initial commit

Signed-off-by: Kamal Tufekcic <kamal@lo.sh>

soliton/fuzz/fuzz_targets/fuzz_identity_sign_verify.rs

@@ -0,0 +1,37 @@
+#![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");
+    }
+});