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:
Your Kubernetes server must be at or later than version 1.13. To check the version, enterkubectl 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.
kube-apiserver
component cannot
decrypt data stored in the etcd.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:
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. |
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. |
aescbc | AES-CBC with PKCS#7 padding | Weak | Fast | 32-byte | Not recommended due to CBC's vulnerability to padding oracle attacks. |
kms | Uses envelope encryption scheme: Data is encrypted by data encryption keys (DEKs) using AES-CBC with PKCS#7 padding (prior to v1.25), using AES-GCM starting from v1.25, 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.
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 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:
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 of theEncryptionConfiguration
struct.Set the
--encryption-provider-config
flag on thekube-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:- Save the new encryption config file to
/etc/kubernetes/enc/enc.yaml
on the control-plane node. - 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 ...
- Save the new encryption config file to
Restart your API server.
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 this, 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
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
Verify the stored Secret is prefixed with
k8s:enc:aescbc:v1:
which indicates theaescbc
provider has encrypted the resulting data. Confirm that the key name shown inetcd
matches the key name specified in theEncryptionConfiguration
mentioned above. In this example, you can see that the encryption key namedkey1
is used inetcd
and inEncryptionConfiguration
.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 ofmydata
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.
- 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 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).