I made some minor modifications to the age tool so that I could invoke its decrypt method from a non-tty environment (like from within emacs). I am currently using age to encrypt my org-mode notes, and I have provided some emacs lisp functions below that I use to decrypt/encrypt within memory.

Encryption was simple: simply pipe the current buffer into age -a -r PUBKEY and then replace the current buffer with the output. Decryption was a bit more difficult, as I need to specify the private key. However, I don't want to keep my private key file decrypted on my filesystem, and I can't specify a passphrase to the age cli from within emacs (as there is no tty), so I decided to modify age to optionally accept structured data (json) from stdin. This can be specified using age's new -k option.

The structured data currently expects the structure:

{
    "keys": ["KEY_1", "KEY_2"],
    "data": "BASE64_ENCODED_ENCRYPTED_DATA"
}

When the -k option is specified, age will expect this kind of structured data from its input.

Now personally, In my .emacs.d/init.el file I've defined these emacs lisp functions:

(defun encrypt-age (pubkey)
  (interactive "sPubkey:")
  (shell-command-on-region
   (point-min)
   (point-max)
   (concat "age -a -r " pubkey)
   (current-buffer)
   t
   "*Enc Error Buffer*"
   t))

(defun encrypt-age-my-key ()
  (interactive)
  (shell-command-on-region
   (point-min)
   (point-max)
   (concat "age -a -r age18hsrm9vzj9nw7um46x4v6hz4f3xd35l5nwa4p6dvn4zc64m4d4wsws6a78")
   (current-buffer)
   t
   "*Enc Error Buffer*"
   t))

(defun b64-encode ()
  (copy-to-buffer "*b64buffer*" (point-min) (point-max))
  (with-current-buffer "*b64buffer*"
    (shell-command-on-region
     (point-min)
     (point-max)
     (concat "base64 --wrap=0")
     (current-buffer)
     t
     "*B64 Error Buffer*"
     t)))

(defun decrypt-age (privatekey)
  (interactive "sPrivateKey:")
  (b64-encode)
  (generate-new-buffer "*decryptBuffer*")
  (with-current-buffer "*decryptBuffer*"
    (insert "{\"keys\":[\"")
    (insert privatekey)
    (insert "\"], \"data\":\"")
    (with-current-buffer "*b64buffer*"
      (append-to-buffer "*decryptBuffer*" (point-min) (point-max)))
    (insert "\"}")
    (shell-command-on-region
      (point-min)
      (point-max)
      "age -d -k"
      (current-buffer)
      t
      "*Dec Error Buffer*"
      t))
  (erase-buffer)
  (insert-buffer "*decryptBuffer*")
  (kill-buffer "*decryptBuffer*")
  (kill-buffer "*b64buffer*"))

; need private key to not be written to command line, so therefore the json needs to be constructed in emacs before written to pipe!
; create buffer 1 by taking current buffer and base64 encoding it
; create buffer 2 -> add intro text -> add key -> insert buffer 1 -> append end text -> pipe to age
(setq make-backup-files nil) ; I think this tells emacs to not temporarily save buffers to disks. Not good for the kind of promise I want!
(global-set-key (kbd "C-x e") 'encrypt-age-my-key)
(global-set-key (kbd "C-x d") 'decrypt-age)

I haven't written many emacs lisp functions before, so definitely file an issue if you have some ideas as to how this could use some improvement :)

Also, if you end up using something like this, you will probably want to change that public key hard-coded in encrypt-age-my-key to one of your own!

In the end, this satisfies my requirements, which are:

• No need to keep an age private key decrypted somewhere in a file
• Not passing an age private key through a command line parameter, which is visible to processes on the system
• Make it possible for emacs (or other tools) to open an encrypted file, decrypt the file in memory, make edits to the file in memory, and then re-encrypt the file before writing the file out to disk again

age is a simple, modern and secure file encryption tool, format, and Go library.

It features small explicit keys, no config options, and UNIX-style composability.

$ age-keygen -o key.txt
Public key: age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
$ tar cvz ~/data | age -r age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p > data.tar.gz.age
$ age --decrypt -i key.txt data.tar.gz.age > data.tar.gz

The format specification is at age-encryption.org/v1. age was designed by @Benjojo12 and @FiloSottile.

An alternative interoperable Rust implementation is available at github.com/str4d/rage.

The author pronounces it [aɡe̞], like the Italian “aghe”.

For the full documentation, read the age(1) man page.

Usage:
    age [--encrypt] (-r RECIPIENT | -R PATH)... [--armor] [-o OUTPUT] [INPUT]
    age [--encrypt] --passphrase [--armor] [-o OUTPUT] [INPUT]
    age --decrypt [-i PATH]... [-o OUTPUT] [INPUT]

Options:
    -e, --encrypt               Encrypt the input to the output. Default if omitted.
    -d, --decrypt               Decrypt the input to the output.
    -o, --output OUTPUT         Write the result to the file at path OUTPUT.
    -a, --armor                 Encrypt to a PEM encoded format.
    -p, --passphrase            Encrypt with a passphrase.
    -r, --recipient RECIPIENT   Encrypt to the specified RECIPIENT. Can be repeated.
    -R, --recipients-file PATH  Encrypt to recipients listed at PATH. Can be repeated.
    -i, --identity PATH         Use the identity file at PATH. Can be repeated.

INPUT defaults to standard input, and OUTPUT defaults to standard output.
If OUTPUT exists, it will be overwritten.

RECIPIENT can be an age public key generated by age-keygen ("age1...")
or an SSH public key ("ssh-ed25519 AAAA...", "ssh-rsa AAAA...").

Recipient files contain one or more recipients, one per line. Empty lines
and lines starting with "#" are ignored as comments. "-" may be used to
read recipients from standard input.

Identity files contain one or more secret keys ("AGE-SECRET-KEY-1..."),
one per line, or an SSH key. Empty lines and lines starting with "#" are
ignored as comments. Passphrase encrypted age files can be used as
identity files. Multiple key files can be provided, and any unused ones
will be ignored. "-" may be used to read identities from standard input.

When --encrypt is specified explicitly, -i can also be used to encrypt to an
identity file symmetrically, instead or in addition to normal recipients.

Files can be encrypted to multiple recipients by repeating -r/--recipient. Every recipient will be able to decrypt the file.

$ age -o example.jpg.age -r age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p \
    -r age1lggyhqrw2nlhcxprm67z43rta597azn8gknawjehu9d9dl0jq3yqqvfafg example.jpg

Multiple recipients can also be listed one per line in one or more files passed with the -R/--recipients-file flag.

$ cat recipients.txt
# Alice
age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
# Bob
age1lggyhqrw2nlhcxprm67z43rta597azn8gknawjehu9d9dl0jq3yqqvfafg
$ age -R recipients.txt example.jpg > example.jpg.age

If the argument to -R (or -i) is -, the file is read from standard input.

Files can be encrypted with a passphrase by using -p/--passphrase. By default age will automatically generate a secure passphrase. Passphrase protected files are automatically detected at decrypt time.

$ age -p secrets.txt > secrets.txt.age
Enter passphrase (leave empty to autogenerate a secure one):
Using the autogenerated passphrase "release-response-step-brand-wrap-ankle-pair-unusual-sword-train".
$ age -d secrets.txt.age > secrets.txt
Enter passphrase:

If an identity file passed to -i is a passphrase encrypted age file, it will be automatically decrypted.

$ age-keygen | age -p > key.age
Public key: age1yhm4gctwfmrpz87tdslm550wrx6m79y9f2hdzt0lndjnehwj0ukqrjpyx5
Enter passphrase (leave empty to autogenerate a secure one):
Using the autogenerated passphrase "hip-roast-boring-snake-mention-east-wasp-honey-input-actress".
$ age -r age1yhm4gctwfmrpz87tdslm550wrx6m79y9f2hdzt0lndjnehwj0ukqrjpyx5 secrets.txt > secrets.txt.age
$ age -d -i key.age secrets.txt.age > secrets.txt
Enter passphrase for identity file "key.age":

Passphrase-protected identity files are not necessary for most use cases, where access to the encrypted identity file implies access to the whole system. However, they can be useful if the identity file is stored remotely.

As a convenience feature, age also supports encrypting to ssh-rsa and ssh-ed25519 SSH public keys, and decrypting with the respective private key file. (ssh-agent is not supported.)

$ age -R ~/.ssh/id_ed25519.pub example.jpg > example.jpg.age
$ age -d -i ~/.ssh/id_ed25519 example.jpg.age > example.jpg

Note that SSH key support employs more complex cryptography, and embeds a public key tag in the encrypted file, making it possible to track files that are encrypted to a specific public key.

Combining SSH key support and -R, you can easily encrypt a file to the SSH keys listed on a GitHub profile.

$ curl https://github.com/benjojo.keys | age -R - example.jpg > example.jpg.age

Keep in mind that people might not protect SSH keys long-term, since they are revokable when used only for authentication, and that SSH keys held on YubiKeys can't be used to decrypt files.

On Windows, Linux, macOS, and FreeBSD you can use the pre-built binaries.

https://dl.github.com/johnkord/age/latest?for=linux/amd64
https://dl.github.com/johnkord/age/v1.0.0-rc.1?for=darwin/arm64
...

If your system has a supported version of Go, you can build from source.

go install github.com/johnkord/age/cmd/...@latest

Help from new packagers is very welcome.