android-encrypted-archiver/.planning/phases/12-user-key-input/12-02-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
12-user-key-input	02	crypto	argon2id rpassword kdf salt password-authentication	phase plan provides 12-user-key-input 01 CLI --key/--key-file key input, KeySource enum, resolve_key()	Full --password support with Argon2id KDF and 16-byte random salt Salt storage in archive format (flags bit 4, 16 bytes between header and TOC) Interactive password prompt via rpassword with confirmation on pack resolve_key_for_pack() and resolve_key_for_unpack() two-phase API	kotlin-decoder format-spec	added patterns argon2 0.5 rpassword 7.4 two-phase key resolution for password (salt lifecycle) flags-based optional format sections	created modified Cargo.toml src/key.rs src/format.rs src/archive.rs src/main.rs tests/round_trip.rs	Two-phase key resolution: resolve_key_for_pack() generates salt, resolve_key_for_unpack() reads salt from archive Salt stored as 16 plaintext bytes between header (offset 40) and TOC (offset 56) when flags bit 4 set Argon2id with default parameters (Argon2::default()) for key derivation pack prompts for password confirmation (enter twice), unpack prompts once	Flags-based optional format sections: bit 4 signals 16-byte salt between header and TOC Two-phase key resolution pattern: pack generates salt, unpack reads salt then derives key	KEY-03 KEY-04 KEY-05 KEY-06	5min	2026-02-26

Phase 12 Plan 02: Password-Based Key Derivation Summary

Argon2id KDF with 16-byte random salt stored in archive format, completing --password support via rpassword interactive prompt

Performance

• Duration: 5 min
• Started: 2026-02-26T20:56:34Z
• Completed: 2026-02-26T21:01:33Z
• Tasks: 2
• Files modified: 6

Accomplishments

• Argon2id KDF derives 32-byte key from password + 16-byte random salt using argon2 crate
• Archives created with --password store salt in format (flags bit 4, 16 bytes at offset 40-55, TOC at 56)
• All three key input methods (--key, --key-file, --password) fully functional end-to-end
• Wrong password correctly rejected via HMAC/decryption failure
• All 52 tests pass: 25 unit + 7 golden + 20 integration (5 new password tests added)

Task Commits

Each task was committed atomically:

1. Task 1: Implement Argon2id KDF, rpassword prompt, and salt format - 035879b (feat)
2. Task 2: Wire salt into archive pack/unpack, update main.rs, and add tests - 4077847 (feat)

Files Created/Modified

• Cargo.toml - Added argon2 0.5 and rpassword 7.4 dependencies
• src/key.rs - derive_key_from_password(), prompt_password(), resolve_key_for_pack/unpack(), ResolvedKey struct
• src/format.rs - FLAG_KDF_SALT, SALT_SIZE constants, read_salt/write_salt functions, relaxed flags validation
• src/archive.rs - Pack accepts optional salt, read_archive_metadata returns salt, read_archive_salt() helper
• src/main.rs - Two-phase password key resolution for pack/unpack/inspect
• tests/round_trip.rs - 5 new tests: password roundtrip, wrong password, salt flag, no-salt flag, directory password

Decisions Made

• Two-phase key resolution API: resolve_key_for_pack() generates random salt and returns ResolvedKey with key+salt; resolve_key_for_unpack() reads salt from archive before deriving key
• Salt is 16 bytes of plaintext between header and TOC (not encrypted), signaled by flags bit 4 (0x10)
• Argon2id with default parameters (19 MiB memory, 2 iterations, 1 parallelism) for key derivation
• Pack prompts password twice (confirmation), unpack prompts once
• Legacy resolve_key() kept for inspect keyless path (errors on password variant)

Deviations from Plan

None - plan executed exactly as written.

Issues Encountered

None

User Setup Required

None - no external service configuration required.

Next Phase Readiness

• All three key input methods complete: --key (hex), --key-file (raw bytes), --password (Argon2id)
• Phase 12 is now complete - all user key input requirements fulfilled
• Future work: Kotlin decoder may need password/salt support for interop

Self-Check: PASSED

All 6 modified files verified present. Both task commits (035879b, 4077847) found in git log.

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Phase: 12-user-key-input Completed: 2026-02-26