libsoliton/soliton/fuzz/fuzz_targets/fuzz_identity_sign_verify.rs

#![no_main]
use libfuzzer_sys::fuzz_target;
use soliton::identity::{generate_identity, hybrid_sign, hybrid_verify, GeneratedIdentity, IdentityPublicKey, IdentitySecretKey};
use std::sync::LazyLock;

struct SignerKeys {
    pk: IdentityPublicKey,
    sk: IdentitySecretKey,
}

// Fixed signer — keygen is expensive, amortise across corpus runs.
static SIGNER: LazyLock<SignerKeys> = LazyLock::new(|| {
    let GeneratedIdentity { public_key: pk, secret_key: sk, .. } = generate_identity().unwrap();
    SignerKeys { pk, sk }
});

fuzz_target!(|data: &[u8]| {
    if data.is_empty() {
        return;
    }

    // Property 1: sign(msg) → verify(msg, sig) must always succeed.
    let Ok(sig) = hybrid_sign(&SIGNER.sk, data) else {
        panic!("hybrid_sign failed on a valid key");
    };
    if hybrid_verify(&SIGNER.pk, data, &sig).is_err() {
        panic!("hybrid_verify rejected a freshly-signed message");
    }

    // Property 2: verify(tampered_msg, sig) must always fail.
    // Flip the LSB of the first byte — always changes the message content.
    let mut tampered = data.to_vec();
    tampered[0] ^= 0x01;
    if hybrid_verify(&SIGNER.pk, &tampered, &sig).is_ok() {
        panic!("hybrid_verify accepted a message that differs by exactly one bit");
    }
});