Wednesday, 6 June 2018

Data Encryption at Rest

Data security and protection is currently a hot topic. It seems that we reached the point when the pendulum is swinging back again. After years of voluntary openness by sharing personal information freely with social networks, people are getting more and more concerned about how their personal data is used in order to profile or influence them. Social network vendors are getting currently bad press, but maybe we should ask ourself the fair question "Didn't we know all the time that their services are not for free and that we are paying them with our data?". Maybe not strictly related to prominent (so called) 'data scandals' but at least following the movement of the pendulum is the new European GDPR regulation around data protection. Even if I think that it tends to 'overshoot the mark' (as we would say in German) and leaves data controllers and processors sometimes in the dark (unexpected rhyme ...), it is a good reason for me address some security topics again from a technical point of view. So this article has the subject of 'Data Encryption at Rest' on Linux servers.

To be more accurate this article is mainly focusing on how to ensure that folders are encrypted under Linux. Linux provides the following ways to encrypt your data:
  • Partition level: This allows you to define an encrypted partition on a hard drive. I think that this is the most commonly seen way of encrypting data with Linux. Most Linux distributions are providing this option already during the installation
  • Folder level: Allows you to encrypt specific folders by i.e. mounting them under as specific path. The 'ecryptfs' solution can be used for such a purpose.
  • File level:  It is also possible to encrypt single files. The PGP (Pretty Good Privacy) tools can be used for this purpose.

This article focuses on the 'Folder level' encryption. It has the advantage that you can define encrypted folders on-demand without the need to repartition your drives. It also doesn't just work on single files but allows you to mount your folder directly. Each file which is stored in the encrypted folder is encrypted separately. This is especially useful if you want to encrypt only specific data by providing only specific users unencrypted access. One use case would be to only allow your CIFS service (File Server service) unencrypted access to the folder. I can also easily see that database systems could leverage this feature, whereby I didn't test which performance implication might be seen when using folder level encryption with DBMS.

  • Step 0 - Install 'ecryptfs'
apt-get -y install ecryptfs-utils
  • Step 1 - Create a hidden directory: Let's assume that we have a folder /mnt/data which is the mount point of your main data partition (in my case an EXT4 partition on a RAD1 of 2 spinning HDD-s. We create a hidden folder named encrypted there:
mkdir /mnt/data/.encrypted

  • Step 2 - Create a second folder: This folder is used as our mount point. All access needs to happen via this second folder.
mkdir /mnt/encrypted
  • Step 2 - Mount the hidden folder as an encrypted one: Let's assume we want to access our encryption folder under /mnt/encrypted. This means that each write to the newly mounted folder is involving the encryption of the written data. Here a small script which does the job:
#!/bin/bash
mount -t ecryptfs\
-o rw,relatime,ecryptfs_fnek_sig=82028e5be8a0a05b,\
ecryptfs_sig=55028e0be5a0a08a,ecryptfs_cipher=aes,\
ecryptfs_key_bytes=16,ecryptfs_unlink_sigs\ /mnt/data/.encrypted /mnt/encrypted

The mount command will ask your for the passphrase. The passphrase will be used for every remount.

WARNING: If you loose your passphrase, then you will no longer be able to read your previously encrypted data.

This is what's stored in your mounted folder:

root@ubuntu-server:/mnt/encrypted# ls
hello2.txt  hello.txt
root@ubuntu-server:/mnt/encrypted# cat hello.txt 
Hello world!

Whereby the original folder contains the encrypted data:

root@ubuntu-server:/mnt/data/.encrypted# ls
ECRYPTFS_FNEK_ENCRYPTED.FWYW-ctPtO0USURgl98vtKSoykT9hmQROUa3cBMaMT0UyWKbxkF7KQOiU---  ECRYPTFS_FNEK_ENCRYPTED.FWYW-ctPtO0USURgl98vtKSoykT9hmQROUa3TeggyUTAxFqhqUkBB.a-Bk--
root@ubuntu-server:/mnt/data/.encrypted# cat ECRYPTFS_FNEK_ENCRYPTED.FWYW-ctPtO0USURgl98vtKSoykT9hmQROUa3cBMaMT0UyWKbxkF7KQOiU---
??tY?ì
?"3DUfw`n6?
           ?3ﯙY7?_?_CONSOLE"?[堠zx?ŷZ?G??铅?Lj*?9?.fEN??`????R?:??83?F???{???
                                                                            ??_Z&tx?,?2!?w


Access to the decrypted data is possible under the following circumstances:

  • The logged-in user has permission to read or write the folder /mnt/encrypted
  • The folder /mnt/data/.encrypted was mounted to /mnt/encrypted by providing the passphrase
It's especially no longer possible to read the unencrypted data after removing the hard disk physically from a machine. As said, it's necessary to know the passphrase in order to decrypt the data of this folder again.

Hope this article is helpful :-) .

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