doc: add age(1) and age-keygen(1) man pages

Closes #131

.github/workflows/ronn.yml

@@ -0,0 +1,22 @@
+on:
+  push:
+    paths:
+      - '**.ronn'
+name: Generate man pages
+jobs:
+  ronn:
+    runs-on: ubuntu-latest
+    name: Ronn
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Run ronn
+        uses: ./.github/workflows/ronn
+        id: ronn
+      - name: Commit and push if changed
+        run: |-
+          git config user.name "GitHub Actions"
+          git config user.email "[email protected]"
+          git add -A
+          git commit -m "doc: regenerate groff and html man pages" || exit 0
+          git push

.github/workflows/ronn/Dockerfile

@@ -0,0 +1,8 @@
+FROM ruby:3.0.1-buster
+
+RUN apt-get update && apt-get install -y groff
+RUN bundle config --global frozen 1
+COPY Gemfile Gemfile.lock ./
+RUN bundle install
+ENTRYPOINT ["bash", "-O", "globstar", "-c", \
+    "/usr/local/bundle/bin/ronn **/*.ronn"]

.github/workflows/ronn/Gemfile

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "ronn", "~> 0.7.3"

.github/workflows/ronn/Gemfile.lock

@@ -0,0 +1,20 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    hpricot (0.8.6)
+    mustache (1.1.1)
+    rdiscount (2.2.0.2)
+    ronn (0.7.3)
+      hpricot (>= 0.8.2)
+      mustache (>= 0.7.0)
+      rdiscount (>= 1.5.8)
+
+PLATFORMS
+  aarch64-linux
+  x86_64-linux
+
+DEPENDENCIES
+  ronn (~> 0.7.3)
+
+BUNDLED WITH
+   2.2.15

.github/workflows/ronn/action.yml

@@ -0,0 +1,4 @@
+name: Ronn
+runs:
+  using: docker
+  image: Dockerfile

HomebrewFormula/age.rb

@@ -16,5 +16,7 @@ def install
     mkdir bin
     system "go", "build", "-trimpath", "-o", bin, "-ldflags", "-X main.Version=v#{version}", "filippo.io/age/cmd/..."
     prefix.install_metafiles
+    man1.install "doc/age.1"
+    man1.install "doc/age-keygen.1"
   end
 end

cmd/age-keygen/keygen.go

@@ -27,7 +27,7 @@ Options:
     -o, --output OUTPUT       Write the result to the file at path OUTPUT.
     -y                        Convert an identity file to a recipients file.
 
-age-keygen generates a new standard X25519 key pair, and outputs it to
+age-keygen generates a new native X25519 key pair, and outputs it to
 standard output or to the OUTPUT file.
 
 If an OUTPUT file is specified, the public key is printed to standard error.

doc/age-keygen.1.ronn

@@ -0,0 +1,57 @@
+age-keygen(1) -- generate age(1) key pairs
+====================================================
+
+## SYNOPSIS
+
+`age-keygen` [`-o` <OUTPUT>]<br>
+`age-keygen` `-y` [`-o` <OUTPUT>] [<INPUT>]<br>
+
+## DESCRIPTION
+
+`age-keygen` generates a new native age(1) key pair, and outputs the identity to
+standard output or to the <OUTPUT> file. The output includes the public key and
+the current time as comments.
+
+If the output is not going to a terminal, `age-keygen` prints the public key to
+standard error.
+
+## OPTIONS
+
+* `-o`, `--output`=<OUTPUT>:
+    Write the identity to <OUTPUT> instead of standard output.
+
+    If <OUTPUT> already exists, it is not overwritten.
+
+* `-y`:
+    Read an identity file from <INPUT> or from standard input and output the
+    corresponding recipient(s), one per line, with no comments.
+
+* `--version`:
+    Print the version and exit.
+
+## EXAMPLES
+
+Generate a new identity:
+
+    $ age-keygen
+    # created: 2021-01-02T15:30:45+01:00
+    # public key: age1lvyvwawkr0mcnnnncaghunadrqkmuf9e6507x9y920xxpp866cnql7dp2z
+    AGE-SECRET-KEY-1N9JEPW6DWJ0ZQUDX63F5A03GX8QUW7PXDE39N8UYF82VZ9PC8UFS3M7XA9
+
+Write a new identity to `key.txt`:
+
+    $ age-keygen -o key.txt
+    Public key: age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
+
+Convert an identity to a receipient:
+
+    $ age-keygen -y key.txt
+    age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
+
+## SEE ALSO
+
+age(1)
+
+## AUTHORS
+
+Filippo Valsorda <[email protected]>

doc/age.1.ronn

@@ -0,0 +1,221 @@
+age(1) -- simple, modern, and secure file encryption
+====================================================
+
+## SYNOPSIS
+
+`age` [`--encrypt`] (`-r` <RECIPIENT> | `-R` <PATH>)... [`--armor`] [`-o` <OUTPUT>] [<INPUT>]<br>
+`age` [`--encrypt`] `--passphrase` [`--armor`] [`-o` <OUTPUT>] [<INPUT>]<br>
+`age` `--decrypt` [`-i` <PATH>]... [`-o` <OUTPUT>] [<INPUT>]<br>
+
+## DESCRIPTION
+
+`age` encrypts or decrypts <INPUT> to <OUTPUT>. The <INPUT> argument is
+optional and defaults to standard input. Only a single <INPUT> file may be
+specified. If `-o` is not specified, <OUTPUT> defaults to standard output.
+
+If `--passphrase` is specified, the file is encrypted with a passphrase
+requested interactively. Otherwise, it's encrypted to one or more
+[RECIPIENTS][RECIPIENTS AND IDENTITIES] specified with `-r`/`--recipient` or
+`-R`/`--recipients-file`. Every recipient can decrypt the file.
+
+In `--decrypt` mode, passphrase-encrypted files are detected automatically and
+the passphrase is requested interactively. Otherwise, one or more
+[IDENTITIES][RECIPIENTS AND IDENTITIES] specified with `-i`/`--identity` are
+used to decrypt the file.
+
+`age` encrypted files are binary and not malleable, with around 200 bytes of
+overhead per recipient, plus 16 bytes every 64KiB of plaintext.
+
+## OPTIONS
+
+* `-o`, `--output`=<OUTPUT>:
+    Write encrypted or decrypted file to <OUTPUT> instead of standard output.
+    If <OUTPUT> already exists it will be overwritten.
+
+    If encrypting without `--armor`, `age` will refuse to output binary to a
+    TTY. This can be forced by specifying `-` as <OUTPUT>.
+
+* `--version`:
+    Print the version and exit.
+
+### Encryption options
+
+* `-e`, `--encrypt`:
+    Encrypt <INPUT> to <OUTPUT>. This is the default.
+
+* `-r`, `--recipient`=<RECIPIENT>:
+    Encrypt to the explicitly specified <RECIPIENT>. See the
+    [RECIPIENTS AND IDENTITIES][] section for possible recipient formats.
+
+    This option can be repeated and combined with `-R`/`--recipients-file`,
+    and the file can be decrypted by all provided recipients independently.
+
+* `-R`, `--recipients-file`=<PATH>:
+    Encrypt to the [RECIPIENTS][RECIPIENTS AND IDENTITIES] listed in the
+    file at <PATH>, one per line. Empty lines and lines starting with `#`
+    are ignored as comments.
+
+    If <PATH> is `-`, the recipients are read from standard input. In
+    this case, the <INPUT> argument must be specified.
+
+    This option can be repeated and combined with `-r`/`--recipient`,
+    and the file can be decrypted by all provided recipients independently.
+
+* `-p`, `--passphrase`:
+    Encrypt with a passphrase, requested interactively from the terminal.
+    `age` will offer to auto-generate a secure passphrase.
+
+    This options can't be used with `-r`/`--recipient` or
+    `-R`/`--recipients-file`.
+
+* `-a`, `--armor`:
+    Encrypt to an ASCII-only "armored" encoding.
+
+    `age` armor is a strict version of PEM with type `AGE ENCRYPTED FILE`,
+    canonical "strict" Base64, no headers, and no support for leading and
+    trailing extra data.
+
+    Decryption transparently detects and decodes ASCII armoring.
+
+### Decryption options
+
+* `-d`, `--decrypt`:
+    Decrypt <INPUT> to <OUTPUT>.
+
+    If <INPUT> is passphrase encrypted, it will be automatically detected
+    and the passphrase will be requested interactively. Otherwise, the
+    [IDENTITIES][RECIPIENTS AND IDENTITIES] specified with `-i`/`--identity`
+    are used.
+
+    ASCII armoring is transparently detected and decoded.
+
+* `-i`, `--identity`=<PATH>:
+    Decrypt using the [IDENTITIES][RECIPIENTS AND IDENTITIES] at <PATH>.
+
+    <PATH> may be one of the following:
+
+    a\. A file listing [IDENTITIES][RECIPIENTS AND IDENTITIES] one per line.
+    Empty lines and lines starting with "`#`" are ignored as comments.
+
+    b\. An SSH private key file, in PKCS#1, PKCS#8, SEC 1, or OpenSSH format.
+    If the private key is password-protected, the password is requested
+    interactively only if the SSH identity matches the file. See the
+    [SSH keys][] section for more information, including supported key types.
+
+    c\. "`-`", causing one of the options above to be read from standard input.
+    In this case, the <INPUT> argument must be specified.
+
+    This option can be repeated. Identities are tried in the order in which
+    are provided, and the first one matching one of the file's recipients is
+    used. Unused identities are ignored.
+
+    If `-e`/`--encrypt` is explicitly specified (to avoid confusion),
+    `-i`/`--identity` may also be used to encrypt to the `RECIPIENTS`
+    corresponding to the `IDENTITIES` listed at <PATH>. This allows using an
+    identity file as a symmetric key, if desired.
+
+## RECIPIENTS AND IDENTITIES
+
+`RECIPIENTS` are public values, like a public key, that a file can be encrypted
+to. `IDENTITIES` are private values, like a private key, that allow decrypting
+a file encrypted to the corresponding `RECIPIENT`.
+
+### Native X25519 keys
+
+Native `age` key pairs are generated with age-keygen(1), and provide small
+encodings and strong encryption based on X25519. They are the recommended
+recipient type for most applications.
+
+A `RECIPIENT` encoding begins with `age1` and looks like the following:
+
+    age1gde3ncmahlqd9gg50tanl99r960llztrhfapnmx853s4tjum03uqfssgdh
+
+An `IDENTITY` encoding begins with `AGE-SECRET-KEY-1` and looks like the
+following:
+
+    AGE-SECRET-KEY-1KTYK6RVLN5TAPE7VF6FQQSKZ9HWWCDSKUGXXNUQDWZ7XXT5YK5LSF3UTKQ
+
+An encrypted file can't be linked to the native recipient it's encrypted to
+without access to the corresponding identity.
+
+### SSH keys
+
+As a convenience feature, `age` also supports encrypting to RSA or Ed25519
+ssh(1) keys. RSA keys must be at least 2048 bits. This feature employs more
+complex cryptography, and should only be used when a native key is not available
+for the recipient. Note that SSH keys might not be protected long-term by the
+recipient, since they are revokable when used only for authentication.
+
+A `RECIPIENT` encoding is an SSH public key in `authorized_keys` format
+(see the `AUTHORIZED_KEYS FILE FORMAT` section of sshd(8)), starting with
+`ssh-rsa` or `ssh-ed25519`, like the following:
+
+    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABgQDULTit0KUehbi[...]GU4BtElAbzh8=
+    ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIH9pO5pz22JZEas[...]l1uZc31FGYMXa
+
+The comment at the end of the line, if present, is ignored.
+
+In recipient files passed to `-R`/`--recipients-file`, unsupported but valid
+SSH public keys are ignored with a warning, to facilitate using
+`authorized_keys` or GitHub `.keys` files. (See [EXAMPLES][].)
+
+An `IDENTITY` is an SSH private key _file_ passed individually to
+`-i`/`--identity`. Note that keys held on hardware tokens such as YubiKeys
+or accessed via ssh-agent(1) are not supported.
+
+An encrypted file _can_ be linked to the SSH public key it was encrypted to.
+This is so that `age` can identify the correct SSH private key before
+requesting its password, if any.
+
+## EXAMPLES
+
+Generate a new identity, encrypt data, and decrypt:
+
+    $ age-keygen -o key.txt
+    Public key: age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
+
+    $ tar cvz ~/data | age -r age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p > data.tar.gz.age
+
+    $ age -d -o data.tar.gz -i key.txt data.tar.gz.age
+
+Encrypt `example.jpg` to multiple recipients and output to `example.jpg.age`:
+
+    $ age -o example.jpg.age -r age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p \
+        -r age1lggyhqrw2nlhcxprm67z43rta597azn8gknawjehu9d9dl0jq3yqqvfafg example.jpg
+
+Encrypt to a list of recipients:
+
+    $ cat > recipients.txt
+    # Alice
+    age1ql3z7hjy54pw3hyww5ayyfg7zqgvc7w3j2elw8zmrj2kg5sfn9aqmcac8p
+    # Bob
+    age1lggyhqrw2nlhcxprm67z43rta597azn8gknawjehu9d9dl0jq3yqqvfafg
+
+    $ age -R recipients.txt example.jpg > example.jpg.age
+
+Encrypt and decrypt a file using a passphrase:
+
+    $ 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:
+
+Encrypt and decrypt with an SSH public key:
+
+    $ age -R ~/.ssh/id_ed25519.pub example.jpg > example.jpg.age
+
+    $ age -d -i ~/.ssh/id_ed25519 example.jpg.age > example.jpg
+
+Encrypt to the SSH keys of a GitHub user:
+
+    $ curl https://github.com/benjojo.keys | age -R - example.jpg > example.jpg.age
+
+## SEE ALSO
+
+age-keygen(1)
+
+## AUTHORS
+
+Filippo Valsorda <[email protected]>