Encrypting Secret Data at Rest
This page shows how to enable and configure encryption of secret data at rest.
- Before you begin
- Configuration and determining whether encryption at rest is already enabled
- Understanding the encryption at rest configuration.
- Encrypting your data
- Verifying that data is encrypted
- Ensure all secrets are encrypted
- Rotating a decryption key
- Decrypting all data
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:
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. 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 going into storage. 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.
Caution: IMPORTANT: If any resource is not readable via the encryption config (because keys were changed), the only recourse is to delete that key from the underlying etcd directly. Calls that attempt to read that resource will fail until it is deleted or a valid decryption key is provided.
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 at rest 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 random nonce | Must be rotated every 200k writes | Fastest | 16, 24, or 32-byte | Is not recommended for use except when an automated key rotation scheme is implemented. |
kms |
Uses envelope encryption scheme: Data is encrypted by data encryption keys (DEKs) using AES-CBC with PKCS#7 padding, DEKs are encrypted by key encryption keys (KEKs) according to configuration in Key Management Service (KMS) | Strongest | Fast | 32-bytes | The recommended choice for using a third party tool for key management. Simplifies key rotation, with a new DEK generated for each encryption, and KEK rotation controlled by the user. Configure the KMS provider |
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.
Storing the raw encryption key in the EncryptionConfig only moderately improves your security posture, compared to no encryption.
Please use kms
provider for additional security. 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 EncryptionConfig 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:
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
Place that value in the secret field.
Set the
--encryption-provider-config
flag on thekube-apiserver
to point to the location of the config file.Restart your API server.
Caution: Your config file contains keys that can decrypt content in etcd, so you must properly restrict permissions on your masters so only the user who runs the kube-apiserver can read it.
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, you can use the etcdctl
command line
program to retrieve the contents of your secret.
Create a new secret called
secret1
in thedefault
namespace:kubectl create secret generic secret1 -n default --from-literal=mykey=mydata
Using the etcdctl commandline, 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.Verify the stored secret is prefixed with
k8s:enc:aescbc:v1:
which indicates theaescbc
provider has encrypted the resulting data.Verify the secret is correctly decrypted when retrieved via the API:
kubectl describe secret secret1 -n default
should match
mykey: bXlkYXRh
, mydata is 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. 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.
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 kube-apiserver
processes are running.
- Generate a new key and add it as the second key entry for the current provider on all servers
- Restart all
kube-apiserver
processes to ensure each server can decrypt using the new key - Make the new key the first entry in the
keys
array so that it is used for encryption in the config - Restart all
kube-apiserver
processes to ensure each server now encrypts using the new key - Run
kubectl get secrets --all-namespaces -o json | kubectl replace -f -
to encrypt all existing secrets with the new key - Remove the old decryption key from the config after you back up etcd with the new key in use and update all secrets
With a single kube-apiserver
, step 2 may be skipped.
Decrypting all data
To disable encryption at rest place the identity
provider as the first entry in the config:
apiVersion: apiserver.config.k8s.io/v1
kind: EncryptionConfiguration
resources:
- resources:
- secrets
providers:
- identity: {}
- aescbc:
keys:
- name: key1
secret: <BASE 64 ENCODED SECRET>
and restart all kube-apiserver
processes. Then run the command kubectl get secrets --all-namespaces -o json | kubectl replace -f -
to force all secrets to be decrypted.
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