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# Clevis

## Welcome to Clevis!
Clevis is a pluggable framework for automated decryption. It can be used to
provide automated decryption of data or even automated unlocking of LUKS
volumes.

### Encrypting Data

What does this look like? Well, the first step is encrypting some data. We do
this with a simple command:

    $ clevis encrypt PIN CONFIG < PLAINTEXT > CIPHERTEXT.jwe

This command takes plaintext on standard input and produces an encrypted JWE
object on standard output. Besides the plaintext, we need to specify two
additional input parameters.

First, is the pin. In clevis terminology, a pin is a plugin which implements
automated decryption. We simply pass the name of a pin here.

Second, is the config. The config is a JSON object which will be passed
directly to the pin. It contains all the necessary configuration to perform
encryption and setup automated decryption.

To decrypt our JWE, we simply perform the following:

```bash
$ clevis decrypt < CIPHERTEXT.jwe > PLAINTEXT
```

Notice that no additional input or interaction is required for the decrypt
command. Let's look at some more concrete examples.

#### PIN: Tang

[Tang](http://github.com/latchset/tang) is a server implementation which
provides cryptographic binding services without the need for an escrow.
Clevis has full support for Tang. Here is an example of how to use Clevis with
Tang:

```bash
$ echo hi | clevis encrypt tang '{"url": "http://tang.local"}' > hi.jwe
The advertisement is signed with the following keys:
        kWwirxc5PhkFIH0yE28nc-EvjDY

Do you wish to trust the advertisement? [yN] y
```

In this example, we encrypt the message "hi" using the Tang pin. The only
parameter needed in this case is the URL of the Tang server. During the
encryption process, the Tang pin requests the key advertisement from the
server and asks you to trust the keys. This works similarly to SSH.

Alternatively, you can manually load the advertisement using the `adv`
parameter. This parameter takes either a string referencing the file where the
advertisement is stored, or the JSON contents of the advertisement itself. When
the advertisement is specified manually like this, Clevis presumes that the
advertisement is trusted.

#### PIN: TPM2

Clevis provides support to encrypt a key in a Trusted Platform Module 2.0 (TPM2)
chip. The cryptographically-strong, random key used for encryption is encrypted
using the TPM2 chip, and then at decryption time is decrypted using the TPM2 to
allow clevis to decrypt the secret stored in the JWE.

For example:

```bash
$ echo hi | clevis encrypt tpm2 '{}' > hi.jwe
```

Clevis store the public and private keys of the encrypted key in the JWE object,
so those can be fetched on decryption to unseal the key encrypted using the TPM2.

#### PIN: Shamir Secret Sharing

Clevis provides a way to mix pins together to provide sophisticated unlocking
policies. This is accomplished by using an algorithm called Shamir Secret
Sharing (SSS).

SSS is a thresholding scheme. It creates a key and divides it into a number of
pieces. Each piece is encrypted using another pin (possibly even SSS
recursively). Additionally, you define the threshold `t`. If at least `t`
pieces can be decrypted, then the encryption key can be recovered and
decryption can succeed.

Here is an example where we use the SSS pin with both the Tang and HTTP pins:

```bash
$ echo hi | clevis encrypt sss \
'{"t": 2, "pins": {"http": {"url": "http://server.local/key"}, "tang": {"url": "http://tang.local"}}}' \
> hi.jwe
```

In the above example, we define two child pins and have a threshold of 2.
This means that during decryption **both** child pins must succeed in order for
SSS itself to succeed.

Here is another example where we use just the HTTP pin:

```bash
$ echo hi | clevis encrypt sss \
'{"t": 1, "pins": {"http": [{"url": "http://server1.local/key"}, {"url": "http://server1.local/key"}]}}' \
> hi.jwe
```

In this example, we define two child instances of the HTTP pin - each with its
own configuration. Since we have a threshold of 1, if **either** of the HTTP
pin instances succeed during decryption, SSS will succeed.

### Binding LUKS Volumes

Clevis can be used to bind a LUKS volume using a pin so that it can be
automatically unlocked.

How this works is rather simple. We generate a new, cryptographically strong
key. This key is added to LUKS as an additional passphrase. We then encrypt
this key using Clevis, and store the output JWE inside the LUKS header using
[LUKSMeta](http://github.com/latchset/luksmeta).

Here is an example where we bind `/dev/sda1` using the Tang pin:

```bash
$ sudo clevis luks bind -d /dev/sda1 tang '{"url": "http://tang.local"}'
The advertisement is signed with the following keys:
        kWwirxc5PhkFIH0yE28nc-EvjDY

Do you wish to trust the advertisement? [yN] y
Enter existing LUKS password:
```

Upon successful completion of this binding process, the disk can be unlocked
using one of the provided unlockers.

#### Network based unlocking
If you want to use network based unlocking you will need to specify `rd.neednet=1` as kernel argument or use `--hostonly-cmdline` when creating dracut.

#### Unlocker: Dracut

The Dracut unlocker attempts to automatically unlock volumes during early
boot. This permits automated root volume encryption. Enabling the Dracut
unlocker is easy. Just rebuild your initramfs after installing Clevis:

```bash
$ sudo dracut -f
```

Upon reboot, you will be prompted to unlock the volume using a password. In
the background, Clevis will attempt to unlock the volume automatically. If it
succeeds, the password prompt will be cancelled and boot will continue.

#### Unlocker: Initramfs-tools

When using Clevis with initramfs-tools, in order to rebuild your
initramfs you will need to run:

```bash
sudo update-initramfs -u -k 'all'
```

Upon reboot it will behave exactly as if using Dracut.

#### Unlocker: UDisks2

Our UDisks2 unlocker runs in your desktop session. You should not need to
manually enable it; just install the Clevis UDisks2 unlocker and restart your
desktop session. The unlocker should be started automatically.

This unlocker works almost exactly the same as the Dracut unlocker. If you
insert a removable storage device that has been bound with Clevis, we will
attempt to unlock it automatically in parallel with a desktop password prompt.
If automatic unlocking succeeds, the password prompt will be dismissed without
user intervention.

#### Unlocker: Clevis command

A LUKS device bound to a Clevis policy can also be unlocked by using the clevis
luks unlock command.

```bash
$ sudo clevis luks unlock -d /dev/sda1
```

#### Unbinding LUKS volumes

LUKS volumes can be unbound using the clevis luks unbind command. For example:

```bash
$ sudo clevis luks unbind -d /dev/sda1 -s 1
```

#### Listing pins bound to LUKS volumes

The pins that are bound to a given LUKS volume can be listed using the clevis
luks list command. For example:

```bash
$ sudo clevis luks list -d /dev/sda1
```

## Installing Clevis

Please don't install Clevis directly. Instead, use your preferred
distribution's packages.

### Fedora 24+

This command installs the core Clevis commands, the Dracut unlocker and the
UDisks2 unlocker, respectively.

```bash
$ sudo dnf install clevis clevis-dracut clevis-udisks2
```
