keenv

keenv puts secrets from a KeePass database into one command and nowhere else: into its environment with keenv run, or into an in-memory config it reads through a pipe with keenv conf. The values never reach a file, an export, or the shell history: they exist between unlocking the database and execing the command, and the process that held them is replaced. Windows has no exec, and a short-lived process stands in for it there, as the Windows section shows.

It is the tool the Oberon Systems keyring policy names for local secrets.

Contents

• Why
• Installation
• Configuration
• Usage
• Remembering the password
• Config files
• macOS
• Windows
• How it works
• Development

Why

The usual ways of getting a secret into a process all leave it somewhere: export puts it in every child of the shell for the rest of the session, a .env full of plaintext puts it on disk, and eval $(something) puts it in the history file as well.

keenv reads the value out of the database at the moment it is needed, builds the environment for exactly one command, and replaces itself with that command. There is no keenv export and no keenv eval, on purpose.

Installation

pip install keenv

The database itself is read in process through pykeepass, so KeePassXC does not have to be installed.

keenv runs on Linux, macOS and Windows. The macOS section lists what is weaker there and how keenv conf works with sudo. On Windows it is a reduced client, described in the Windows section.

Installing on Windows

keenv needs Python 3.10 or later. Install Python from python.org or with winget, then install keenv with pipx, which keeps it in its own environment and puts it on PATH:

winget install Python.Python.3.12
py -m pip install --user pipx
py -m pipx ensurepath
py -m pipx install keenv

Open a new terminal after ensurepath, so that it reads the updated PATH. Plain pip works as well:

py -m pip install keenv

Check the install:

keenv --help

Expected output starts with:

usage: keenv [-h] {run,check,lock,conf} ...

If keenv is not found, the Python Scripts directory is not on PATH. py -m keenv runs the same program without it:

py -m keenv --help

For the agent and keenv conf on a Windows machine, install keenv inside WSL instead, where it is the Linux client with everything this README describes.

Configuration

keenv reads two files, both optional. keenv.yaml names the database and maps environment variables onto entries:

vault: ~/Dropbox/oberon.kdbx
keyfile: ~/.keys/oberon.keyx

env:
  AWS_ACCESS_KEY_ID:
    entry: Oberon/R2/indech-state
    field: username
  AWS_SECRET_ACCESS_KEY:
    entry: Oberon/R2/indech-state
    field: password

.env is the same mapping in the shape people already write, where a value may be a keenv:// reference instead of a literal:

AWS_ACCESS_KEY_ID=keenv://Oberon/R2/indech-state/username
AWS_SECRET_ACCESS_KEY=keenv://Oberon/R2/indech-state/password
TF_LOG=INFO

A reference is keenv://<entry path>/<field>. The last segment is the field and everything before it is the path to the entry, so a field whose name contains a slash cannot be addressed. username, password, url, notes and title are matched case-insensitively; any other name is looked up as a custom attribute, with its spelling preserved.

The entry path starts at the top-level groups, one level below the root group KeePass shows at the top of its tree, so Oberon/R2/indech-state and not Root/Oberon/R2/indech-state. A path that does name the root group first is accepted too, under either the group's real name or a plain root, so a path copied straight out of KeePass works as it stands.

Values that are not references pass through literally. A # only starts a comment at the beginning of a line, never in the middle of one, because a secret may contain it.

Before anything else, keenv expands the .env the way a shell sourcing it would, so a file that works under source .env works under keenv run:

PROJECT=balor
SUIL_BASE_DIR="${PWD}/${PROJECT}"
TF_LOG="${TF_LOG:-INFO}"
AGE_KEY=keenv://Oberon/vaults/${PROJECT}-age/password
LITERAL='no ${expansion} here'
PRICE="100\$"

A name is looked up in the environment keenv was called in, in the .env files read before this one, and in the lines above it in the same file, which is why ${PROJECT} works there. It expands inside a keenv:// reference as well, so one file can serve several environments. Single quotes expand nothing and \$ is a dollar of its own.

A name that is not set expands to nothing, silently, as it does in a shell; ${NAME:-default} is how a value is given instead. keenv.yaml is not expanded - only the .env is.

A value read out of the database is never substituted into another value: ${NAME} naming a keenv:// variable is an error, not a secret quietly copied somewhere it was not asked for.

More than one .env can be read. Repeat -e, or list the files under env_files: in keenv.yaml:

env_files:
  - .env
  - secrets.env

The files are read in the order given, and a later one overrides an earlier one. -e replaces the list in keenv.yaml and does not add to it, and either one replaces the default ./.env. A path under env_files: may start with ~ and is otherwise relative to the directory keenv is called in.

The layers apply in this order, each one overriding the last:

A file that is not there is an empty layer, not an error. Having nothing to resolve after both layers is an error.

A .env may carry the settings of keenv.yaml as # comments, which anything else reading the file skips. Of several files the later one wins, and any other # keenv: directive is an error:

# keenv: vault ~/Dropbox/oberon.kdbx
# keenv: keyfile ~/oberon.keyx
# keenv: ttl 0

ttl is read from keenv.yaml and from a .env, and nowhere else. It has no flag and no environment variable, so nothing outside the files you can see can start remembering your master password.

keenv.yaml is validated against a pydantic model that rejects keys it does not know, so vualt: is reported as a mistake rather than quietly ignored.

Usage

Run a command with the resolved environment:

keenv run -- tofu -chdir=circuits/live/ramnode/compute plan

Check that every reference still points at something, without printing any value:

keenv check

Expected output:

AWS_ACCESS_KEY_ID            keenv://Oberon/R2/indech-state/UserName               20 chars  keenv.yaml
AWS_SECRET_ACCESS_KEY        keenv://Oberon/R2/indech-state/Password               40 chars  keenv.yaml
TF_LOG                       literal                                                4 chars  .env

The last column is the file the variable came from, which is the quickest way to see that a .env is overriding keenv.yaml. The table goes to stdout and the count that closes it to stderr, so keenv check > list writes the table and nothing else.

Point at another database and other mappings:

keenv run --vault ~/other.kdbx -e deploy.env -e secrets.env -- ./deploy.sh

Exit codes are 0 on success, 1 for anything keenv can explain, 2 for a usage mistake, 127 when the command does not exist, and 130 when the run was cancelled at a prompt. Otherwise the exit code is the command's own, because the command replaces keenv.

Ctrl-C at the master password or the PIN ends the run on one line, not on a traceback, and an agent that had been forked but never filled is dropped with it.

Colour

keenv colours what it says in Solarized dark: yellow for something worth knowing that it carried on past, green for a thing that worked, red for the line a run ends on. A keenv:// reference in the check table is blue, and the file a variable came from is dimmed.

Colour is for terminals only. It goes away when the output is a pipe or a file, when NO_COLOR is set to anything, when TERM is dumb, and when --no-color is passed:

keenv check --no-color

Remembering the password

By default keenv remembers nothing. Every run asks for the master password, and none of it outlives the process. Stay in that mode unless typing the password is genuinely in the way.

Setting ttl: turns on an agent that remembers it for a while, behind a PIN:

vault: ~/Dropbox/oberon.kdbx
ttl: 5m

The first run after that asks for the password and for a new PIN. Later runs ask only for the PIN:

$ keenv run -- tofu plan
Master password for /home/you/oberon.kdbx:
New PIN (4 to 8 digits), press Enter to skip:
Repeat PIN [3]:

$ keenv run -- tofu apply
PIN [3]:

While a PIN prompt is open, the line under it names the database, as vault: /home/you/oberon.kdbx, or above it on a TERM=dumb terminal such as an Emacs shell. The number in brackets is how many tries are left. ttl: 0 is the same as no ttl at all and never asks for a PIN, which lets a .env switch the agent off for one project.

Pressing Enter at the first New PIN instead of typing one skips the agent for that run. keenv says running without the agent, waits two seconds so that Ctrl-C can still stop the run, and goes on with the database it has already opened. Nothing is remembered, so the next run asks for the password again.

Once anything has been typed, there is no skipping. A PIN that will not do is asked again, New PIN [2], then [1], and the repeat has three tries of its own. A PIN to an agent that is up has three tries too, and an empty one counts as wrong. Run out of tries and the run fails and the agent is closed, without falling back to the master password.

The PIN prompts get sixty seconds in all. A prompt left open longer fails the run and closes the agent, so a walked-away terminal does not keep the master password waiting in memory.

keenv lock forgets it at once, without waiting for the TTL. There is no keenv unlock on purpose: the first run that needs the password is the unlock, so there is no separate state to remember to set up.

A run whose password or PIN is turned down leaves no agent behind, and an agent that is up but holds nothing is not an error either: the next keenv run simply asks for the password and a new PIN again.

What is kept, and where

The agent never holds the master password in the clear. The client seals it before the agent ever sees it:

keystream = argon2id(PIN, random salt, 128 bytes)
blob      = password padded to 128 bytes XOR keystream

The agent holds that salt and that blob, and nothing else. The PIN is not stored, not even as a hash: it is checked by unsealing the blob and offering the result to the database, so a wrong PIN yields rubbish and the database is what turns it down. Rubbish that is not even text never came out of a seal, and keenv names that a wrong PIN before it gets that far. The padding is what keeps the blob from betraying how long the password is.

The agent is forked before the password is read, so the plaintext is never in its address space, not even inherited across the fork. It runs with core dumps disabled, with PR_SET_DUMPABLE cleared so no other process of yours can attach to it or read its memory, and with its pages kept out of swap where the limits allow.

Its socket and lock file sit in $XDG_RUNTIME_DIR/keenv/, named after a hash of the database path. Each database therefore gets one agent, shared by every project pointing at it. That directory is a tmpfs owned by you, so nothing survives a reboot, and nothing cryptographic is written there in any case: the lock file holds a pid, a socket path and a version.

macOS has neither PR_SET_DUMPABLE nor a runtime tmpfs. The macOS section says what the agent does there instead.

The limits, plainly

ttl takes 30s, 5m or a bare count of seconds, from 0, which turns the agent off, to fifteen minutes. Anything longer is a configuration error rather than a value quietly cut down to fit. The clock is idle-based: every successful run puts it back.

Five failures inside five minutes and the agent wipes itself and exits. That catches a typo and a stuck script. It is not a defence against a hostile program: the agent never sees the PIN, so a program bent on guessing simply would not report its failures. What actually prices an attack is the cost of Argon2 and the length of the PIN.

Four digits are accepted, but keenv says what they cost and asks you to confirm.

Two things this does not protect against, said outright:

• Anyone who can both dump the agent's memory and obtain a copy of the .kdbx can search for the PIN offline, at the price above. A database kept in a synced folder is well within reach of that.
• The client necessarily holds the password in the clear for as long as it takes to open the database. It is closed to your other processes with PR_SET_DUMPABLE meanwhile, and execvpe then replaces it, which is the same guarantee the default mode gives.

A key file is a different trade and needs none of this. It already opens the database without a prompt, so ttl does nothing alongside one, and keenv says so rather than starting an agent that would hold nothing.

Config files

keenv conf renders a config file out of the database and runs a command on the rendered copy, without that copy ever becoming a file. The command is given in full after --, as with keenv run, and {} marks where it takes the config:

keenv conf ~/vpn/work.ovpn -- sudo /usr/sbin/openvpn --config {} --auth-user-pass
keenv conf ~/app.toml -- myapp -c {}
keenv conf ~/tool.yaml -- tool --config={}

keenv puts /proc/<pid>/fd/3 in place of the {}, so any flag the command reads its config with will do. A command without a {}, or with more than one, is refused: the config reaches the command once, on descriptor 3. Standard input, output and error stay the terminal, so the command can still ask for a password or a one-time code there.

The template is the config as the command reads it, where a line holding nothing but a keenv:// reference is replaced by the value of that field, which may span several lines. For OpenVPN that fits the inline blocks version 2.6 reads secrets from:

# keenv: vault ~/Dropbox/oberon.kdbx
# keenv: keyfile ~/.keys/oberon.keyx
client
remote vpn.example.com 1194
<key>
keenv://Oberon/vpn/work/client-key
</key>
<auth-user-pass>
keenv://Oberon/vpn/work/username
keenv://Oberon/vpn/work/password
</auth-user-pass>

A reference in the middle of a line is left as it is, because an entry path may contain spaces and could not be told apart from the rest of the line. Nothing else in the template is expanded either, so a $ stays a $.

The template carries its own settings. # keenv: vault and # keenv: keyfile name the database and the key file, and are cut out of what the command gets. keenv.yaml and .env are not read. KEENV_VAULT, KEENV_KEYFILE, --vault and --keyfile override the template in the same order as they override keenv.yaml. Any other # keenv: directive is an error.

There is no PIN and no agent here. A command such as a VPN is brought up once for a long session, so keenv conf asks for the master password, or opens the database with the key file, and remembers nothing. # keenv: ttl is refused. The directives are # comments, so the format has to take # as a comment, as OpenVPN, YAML and TOML do.

Where the config lives

The rendered config is written into a pipe, whose write end keenv closes before it replaces itself with the command. The read end stays open as descriptor 3 of that process, whose pid exec leaves unchanged. Reading the config drains the pipe, so once the command has read it the config exists nowhere but in that command's memory.

A pipe rather than a file, and descriptor 3 rather than anything else:

• A temporary file, even on tmpfs, has a name that another process of yours can open, and outlives the command unless something deletes it.
• The environment is readable in /proc/<pid>/environ, and sudo resets it.
• Standard input has to stay the terminal. OpenVPN asks for passwords through systemd-ask-password, which only uses the terminal when standard input is one, and otherwise posts the question to a system-wide agent instead.

Through sudo

sudo closes every descriptor above 2 in the command it starts, but not its own, and sudo keeps running as the parent of that command. So the path is /proc/<pid>/fd/3 rather than /dev/fd/3: it names descriptor 3 of the process keenv became, which is sudo itself, and the command, running as root, opens it there. Nothing in sudoers has to change, and sudo -C is not needed.

This relies on sudo staying the parent of the command, which it does whenever it keeps a PAM session or a pseudo-terminal, as it does by default. A sudo that replaced itself with the command would have closed the descriptor, and the command then fails to open its config rather than starting without it.

What reaches the config, and when

Nothing is left for a process of your own to read at any point:

• keenv conf and keenv run close themselves to your other processes with PR_SET_DUMPABLE before they ask for the master password. From then on only root can read their memory or open their /proc/<pid>/fd.
• sudo is setuid, so the process stays closed through the exec and while sudo asks for its own password.
• The command reads the pipe as soon as it starts. Anyone reading it first drains it, and the command then fails on an empty config rather than coming up quietly with a stolen one.

Two limits, said outright:

• Root can read the config out of the command's memory at any time, as it can read anything.
• The config is read once. OpenVPN rereads its config on SIGHUP and finds the pipe empty, so restart it with SIGUSR1, which keeps the config it has.

macOS

keenv runs on macOS as well as on Linux. Every difference is a separate branch in the code, so nothing described above changes on Linux. What differs on macOS:

• There is no PR_SET_DUMPABLE. keenv and its agent run open to your other processes, as far as the system's own debugging restrictions allow, so another process of yours may be able to read their memory.
• There is no mlockall, so nothing keeps the agent's pages out of swap. The swap on macOS is encrypted.
• Without XDG_RUNTIME_DIR the agent keeps its socket and lock file in $TMPDIR/keenv/. That directory is private to you but is not a tmpfs, and the agent's TTL, not a logout, is what clears it.
• keenv conf puts /dev/fd/3 in place of the {}, since there is no /proc.

Examples on macOS

Everything except sudo inside the keenv conf command works as on Linux:

keenv run -- tofu plan
keenv check
keenv lock
keenv conf ~/app.toml -- myapp -c {}
keenv conf ~/tool.yaml -- tool --config={}

With ttl set in keenv.yaml and no XDG_RUNTIME_DIR, the agent shows up in $TMPDIR after the first run:

ls "$TMPDIR/keenv"

Expected output, one pair per database:

<hash>.lock  <hash>.sock

keenv conf with sudo on macOS

/dev/fd/3 names descriptor 3 of the process that opens it, and sudo closes that descriptor in the command it starts. A command that begins with sudo is therefore refused on macOS, before the database is opened:

keenv conf ~/vpn/work.ovpn -- sudo openvpn --config {}

Expected output, with exit code 1:

keenv: on macOS sudo closes the descriptor the config is on; run keenv itself under sudo: sudo keenv conf work.ovpn -- openvpn --config {}

Run keenv itself under sudo instead:

sudo keenv conf ~/vpn/work.ovpn -- openvpn --config {}
sudo keenv conf --vault /Users/me/Dropbox/oberon.kdbx ~/vpn/work.ovpn -- openvpn --config {}

keenv then runs as root, and the master password prompt is the same. Whether a ~ in # keenv: vault means your home or root's depends on how sudo treats HOME, so name the database by its absolute path there or pass --vault.

Windows

keenv on Windows is a reduced client: run and check work, lock has nothing to drop, and conf is refused. Every difference is a separate branch in the code, so nothing described for Linux or macOS changes. For the full client, run keenv inside WSL, as Installing on Windows describes.

What differs on Windows

• There is no agent. A ttl in keenv.yaml is ignored with a warning, so every run asks for the master password, or opens the database with its key file.
• keenv lock has no agent to drop, says so and exits with 0.
• keenv conf is refused. Windows has no descriptor path a command can open its config through, and a temporary file is exactly what conf exists to avoid.
• The master password is read from the console itself, never from standard input, so a pipe into the command keeps its first line.
• There is no PR_SET_DUMPABLE and no mlockall, so nothing closes keenv to your other processes or keeps its pages out of the page file.
• Colour needs a console that takes escape sequences, as Windows Terminal and current Windows consoles do. Without one, keenv prints plain text.

How keenv run works on Windows

Windows has no exec, so the process that opened the database cannot become the command. A process that started the command and waited for it would keep the whole decrypted database in its memory for as long as the command runs. keenv run is therefore split in two:

keenv run -- app              waiter: never reads a config or a secret
  +- python -m keenv run ...  resolver: prompt, database, values
       +- app                 the command, with the values in its environment

1. The waiter starts the resolver on the same arguments and then ignores Ctrl-C, which reaches the prompt or the command on the shared console.
2. The resolver reads keenv.yaml and .env, opens the database, resolves every reference and starts the command with the result.
3. The resolver hands the waiter a handle on the command and exits. Windows frees its memory, and the database and the values go with it.
4. The waiter waits on that handle and exits with the command's exit code.

A resolver that cannot hand the command over kills it and fails, rather than waiting on it and keeping the database in memory for the command's lifetime.

The limits on Windows, plainly

• For the seconds the resolver lives, another process running as you can read its memory, database included. Windows lets processes of one user open each other, and has no equivalent of PR_SET_DUMPABLE.
• The command holds the values in its environment for its whole life, as on every system, and a process running as you can read that environment.
• Without an agent there is no PIN. A key file saves typing the master password, at the price of a file that opens the database on its own.

Examples on Windows

The examples are for cmd.exe. check, lock and run take the same flags as on Linux:

keenv check
keenv lock
keenv run -- terraform plan
keenv run --vault C:\Users\me\oberon.kdbx -e deploy.env -- deploy.cmd

The command's exit code comes back through the waiter:

keenv run -- cmd /c "exit 3"
echo %ERRORLEVEL%

Expected output of the second line:

3

keenv lock is expected to print:

keenv: no agents on Windows, nothing to drop

A ttl in keenv.yaml is expected to print this before the password prompt:

keenv: ttl does nothing on Windows, which has no agent

keenv conf is refused with exit code 1:

keenv conf work.ovpn -- openvpn --config {}

Expected output:

keenv: keenv conf is not available on Windows: there is no way to hand a config over in memory only

How it works

1. Both layers are read and merged into one list of variables. A name defined in both takes its value from .env, and keenv check names the file each variable came from.
2. keenv clears PR_SET_DUMPABLE, so from here on only root can read its memory or its descriptors. This step is Linux only, see macOS.
3. If any of the variables is a keenv:// reference, the database is opened once. The master password is asked for on /dev/tty, never on stdin, so a password prompt can never swallow the first line of a pipe. A key file replaces the prompt, and ttl: replaces it with a PIN for as long as the agent lives.
4. Every reference is resolved from that one open database.
5. The resolved variables are laid over a copy of the current environment and handed to os.execvpe.

Step 5 is what keeps the secrets contained: execvpe replaces the process image, so nothing that held the values is still running once the command starts, and the shell that invoked keenv never saw them. Windows has no execvpe; the Windows section shows the two processes that stand in for it there.

Development

make init
make test
make lint

make init creates .venv, installs the package in editable mode and wires up the pre-commit hooks. The test suite builds its own throwaway database in a temporary directory; no test opens a real vault.

Commits go through commitizen:

.venv/bin/cz commit