---
phase: 02-core-archiver
plan: 01
subsystem: crypto, format, cli
tags: [aes-256-cbc, hmac-sha256, gzip, clap, flate2, pkcs7, binary-format]

# Dependency graph
requires:
  - phase: 01-format-spec
    provides: "FORMAT.md binary format specification (byte-level field definitions)"
provides:
  - "Rust project with Cargo.toml and all crypto/compression/format dependencies"
  - "CLI skeleton with pack/unpack/inspect subcommands (clap derive)"
  - "Binary format types (Header, TocEntry) with serialize/deserialize matching FORMAT.md"
  - "AES-256-CBC encrypt/decrypt pipeline with PKCS7 padding"
  - "HMAC-SHA-256 compute/verify (encrypt-then-MAC over IV||ciphertext)"
  - "SHA-256 hash for file integrity verification"
  - "Gzip compress/decompress with deterministic mtime(0)"
  - "Compression heuristic for known compressed file extensions"
  - "Hardcoded 32-byte AES key constant"
affects: [02-core-archiver, 03-round-trip-verification]

# Tech tracking
tech-stack:
  added: [aes 0.8, cbc 0.1, hmac 0.12, sha2 0.10, flate2 1.1, clap 4.5, rand 0.9, anyhow 1.0]
  patterns: [manual binary serialization with to_le_bytes/from_le_bytes, RustCrypto type aliases for cipher modes, GzBuilder mtime(0) for reproducibility]

key-files:
  created:
    - Cargo.toml
    - src/main.rs
    - src/cli.rs
    - src/key.rs
    - src/format.rs
    - src/crypto.rs
    - src/compression.rs
    - src/archive.rs
  modified: []

key-decisions:
  - "Used rand::Fill::fill() instead of try_fill() for IV generation (correct rand 0.9 API)"
  - "Edition 2021 to match plan specification"
  - "Dead-code warnings expected and acceptable until pack/unpack/inspect wire up modules in Plan 02-02"

patterns-established:
  - "Type aliases for cipher modes: type Aes256CbcEnc = cbc::Encryptor<aes::Aes256>"
  - "Manual binary serialization: to_le_bytes()/from_le_bytes() for all multi-byte fields"
  - "HMAC-SHA-256 scope: IV (16 bytes) || ciphertext (encrypted_size bytes)"
  - "Compression heuristic: extension-based auto-detection + CLI override via --no-compress"
  - "GzBuilder::new().mtime(0) for deterministic gzip output"

requirements-completed: [FMT-01, FMT-02, FMT-03, FMT-04, ENC-01, ENC-02, ENC-03, ENC-04, ENC-05, CMP-01, CMP-02, INT-01, CLI-01]

# Metrics
duration: 4min
completed: 2026-02-24
---

# Phase 2 Plan 1: Project Foundation Summary

**Rust project with AES-256-CBC/HMAC-SHA-256 crypto pipeline, binary format serialization matching FORMAT.md, gzip compression, and clap CLI skeleton**

## Performance

- **Duration:** 4 min
- **Started:** 2026-02-24T20:54:36Z
- **Completed:** 2026-02-24T20:58:28Z
- **Tasks:** 2
- **Files modified:** 8

## Accomplishments
- Complete Rust project structure with 7 source modules and all dependencies
- Binary format types (Header: 40 bytes, TocEntry: 101+N bytes) with byte-accurate serialization matching FORMAT.md Sections 4 and 5
- Full crypto pipeline: AES-256-CBC encrypt/decrypt, HMAC-SHA-256 compute/verify, SHA-256 hash, random IV generation
- Gzip compression/decompression with reproducible output and smart compression heuristic

## Task Commits

Each task was committed atomically:

1. **Task 1: Project scaffolding with Cargo, CLI skeleton, and key module** - `c647f3a` (feat)
2. **Task 2: Format types, crypto pipeline, and compression module** - `6292b41` (feat)

## Files Created/Modified
- `Cargo.toml` - Project manifest with aes, cbc, hmac, sha2, flate2, clap, rand, anyhow
- `src/main.rs` - CLI entry point with clap parse and dispatch to pack/unpack/inspect
- `src/cli.rs` - Clap derive structs: Cli, Commands enum (Pack/Unpack/Inspect)
- `src/key.rs` - Hardcoded 32-byte AES-256 key constant
- `src/format.rs` - Header and TocEntry structs with write/read serialization, entry_size, compute_toc_size
- `src/crypto.rs` - encrypt_data, decrypt_data, compute_hmac, verify_hmac, sha256_hash, generate_iv
- `src/compression.rs` - compress, decompress, should_compress
- `src/archive.rs` - Stub module for pack/unpack/inspect orchestration (Plan 02-02)

## Decisions Made
- Used `rand::Fill::fill()` instead of `try_fill()` for IV generation (correct rand 0.9 API for array fill)
- Kept edition 2021 as specified in the plan for broad compatibility
- Dead-code warnings are expected and acceptable -- modules are not yet called from main; they will be wired in Plan 02-02

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 3 - Blocking] Fixed rand 0.9 API for IV generation**
- **Found during:** Task 2 (crypto.rs implementation)
- **Issue:** `try_fill()` method does not exist on `[u8; 16]` in rand 0.9. The `Fill` trait provides `fill()`, not `try_fill()`.
- **Fix:** Changed from `iv.try_fill(&mut rand::rng())` to `rand::Fill::fill(&mut iv, &mut rand::rng())`
- **Files modified:** src/crypto.rs
- **Verification:** cargo build succeeds
- **Committed in:** 6292b41 (Task 2 commit)

---

**Total deviations:** 1 auto-fixed (1 blocking)
**Impact on plan:** Minor API correction for rand 0.9. No scope creep.

## Issues Encountered
None beyond the rand API correction noted above.

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

## Next Phase Readiness
- All building-block modules are implemented and compile successfully
- Ready for Plan 02-02: Pack, inspect, and unpack commands with full archive orchestration
- The archive.rs module is a stub awaiting the orchestration logic
- 25 dead-code warnings will be resolved when modules are wired into commands

## Self-Check: PASSED

All 8 created files verified present. Both task commits (c647f3a, 6292b41) verified in git log.

---
*Phase: 02-core-archiver*
*Completed: 2026-02-24*