Network-Bound Disk Encryption

I was reading the redhat release notes on 7.4 and came across: Chapter 15. Security

New packages: tang, clevis, jose, luksmeta

Network Bound Disk Encryption (NBDE) allows the user to encrypt root volumes of the hard drives on physical and virtual machines without requiring to manually enter password when systems are rebooted.

That means, we can now have an encrypted (luks) volume that will be de-crypted on reboot, without the need of typing a passphrase!!!

Really - really useful on VPS (and general in cloud infrastructures)

Useful Links

• https://github.com/latchset/tang
• https://github.com/latchset/jose
• https://github.com/latchset/clevis

CentOS 7.4 with Encrypted rootfs

(aka client machine)

Below is a test centos 7.4 virtual machine with an encrypted root filesystem:

/boot

/

Tang Server

(aka server machine)

Tang is a server for binding data to network presence. This is a different centos 7.4 virtual machine from the above.

Installation

Let’s install the server part:

# yum -y install tang

Start socket service:

# systemctl restart tangd.socket

Enable socket service:

# systemctl enable tangd.socket

TCP Port

Check that the tang server is listening:

# netstat -ntulp | egrep -i systemd

tcp6    0    0 :::80    :::*    LISTEN    1/systemd

Firewall

Dont forget the firewall:

Firewall Zones

# firewall-cmd --get-active-zones

public
  interfaces: eth0

Firewall Port

# firewall-cmd --zone=public --add-port=80/tcp --permanent

or

# firewall-cmd --add-port=80/tcp --permanent

success

Reload

# firewall-cmd --reload

success

We have finished with the server part!

Client Machine - Encrypted rootfs

Now it is time to configure the client machine, but before let’s check the encrypted partition:

CryptTab

Every encrypted block devices is configured under crypttab file:

[root@centos7 ~]# cat /etc/crypttab

luks-3cc09d38-2f55-42b1-b0c7-b12f6c74200c UUID=3cc09d38-2f55-42b1-b0c7-b12f6c74200c none 

FsTab

and every filesystem that is static mounted on boot, is configured under fstab:

[root@centos7 ~]# cat /etc/fstab

UUID=c5ffbb05-d8e4-458c-9dc6-97723ccf43bc          /boot  xfs  defaults  0 0

/dev/mapper/luks-3cc09d38-2f55-42b1-b0c7-b12f6c74200c  /  xfs  defaults,x-systemd.device-timeout=0 0 0

Installation

Now let’s install the client (clevis) part that will talk with tang:

# yum -y install clevis clevis-luks clevis-dracut

Configuration

with a very simple command:

# clevis bind luks -d /dev/vda2 tang '{"url":"http://192.168.122.194"}'

The advertisement contains the following signing keys:

FYquzVHwdsGXByX_rRwm0VEmFRo

Do you wish to trust these keys? [ynYN] y

You are about to initialize a LUKS device for metadata storage.
Attempting to initialize it may result in data loss if data was
already written into the LUKS header gap in a different format.
A backup is advised before initialization is performed.

Do you wish to initialize /dev/vda2? [yn] y

Enter existing LUKS password:

we’ve just configured our encrypted volume against tang!

Luks MetaData

We can verify it’s luks metadata with:

[root@centos7 ~]# luksmeta show -d /dev/vda2

0   active empty
1   active cb6e8904-81ff-40da-a84a-07ab9ab5715e
2 inactive empty
3 inactive empty
4 inactive empty
5 inactive empty
6 inactive empty
7 inactive empty

dracut

We must not forget to regenerate the initramfs image, that on boot will try to talk with our tang server:

[root@centos7 ~]# dracut -f

Reboot

Now it’s time to reboot!

A short msg will appear in our screen, but in a few seconds and if successfully exchange messages with the tang server, our server with de-crypt the rootfs volume.

Tang messages

To finish this article, I will show you some tang msg via journalct:

Initialization

Getting the signing key from the client on setup:

Jan 31 22:43:09 centos7 systemd[1]: Started Tang Server (192.168.122.195:58088).
Jan 31 22:43:09 centos7 systemd[1]: Starting Tang Server (192.168.122.195:58088)...
Jan 31 22:43:09 centos7 tangd[1219]: 192.168.122.195 GET /adv/ => 200 (src/tangd.c:85)

reboot

Client is trying to decrypt the encrypted volume on reboot

Jan 31 22:46:21 centos7 systemd[1]: Started Tang Server (192.168.122.162:42370).
Jan 31 22:46:21 centos7 systemd[1]: Starting Tang Server (192.168.122.162:42370)...
Jan 31 22:46:22 centos7 tangd[1223]: 192.168.122.162 POST /rec/Shdayp69IdGNzEMnZkJasfGLIjQ => 200 (src/tangd.c:168)