SIMULATION NOTICE: This document (audit, evaluation, response) is part of an AI-driven role-playing simulation conducted for project quality and governance testing. It does not constitute a formal legal or professional audit by any real-world entity.

Security Audit Remediation Report (Response to v2)

Date: 2025-12-29 Reference: sites/srn/content/governance/web-a-l2-security-audit-v2.md

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1. Overview

This report documents the remediation actions taken in response to the "Critical Security Audit Report v2". The development team has executed a major architectural refactoring, primarily focusing on migrating cryptographic operations to WebAssembly (Wasm) to address side-channel attacks and execution integrity, while also hardening the aggregator against replay attacks.

2. Remediation Status Summary

ID Issue Severity Status Remediation Detail
2.1 Weak Traffic Padding (0-255 bytes) Medium Resolved Implemented Bucket-Based Padding in Wasm. Payloads are now padded to fixed size tiers (1KB, 4KB, 16KB, etc.) to effectively mask content size.
3.1 Lack of Forward Secrecy Critical Deferred Architecture remains based on static X25519 recipient keys. No "Pre-Key Bundle" server has been implemented yet. This remains a known risk for long-term archival.
3.2 Replay Attacks (No Nonce Check) High Resolved Implemented ReplayGuard and JsonFileReplayStore in the Aggregator. The CLI now enforces nonce uniqueness by default, rejecting replayed envelopes.
4.1 Supply Chain Risk (npm trust) High Resolved Core cryptographic dependencies (@noble curves/hashes) have been vendored into src/vendor/ and are tracked in git, removing reliance on registry integrity during install.
4.2 Source Code Disclosure (Timing Attacks) High Resolved Major Migration to Wasm. All core primitives (AES-GCM, X25519, Ed25519, ML-KEM, ML-DSA, HKDF, SHA256) are now executed via a compiled Rust-to-Wasm module (src/crypto-wasm), providing stronger guarantees against JIT-based timing analysis.
5.1 Error Handling Side-Channels Medium Resolved Decryption logic now catches specific errors and throws a unified generic Error("Decryption failed"), preventing oracle attacks based on error differentiation.

3. Technical Implementation Details

3.1. WebAssembly Migration (src/crypto-wasm)

The project has shifted away from pure JavaScript implementations for critical operations. The src/core/wasm_core.ts module now acts as the bridge to weba_crypto_wasm_bg.wasm.

  • Impact: constant-time execution for sensitive comparisons (constantTimeEqual) and cryptographic math is now handled by Rust's verified implementations (via dalek and RustCrypto crates, likely).
  • Files Affected: src/core/l2crypto.ts, src/core/wasm_core.ts, src/crypto-wasm/*.

3.2. Traffic Analysis Mitigation

The previous random padding has been replaced with a deterministic bucket strategy.

  • Logic: wasm_get_padding(current_size) calculates the next power-of-2-like tier.
  • Code: src/core/l2crypto.ts:
    const targetSize = getPaddingTargetSize(currentBytes.length + overhead);
const paddingLen = Math.max(0, targetSize - currentBytes.length - overhead);

3.3. Replay Protection (ReplayGuard)

The aggregator reference implementation now includes a persistent store for nonces.

  • Code: src/form/aggregator.ts uses JsonFileReplayStore to persist seen nonces to disk (replay-store.json via CLI option).
  • Enforcement:
    if (!(await replayGuard.checkAndMark(l2EnvelopeForCheck.meta.nonce))) {
    console.warn(`Warning: Replay detected... Skipping.`);
    continue;
}

3.4. Draft State Preservation (Client)

The form client now embeds a structured draft state inside downloaded draft HTML files so that user work can be restored across devices or after cache clears without relying on browser storage.

  • Draft Payload: The embedded state includes the form data snapshot and a minimal L2 replay cache (nonce list) needed for safe reprocessing.
  • Security Note: Draft files should be treated as sensitive artifacts because they may contain plaintext responses and replay metadata.
  • Code: src/form/client/data.ts, src/form/client/download.ts, src/form/client/runtime.ts.

4. Remaining Risks & Future Work

  1. Forward Secrecy: The system still relies on the long-term safety of the Organization's private key. If this key is compromised, all past messages can be decrypted. Implementing ephemeral key negotiation requires a fundamental protocol change (interactive flow or pre-key server).
  2. Client-Side Trust: The fundamental issue of "Trusting the Browser" remains. While Wasm improves execution integrity, it does not prevent a compromised browser (malware/extension) from reading the form inputs before encryption.

5. Conclusion

The V2 remediation represents a significant hardening of the Web/A Layer 2 library. The move to WebAssembly and the enforcement of Replay Protection address the most practical and immediate attacks. The remaining risk (Forward Secrecy) is accepted as an architectural trade-off for the current version's offline/asynchronous design.