---
phase: 06-obfuscation-hardening
verified: 2026-02-24T23:32:25Z
status: human_needed
score: 4/4
re_verification: false
human_verification:
  - test: "Run Kotlin cross-validation tests with kotlinc/java installed"
    expected: "All 6 tests pass (Rust pack -> Kotlin decode -> SHA-256 match)"
    why_human: "kotlinc and java are not available in the current environment; Kotlin code is structurally verified but not runtime-tested"
---

# Phase 6: Obfuscation Hardening Verification Report

**Phase Goal:** Archive format resists casual analysis -- binwalk, file, strings, and hex editors reveal nothing useful
**Verified:** 2026-02-24T23:32:25Z
**Status:** human_needed
**Re-verification:** No -- initial verification

## Goal Achievement

### Observable Truths

| # | Truth | Status | Evidence |
|---|-------|--------|----------|
| 1 | File table (names, sizes, offsets) is encrypted with its own IV -- hex dump of archive reveals no plaintext metadata | VERIFIED | TOC encrypted via `crypto::encrypt_data(&toc_plaintext, &KEY, &toc_iv)` in archive.rs:162,195. `strings` on archive reveals no filenames. Tested with multi-file archive -- no "hello", "test", ".txt" in output. |
| 2 | All headers are XOR-obfuscated with a fixed key -- no recognizable structure patterns in first 256 bytes | VERIFIED | First bytes of archive are `a5d6 e46c e074 4cc8` instead of `00ea7263`. XOR_KEY `[0xA5, 0x3C, 0x96, 0x0F, 0xE1, 0x7B, 0x4D, 0xC8]` applied in archive.rs:216-217 via `format::xor_header_buf()`. |
| 3 | Random decoy padding exists between data blocks -- file boundaries are not detectable by size analysis | VERIFIED | `rng.random_range(64..=4096)` generates random padding (archive.rs:111). Random bytes written after each ciphertext block (archive.rs:231). `inspect` shows `Padding after: 1718 bytes` for test archive. |
| 4 | All three decoders (Rust, Kotlin, Shell) still produce byte-identical output after obfuscation is applied | VERIFIED (partial: Kotlin not runtime-tested) | Rust: 38 cargo tests pass (25 unit + 7 golden + 6 round-trip). Shell: 7/7 cross-validation tests pass. Kotlin: code structurally correct (XOR bootstrapping, TOC decryption) but kotlinc/java not available in environment. |

**Score:** 4/4 truths verified (1 needs human runtime confirmation for Kotlin)

### Required Artifacts

| Artifact | Expected | Status | Details |
|----------|----------|--------|---------|
| `src/format.rs` | XOR_KEY constant, xor_header_buf(), read_header_auto() with XOR bootstrapping | VERIFIED | XOR_KEY at line 13, xor_header_buf() at line 85, read_header_auto() at line 149, write_header_to_buf() at line 95, serialize_toc() at line 171, read_toc_from_buf() at line 182, parse_header_from_buf() at line 111. 6 new XOR-related unit tests (lines 509-661). |
| `src/archive.rs` | Updated pack() with TOC encryption + decoy padding + XOR header; updated unpack()/inspect() with de-obfuscation | VERIFIED | pack() at line 58: TOC encryption (lines 160-163), decoy padding (lines 111-113), XOR header (lines 216-217). read_archive_metadata() shared helper at line 32 for unpack/inspect de-obfuscation. |
| `src/crypto.rs` | generate_iv() used for toc_iv | VERIFIED | generate_iv() at line 8, encrypt_data() at line 18, decrypt_data() at line 34. Used by archive.rs for toc_iv generation. |
| `kotlin/ArchiveDecoder.kt` | XOR_KEY constant, xorHeader(), TOC decryption, updated decode() | VERIFIED | XOR_KEY at line 39, xorHeader() at line 266, XOR bootstrapping in decode() at line 293-296, TOC decryption at lines 302-315. |
| `shell/decode.sh` | XOR_KEY_HEX, XOR de-obfuscation loop, TOC decryption via openssl, TOC_FILE abstraction | VERIFIED | XOR_KEY_HEX at line 107, hex_to_bin() at line 113, XOR bootstrapping loop at lines 138-161, header temp file parsing at lines 164-181, TOC decryption at lines 188-204, TOC_FILE/TOC_BASE_OFFSET abstraction throughout TOC parsing loop. |
| `kotlin/test_decoder.sh` | Cross-validation tests using obfuscated archives | VERIFIED | 5 test cases (single text, multiple files, no-compress, empty file, large file) with SHA-256 verification. |
| `shell/test_decoder.sh` | Cross-validation tests using obfuscated archives | VERIFIED | 6 test cases (single text, multiple files, no-compress, empty file, large file, Cyrillic filename) with SHA-256 verification. All 7 file verifications pass. |

### Key Link Verification

| From | To | Via | Status | Details |
|------|----|-----|--------|---------|
| archive.rs pack() | format.rs xor_header_buf() | XOR applied to 40-byte header buffer after write_header_to_buf | WIRED | archive.rs:216 `write_header_to_buf`, line 217 `xor_header_buf` |
| archive.rs pack() | crypto.rs encrypt_data() | TOC plaintext buffer encrypted with toc_iv | WIRED | archive.rs:162 `crypto::encrypt_data(&toc_plaintext, &KEY, &toc_iv)`, line 195 re-encryption with correct offsets |
| archive.rs unpack()/inspect() | format.rs read_header_auto() + crypto.rs decrypt_data() | XOR bootstrapping on header, then TOC decryption | WIRED | read_archive_metadata() at line 32-51: read_header_auto (line 34), decrypt_data for TOC (line 43) |
| kotlin decode() | xorHeader() | XOR bootstrapping on header bytes before parseHeader | WIRED | ArchiveDecoder.kt:293-296: magic check, xorHeader(headerBytes) call |
| kotlin decode() | decryptAesCbc() | Encrypted TOC bytes decrypted with tocIv before parseToc | WIRED | ArchiveDecoder.kt:307 `decryptAesCbc(encryptedToc, header.tocIv, KEY)` |
| shell decode.sh | openssl enc -d | Encrypted TOC extracted and decrypted | WIRED | decode.sh:192 dd extract, lines 195-197 openssl decrypt, TOC_FILE variable set to decrypted temp file |

### Requirements Coverage

| Requirement | Source Plan | Description | Status | Evidence |
|-------------|-----------|-------------|--------|----------|
| FMT-06 | 06-01, 06-02 | XOR-obfuscation of headers with fixed key | SATISFIED | XOR_KEY constant identical across all 3 implementations. Header bytes obfuscated -- first 4 bytes are `a5d6e46c` not `00ea7263`. XOR bootstrapping in all decoders. |
| FMT-07 | 06-01, 06-02 | Encrypted file table with separate IV | SATISFIED | TOC encrypted via AES-256-CBC with random toc_iv stored in header. All 3 decoders decrypt TOC before parsing entries. `strings` reveals no filenames. |
| FMT-08 | 06-01, 06-02 | Decoy padding (random data between blocks) | SATISFIED | Random padding 64-4096 bytes per file (archive.rs:111). Random bytes via `rand::Fill` (line 113). All decoders use absolute data_offset from TOC entries, naturally skipping padding. |

### Anti-Patterns Found

| File | Line | Pattern | Severity | Impact |
|------|------|---------|----------|--------|
| src/archive.rs | 140,148 | "placeholder" in comment about data_offset=0 | Info | Not a stub -- placeholder offsets are immediately replaced with real values at line 185 in the two-pass algorithm. No issue. |

### Human Verification Required

### 1. Kotlin Cross-Validation Tests

**Test:** Run `bash kotlin/test_decoder.sh` on a system with kotlinc and java installed
**Expected:** All 6 tests pass (Rust pack with obfuscation -> Kotlin decode -> SHA-256 match)
**Why human:** kotlinc and java are not installed in the current environment. The Kotlin code is structurally verified (XOR_KEY, xorHeader(), TOC decryption all present and correctly wired), but has not been runtime-tested in this verification cycle.

### Gaps Summary

No gaps found. All four success criteria from the ROADMAP are met:

1. **File table encrypted with its own IV** -- hex dump reveals no plaintext metadata (verified with `strings` scan)
2. **Headers XOR-obfuscated** -- no recognizable structure in first bytes (verified: `a5d6e46c` instead of `00ea7263`)
3. **Random decoy padding between blocks** -- file boundaries not detectable (verified: `Padding after: 1718 bytes` in inspect output)
4. **All three decoders produce byte-identical output** -- Rust 38/38 tests pass, Shell 7/7 cross-validation pass, Kotlin structurally verified (needs runtime confirmation)

All 38 Rust tests pass (25 unit + 7 golden + 6 round-trip integration). All 7 Shell cross-validation tests pass. The only item requiring human action is running the Kotlin cross-validation tests with kotlinc/java installed.

Requirements FMT-06, FMT-07, FMT-08 are all satisfied with implementation evidence across all three decoder implementations.

---
_Verified: 2026-02-24T23:32:25Z_
_Verifier: Claude (gsd-verifier)_