Make RSA key length configurable (#506)

* make key length configurable

* adapted changelog

* rename key length enum variants

* cargo fmt

* fix unit tests

* fmt

* improve crd schema

* add comments

* yaml lint

* add documentation

* improvements

* fixes

* Apply suggestions from code review

Co-authored-by: Sebastian Bernauer <sebastian.bernauer@stackable.de>

* set default key length to 2048

* adapt key length default and values

* use constants for key length

* trailing whitespace

* Apply suggestions from code review

Co-authored-by: Sebastian Bernauer <sebastian.bernauer@stackable.de>

* explicitly use serde default

* improve docs

* fix clippy /test

* improve docs

* fmt

* fix test

* Update rust/operator-binary/src/crd.rs

Co-authored-by: Sebastian Bernauer <sebastian.bernauer@stackable.de>

* regenerate charts

* bump tonic due to cargo deny

* rename struct

* improve doc header

* Update deploy/helm/secret-operator/crds/crds.yaml

Co-authored-by: Techassi <sascha.lautenschlaeger@stackable.tech>

* consistently switched to key pair instead of keypair

* improve docs

* regenerate charts

* fix

* fix

---------

Co-authored-by: Sebastian Bernauer <sebastian.bernauer@stackable.de>
Co-authored-by: Techassi <sascha.lautenschlaeger@stackable.tech>

Author: 3 people

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to this project will be documented in this file.
 
 - Active Directory's `samAccountName` generation can now be customized ([#454]).
 - Added experimental cert-manager backend ([#482]).
+- Make RSA key length configurable ([#506]).
 
 ### Fixed
 
@@ -25,6 +26,7 @@ All notable changes to this project will be documented in this file.
 [#495]: https://github.com/stackabletech/secret-operator/pull/495
 [#497]: https://github.com/stackabletech/secret-operator/pull/497
 [#505]: https://github.com/stackabletech/secret-operator/pull/505
+[#506]: https://github.com/stackabletech/secret-operator/pull/506
 
 ## [24.7.0] - 2024-07-24
 

Cargo.lock

@@ -40,7 +40,7 @@ spec:
                       description: |-
                         The [`autoTls` backend](https://docs.stackable.tech/home/nightly/secret-operator/secretclass#backend-autotls) issues a TLS certificate signed by the Secret Operator. The certificate authority can be provided by the administrator, or managed automatically by the Secret Operator.
 
-                        A new certificate and keypair will be generated and signed for each Pod, keys or certificates are never reused.
+                        A new certificate and key pair will be generated and signed for each Pod, keys or certificates are never reused.
                       properties:
                         ca:
                           description: Configures the certificate authority used to issue Pod certificates.
@@ -58,6 +58,28 @@ spec:
 
                                 If `autoGenerate: true` then the Secret Operator will prepare a new CA certificate the old CA approaches expiration. If `autoGenerate: false` then the Secret Operator will log a warning instead.
                               type: string
+                            keyGeneration:
+                              default:
+                                rsa:
+                                  length: 2048
+                              description: The algorithm used to generate a key pair and required configuration settings. Currently only RSA and a key length of 2048, 3072 or 4096 bits can be configured.
+                              oneOf:
+                                - required:
+                                    - rsa
+                              properties:
+                                rsa:
+                                  properties:
+                                    length:
+                                      description: The amount of bits used for generating the RSA keypair. Currently, `2048`, `3072` and `4096` are supported. Defaults to `2048` bits.
+                                      enum:
+                                        - 2048
+                                        - 3072
+                                        - 4096
+                                      type: integer
+                                  required:
+                                    - length
+                                  type: object
+                              type: object
                             secret:
                               description: Reference (name and namespace) to a Kubernetes Secret object where the CA certificate and key is stored in the keys `ca.crt` and `ca.key` respectively.
                               properties:

deploy/helm/secret-operator/crds/crds.yaml

@@ -1,5 +1,5 @@
 ---
-# Migrates the TLS CA keypair from the hard-coded default namespace to the operator namespace
+# Migrates the TLS CA key pair from the hard-coded default namespace to the operator namespace
 # See https://github.com/stackabletech/secret-operator/issues/453
 apiVersion: batch/v1
 kind: Job
@@ -52,4 +52,4 @@ spec:
               echo "$source_ca_secret" | jq 'del(.metadata["namespace","creationTimestamp","resourceVersion","selfLink","uid"])' | kubectl apply -n $TARGET_NAMESPACE -f -
             fi
           fi
-      restartPolicy: Never
+      restartPolicy: Never

deploy/helm/secret-operator/templates/secret_migration_job.yaml

@@ -0,0 +1,15 @@
+---
+apiVersion: secrets.stackable.tech/v1alpha1
+kind: SecretClass
+metadata:
+  name: tls
+spec:
+  backend:
+    autoTls:
+      ca:
+        secret:
+          name: secret-provisioner-tls-ca
+          namespace: default
+        keyGeneration: # <1>
+          rsa: # <2>
+            length: 4096 # <3>

docs/modules/secret-operator/examples/secretclass-tls-key-length.yaml

@@ -31,13 +31,33 @@ Each SecretClass is a associated with a single backend, which dictates the mecha
 Issues a TLS certificate signed by the Secret Operator.
 The certificate authority can be provided by the administrator, or managed automatically by the Secret Operator.
 
-A new certificate and keypair will be generated and signed for each Pod, keys or certificates are never reused.
+A new certificate and key pair will be generated and signed for each Pod, keys or certificates are never reused.
 
 CAUTION: Attributes of the certificate (such as the expiration date, fingerprint, or serial number) will be regenerated for each
          Pod, and should not be expected to be stable.
 
 xref:scope.adoc[Scopes] are used to populate the claims (such as `subjectAlternateName`) of the provisioned certificates.
 
+[#backend-tls-certificate-key-pair-generation]
+=== `TLS certificate key pair generation`
+
+Currently, only RSA is supported in the `autoTls` backend.
+You can however configure the key length for generated private keys. If not specified it will default to `2048` bits.
+
+----
+include::example$secretclass-tls-key-length.yaml[]
+----
+<1> `autoTls.ca.keyGeneration` specifies which algorithm and additional parameters are used
+<2> `autoTls.ca.keyGeneration.rsa` specifies the RSA key pair algorithm (RSA currently is the only one supported)
+<3> `autoTls.ca.keyGeneration.rsa.length` specifies the amount of bits used for generating the RSA key pair. Currently, `2048`, `3072` and `4096` are supported. Defaults to `2048` bits.
+
+CAUTION: Using more than `2048` bits will significantly increase the computation time to create new key pairs.
+The SSL Labs https://github.com/ssllabs/research/wiki/SSL-and-TLS-Deployment-Best-Practices[SSL and TLS Deployment Best Practices] as of 2024-10-01 recommend
+
+>  For most websites, using RSA keys stronger than 2,048 bits and ECDSA keys stronger than 256 bits is a waste of CPU power and might impair user experience
+
+If options higher than `2048` are chosen, the CPU resources for the secret operator should be increased in order to avoid Pods being stuck in `Pending` waiting for the computation of their key pair.
+
 ==== Certificate lifetime
 
 By default the Secret Operator will generally aim to use as short-lived certificates as possible.
@@ -375,7 +395,7 @@ The secret contains the following files:
 Both stores are encrypted, with an empty string as the passphrase.
 
 NOTE: When using the xref:#backend-k8ssearch[] backend, it is _strongly_ recommended to store secrets in the use the xref:#format-tls-pem[] format instead.
-The secret operator supports converting PEM keypairs into PKCS#12, but not the other way around.
+The secret operator supports converting PEM key pairs into PKCS#12, but not the other way around.
 
 [#format-kerberos]
 === Kerberos

docs/modules/secret-operator/pages/secretclass.adoc

@@ -6,7 +6,7 @@ fn main() {
     let out_dir = PathBuf::from(std::env::var("OUT_DIR").expect("OUT_DIR is required"));
     tonic_build::configure()
         .file_descriptor_set_path(out_dir.join("file_descriptor_set.bin"))
-        .compile(&["vendor/csi/csi.proto"], &["vendor/csi"])
+        .compile_protos(&["vendor/csi/csi.proto"], &["vendor/csi"])
         .unwrap();
     built::write_built_file().unwrap();
 }

rust/operator-binary/build.rs

@@ -34,6 +34,7 @@ use tracing::{info, info_span, warn};
 
 use crate::{
     backend::SecretBackendError,
+    crd::CertificateKeyGeneration,
     utils::{asn1time_to_offsetdatetime, Asn1TimeParseError, Unloggable},
 };
 
@@ -153,6 +154,9 @@ pub struct Config {
     /// Hence, this value _should_ be larger than the PKI's maximum certificate lifetime,
     /// and smaller than [`Self::ca_certificate_lifetime`].
     pub rotate_if_ca_expires_before: Option<Duration>,
+
+    /// Configuration how TLS private keys should be created.
+    pub key_generation: CertificateKeyGeneration,
 }
 
 /// A single certificate authority certificate.
@@ -188,7 +192,12 @@ impl CertificateAuthority {
         let not_before = now - Duration::from_minutes_unchecked(5);
         let not_after = now + config.ca_certificate_lifetime;
         let conf = Conf::new(ConfMethod::default()).unwrap();
-        let private_key = Rsa::generate(2048)
+
+        let private_key_length = match config.key_generation {
+            CertificateKeyGeneration::Rsa { length } => length,
+        };
+
+        let private_key = Rsa::generate(private_key_length)
             .and_then(PKey::try_from)
             .context(GenerateKeySnafu)?;
         let certificate = X509Builder::new()

rust/operator-binary/src/backend/tls/ca.rs

@@ -28,7 +28,7 @@ use stackable_operator::{
 use time::OffsetDateTime;
 
 use crate::{
-    crd,
+    crd::{self, CertificateKeyGeneration},
     format::{well_known, SecretData, WellKnownSecretData},
     utils::iterator_try_concat_bytes,
 };
@@ -132,12 +132,13 @@ impl SecretBackendError for Error {
 pub struct TlsGenerate {
     ca_manager: ca::Manager,
     max_cert_lifetime: Duration,
+    key_generation: CertificateKeyGeneration,
 }
 
 impl TlsGenerate {
     /// Check if a signing CA has already been instantiated in a specified Kubernetes secret - if
     /// one is found the key is loaded and used for signing certs.
-    /// If no current authority can be found, a new keypair and self signed certificate is created
+    /// If no current authority can be found, a new key pair and self signed certificate is created
     /// and stored for future use.
     /// This allows users to provide their own CA files, but also enables secret-operator to generate
     /// an independent self-signed CA.
@@ -147,6 +148,7 @@ impl TlsGenerate {
             secret: ca_secret,
             auto_generate: auto_generate_ca,
             ca_certificate_lifetime,
+            key_generation,
         }: &crd::AutoTlsCa,
         max_cert_lifetime: Duration,
     ) -> Result<Self> {
@@ -158,11 +160,13 @@ impl TlsGenerate {
                     manage_ca: *auto_generate_ca,
                     ca_certificate_lifetime: *ca_certificate_lifetime,
                     rotate_if_ca_expires_before: Some(*ca_certificate_lifetime / 2),
+                    key_generation: key_generation.clone(),
                 },
             )
             .await
             .context(LoadCaSnafu)?,
             max_cert_lifetime,
+            key_generation: key_generation.clone(),
         })
     }
 }
@@ -171,7 +175,7 @@ impl TlsGenerate {
 impl SecretBackend for TlsGenerate {
     type Error = Error;
 
-    /// Generate a keypair and sign it with the CA key.
+    /// Generate a key pair and sign it with the CA key.
     /// Then add the ca certificate and return these files for provisioning to the volume.
     async fn get_secret_data(
         &self,
@@ -233,7 +237,12 @@ impl SecretBackend for TlsGenerate {
         }
 
         let conf = Conf::new(ConfMethod::default()).unwrap();
-        let pod_key = Rsa::generate(2048)
+
+        let pod_key_length = match self.key_generation {
+            CertificateKeyGeneration::Rsa { length } => length,
+        };
+
+        let pod_key = Rsa::generate(pod_key_length)
             .and_then(PKey::try_from)
             .context(GenerateKeySnafu)?;
         let mut addresses = Vec::new();