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Encrypting Data at Datastore Layer

Overview

This topic reviews how to enable and configure encryption of secret data at the datastore layer. While the examples use the secrets resource, any resource can be encrypted, such as configmaps.

etcd v3 or later is required in order to use this feature.

Configuration and Determining Whether Encryption Is Already Enabled

To activate data encryption, pass the --experimental-encryption-provider-config argument to the Kubernetes API server:

Excerpt of master-config.yaml
kubernetesMasterConfig:
  apiServerArguments:
    experimental-encryption-provider-config:
    - /path/to/encryption-config.yaml

For more information about master-config.yaml and its format, see the Master Configuration Files topic.

Understanding the Encryption Configuration

Encryption configuration file with all available providers
kind: EncryptionConfig
apiVersion: v1
resources: (1)
  - resources: (2)
    - secrets
    providers: (3)
    - aescbc: (4)
        keys:
        - name: key1 (5)
          secret: c2VjcmV0IGlzIHNlY3VyZQ== (6)
        - name: key2
          secret: dGhpcyBpcyBwYXNzd29yZA==
    - secretbox:
        keys:
        - name: key1
          secret: YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXoxMjM0NTY=
    - aesgcm:
        keys:
        - name: key1
          secret: c2VjcmV0IGlzIHNlY3VyZQ==
        - name: key2
          secret: dGhpcyBpcyBwYXNzd29yZA==
    - identity: {}
1 Each resources array item is a separate configuration and contains a complete configuration.
2 The resources.resources field is an array of Kubernetes resource names (resource or resource.group) that should be encrypted.
3 The providers array is an ordered list of the possible encryption providers. Only one provider type can be specified per entry (identity or aescbc can be provided, but not both in the same item).
4 The first provider in the list is used to encrypt resources going into storage.
5 Arbitrary name of the secret.
6 Base64 encoded random key. Different providers have different key lengths. See instructions on how to generate the key.

When reading resources from storage, each provider that matches the stored data attempts to decrypt the data in order. If no provider can read the stored data due to a mismatch in format or secret key, an error is returned, which prevents clients from accessing that resource.

If any resource is not readable via the encryption configuration (because keys were changed), the only recourse is to delete that key from the underlying etcd directly. Calls attempting to read that resource will fail until it is deleted or a valid decryption key is provided.

Available Providers

Name Encryption Strength Speed Key Length Other Considerations

identity

None

N/A

N/A

N/A

Resources written as-is without encryption. When set as the first provider, the resource will be decrypted as new values are written.

aescbc

AES-CBC with PKCS#7 padding

Strongest

Fast

32-byte

The recommended choice for encryption, but may be slightly slower than secretbox.

secretbox

XSalsa20 and Poly1305

Strong

Faster

32-byte

A newer standard and may not be considered acceptable in environments that require high levels of review.

aesgcm

AES-GCM with a random initialization vector (IV)

Must be rotated every 200,000 writes

Fastest

16, 24, or 32-byte

Is not recommended for use except when an automated key rotation scheme is implemented.

Each provider supports multiple keys. The keys are tried in order for decryption. If the provider is the first provider, the first key is used for encryption.

Kubernetes has no proper nonce generator and uses a random IV as nonce for AES-GCM. Since AES-GCM requires a proper nonce to be secure, AES-GCM is not recommended. The 200,000 write limit just limits the possibility of a fatal nonce misuse to a reasonable low margin.

Encrypting Data

Create a new encryption configuration file.

kind: EncryptionConfig
apiVersion: v1
resources:
  - resources:
    - secrets
    providers:
    - aescbc:
        keys:
        - name: key1
          secret: <BASE 64 ENCODED SECRET>
    - identity: {}

To create a new secret:

  1. Generate a 32-byte random key and base64 encode it. For example, on Linux and macOS use:

    $ head -c 32 /dev/urandom | base64

    The encryption key must be generated with an appropriate cryptographically secure random number generator like /dev/urandom. For example, math/random from Golang or random.random() from Python are not suitable.

  2. Place that value in the secret field.

  3. Restart the API server:

    # master-restart api
# master-restart controllers

The encryption provider configuration file contains keys that can decrypt content in etcd, so you must properly restrict permissions on masters so only the user who runs the master API server can read it.

Verifying that Data is Encrypted

Data is encrypted when written to etcd. After restarting the API server, any newly created or updated secrets should be encrypted when stored. To check, you can use the etcdctl command line program to retrieve the contents of your secret.

  1. Create a new secret called secret1 in the default namespace:

    $ oc create secret generic secret1 -n default --from-literal=mykey=mydata

  2. Using the etcdctl command line, read that secret out of etcd:

    $ ETCDCTL_API=3 etcdctl get /kubernetes.io/secrets/default/secret1 -w fields [...] | grep Value

    […​] must be the additional arguments for connecting to the etcd server.

    The final command will look similar to:

    $ ETCDCTL_API=3 etcdctl get /kubernetes.io/secrets/default/secret1 -w fields \
--cacert=/var/lib/origin/openshift.local.config/master/ca.crt \
--key=/var/lib/origin/openshift.local.config/master/master.etcd-client.key \
--cert=/var/lib/origin/openshift.local.config/master/master.etcd-client.crt \
--endpoints 'https://127.0.0.1:4001' | grep Value

  3. Verify that the output of the command above is prefixed with k8s:enc:aescbc:v1: which indicates the aescbc provider has encrypted the resulting data.

  4. Verify the secret is correctly decrypted when retrieved via the API:

    $ oc get secret secret1 -n default -o yaml | grep mykey

    This should match mykey: bXlkYXRh.

Ensure All Secrets are Encrypted

Since secrets are encrypted when written, performing an update on a secret will encrypt that content.

$ oc adm migrate storage --include=secrets --confirm

This command reads all secrets, then updates them to apply server-side encryption. If an error occurs due to a conflicting write, retry the command.

For larger clusters, you can subdivide the secrets by namespace or script an update.

Rotating a Decryption Key

Changing the secret without incurring downtime requires a multi-step operation, especially in the presence of a highly available deployment where multiple API servers are running.

  1. Generate a new key and add it as the second key entry for the current provider on all servers.

  2. Restart all API servers to ensure each server can decrypt using the new key.

    If using a single API server, you can skip this step.

    		 
    # master-restart api
# master-restart controllers

  3. Make the new key the first entry in the keys array so that it is used for encryption in the configuration.

  4. Restart all API servers to ensure each server now encrypts using the new key.

    # master-restart api
# master-restart controllers

  5. Run the following to encrypt all existing secrets with the new key:

    $ oc adm migrate storage --include=secrets --confirm

  6. After you back up etcd with the new key in use and update all secrets, remove the old decryption key from the configuration.

Decrypting Data

To disable encryption at the datastore layer:

  1. Place the identity provider as the first entry in the configuration:

kind: EncryptionConfig
apiVersion: v1
resources:
  - resources:
    - secrets
    providers:
    - identity: {}
    - aescbc:
        keys:
        - name: key1
          secret: <BASE 64 ENCODED SECRET>

  1. Restart all API servers:

    # master-restart api
# master-restart controllers

  2. Run the following to force all secrets to be decrypted:

    $ oc adm migrate storage --include=secrets --confirm