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ContentsContents
Security Guide
  1. About This Guide
  2. 1 Security and Confidentiality
  3. I Authentication
    1. 2 Authentication with PAM
    2. 3 Using NIS
    3. 4 Setting Up Authentication Servers and Clients Using YaST
    4. 5 LDAP—A Directory Service
    5. 6 Network Authentication with Kerberos
    6. 7 Active Directory Support
  4. II Local Security
    1. 8 Configuring Security Settings with YaST
    2. 9 Authorization with PolKit
    3. 10 Access Control Lists in Linux
    4. 11 Encrypting Partitions and Files
    5. 12 Certificate Store
    6. 13 Intrusion Detection with AIDE
  5. III Network Security
    1. 14 X Window System and X Authentication
    2. 15 SSH: Secure Network Operations
    3. 16 Masquerading and Firewalls
    4. 17 Configuring a VPN Server
    5. 18 Managing X.509 Certification
  6. IV Confining Privileges with AppArmor
    1. 19 Introducing AppArmor
    2. 20 Getting Started
    3. 21 Immunizing Programs
    4. 22 Profile Components and Syntax
    5. 23 AppArmor Profile Repositories
    6. 24 Building and Managing Profiles with YaST
    7. 25 Building Profiles from the Command Line
    8. 26 Profiling Your Web Applications Using ChangeHat
    9. 27 Confining Users with pam_apparmor
    10. 28 Managing Profiled Applications
    11. 29 Support
    12. 30 AppArmor Glossary
  7. V SELinux
    1. 31 Configuring SELinux
  8. VI The Linux Audit Framework
    1. 32 Understanding Linux Audit
    2. 33 Setting Up the Linux Audit Framework
    3. 34 Introducing an Audit Rule Set
    4. 35 Useful Resources
  9. A GNU Licenses
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11 Encrypting Partitions and Files

11.1 Setting Up an Encrypted File System with YaST
11.2 Encrypting Files with GPG

Encrypting files, partitions, and entire disks prevents unauthorized access to your data and protects your confidential files and documents.

You can choose between the following encryption options:

Encrypting a Hard Disk Partition

It is possible to create an encrypted partition with YaST during installation or in an already installed system. For further info, see Section 11.1.1, “Creating an Encrypted Partition during Installation” and Section 11.1.2, “Creating an Encrypted Partition on a Running System”. This option can also be used for removable media, such as external hard disks, as described in Section 11.1.4, “Encrypting the Content of Removable Media”.

Creating an Encrypted Virtual Disk

You can create a file-based encrypted virtual disk on your hard disk or a removable medium with YaST. The encrypted virtual disk can then be used as a regular folder for storing files or directories. For more information, refer to Section 11.1.3, “Creating an Encrypted Virtual Disk”.

Encrypting Single Files with GPG

To quickly encrypt one or more files, you can use the GPG tool. See Section 11.2, “Encrypting Files with GPG” for more information.

Warning
Warning: Encryption Offers Limited Protection

Encryption methods described in this chapter cannot protect your running system from being compromised. After the encrypted volume is successfully mounted, everybody with appropriate permissions can access it. However, encrypted media are useful in case of loss or theft of your computer, or to prevent unauthorized individuals from reading your confidential data.

11.1 Setting Up an Encrypted File System with YaST

Use YaST to encrypt partitions or parts of your file system during installation or in an already installed system. However, encrypting a partition in an already-installed system is more difficult, because you need to resize and change existing partitions. In such cases, it may be more convenient to create an encrypted file of a defined size, in which to store other files or parts of your file system. To encrypt an entire partition, dedicate a partition for encryption in the partition layout. The standard partitioning proposal, as suggested by YaST, does not include an encrypted partition by default. Add an encrypted partition manually in the partitioning dialog.

11.1.1 Creating an Encrypted Partition during Installation

Warning
Warning: Password Input

Make sure to memorize the password for your encrypted partitions well. Without that password, you cannot access or restore the encrypted data.

The YaST expert dialog for partitioning offers the options needed for creating an encrypted partition. To create a new encrypted partition proceed as follows:

  1. Run the YaST Expert Partitioner with System › Partitioner.

  2. Select a hard disk, click Add, and select a primary or an extended partition.

  3. Select the partition size or the region to use on the disk.

  4. Select the file system, and mount point of this partition.

  5. Activate the Encrypt device check box.

    Note
    Note: Additional Software Required

    After checking Encrypt device, a pop-up window asking for installing additional software may appear. Confirm to install all the required packages to ensure that the encrypted partition works well.

  6. If the encrypted file system needs to be mounted only when necessary, enable Do not mount partition in the Fstab Options. otherwise enable Mount partition and enter the mount point.

  7. Click Next and enter a password which is used to encrypt this partition. This password is not displayed. To prevent typing errors, you need to enter the password twice.

  8. Complete the process by clicking Finish. The newly-encrypted partition is now created.

During the boot process, the operating system asks for the password before mounting any encrypted partition which is set to be auto-mounted in /etc/fstab. Such a partition is then available to all users when it has been mounted.

To skip mounting the encrypted partition during start-up, press Enter when prompted for the password. Then decline the offer to enter the password again. In this case, the encrypted file system is not mounted and the operating system continues booting, blocking access to your data.

To mount an encrypted partition which is not mounted during the boot process, open a file manager and click the partition entry in the pane listing common places on your file system. You will be prompted for a password and the partition will be mounted.

When you are installing your system on a machine where partitions already exist, you can also decide to encrypt an existing partition during installation. In this case follow the description in Section 11.1.2, “Creating an Encrypted Partition on a Running System” and be aware that this action destroys all data on the existing partition.

11.1.2 Creating an Encrypted Partition on a Running System

Warning
Warning: Activating Encryption on a Running System

It is also possible to create encrypted partitions on a running system. However, encrypting an existing partition destroys all data on it, and requires re-sizing and restructuring of existing partitions.

On a running system, select System › Partitioner in the YaST control center. Click Yes to proceed. In the Expert Partitioner, select the partition to encrypt and click Edit. The rest of the procedure is the same as described in Section 11.1.1, “Creating an Encrypted Partition during Installation”.

11.1.3 Creating an Encrypted Virtual Disk

Instead of encrypting an entire disk or partition, you can use YaST to set up a file-based encrypted virtual disk. It will appear as a regular file in the file system, but can be mounted and used like a regular folder. Unlike encrypted partitions, encrypted virtual disks can be created without re-partitioning the hard disk.

To set up an encrypted virtual disk, you need to create an empty file first. This file is called a loop file and is going to contain the encrypted data. In the terminal, switch to the desired directory and run the touch LOOP_FILE command (where LOOP_FILE is the desired name, for example: secret). We recommend to create an empty directory that will act as a mount point for the encrypted virtual disk. To do this, use the mkdir MOUNT_DIR command (replace MOUNT_DIR with the actual path and directory name, for example ~/my_docs). LOOP_FILE must reside outside of MOUNT_DIR.

To set up an encrypted virtual disk, launch YaST, switch to the System section, and start the Partitioner. Switch to the Crypt Files section and press Add Crypt File. Enter the path to the created loop file (LOOP_FILE) into the Path Name of Loop File field. Enable the Create Loop File option, specify the desired size, and press Next. In the Mount Point field, enter the path to the directory that serves as a mount point (MOUNT_DIR, in this example it is ~/my_docs). Make sure that the Encrypt Device option is enabled and press Next. Provide the desired password and press Finish.

YaST changes the owner of the mount point to root by default. If the content should be accessible to other users, change the group and permissions, for example with chgrp users MOUNT_DIR and chmod 775 MOUNT_DIR.

11.1.4 Encrypting the Content of Removable Media

YaST treats removable media (like external hard disks or flash disks) the same as any other storage device. Virtual disks or partitions on external media can be encrypted as described above. However, you should disable mounting at boot time, because removable media is usually connected only when the system is up and running.

If you encrypted your removable device with YaST, the GNOME desktop automatically recognizes the encrypted partition and prompts for the password when the device is detected. If you plug in a FAT-formatted removable device when running GNOME, the desktop user entering the password automatically becomes the owner of the device. For devices with a file system other than FAT, change the ownership explicitly for users other than root to give them read-write access to the device.

If you have created a virtual disk as described in Section 11.1.3, “Creating an Encrypted Virtual Disk” but with the loop file on a removable disk, then you need to mount the file manually as follows: 

tux > sudo cryptsetup luksOpen  FILE NAME
sudo mount /dev/mapper/NAME DIR

In the commands above, FILE refers to the path to the loop file, NAME is a user-defined name, and DIR is the path to the mount point. For example: 

tux > sudo cryptsetup luksOpen /run/media/tux/usbstick/secret my_secret
tux > sudo mount /dev/mapper/my_secret /home/tux/my_docs

11.2 Encrypting Files with GPG

The GPG encryption software can be used to encrypt individual files and documents.

To encrypt a file with GPG, you need to generate a key pair first. To do this, run the gpg --gen-key and follow the on-screen instructions. When generating the key pair, GPG creates a user ID (UID) to identify the key based on your real name, comments, and email address. You need this UID (or just a part of it like your first name or email address) to specify the key you want to use to encrypt a file. To find the UID of an existing key, use the gpg --list-keys command. To encrypt a file use the following command: 

tux > gpg -e -r UID
  FILE

Replace UID with part of the UID (for example, your first name) and FILE with the file you want to encrypt. For example: 

tux > gpg -e -r Tux secret.txt

This command creates an encrypted version of the specified file recognizable by the .gpg file extension (in this example, it is secret.txt.gpg).

To decrypt an encrypted file, use the following command: 

tux > gpg -d -o DECRYPTED_FILE
  ENCRYPTED_FILE

Replace DECRYPTED_FILE with the desired name for the decrypted file and ENCRYPTED_FILE with the encrypted file you want to decrypt.

Keep in mind that the encrypted file can be only decrypted using the same key that was used for encryption. If you want to share an encrypted file with another person, you have to use that person's public key to encrypt the file.

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