Encrypting Secret Data at Rest

This page shows how to enable and configure encryption of secret data at rest.

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:

  • Killercoda
  • Play with Kubernetes
  Your Kubernetes server must be at or later than version 1.13. To check the version, enter kubectl version.

• etcd v3.0 or later is required

Configuration and determining whether encryption at rest is already enabled

The kube-apiserver process accepts an argument --encryption-provider-config that controls how API data is encrypted in etcd. The configuration is provided as an API named EncryptionConfiguration. An example configuration is provided below.

Understanding the encryption at rest configuration.

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - identity: {}
      - aesgcm:
          keys:
            - name: key1
              secret: c2VjcmV0IGlzIHNlY3VyZQ==
            - name: key2
              secret: dGhpcyBpcyBwYXNzd29yZA==
      - aescbc:
          keys:
            - name: key1
              secret: c2VjcmV0IGlzIHNlY3VyZQ==
            - name: key2
              secret: dGhpcyBpcyBwYXNzd29yZA==
      - secretbox:
          keys:
            - name: key1
              secret: YWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXoxMjM0NTY=

Each resources array item is a separate config and contains a complete configuration. The resources.resources field is an array of Kubernetes resource names (resource or resource.group) that should be encrypted. The providers array is an ordered list of the possible encryption providers.

Only one provider type may be specified per entry (identity or aescbc may be provided, but not both in the same item). The first provider in the list is used to encrypt resources written into the storage. When reading resources from storage, each provider that matches the stored data attempts in order to decrypt the data. 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.

For more detailed information about the EncryptionConfiguration struct, please refer to the encryption configuration API.

Providers:

Each provider supports multiple keys - the keys are tried in order for decryption, and if the provider is the first provider, the first key is used for encryption.

By default, the identity provider is used to protect Secrets in etcd, which provides no encryption. EncryptionConfiguration was introduced to encrypt Secrets locally, with a locally managed key.

Encrypting Secrets with a locally managed key protects against an etcd compromise, but it fails to protect against a host compromise. Since the encryption keys are stored on the host in the EncryptionConfiguration YAML file, a skilled attacker can access that file and extract the encryption keys.

Envelope encryption creates dependence on a separate key, not stored in Kubernetes. In this case, an attacker would need to compromise etcd, the kubeapi-server, and the third-party KMS provider to retrieve the plaintext values, providing a higher level of security than locally stored encryption keys.

Encrypting your data

Create a new encryption config file:

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - aescbc:
          keys:
            - name: key1
              secret: <BASE 64 ENCODED SECRET>
      - identity: {}

To create a new Secret, perform the following steps:

1. Generate a 32-byte random key and base64 encode it. If you're on Linux or macOS, run the following command:

   head -c 32 /dev/urandom | base64
   

2. Place that value in the secret field of the EncryptionConfiguration struct.

3. Set the --encryption-provider-config flag on the kube-apiserver to point to the location of the config file.

   You will need to mount the new encryption config file to the kube-apiserver static pod. Here is an example on how to do that:

   1. Save the new encryption config file to /etc/kubernetes/enc/enc.yaml on the control-plane node.
   2. Edit the manifest for the kube-apiserver static pod: /etc/kubernetes/manifests/kube-apiserver.yaml similarly to this:

   apiVersion: v1
   kind: Pod
   metadata:
     annotations:
       kubeadm.kubernetes.io/kube-apiserver.advertise-address.endpoint: 10.10.30.4:6443
     creationTimestamp: null
     labels:
       component: kube-apiserver
       tier: control-plane
     name: kube-apiserver
     namespace: kube-system
   spec:
     containers:
     - command:
       - kube-apiserver
       ...
       - --encryption-provider-config=/etc/kubernetes/enc/enc.yaml  # <-- add this line
       volumeMounts:
       ...
       - name: enc                           # <-- add this line
         mountPath: /etc/kubernetes/enc      # <-- add this line
         readonly: true                      # <-- add this line
       ...
     volumes:
     ...
     - name: enc                             # <-- add this line
       hostPath:                             # <-- add this line
         path: /etc/kubernetes/enc           # <-- add this line
         type: DirectoryOrCreate             # <-- add this line
     ...
   

4. Restart your API server.

Verifying that 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 check this, 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:

   kubectl 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 /registry/secrets/default/secret1 [...] | hexdump -C

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

   For example:

   ETCDCTL_API=3 etcdctl \
      --cacert=/etc/kubernetes/pki/etcd/ca.crt   \
      --cert=/etc/kubernetes/pki/etcd/server.crt \
      --key=/etc/kubernetes/pki/etcd/server.key  \
      get /registry/secrets/default/secret1 | hexdump -C
   

   The output is similar to this (abbreviated):

   00000000  2f 72 65 67 69 73 74 72  79 2f 73 65 63 72 65 74  |/registry/secret|
   00000010  73 2f 64 65 66 61 75 6c  74 2f 73 65 63 72 65 74  |s/default/secret|
   00000020  31 0a 6b 38 73 3a 65 6e  63 3a 61 65 73 63 62 63  |1.k8s:enc:aescbc|
   00000030  3a 76 31 3a 6b 65 79 31  3a c7 6c e7 d3 09 bc 06  |:v1:key1:.l.....|
   00000040  25 51 91 e4 e0 6c e5 b1  4d 7a 8b 3d b9 c2 7c 6e  |%Q...l..Mz.=..|n|
   00000050  b4 79 df 05 28 ae 0d 8e  5f 35 13 2c c0 18 99 3e  |.y..(..._5.,...>|
   [...]
   00000110  23 3a 0d fc 28 ca 48 2d  6b 2d 46 cc 72 0b 70 4c  |#:..(.H-k-F.r.pL|
   00000120  a5 fc 35 43 12 4e 60 ef  bf 6f fe cf df 0b ad 1f  |..5C.N`..o......|
   00000130  82 c4 88 53 02 da 3e 66  ff 0a                    |...S..>f..|
   0000013a
   

3. Verify the stored Secret is prefixed with k8s:enc:aescbc:v1: which indicates the aescbc provider has encrypted the resulting data. Confirm that the key name shown in etcd matches the key name specified in the EncryptionConfiguration mentioned above. In this example, you can see that the encryption key named key1 is used in etcd and in EncryptionConfiguration.

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

   kubectl get secret secret1 -n default -o yaml
   

   The output should contain mykey: bXlkYXRh, with contents of mydata encoded, check decoding a Secret to completely decode the Secret.

Ensure all Secrets are encrypted

Since Secrets are encrypted on write, performing an update on a Secret will encrypt that content.

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

The command above reads all Secrets and then updates them to apply server side encryption.

Rotating a decryption key

Changing a Secret without incurring downtime requires a multi-step operation, especially in the presence of a highly-available deployment where multiple kube-apiserver processes 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 kube-apiserver processes to ensure each server can decrypt using the new key
3. Make the new key the first entry in the keys array so that it is used for encryption in the config
4. Restart all kube-apiserver processes to ensure each server now encrypts using the new key
5. Run kubectl get secrets --all-namespaces -o json | kubectl replace -f - to encrypt all existing Secrets with the new key
6. Remove the old decryption key from the config after you have backed up etcd with the new key in use and updated all Secrets

When running a single kube-apiserver instance, step 2 may be skipped.

Decrypting all data

To disable encryption at rest, place the identity provider as the first entry in the config and restart all kube-apiserver processes.

apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
  - resources:
      - secrets
    providers:
      - identity: {}
      - aescbc:
          keys:
            - name: key1
              secret: <BASE 64 ENCODED SECRET>

Then run the following command to force decrypt all Secrets:

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

What's next

• Learn more about the EncryptionConfiguration configuration API (v1).