libsoliton/soliton/fuzz/fuzz_targets/fuzz_xwing_roundtrip.rs

#![no_main]
use libfuzzer_sys::fuzz_target;
use soliton::primitives::xwing;
use std::sync::LazyLock;

// Fixed keypair for ciphertext mutation testing — keygen is expensive.
static KP: LazyLock<(xwing::PublicKey, xwing::SecretKey)> =
    LazyLock::new(|| xwing::keygen().unwrap());

const CT_SIZE: usize = 1120;

// Two modes selected by data[0] & 0x01:
//   0 (even) — encapsulate + decapsulate roundtrip: proves freshly produced
//              ciphertexts always decapsulate without error.
//   1 (odd)  — fuzz ciphertext bytes: decapsulate must never panic on any ct.
fuzz_target!(|data: &[u8]| {
    if data.is_empty() {
        return;
    }
    if data[0] & 0x01 != 0 {
        // Mode A: arbitrary ciphertext → decapsulate must not panic.
        if data.len() < 1 + CT_SIZE {
            return;
        }
        let Ok(ct) = xwing::Ciphertext::from_bytes(data[1..1 + CT_SIZE].to_vec()) else { return; };
        let _ = xwing::decapsulate(&KP.1, &ct);
    } else {
        // Mode B: encapsulate → decapsulate → must succeed.
        // Exercises the full KEM path with freshly-generated randomness.
        let Ok((ct, _ss)) = xwing::encapsulate(&KP.0) else {
            panic!("encapsulate failed on a valid public key");
        };
        if xwing::decapsulate(&KP.1, &ct).is_err() {
            panic!("decapsulate failed on a ciphertext produced by encapsulate");
        }
    }
});