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.

Critical Security Re-Assessment v3: Post-Remediation Review

Auditor: Web/A Security Audit Team (Red Team) Date: 2025-12-29 Subject: Evaluation of Remediation Actions (v2 Audit Response)

Related

• Remediation Report (Response to v2)
• Security Audit v2

1. Executive Summary

We have reviewed the remediation report and the updated codebase. The development team has made significant tactical improvements, most notably the migration of the cryptographic core to WebAssembly (Rust) and the introduction of a replay protection mechanism.

However, the architecture remains structurally vulnerable regarding long-term confidentiality (Forward Secrecy) and endpoint integrity. The current state represents a "consumer-grade" improvement but falls short of the "enterprise-grade" or "classified-grade" security required for high-value data (e.g., medical records, financial transactions).

Revised Verdict: MEDIUM-HIGH RISK. (Down from HIGH RISK, but still unsuitable for hostile environments.)

2. Analysis of Remediation Actions

2.1. WebAssembly Migration (Critique of src/crypto-wasm)

Status: APPROVED with CAVEATS The move to Rust via wasm-bindgen significantly raises the bar for side-channel attacks. The use of standard crates (aes-gcm, curve25519-dalek, ml-kem, ml-dsa) is commendable.

• Strengths: constant_time_equal is now actually constant-time (delegating to subtle crate). Key generation and signing leverage the rand::thread_rng within Wasm, which generally maps to crypto.getRandomValues, avoiding weak JS PRNGs.
• Weaknesses: The Foreign Function Interface (FFI) boundary creates a new attack surface. While no unsafe blocks were observed in lib.rs, the correctness of the data passing (copying slices) relies on wasm-bindgen. The "Glue Code" (wasm_core.ts) is now the single point of failure; if the JS runtime is compromised, the Wasm module is just a black box that can be fed bad data.

2.2. Traffic Analysis (Bucket Padding)

Status: PARTIALLY EFFECTIVE The implementation of get_padding_target_size (1KB, 4KB, 16KB...) is a massive improvement over the previous "0-255 bytes random" approach.

• Flaw: The "Bucketing" strategy is deterministic. If an input is 1025 bytes, it jumps to 4096. If it is 4096, it stays at 4096. An attacker can potentially infer the range of the input size. For strictly defined forms (e.g., "Yes/No"), this is effective. For free-text fields, metadata leakage is still possible if the distribution of input lengths is known.
• Gap: There is no "Decoy Traffic" mechanism. An observer sees when a user submits a form.

2.3. Replay Protection (ReplayGuard)

Status: INSUFFICIENT DEPLOYMENT The mechanism exists (JsonFileReplayStore) but its enforcement is Optional and relies on the aggregator tool's CLI flags.

• Critical Failure: Security controls must be Secure by Default. If a developer writes their own aggregator script and forgets to check the nonce (which the library permits), the vulnerability persists. The library should require a ReplayStore interface to be passed to decryptLayer2, or at least default to an in-memory store that warns/fails on duplicates.

2.4. Forward Secrecy

Status: FAILED (Deferred) The refusal to implement ephemeral key negotiation (Pre-Keys) is the most significant remaining architectural flaw.

• Risk: The "Offline" excuse is invalid. Signal and WhatsApp handle offline messaging via Pre-Key Bundles uploaded to a server. Web/A could easily implement a "Key Server" that hosts one-time keys for organizations.
• Reality: By relying on static X25519 keys, the project is effectively building "PGP for 2025" - a technology known for catastrophic retroactive decryption upon key compromise.

3. Comparison to Market Standards

Conclusion: Web/A is superior to standard TLS forms only in its ability to protect data at rest on the server, but it is significantly inferior to modern messaging protocols regarding key management and forward secrecy.

4. Mandatory Requirements (The "High Bar")

To consider this system "Secure" for high-value usage, we demand the following:

1. Mandatory Replay Checks: Refactor decryptLayer2 to require a nonce-check callback. If the callback is missing, it should default to a "Safe Mode" that creates an in-memory set (protecting against immediate bursts) or explicitly requires an "I_KNOW_WHAT_I_AM_DOING" flag to bypass.
2. Pre-Key Infrastructure Plan: You must produce a concrete design document for an "Offline Pre-Key Server". This allows the "Form Loader" to fetch a unique, one-time public key for the encryption, ensuring that even if the Org Root Key is stolen later, past messages remain secure.
3. Client-Side Integrity (SRI/CSP): The documentation must explicitly provide a strict Content Security Policy (CSP) and Subresource Integrity (SRI) hashes for the mkform.js and Wasm artifacts. Without this, the "Man-in-the-Browser" attack is trivial.
4. Formal Audit of Rust Bindings: While safe, the logical mapping between TS and Rust needs a second pair of eyes, specifically focusing on the get_shared_secret and hkdf flows to ensure no intermediate values are inadvertently leaked or logged.

Signed, Red Team Lead

5. Publisher Response (Draft)

This section records the current response plan and documentation deliverables. It does not alter the audit findings above.

1. Mandatory Replay Checks: Will be enforced by default at the API boundary with explicit opt-out only. Status: Planned.
2. Pre-Key Infrastructure Plan: Design document published. Status: Draft Published.
   • Offline Pre-Key Server Plan
3. Client-Side Integrity (SRI/CSP): Strict CSP/SRI template published in the L2 Encryption paper. Status: Guidance Published.
   • Web/A L2 Encryption
4. Formal Audit of Rust Bindings: Third-party review scope to be defined (focus: shared secret + HKDF flows). Status: Planned.
5. Decoy Traffic: Roadmap entry added for high-sensitivity deployments. Status: Planned.