---
phase: 06-obfuscation-hardening
plan: 01
subsystem: crypto
tags: [xor, aes-256-cbc, obfuscation, binary-format, padding]

# Dependency graph
requires:
  - phase: 02-core-archiver
    provides: pack/unpack/inspect pipeline with AES-256-CBC encryption
  - phase: 03-round-trip-verification
    provides: unit tests, golden vectors, integration tests
provides:
  - XOR header obfuscation with cyclic 8-byte key
  - AES-256-CBC encrypted TOC with random toc_iv
  - Decoy random padding (64-4096 bytes) between data blocks
  - XOR bootstrapping auto-detection (plain vs obfuscated headers)
  - Buffer-based header/TOC serialization helpers
affects: [06-02 (Kotlin/Shell decoder updates), cross-validation tests]

# Tech tracking
tech-stack:
  added: []
  patterns: [xor-header-obfuscation, toc-encryption, decoy-padding, read_archive_metadata-helper]

key-files:
  created: []
  modified:
    - src/format.rs
    - src/archive.rs

key-decisions:
  - "Always enable all 3 obfuscation features (no --no-obfuscate flag in v1)"
  - "Decoy padding range 64-4096 bytes per file (FORMAT.md allows up to 65535)"
  - "Shared read_archive_metadata() helper for unpack/inspect de-obfuscation"
  - "Two-pass TOC serialization: first pass for size, second with correct data_offsets"

patterns-established:
  - "XOR bootstrapping: check magic first, attempt XOR de-obfuscation on mismatch"
  - "Buffer-based serialization: write_header_to_buf() and serialize_toc() for encryption pipeline"
  - "read_archive_metadata() as shared de-obfuscation entry point"

requirements-completed: [FMT-06, FMT-07, FMT-08]

# Metrics
duration: 3min
completed: 2026-02-25
---

# Phase 6 Plan 1: Rust Obfuscation Pipeline Summary

**XOR-obfuscated headers, AES-encrypted TOC, and random decoy padding in Rust archiver with full backward-compatible decode**

## Performance

- **Duration:** 3 min
- **Started:** 2026-02-24T23:16:21Z
- **Completed:** 2026-02-24T23:20:06Z
- **Tasks:** 2/2
- **Files modified:** 2

## Accomplishments
- Archives are completely unrecognizable: no magic bytes, no plaintext filenames, no detectable structure
- Flags byte is 0x0F when compression + all 3 obfuscation features are active
- All 38 existing tests pass (25 unit + 7 golden + 6 round-trip integration) -- zero failures
- XOR bootstrapping allows transparent detection of both plain and obfuscated headers

## Task Commits

Each task was committed atomically:

1. **Task 1: Add XOR header obfuscation and TOC encryption to format.rs** - `8ac2512` (feat)
2. **Task 2: Update pack/unpack/inspect with full obfuscation pipeline** - `b6fa51d` (feat)

## Files Created/Modified
- `src/format.rs` - Added XOR_KEY constant, xor_header_buf(), write_header_to_buf(), read_header_auto() with XOR bootstrapping, serialize_toc(), read_toc_from_buf(), parse_header_from_buf(), plus 6 new unit tests
- `src/archive.rs` - Updated pack() with TOC encryption + decoy padding + XOR header; updated unpack()/inspect() with shared read_archive_metadata() de-obfuscation helper

## Decisions Made
- Always enable all 3 obfuscation features in pack() -- no opt-out flag in v1 (the whole point is hardening)
- Decoy padding range 64-4096 bytes per file -- meaningful noise without significant size inflation
- Two-pass TOC serialization approach: first serialize with placeholder offsets to determine encrypted TOC size, then re-serialize with correct data_offsets and re-encrypt (encrypted size is identical because plaintext length is unchanged)
- Shared read_archive_metadata() function factored out for both unpack() and inspect() to avoid code duplication

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- Rust archiver produces fully obfuscated archives; decoders will use same de-obfuscation patterns
- Plan 06-02 should update Kotlin ArchiveDecoder.kt and Shell decode.sh to handle XOR headers, encrypted TOC, and padding_after > 0
- Cross-validation tests should confirm byte-identical extraction across all three decoders

## Self-Check: PASSED

- FOUND: src/format.rs
- FOUND: src/archive.rs
- FOUND: 06-01-SUMMARY.md
- FOUND: commit 8ac2512
- FOUND: commit b6fa51d

---
*Phase: 06-obfuscation-hardening*
*Completed: 2026-02-25*