File Key Management Encryption Plugin

MariaDB Encryption supports the use of multiple encryption keys. Each key uses a 32-bit integer as a key identifier and can be versioned, allowing you to automatically re-encrypt data from older to newer versions of the key.

In order to use data-at-rest encryption, you need to load a plugin to manage the encryption keys.

The File Key Management plugin that ships with MariaDB is a basic key management plugin that reads keys from a plain-text file. It can also serve as example and as a starting point when developing a key management plugin.

Configuring the File Key Management Plugin

Creating the Key File

In order to encrypt your tables with keys using the File Key Management plugin, you first need to create the file that contains the keys. You can then, optionally, encrypt the key file to make it less accessible from the file system.

There are two parts to an encryption key entry. First a 32-bit integer used as a key identifier, then the hex-encoded encryption key, separated by a semicolon. The File Key Management plugin supports 128-, 192- and 256-bit keys. You can generate keys using OpenSSL. For instance, to create a random 128-bit encryption key, you would run the following command:

$ openssl rand -hex 16
3b2bb95eba5a9f0045601f258491ef85

You can copy this key to file using a text editor, or you can append a series of keys to a new file.

# openssl rand -hex 16 >> /etc/mysql/keys
# openssl rand -hex 16 >> /etc/mysql/keys
# openssl rand -hex 16 >> /etc/mysql/keys

Once you have created this file, open it in your preferred text editor and add the key identifier to start of each line.

# Keys
1;a3c93624f4968eb95056b6902de874ef
2;04e478eefe15b03c836282464b0e94a2
3;8c8ada2dfb4542b8e2673703f0364079

The identifiers give you a way to reference the keys from MariaDB. In the example above, you can use 1, 2 or 3 as key identifiers with the ENCRYPTION_KEY_ID table option.

Encrypting the Key File

By enabling the File Key Management plugin and setting the appropriate path on the file_key_management_filename system variable, you can begin using the plugin to manage your encryption keys. But, there is a security risk in doing so, given that the keys are stored in plain text on your system. You can reduce this exposure using file permissions, but it's better to encrypt the whole key file to further restrict access.

You can encrypt the key file using OpenSSL.

# openssl enc -aes-256-cbc -md sha1 -k your_passwd \
      -in /etc/mysql/keys -out /etc/mysql/keys.enc

Running this command reads the keys file created above and creates a new encrypted keys.enc, using the password given to the -k option. Once you've finished preparing your system, delete the plain text key file, as it's no longer necessary.

Installing the File Key Management Plugin

Although the plugin's shared library is distributed with MariaDB by default as auth_pam.so, the plugin is not actually loaded by default. You need to install it with INSTALL PLUGIN. For example:

INSTALL PLUGIN file_key_management SONAME 'file_key_management';

You can also load the plugin by providing the --plugin-load or the --plugin-load-add options with the name of the shared library as an argument, which is file_key_management.so. This can be specified as a command-line argument to mysqld or it can be specified in a relevant server option group in an option file. For example:

[mysqld]
...
plugin-load = file_key_management

Enabling the File Key Management Plugin

To enable the File Key Management plugin, you also need to set the plugin's system variables. The file_key_management_filename system variable is the only required one. For example:

[mysqld]
...
file_key_management_filename = /etc/mysql/keys.enc
file_key_management_filekey = FILE:/etc/mysql/.key
file_key_management_encryption_algorithm = aes_cbc

Once you've updated the configuration file, restart the MariaDB server to apply the changes and make the encryption plugin available for use.

Handling an Encrypted Key File

In the event that you chose to encrypt the key file, you will need to provide the decryption key via the file_key_management_filekey system variable. This system variable can be provided in two forms:

• You can give it the password you used when you created the encrypted key.enc file with OpenSSL.
• Using the FILE: prefix, you can give it the path to a file containing the password.

When encrypting your key file, it is best practice to store the password in a separate file. When the password is set as the variable, other users can see it by inspecting the value of the variable with the SHOW VARIABLES statement.

Choosing an Encryption Algorithm

The File Key Management plugin supports two encryption algorithms: AES_CBC and AES_CTR. The recommended algorithm is CTR, but CTR is only available when MariaDB is built with recent versions of OpenSSL.

When set to ABS_CBC, MariaDB uses AES with 128-bit keys in the Cipher Block Chaining mode. When set to AES_CTR, MariaDB uses AES with 128-bit keys in the Counter mode for encrypting tablespace pages, (that is, with InnoDB, XtraDB and Aria), and uses AES in authenticated GCM mode for temporary files, (where the cipher text is allowed to be larger than the plain text).

System Variables

file_key_management_encryption_algorithm

• Description: Defines the algorithm to use for encryption.
• Commandline: --file-key-management-encryption-algorithm=value
• Scope: Global
• Dynamic: No
• Data Type: enum
• Default Value: aes_cbc

file_key_management_filekey

• Description: Defines the key or path to the file that contains the key to use in decrypting the file with the encryption keys, which allows you to better secure it on your file system.
• Commandline: --file-key-management-filekey=value
• Scope: Global
• Dynamic: No
• Data Type: string
• Default Value: (empty)

file_key_management_filename

• Description: Defines the path to the file that contains the encryption keys.
• Commandline: --file-key-management-filename=value
• Scope: Global
• Dynamic: No
• Data Type: string
• Default Value: (empty)