initial commit

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

soliton/fuzz/fuzz_targets/fuzz_ratchet_roundtrip.rs

@@ -0,0 +1,32 @@
+#![no_main]
+#![allow(deprecated)] // Fuzz targets exercise from_bytes directly.
+use libfuzzer_sys::fuzz_target;
+use soliton::ratchet::RatchetState;
+
+fuzz_target!(|data: &[u8]| {
+    // from_bytes → to_bytes → from_bytes round-trip:
+    // any serializable state must re-serialize to identical bytes
+    // (except the epoch field at bytes 1..9, which increments on each to_bytes).
+    //
+    // States near the epoch ceiling are legitimately non-serializable
+    // (can_serialize() returns false). These are usable for encrypt/decrypt
+    // but not persistable — skip them.
+    let Ok(state1) = RatchetState::from_bytes(data) else { return; };
+    if !state1.can_serialize() { return; }
+    let Ok((bytes1, epoch1)) = state1.to_bytes() else {
+        panic!("to_bytes failed on a state where can_serialize() returned true");
+    };
+    let Ok(state2) = RatchetState::from_bytes(&bytes1) else {
+        panic!("from_bytes rejected bytes produced by to_bytes");
+    };
+    if !state2.can_serialize() { return; }
+    let Ok((bytes2, epoch2)) = state2.to_bytes() else {
+        panic!("second to_bytes failed on a serializable round-tripped state");
+    };
+    // Version byte must match.
+    assert_eq!(bytes1[0], bytes2[0], "version byte mismatch after round-trip");
+    // All fields after epoch must match.
+    assert_eq!(bytes1[9..], bytes2[9..], "fields after epoch diverged after round-trip");
+    // Epoch must advance by exactly 1 per to_bytes call.
+    assert_eq!(epoch2, epoch1 + 1, "epoch did not advance by 1");
+});