+
+[dependencies.ewasm_api]
+git = "https://github.com/ewasm/ewasm-rust-api"
+rev = "1c01982"
+default-features = false
+features = ["std", "eth2", "qimalloc"]
+
+# [profile.release]
+# lto = true
+# debug = false
+
+[lib]
+crate-type = ["cdylib"]

scripts/mimc-stark-verifier/src/lib.rs

@@ -0,0 +1,40 @@
+extern crate stark_verifier;
+extern crate ewasm_api;
+extern crate num_bigint;
+
+use std::str::FromStr;
+use num_traits::pow::Pow;
+
+use ewasm_api::*;
+use stark_verifier::deserializer;
+use stark_verifier::{verify_mimc_proof, MODULUS};
+use num_bigint::{BigInt, BigUint};
+
+fn process_block(pre_state_root: types::Bytes32, block_data: &[u8]) -> types::Bytes32 {
+    let (stark_proof, _) = deserializer::from_bytes(&block_data).expect("couldn't deserialize");
+
+    // TODO: package subsequent parameters in the proof itself
+    const LOG_STEPS: usize = 13;
+    let mut constants: Vec<BigInt> = Vec::new();
+    let modulus: BigInt = num_bigint::BigInt::from_str(MODULUS).expect("modulus couldn't be deserialized into bigint");
+
+    for i in 0..64 {
+        let constant = BigInt::from(i as u8).pow(BigUint::from(7u8)) ^ BigInt::from(42u8);
+        constants.push(constant);
+    }
+
+    let output = BigInt::from_str("95224774355499767951968048714566316597785297695903697235130434363122555476056").unwrap();
+
+    match verify_mimc_proof(BigInt::from(3u8), 2usize.pow(LOG_STEPS as u32), &constants, output, stark_proof, &modulus) {
+        true => types::Bytes32 { bytes: [0u8; 32] },
+        false => types::Bytes32 { bytes: [1u8; 32] }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn main() {
+    let pre_state_root = eth2::load_pre_state_root();
+    let block_data = eth2::acquire_block_data();
+    let post_state_root = process_block(pre_state_root, &block_data);
+    eth2::save_post_state_root(post_state_root)
+}