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Welcome to Deo!

Deo is a system service and client for binding data to your local network. The concept of this application is simple, but let's look at an example.

Use Case: Network-bound Automatic Disk Decryption

Suppose you have a disk with sensitive data. If it breaks, you can't just send it back for repair. This could expose the data. Nor can you just throw it away.

You could encrypt the disk. This would let you repair or discard the disk. But now you have to remember a password and manually enter it on every boot. This doesn't scale.

What you need is a way to encrypt the disk using a high entropy key and then making it so that this key can be used automatically when you are on the network, but not otherwise.

The solution to this problem is encrypting the key in such a way that it can only be decrypted when you are on the network. Hence, you bind the key to the network.

This is precisely what Deo does. Let's look at how it works.

Online Operation

First, you encrypt some data to one or more particular servers. As mentioned in the example above, this data is usually a key to decrypt some secondary data.

$ deo encrypt -a anchor.pem ... < key.txt > key.enc

Second, this key can be decrypted so long as your have access to the server it was encrypted to.

$ deo decrypt < key.enc > key.txt

That's it!

You can encrypt the data to as many servers as you want in a single pass. The encryption will not succeed unless all servers can be reached. Each server should have a unique certificate; no sharing is required (and is strongly discouraged). Server certificates can be rotated using standard CA tools like certmonger.

If a payload is encrypted to multiple servers, only one of those servers is required to be online for decryption. This lets you have load balancing and redundancy for the decryption service.

Offline Operation

Deo encryption (but not, of course, decryption) can also be performed in offline mode. Start by downloading the encryption certificate chain:

$ deo query -a anchor.pem > one.pem

Now you can perform encryption offline:

$ deo encrypt -a anchor.pem one.pem < key.txt > key.enc

You can even mix online and offline mode:

$ deo encrypt -a anchor.pem one.pem < key.txt > key.enc
Security Considerations

Deo tries very hard to always do the right thing.

In particular, you may notice that the deo client takes anchor.pem as an option. This is because we always validate whatever certificates we encounter. This includes pem files stored locally. We force you to use this argument to think carefully about which certificates you trust.

Deo Server

The Deo server is a simple systemd activated service. It listens on port 5700 by default. The most complex thing is getting the certificate setup right. Here again, we test to make sure you don't expose sensitive certificates.

Unlike most services, Deo uses two certificate/key pairs. All certificate material is stored in PEM format.

The first certificate/key pair is for encrypting all communications. This is just a standard TLS certificate setup. Simply place the certificate, its private key and any required intermediate certificates into /etc/deo/decryptd.pem.

The second certificate/key pair is used for encryption and decryption of the client secrets and is setup in a slightly more complicated two-step process.

First, all three components (the certificate, the private key and any required intermediate certificates) should be placed in a .pem file of your choosing in the /etc/deo/decrypt.d/ directory. When the server receives a decryption request, it will attempt to decrypt the data using the certificates stored here. Hence, installing this .pem file into this directory permits the server to decrypt incoming decryption requests using this certificate.

Second, the certificate itself and any intermediate certificates (but not the private key), should be placed into /etc/deo/encrypt.pem. This data is returned directly to clients who query for the encryption certificate chain. On important note is necessary. This file MUST contain a certificate with a subject with a commonName that resolves to the decryption server (including the port if a non-standard port is used). This is the hostname that the client will use during decryption. This hostname may be an IP address.

Why place the same certificate information in two different places? The Deo decryption service advertises only one encryption certificate chain but can handle decryption requests for multiple certificates. This allows for easy transitional certificate rotation. You can swap in a new certificate (for new encryption and decryption requests) but still retain the old certificate to handle decryption requests for already encrypted data.

Once certificates are installed, just run the following as root:

# systemctl enable deo-decryptd.socket
# systemctl start deo-decryptd.socket
Using Deo with Disks

First, you must have a Deo server running somewhere on your network. For more information on this step, see the above section.

Second, you must have a client with LUKS disk encryption already enabled.


Both of the following commands are run as root.

First, we will configure the initramfs for networking. If you are using IPv4 DHCP, no configuration is needed. For other setups, please consult the dracut documentation.

Second, we will add a new random key to the pre-existing LUKS encrypted disk and then encrypt it using Deo in a known location. This command works exactly like the encrypt command with the exception that a LUKS encrypted disk is specified rather than passing data using stdin/stdout:

# deo cryptsetup -d /dev/sda1 -a anchor.pem

Finally, we need to rebuild the system's initramfs:

# dracut -f

That's it! Once you reboot, the disk should unlock automatically so long as one of the specified encryption targets is available.

Future Improvements

Here is a list of things we could improve:

  1. Check certificate expiration. Does OpenSSL do this for us?
  2. Support CRL/OCSP checking and maybe OCSP stapling.
Concluding Thoughts

Deo is still a new project and may have some rough edges. We'd love to hear your feedback!

sudo make install


A service for binding data to networks



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