Lustig Fairchild
Five-Year Diary

The sealed format

A sealed copy is your whole diary in one file: every diary, every line and every photograph, encrypted with a passphrase you choose. The format is published so that a sealed copy never depends on the app.

Five-Year Diary makes one from Settings › Your words › Seal a copy, and writes it where you tell it — on the phone, a memory card or a cloud drive. Anyone who has the passphrase can open it, on any computer.

What is here

  • The specification — five-year-diary/3, complete: a developer on any platform can write a reader, or a writer, from it alone. AES-256-GCM, a key from PBKDF2-HMAC-SHA256, zlib and a JSON container — all of it in every platform’s standard library.
  • The reference reader — one file of Python 3.8 or later, standard library only. It needs nothing installed, and it sends nothing anywhere.
  • The test vectors — 76 files, each with what it must open to or the reason it must be refused. A reader that agrees with all of them agrees with the app on every case they cover.

Opening a sealed copy without the app

  1. Install Python 3 from python.org (opens in a new tab) if your computer does not have it.
  2. Save the reader in the same folder as your sealed file.
  3. In a terminal, in that folder, run python3 five_year_diary_open.py five-year-diary-sealed-2026-12-31.json — on Windows, py in place of python3.
  4. Type your passphrase when asked. It is read from the terminal, never from the command line.

Every line is printed with its diary and date. The reader is written to prove the format, not to be fast: a sealed copy with many photographs takes minutes.

To check a reader of your own against the vectors, python3 five_year_diary_open.py --vectors golden-vectors.json shows how this one does it.

The passphrase

There is no way around it. A sealed copy opens with its passphrase and with nothing else — not with the app, not by us, not by anyone. That is what makes it safe to keep on a cloud drive or to send to yourself. Keep the passphrase somewhere apart from the file.

If the app, or we, are gone

  • Your diary stays on your phone. Five-Year Diary has no account and no server; nothing in it depends on us being here.
  • Plain text export is free. Settings › Your words › Export writes a diary as text or Markdown that any computer opens.
  • Sealed copies stay open to you. This page, the specification, the reader and the vectors are all you need, and you may keep your own copies of them.

Licence

This page, the specification, the reader and the test vectors are dedicated to the public domain under CC0 1.0 (opens in a new tab): to the extent possible under law, Lustig Fairchild Ltd. has waived all copyright and related rights to them. Copy, host, translate, port and change them, for any purpose, without asking.

How the app itself handles your diary is in its privacy policy.

Need help, or have an idea?

Questions, bug reports and feature requests are read and answered directly. Please include your device and system version — it makes a fix much quicker. One message is often all it takes: the detail you add today is what makes the next release better for everyone using the same app.

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