android-encrypted-archiver/.planning/phases/05-shell-decoder/05-01-SUMMARY.md

phase, plan, subsystem, tags, requires, provides, affects, tech-stack, key-files, key-decisions, patterns-established, requirements-completed, duration, completed

phase	plan	subsystem	tags	requires	provides	affects	tech-stack	key-files	key-decisions	patterns-established	requirements-completed	duration	completed
05-shell-decoder	01	shell-decoder	posix-sh busybox openssl aes-256-cbc dd xxd od hmac sha256	phase provides 01-format-specification FORMAT.md binary format spec with shell decoder reference (Section 13) phase provides 02-core-archiver Rust archiver for creating test archives	shell/decode.sh -- busybox-compatible POSIX shell decoder script Full decode pipeline: header -> TOC -> HMAC verify -> decrypt -> decompress -> SHA-256 verify -> write	06-obfuscation	added patterns sh dd openssl-enc xxd od gunzip sha256sum posix-shell-binary-parsing xxd-od-fallback hmac-graceful-degradation	created shell/decode.sh	POSIX sh (not bash) for maximum busybox compatibility xxd/od auto-detection at startup for hex conversion Graceful HMAC degradation when openssl lacks -mac support Extract ciphertext to temp file before decryption (avoids pipe issues) LC_ALL=C for predictable byte handling	dd-based binary parsing with hex byte-swap for little-endian integers Temp file cleanup via trap on EXIT HMAC computed from raw archive bytes (IV from TOC offset + ciphertext), not from hex variables	SHL-01 SHL-02 SHL-03	3min	2026-02-25

Phase 5 Plan 1: Shell Decoder Summary

Busybox-compatible POSIX shell decoder with full decode pipeline (dd+xxd/od for parsing, openssl enc for AES-256-CBC decryption, HMAC verification with graceful degradation, SHA-256 integrity checks)

Performance

• Duration: 3 min
• Started: 2026-02-24T22:37:48Z
• Completed: 2026-02-24T22:40:29Z
• Tasks: 1
• Files created: 1

Accomplishments

• Created self-contained POSIX shell decoder script (250 lines) implementing full FORMAT.md Section 10 decode pipeline
• Verified byte-identical extraction against Rust archiver output (ASCII and Cyrillic filenames)
• Implemented xxd/od auto-detection fallback for hex conversion on minimal busybox systems
• HMAC graceful degradation: detects openssl HMAC support at startup, skips with warning if unavailable

Task Commits

Each task was committed atomically:

1. Task 1: Create shell/decode.sh with full decode pipeline - 6df2639 (feat)

Files Created/Modified

• shell/decode.sh - Busybox-compatible POSIX shell script implementing complete archive decode pipeline

Decisions Made

• Used POSIX sh (not bash) with no bash-specific syntax for maximum compatibility
• Auto-detect xxd vs od at startup; define read_hex using whichever is available
• Graceful HMAC degradation: test openssl HMAC capability at startup, set SKIP_HMAC flag
• Extract ciphertext to temp file before decryption (avoids pipe buffering issues with openssl enc)
• Set LC_ALL=C at script top for predictable byte handling across locales
• Used printf-based substring extraction instead of bash ${var:offset:len} for POSIX compliance

Deviations from Plan

None - plan executed exactly as written.

Issues Encountered

None.

User Setup Required

None - no external service configuration required.

Next Phase Readiness

• Shell decoder complete, ready for cross-validation testing in Plan 2
• Script verified against Rust archiver with both ASCII and Cyrillic filenames
• Phase 6 (obfuscation) can extend the script with XOR header deobfuscation and TOC decryption

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Phase: 05-shell-decoder Completed: 2026-02-25