Add support for age encryption via age.el

[fapdash]

• require age.el if the package is installed https://github.com/anticomputer/age.el
• add new customizable variable org-journal-encryption-extension to control the file extension appended to the file name to trigger transparent encryption
• recognize .age files as journal files
• generate encrypted files based on chosen file extension instead of hard coding .gpg
• support .age files in org-journal-re-encrypt-journals - only re-encrypt files for the currently chosen encryption extension - functional change: don't edit/re-save files that aren't encrypted. I assume that they where handled by this function in the past was an oversight and not intended. - allow multiple recipients for age encryption

closes #441

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age encyrption works with this change.
TODOs from age encrypted journal files get added to the agenda. (org-journal-enable-agenda-integration)

I wasn't sure how to do optional dependencies for Emacs packages.
If someone tries to set age as extension the org-journal-re-encrypt-journals
function will fail because of missing functions, of course.

org-journal-re-encrypt-journals works for me if age-default-recipient and age-default-identity are set,
but things got a bit weird when I hadn't set those.
I might be missing some settings, but at some point age encryption wasn't working at all and I had to restart Emacs.

Theoretically org-journal would work with any encryption that implements transparent, as long as the org-journal--list-files and org-journal--dir-and-file-format->pattern would get consider the value of org-journal-encryption-extension in their regexes. If we don't want to implement this then it's probably better to make org-journal-encryption-extension of :type '(choice (const :tag "age" age) (const :tag "gpg" gpg)) instead of 'string.

Instructions for testing

• Get age binaries: https://github.com/FiloSottile/age/releases/latest
• Place binaries in $PATH

Create age keys:

age-keygen -o key.txt
age-keygen -y key.txt > key.pub

Example age.el configuration for testing:

(use-package age
  :ensure t
  :demand t
  :custom
  (age-program "age")
  (age-default-identity "~/.age/key.txt")
  (age-default-recipient '("~/.age/key.pub"))
  :config
  (age-file-enable))

Activate age encrption for org-journal:

(setq 
  org-journal-encrypt-journal t
  org-journal-encryption-extension "age")

[fapdash]

@rosstimson Can you please test if this is working for you?

[rosstimson]

@fapdash Thanks for your work here. I don't think it is encrypting the file properly.

My relevant config looks like:

(use-package age
    :mode ("\\.age\\'" . age-encryption-mode)
    :custom
    (age-default-identity (expand-file-name ".age/rosstimson.txt" (getenv "HOME")))
    ;; My public age key
    (age-default-recipient "age17ll5hultu5gpye40nlj7z7ktcxl8ne9xvtd6udzugkmwlmt83uns82smww")
    :config
    (age-file-enable))

(use-package org-journal
    :after org
    :bind ("C-c j" . org-journal-new-entry)
    :custom
    (org-journal-file-type 'monthly)
    (org-journal-date-format "%A, %d %B %Y")
    (org-journal-encrypt-journal t)
    (org-journal-encryption-extension "age")
    (org-journal-dir (concat (concat org-directory "/journal/") (format-time-string "%Y"))))

If I create a test file of foo.age and save some text then check it in terminal with less I can see that it is age encrypted and it automatically decrypts when I open it within emacs.

I then shifted my existing gpg encrypted journal files into a backup dir and used org-journal-new-entry to create a new journal entry, when I check the file in the terminal it shows as plain text rather than encrypted, it does indeed have have the .age extension though.

I've rebuilt the org-journal package with your branch and restarted emacs of course, if I enter the customize stuff I can see your newly added org-journal-encryption-extension when I search for it, I saw no errors with my init config.

[fapdash]

@rosstimson Mh, I can't reproduce this.. 🤷
org-journal doesn't really change anything about age.el, the only change you're hitting is that the file extension is changed to .age, which you've confirmed is working.

Can you please check if age-encryption-mode is active in the buffer for your journal .age file after you've created it via org-journal-new-entry?
I don't expect it to make a difference, but can you try without the :mode ("\\.age\\'" . age-encryption-mode) line? (mode activation is already handled by age-file-enable)

[rosstimson]

@fapdash Not sure why it was a problem but you were correct, simply removing the line :mode ("\\.age\\'" . age-encryption-mode) has fixed it. So exact same config as I posted above minus that link.

I can now confirm that this works as expected. Thanks again for your work here. 🎉