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+# LEZ Fuzzing — QA Team Presentation
+
+> **Project:** `lez-fuzzing` — Automated Fuzz Testing for the Logos Execution Zone (LEZ)
+> **Audience:** QA Team
+> **Date:** April 2026
+
+---
+
+## Agenda
+
+1. [What Is This Project?](#1-what-is-this-project)
+2. [Why Fuzzing? (Not Just Unit Tests)](#2-why-fuzzing-not-just-unit-tests)
+3. [Architecture Overview](#3-architecture-overview)
+4. [What We Are Testing — 9 Fuzz Targets](#4-what-we-are-testing--9-fuzz-targets)
+5. [Protocol Invariants — The Safety Net](#5-protocol-invariants--the-safety-net)
+6. [Input Generation Strategy](#6-input-generation-strategy)
+7. [How to Run Locally](#7-how-to-run-locally)
+8. [CI/CD Integration](#8-cicd-integration)
+9. [Performance Characteristics](#9-performance-characteristics)
+10. [Known Limitations & Future Work](#10-known-limitations--future-work)
+11. [Key Takeaways for QA](#11-key-takeaways-for-qa)
+
+---
+
+## 1. What Is This Project?
+
+`lez-fuzzing` is a **coverage-guided, structured mutation fuzzing system** for the **Logos Execution Zone (LEZ)** blockchain protocol.
+
+### High-Level Context
+
+```
+<parent directory>/
+├── logos-execution-zone/     ← Production codebase (LEZ protocol)
+│   ├── nssa/                 ← Node State & State Accumulator
+│   ├── common/               ← Shared types (transactions, blocks)
+│   └── key_protocol/         ← Cryptographic primitives
+└── lez-fuzzing/              ← This repository (fuzzing harness)
+    ├── fuzz_props/           ← Reusable: generators + invariants
+    └── fuzz/                 ← Fuzz targets + pre-seeded corpus
+        └── fuzz_targets/     ← 9 individual fuzz entry points
+```
+
+### What the Fuzzer Does
+
+The fuzzer automatically generates **millions of malformed, adversarial, and boundary-case inputs** and feeds them into the protocol. It then checks that:
+- The process never **panics or crashes unexpectedly**
+- Protocol **invariants** (safety rules) are never violated
+- **Encoding/decoding** is lossless and deterministic
+- **State integrity** is preserved even on rejected transactions
+
+---
+
+## 2. Why Fuzzing? (Not Just Unit Tests)
+
+### The Gap Unit Tests Leave
+
+Unit tests check what engineers **think of** in advance. Fuzzing discovers what engineers **don't think of**.
+
+| Technique | Finds Known Bugs | Finds Unknown Bugs | Coverage Guidance | Scale |
+|---|---|---|---|---|
+| Unit tests | ✅ | ❌ | Manual | Hundreds of cases |
+| Property tests (proptest) | ✅ | Partial | ❌ None | Thousands of cases |
+| **Fuzzing (libFuzzer)** | ✅ | ✅ | ✅ LLVM-driven | **Millions/sec** |
+
+### Bugs Fuzzing Is Uniquely Good At Finding
+
+- **Panic on malformed input** — decoder receives garbled bytes → should return `Err`, not crash
+- **State leakage on rejection** — a rejected transaction changes account balances (silent corruption)
+- **Replay attacks** — a transaction accepted in block N is accepted again in block N+1
+- **Encoding non-determinism** — `encode(decode(encode(x))) ≠ encode(x)`
+- **Integer overflow / underflow** in balance arithmetic
+- **Phantom account attacks** — transfers from accounts that don't exist in genesis state
+
+### Why This Matters for a Blockchain Protocol
+
+On a blockchain, a single invariant violation can lead to:
+- **Double-spend** (state leakage on failure or replay acceptance)
+- **Consensus split** (non-deterministic hashing)
+- **Fund loss** (overflow in balance computation)
+
+---
+
+## 3. Architecture Overview
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                        lez-fuzzing                          │
+│                                                             │
+│  ┌──────────────────────────────────────────────────────┐   │
+│  │                    fuzz_props crate                  │   │
+│  │                                                      │   │
+│  │  arbitrary_types.rs  ← Typed Arbitrary wrappers      │   │
+│  │  generators.rs       ← proptest + libFuzzer helpers  │   │
+│  │  invariants.rs       ← ProtocolInvariant trait       │   │
+│  └──────────────────────────────────────────────────────┘   │
+│                            ↓                                │
+│  ┌──────────────────────────────────────────────────────┐   │
+│  │               fuzz/fuzz_targets/                     │   │
+│  │                                                      │   │
+│  │  fuzz_transaction_decoding.rs                        │   │
+│  │  fuzz_stateless_verification.rs                      │   │
+│  │  fuzz_state_transition.rs           (9 targets)      │   │
+│  │  fuzz_block_verification.rs                          │   │
+│  │  fuzz_encoding_roundtrip.rs                          │   │
+│  │  fuzz_signature_verification.rs                      │   │
+│  │  fuzz_replay_prevention.rs                           │   │
+│  │  fuzz_state_diff_computation.rs                      │   │
+│  │  fuzz_validate_execute_consistency.rs                │   │
+│  └──────────────────────────────────────────────────────┘   │
+│                            ↓                                │
+│  ┌──────────────────────────────────────────────────────┐   │
+│  │              fuzz/corpus/  (pre-seeded)              │   │
+│  │   ~150 minimised seed files per target               │   │
+│  └──────────────────────────────────────────────────────┘   │
+└─────────────────────────────────────────────────────────────┘
+                            ↕ path dependencies
+┌─────────────────────────────────────────────────────────────┐
+│             ../logos-execution-zone  (LEZ)                  │
+│   nssa  ·  common  ·  key_protocol  ·  token_core  …        │
+└─────────────────────────────────────────────────────────────┘
+```
+
+### Technology Stack
+
+| Component | Technology |
+|---|---|
+| Fuzzer engine | **libFuzzer** via `cargo-fuzz` |
+| Coverage instrumentation | **LLVM SanitizerCoverage** |
+| Structured input generation | **`arbitrary` crate** (typed wrappers) |
+| Property-based strategies | **`proptest`** |
+| ZK proof layer | **RISC0** (stubbed out with `RISC0_DEV_MODE=1`) |
+| Serialization format | **Borsh** (binary object representation) |
+| Language | **Rust (nightly toolchain)** |
+| CI | **GitHub Actions** |
+
+---
+
+## 4. What We Are Testing — 9 Fuzz Targets
+
+### Target Map
+
+| # | Target | What Is Being Tested | Key Invariant |
+|---|---|---|---|
+| 1 | `fuzz_transaction_decoding` | Borsh decode of all tx/block types | Never panic; roundtrip stable |
+| 2 | `fuzz_stateless_verification` | `transaction_stateless_check()` signature validation | No panic on any input |
+| 3 | `fuzz_state_transition` | `V03State::transition_from_*()` with 0–8 txs | Balances unchanged on rejection |
+| 4 | `fuzz_block_verification` | Block hash integrity + replayer pipeline | `block_hash()` is deterministic |
+| 5 | `fuzz_encoding_roundtrip` | `decode(encode(tx)) == Ok(tx)` | Encoding is lossless |
+| 6 | `fuzz_signature_verification` | Sign→verify correctness, cross-key soundness | No false positive verifications |
+| 7 | `fuzz_replay_prevention` | Tx accepted in block N rejected in block N+1 | Nonce consumed, replay blocked |
+| 8 | `fuzz_state_diff_computation` | `ValidatedStateDiff` scope correctness | Only declared accounts modified |
+| 9 | `fuzz_validate_execute_consistency` | `validate_on_state` vs `execute_check_on_state` agree | No divergence between validators |
+
+---
+
+### Target Deep-Dives
+
+#### `fuzz_state_transition` — The Core Safety Target
+
+This is the most important target from a protocol correctness standpoint.
+
+```
+Input bytes
+    ↓
+[Generate up to 8 transactions from fuzz bytes]
+    ↓
+[Filter: pass only stateless-valid txs]
+    ↓
+[Apply each tx to V03State]
+    ↓
+[INVARIANT CHECK on rejection]:
+  for every account in genesis:
+    assert balance_before == balance_after
+```
+
+**What it catches:** Any code path where a **rejected** transaction silently mutates account state — the classic "partial write" class of state corruption bug.
+
+---
+
+#### `fuzz_transaction_decoding` — The Crash-Safety Target
+
+```rust
+fuzz_target!(|data: &[u8]| {
+    // 1. If it decodes: roundtrip must be stable
+    if let Ok(tx) = borsh::from_slice::<NSSATransaction>(data) {
+        let re_encoded = borsh::to_vec(&tx).expect("must succeed");
+        // assert stability...
+    }
+
+    // 2. Block decode: must never panic
+    let _ = borsh::from_slice::<Block>(data);
+
+    // 3. HashableBlockData decode: must never panic
+    let _ = borsh::from_slice::<HashableBlockData>(data);
+});
+```
+
+**What it catches:** Panics in the Borsh decoder when receiving malformed bytes (e.g., truncated input, wrong variant tags, overflow in length fields).
+
+---
+
+#### `fuzz_block_verification` — Determinism Target
+
+```rust
+fuzz_target!(|data: &[u8]| {
+    let Ok(block) = borsh::from_slice::<Block>(data) else { return; };
+    let hashable = HashableBlockData::from(block.clone());
+
+    let hash1 = hashable.block_hash();  // first call
+    let hash2 = hashable.block_hash();  // second call — must match
+
+    assert_eq!(hash1, hash2, "block_hash() is not deterministic");
+});
+```
+
+**What it catches:** Non-deterministic hashing — a critical consensus bug where two nodes compute different block hashes for the same block content.
+
+---
+
+## 5. Protocol Invariants — The Safety Net
+
+The [`fuzz_props/src/invariants.rs`](fuzz_props/src/invariants.rs) module defines a **pluggable invariant framework**.
+
+### The `ProtocolInvariant` Trait
+
+```rust
+pub trait ProtocolInvariant {
+    fn name(&self) -> &'static str;
+    fn check(&self, ctx: &InvariantCtx<'_>) -> Option<InvariantViolation>;
+}
+```
+
+Every invariant receives a **snapshot** of the world before and after a transaction:
+
+```rust
+pub struct InvariantCtx<'a> {
+    pub state_before:    &'a V03State,
+    pub state_after:     &'a V03State,
+    pub tx:              &'a NSSATransaction,
+    pub result:          &'a Result<(), NssaError>,
+    pub balances_before: BalanceSnapshot,
+}
+```
+
+### Currently Registered Invariants
+
+| Invariant | Rule |
+|---|---|
+| `StateIsolationOnFailure` | If a tx is **rejected**, all account balances must be identical before and after |
+| `ReplayRejection` | A tx **accepted** in block N must be **rejected** in block N+1 (nonce consumed) |
+
+### How to Add a New Invariant (for QA team)
+
+```rust
+// 1. Define a zero-size struct
+pub struct BalanceConservation;
+
+// 2. Implement the trait
+impl ProtocolInvariant for BalanceConservation {
+    fn name(&self) -> &'static str { "BalanceConservation" }
+    fn check(&self, ctx: &InvariantCtx<'_>) -> Option<InvariantViolation> {
+        let before = ctx.balances_before.total();
+        let after  = /* sum state_after balances */;
+        if before != after {
+            Some(InvariantViolation {
+                invariant: self.name(),
+                message: format!("total balance changed: {} → {}", before, after),
+            })
+        } else {
+            None
+        }
+    }
+}
+
+// 3. Register in assert_invariants()
+let invariants: &[&dyn ProtocolInvariant] = &[
+    &StateIsolationOnFailure,
+    &ReplayRejection,
+    &BalanceConservation,  // ← new
+];
+```
+
+---
+
+## 6. Input Generation Strategy
+
+The [`fuzz_props/src/generators.rs`](fuzz_props/src/generators.rs) module provides two generation layers:
+
+### Layer 1 — Typed `Arbitrary` Wrappers (for libFuzzer)
+
+These give libFuzzer **structured, valid-looking inputs** instead of random bytes:
+
+| Wrapper | Generates |
+|---|---|
+| `ArbNSSATransaction` | Full transaction with realistic fields |
+| `ArbPublicTransaction` | Native token transfer |
+| `ArbProgramDeploymentTransaction` | Smart contract deploy |
+| `ArbPrivateKey` / `ArbPublicKey` | Cryptographic key pairs |
+| `ArbSignature` | ECDSA signatures |
+
+**Why this matters:** Without typed wrappers, libFuzzer would spend most of its time generating bytes that fail Borsh deserialization at the outermost layer — never reaching deeper code paths.
+
+### Layer 2 — proptest Strategies (richer adversarial scenarios)
+
+| Strategy | Tests Scenario |
+|---|---|
+| `arb_native_transfer_tx()` | Valid transfer between known genesis accounts |
+| `arb_borsh_transaction_bytes()` | Valid + intentionally invalid Borsh encodings |
+| `arb_invalid_account_state_tx()` | Phantom accounts, overflow amounts (IS-3) |
+| `arb_duplicate_tx_sequence()` | Duplicated + re-ordered tx sequences (IS-4) |
+| `arb_pathological_sequence()` | Zero-value, self-transfer, max-nonce inputs (IS-5) |
+| `arb_hashable_block_data()` | Block with 0–8 native transfers |
+
+### The Hybrid Approach
+
+```
+libFuzzer mutation engine
+        ↓
+   arbitrary bytes
+        ↓
+ arbitrary_transaction()
+    ├── 50%: ArbNSSATransaction (structured)
+    └── 50%: raw Borsh decode (may fail → libFuzzer learns)
+```
+
+This hybrid means **half the inputs** are structurally valid (reach deep code), and **half** stress the decoder boundary.
+
+---
+
+## 7. How to Run Locally
+
+### Prerequisites
+
+```bash
+# Nightly Rust is required by cargo-fuzz / libFuzzer
+rustup install nightly
+rustup component add llvm-tools-preview --toolchain nightly
+cargo install cargo-fuzz
+```
+
+### Repository Setup
+
+```bash
+# Clone both repositories side-by-side:
+git clone <LEZ_REPO_URL>         logos-execution-zone
+git clone <LEZ_FUZZING_REPO_URL> lez-fuzzing
+
+# Required directory layout:
+#   <parent>/
+#   ├── logos-execution-zone/
+#   └── lez-fuzzing/          ← work from here
+```
+
+### Common Commands
+
+```bash
+# Run ALL targets for 30 seconds each (smoke test)
+just fuzz
+
+# Run regression suite (no mutations — just corpus replay)
+just fuzz-regression
+
+# Run a specific target for 2 minutes
+RISC0_DEV_MODE=1 cargo fuzz run fuzz_state_transition -- -max_total_time=120
+
+# Minimise a crash artifact
+just fuzz-tmin fuzz_state_transition fuzz/artifacts/fuzz_state_transition/crash-abc123
+
+# View all available targets
+cargo fuzz list
+```
+
+> ⚠️ **Always use `RISC0_DEV_MODE=1`** — without it, ZK proof generation runs at ~1 proof/sec, making fuzzing impractical. The `just` recipes set this automatically.
+
+### Adding a New Fuzz Target
+
+```bash
+# Scaffold everything automatically (corpus dir, target file, Cargo.toml, CI matrix)
+just new-target my_feature
+
+# Then implement the target body
+$EDITOR fuzz/fuzz_targets/fuzz_my_feature.rs
+
+# Build and verify
+RISC0_DEV_MODE=1 cargo fuzz build fuzz_my_feature
+just fuzz-regression
+```
+
+---
+
+## 8. CI/CD Integration
+
+Three GitHub Actions jobs run on every pull request:
+
+| Job | Trigger | What It Does | Duration |
+|---|---|---|---|
+| `smoke-fuzz` | Every PR | Runs each target for 30 seconds | ~5 min |
+| `regression` | Every PR | Replays all corpus files (no mutations) | ~2 min |
+| `perf-baseline` | Every PR | Measures exec/sec and fails if throughput drops >20% | ~10 min |
+
+### Failure Workflow
+
+```
+CI detects crash
+      ↓
+cargo fuzz tmin  →  minimised input
+      ↓
+cargo fuzz fmt   →  Rust byte literal
+      ↓
+Add to corpus/   →  permanent regression test
+      ↓
+Open PR          →  regression job blocks reintroduction forever
+```
+
+---
+
+## 9. Performance Characteristics
+
+Measured on a 4-core x86_64 Linux runner with `RISC0_DEV_MODE=1`:
+
+| Target | Throughput | Why |
+|---|---|---|
+| `fuzz_transaction_decoding` | **~200,000 exec/sec** | Pure decode, no state |
+| `fuzz_encoding_roundtrip` | **~150,000 exec/sec** | Decode + encode, no state |
+| `fuzz_block_verification` | **~50,000 exec/sec** | Hash computation |
+| `fuzz_state_transition` | **~5,000 exec/sec** | Full state machine execution |
+| `fuzz_replay_prevention` | **~5,000 exec/sec** | Two state transitions per input |
+| `fuzz_validate_execute_consistency` | **~3,000 exec/sec** | Two paths compared |
+
+### Running on All Cores for Long Sessions
+
+```bash
+RISC0_DEV_MODE=1 cargo fuzz run fuzz_state_transition \
+  -- -max_total_time=3600 -jobs=$(nproc) -workers=$(nproc)
+```
+
+---
+
+## 10. Known Limitations & Future Work
+
+### Current Gaps
+
+| Gap | Impact | Status |
+|---|---|---|
+| `StateIsolationOnFailure` invariant is a partial placeholder | Balance corruption may go undetected | Known — needs full account iterator API from LEZ |
+| `PrivacyPreservingTransaction` excluded from encoding roundtrip | ZK receipts can't be reconstructed in fuzzing loop | Documented; dedicated slow target planned |
+| No version pin between repos | Stale LEZ checkout silently fuzzes wrong code | Known limitation — `just update-lez` is manual |
+
+### Highest-Value Future Extensions (Priority Order)
+
+1. **Complete stub invariants** in [`fuzz_props/src/invariants.rs`](fuzz_props/src/invariants.rs) — `StateIsolationOnFailure` and `ReplayRejection` need their full implementations. **Cost: < 1 day. Impact: immediately hardens all 9 targets.**
+
+2. **Sequencer-vs-Replayer differential target** — Feed the same block to `SequencerCore` and `indexer_core`, assert identical state roots. Catches consensus-splitting divergence. **Cost: 1–2 engineer-weeks. Impact: unique bug class not catchable any other way.**
+
+3. **Add AFL++ as a parallel fuzzing lane** (`just fuzz-afl`) — Same corpus, different mutation engine, finds different bugs. **Cost: ~1 day. Zero corpus migration.**
+
+4. **Add `cargo-mutants` before security audit** — Proves the invariant assertions are actually capable of catching the bugs they claim to detect. **Cost: ~1 day.**
+
+5. **Co-locate fuzz/ into logos-execution-zone/** — Eliminates version drift; standard `cargo fuzz` convention. LEZ CI would run `cargo fuzz build` on every PR. **Cost: ~1 day migration.**
+
+---
+
+## 11. Key Takeaways for QA
+
+### What the Fuzzer Covers
+
+✅ **No crash on any byte sequence** — all decoders handle malformed input gracefully
+✅ **State integrity on rejection** — failed transactions don't mutate balances
+✅ **Replay protection** — spent nonces are permanently rejected
+✅ **Encoding determinism** — identical inputs produce identical bytes every time
+✅ **Signature soundness** — no false positives, no cross-key verification
+✅ **Diff scope** — state changes only affect declared accounts
+
+### What the Fuzzer Does NOT Cover
+
+⚠️ **Business logic correctness** — fuzzing checks safety properties, not "is the amount correct"
+⚠️ **ZK proof validity** — mocked out; proofs are not generated during fuzzing
+⚠️ **Network/consensus layer** — only state machine and encoding layers are fuzzed
+⚠️ **`PrivacyPreservingTransaction` encoding roundtrip** — excluded (ZK receipts)
+
+### QA Team Action Items
+
+| Action | Who | When |
+|---|---|---|
+| Run `just fuzz-regression` before merging LEZ changes | Dev / QA | Each LEZ PR |
+| Review crash artifacts in `fuzz/artifacts/` when CI fails | QA | On CI failure |
+| Add new invariants when new protocol rules are introduced | QA + Dev | Feature additions |
+| Run `just update-lez` before long fuzzing sessions | QA | Before overnight runs |
+| Add new fuzz targets for new transaction types | QA + Dev | New tx types |
+
+---
+
+## Appendix: Project File Map
+
+| File / Directory | Purpose |
+|---|---|
+| [`fuzz_props/src/invariants.rs`](fuzz_props/src/invariants.rs) | `ProtocolInvariant` trait + registered invariants |
+| [`fuzz_props/src/generators.rs`](fuzz_props/src/generators.rs) | `proptest` strategies + `Arbitrary` helpers |
+| [`fuzz/fuzz_targets/`](fuzz/fuzz_targets/) | 9 fuzz entry points |
+| [`fuzz/corpus/`](fuzz/corpus/) | Pre-seeded corpus files (minimised, binary) |
+| [`docs/fuzzing.md`](docs/fuzzing.md) | Full operational guide (how-to, commands, CI) |
+| [`current_vs_alternative_approach.md`](current_vs_alternative_approach.md) | Comparison with AFL++, proptest-only, formal verification |
+| [`colocated_vs_separated.md`](colocated_vs_separated.md) | Architecture decision: separate repo vs. co-located |
+| [`fuzz/Cargo.toml`](fuzz/Cargo.toml) | Fuzz workspace manifest (all 9 `[[bin]]` entries) |
+| [`Cargo.toml`](Cargo.toml) | Root workspace (fuzz_props + LEZ path dependencies) |
+
+---
+
+*Presentation generated from the `lez-fuzzing` repository. For full operational details, see [`docs/fuzzing.md`](docs/fuzzing.md).*
diff --git a/targets_coverage.md b/targets_coverage.md
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+The project contains 9 distinct fuzz targets covering all four required categories:
+
+**Transaction decoding / instruction parsing**
+- [`fuzz_transaction_decoding.rs`](fuzz/fuzz_targets/fuzz_transaction_decoding.rs:9) — raw `&[u8]` fed to the Borsh parser for `NSSATransaction`, `Block`, and `HashableBlockData`; checks no-panic and encode/decode round-trip identity.
+- [`fuzz_encoding_roundtrip.rs`](fuzz/fuzz_targets/fuzz_encoding_roundtrip.rs:15) — structured `Arbitrary` inputs through the custom `to_bytes`/`from_bytes` codec for `PublicTransaction` and `ProgramDeploymentTransaction`; different codec, different types, different invariant.
+
+**Stateless verification checks**
+- [`fuzz_stateless_verification.rs`](fuzz/fuzz_targets/fuzz_stateless_verification.rs:13) — calls the application-level `transaction_stateless_check()` and verifies idempotency (a passing check must pass a second time).
+- [`fuzz_signature_verification.rs`](fuzz/fuzz_targets/fuzz_signature_verification.rs:27) — directly exercises the cryptographic primitive layer (`Signature::new` / `is_valid_for`): correctness for the signing key, no-panic on garbage bytes, no-panic on cross-key mismatch.
+
+**State transition / execution engine**
+- [`fuzz_state_transition.rs`](fuzz/fuzz_targets/fuzz_state_transition.rs:43) — multi-transaction sequences with monotonically increasing block context; asserts that a rejected transaction leaves all genesis account balances unchanged.
+- [`fuzz_replay_prevention.rs`](fuzz/fuzz_targets/fuzz_replay_prevention.rs:36) — applies the same transaction twice and asserts rejection on the second application (nonce consumed after first acceptance).
+- [`fuzz_state_diff_computation.rs`](fuzz/fuzz_targets/fuzz_state_diff_computation.rs:28) — exercises `ValidatedStateDiff::from_public_transaction` and verifies diff containment: only accounts declared in `affected_public_account_ids()` may appear in the diff.
+- [`fuzz_validate_execute_consistency.rs`](fuzz/fuzz_targets/fuzz_validate_execute_consistency.rs:42) — runs `validate_on_state` (read-only) and `execute_check_on_state` (mutating) on cloned state and checks bidirectional agreement: same success/failure verdict, and the diff matches the actual mutations in both directions.
+
+**Block verification / replayer logic**
+- [`fuzz_block_verification.rs`](fuzz/fuzz_targets/fuzz_block_verification.rs:15) — the only block-level target; decodes raw bytes as `Block` / `HashableBlockData` and verifies that `block_hash()` never panics and is deterministic.
+
+Each target differs in entry-point API, input shape, types under test, and the specific invariant asserted, making all nine genuinely distinct.
\ No newline at end of file