Using a KMS provider for data encryption

Using a KMS provider for data encryption

This page shows how to configure a Key Management Service (KMS) provider and plugin to enable secret data encryption.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:
- Katacoda
- Play with Kubernetes
To check the version, enter kubectl version.
Kubernetes version 1.10.0 or later is required
etcd v3 or later is required

FEATURE STATE: Kubernetes v1.12 [beta]

The KMS encryption provider uses an envelope encryption scheme to encrypt data in etcd. The data is encrypted using a data encryption key (DEK); a new DEK is generated for each encryption. The DEKs are encrypted with a key encryption key (KEK) that is stored and managed in a remote KMS. The KMS provider uses gRPC to communicate with a specific KMS plugin. The KMS plugin, which is implemented as a gRPC server and deployed on the same host(s) as the Kubernetes master(s), is responsible for all communication with the remote KMS.

Configuring the KMS provider

To configure a KMS provider on the API server, include a provider of type kms in the providers array in the encryption configuration file and set the following properties:

name: Display name of the KMS plugin.
endpoint: Listen address of the gRPC server (KMS plugin). The endpoint is a UNIX domain socket.
cachesize: Number of data encryption keys (DEKs) to be cached in the clear. When cached, DEKs can be used without another call to the KMS; whereas DEKs that are not cached require a call to the KMS to unwrap.
timeout: How long should kube-apiserver wait for kms-plugin to respond before returning an error (default is 3 seconds).

See Understanding the encryption at rest configuration.

Implementing a KMS plugin

To implement a KMS plugin, you can develop a new plugin gRPC server or enable a KMS plugin already provided by your cloud provider. You then integrate the plugin with the remote KMS and deploy it on the Kubernetes master.

Enabling the KMS supported by your cloud provider

Refer to your cloud provider for instructions on enabling the cloud provider-specific KMS plugin.

Developing a KMS plugin gRPC server

You can develop a KMS plugin gRPC server using a stub file available for Go. For other languages, you use a proto file to create a stub file that you can use to develop the gRPC server code.

Using Go: Use the functions and data structures in the stub file: service.pb.go to develop the gRPC server code
Using languages other than Go: Use the protoc compiler with the proto file: service.proto to generate a stub file for the specific language

Then use the functions and data structures in the stub file to develop the server code.

Notes:

kms plugin version: v1beta1

In response to procedure call Version, a compatible KMS plugin should return v1beta1 as VersionResponse.version.
message version: v1beta1

All messages from KMS provider have the version field set to current version v1beta1.
protocol: UNIX domain socket (unix)

The gRPC server should listen at UNIX domain socket.

Integrating a KMS plugin with the remote KMS

The KMS plugin can communicate with the remote KMS using any protocol supported by the KMS. All configuration data, including authentication credentials the KMS plugin uses to communicate with the remote KMS, are stored and managed by the KMS plugin independently. The KMS plugin can encode the ciphertext with additional metadata that may be required before sending it to the KMS for decryption.

Deploying the KMS plugin

Ensure that the KMS plugin runs on the same host(s) as the Kubernetes master(s).

Encrypting your data with the KMS provider

To encrypt the data:

Create a new encryption configuration file using the appropriate properties for the kms provider:

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - kms:
          name: myKmsPlugin
          endpoint: unix:///tmp/socketfile.sock
          cachesize: 100
          timeout: 3s
      - identity: {}

Set the --encryption-provider-config flag on the kube-apiserver to point to the location of the configuration file.
Restart your API server.

Verifying that the data is encrypted

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

Create a new secret called secret1 in the default namespace:

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

Using the etcdctl command line, read that secret out of etcd:
```
ETCDCTL_API=3 etcdctl get /kubernetes.io/secrets/default/secret1 [...] | hexdump -C
```
where [...] must be the additional arguments for connecting to the etcd server.
Verify the stored secret is prefixed with k8s:enc:kms:v1:, which indicates that the kms provider has encrypted the resulting data.
Verify that the secret is correctly decrypted when retrieved via the API:
```
kubectl describe secret secret1 -n default
```
should match mykey: mydata

Ensuring all secrets are encrypted

Because secrets are encrypted on write, performing an update on a secret encrypts that content.

The following command reads all secrets and then updates them to apply server side encryption. If an error occurs due to a conflicting write, retry the command. For larger clusters, you may wish to subdivide the secrets by namespace or script an update.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -

Switching from a local encryption provider to the KMS provider

To switch from a local encryption provider to the kms provider and re-encrypt all of the secrets:

Add the kms provider as the first entry in the configuration file as shown in the following example.

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - kms:
          name : myKmsPlugin
          endpoint: unix:///tmp/socketfile.sock
          cachesize: 100
      - aescbc:
          keys:
            - name: key1
              secret: <BASE 64 ENCODED SECRET>

Restart all kube-apiserver processes.
Run the following command to force all secrets to be re-encrypted using the kms provider.
```
kubectl get secrets --all-namespaces -o json| kubectl replace -f -
```

Disabling encryption at rest

To disable encryption at rest:

Place the identity provider as the first entry in the configuration file:

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - identity: {}
      - kms:
          name : myKmsPlugin
          endpoint: unix:///tmp/socketfile.sock
          cachesize: 100

Restart all kube-apiserver processes.

Run the following command to force all secrets to be decrypted.

kubectl get secrets --all-namespaces -o json | kubectl replace -f -