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Configuring Encryption at Rest

Overview​

Aerospike Enterprise Edition (EE) can be configured to strongly encrypt data "at rest" - on storage devices (flash, memory, Intel Optane™ Persistent Memory) using NIST standards.

Encryption at rest involves a user-supplied encryption key, which can be rotated, and two server-generated random encryption keys. The server encryption keys are derived from the user-supplied encryption key. Without this user-supplied encryption key, the server's data storage cannot be decrypted. If this key is lost, the data stored on the devices becomes inaccessible.

Encryption at rest requires the asdb-encryption-at-rest feature-key. See Providing the Feature-Key File.

Data encryption key (DEK)​

The data encryption key (DEK) is a symmetric key used to both encrypt and decrypt data on a storage device. The encryption configuration parameter defines whether to use aes-128 or aes-256 as the basis for the DEK.

To create a DEK, the server uses a cryptographically strong random number generator (OpenSSL’s RAND_bytes() function). The size of the DEK is 128 bits if AES-128 is selected, or 256 bits if AES-256 is selected. Each storage device, in a namespace configured with encryption at rest, has a unique DEK. If the device is wiped, the server will generate a new DEK for it.

Aerospike encrypts each record with the XTS-AES block cipher mode (detailed in IEEE P1619 standard for disk encryption and NIST Special Publication (SP) 800-38E), which respectively double the key size of the DEK to 256 bits or 512 bits.

Key encryption key (KEK)​

The key encryption key (KEK) encrypts and decrypt the device's DEK. The KEK is derived from the user-supplied encryption-key-file, acting as the passphrase for the NIST-approved Password-Based Key Derivation Function 2 (PBKDF2).

Aerospike reads the encrypted DEK from each device and decrypts it using the KEK. Aerospike tests whether the device's DEK is valid by checking a "canary" or "verification" value stored in the device header. If the canary value is not decipherable, the process is retried with the user-supplied encryption-old-key-file. This allows for rotating the KEK.

Configuring storage encryption​

Encryption at rest is configured per namespace, using three configuration parameters

These configuration parameters can be supplied through the file system, an environment variable, fetched from HashiCorp Vault, or fetched from a secrets management service using Aerospike Secret Agent.

In the namespace storage-engine configuration:

namespace test {
    ...
    storage-engine device {
        device /dev/sda1
        ...
        encryption-key-file key.dat
        encryption-old-key-file prev-key.dat
        encryption aes-128
    }
    ...
}

Generating a strong encryption key file​

The contents of the user-specified encryption-key-file, like a password, must be unpredictable to an adversary. An adversary who knows the contents of the key file can decrypt your storage device. A large key file is not enough if it is predictable.

For this reason, we recommend an adequate number of random bytes from a reliable source of randomness - NIST recommends 128 bits for PBKDF2 uses. For example:

head --bytes 256 /dev/urandom > key.dat

You should use different keys for different namespaces. In all cases, your encryption key files must be kept private on an encrypted and secure operating system environment or fetched from a secrets management service.

Managing storage encryption​

Enabling or disabling storage encryption​

Enabling namespace storage encryption by setting encryption-key-file for the first time, disabling encryption by removing encryption-key-file from the namespace configuration, or changing the encryption algorithm, requires that you wipe the namespace storage.

This process must be completed one cluster node at a time:

  1. Quiesce the cluster node, then stop the Aerospike server process (asd). You should delay "fill" migrations.
  2. Wipe the namespace storage by using dd or blkdiscard for devices, and rm for file-based storage.
  3. Modify the namespace configuration in aerospike.conf.
  4. Restart the Aerospike server process on the cluster node.

Repeat this process for all the cluster nodes.

note

Prior to Aerospike Database 5.7, this process was also necessary for rotating key encryption keys.

Rotating the KEK​

To rotate the key encryption key, do the following one cluster node at a time:

  1. First, quiesce and shut down the Aerospike server process. You should delay "fill" migrations.
  2. Modify the node's aerospike.conf and set the current user-defined encryption-key-file as the encryption-old-key-file.
  3. Provide a new, randomly generated encryption-key-file.
  4. Restart the Aerospike server process on the cluster node.

Once the node restarts successfully the new KEK will be saved, and the encryption-old-key-file configuration line should be removed. If you don't, then you'll see a warning whenever you restart asd: ignoring invalid old encryption key. The server will start up, and encryption will work, though.

Performance​

Disk encryption typically works on a per-sector basis. However, Aerospike optimizes disk encryption performance by encrypting each record separately. Records on disk are treated as variable-size disk sectors, up to 1MiB in size. Beyond 1MiB records are split into 1-MiB chunks.

The performance impact of storage encryption depends on the host hardware, as well as the average size of the records. A definitive answer regarding the performance impact can thus only be obtained by benchmarking on the deployed hardware with realistic data.

Certain CPUs, such as Intel Xeon chips, provide on-chip hardware acceleration. In one typical hardware configuration, we observed that records smaller than 512 bytes resulted in a 20% drop in TPS performance. Benchmarking 1KiB, 5KiB, and 10KiB record sizes did not lead to any measurable performance loss.