feat(kms): add static single-key backend (#5222)

.vscode/launch.json

@@ -212,13 +212,17 @@
                 // "RUSTFS_KMS_DEFAULT_KEY_ID": "rustfs-master-key",
 
                 // 4. kms vault transit backend test key
-                "RUSTFS_KMS_ENABLE": "true",
-                "RUSTFS_KMS_BACKEND": "vault-transit",
-                "RUSTFS_KMS_VAULT_ADDRESS": "http://127.0.0.1:8200",
-                "RUSTFS_KMS_VAULT_TOKEN": "Dev Token",
-                "RUSTFS_KMS_VAULT_MOUNT_PATH": "transit",
-                "RUSTFS_KMS_DEFAULT_KEY_ID": "rustfs-master-key",
+                // "RUSTFS_KMS_ENABLE": "true",
+                // "RUSTFS_KMS_BACKEND": "vault-transit",
+                // "RUSTFS_KMS_VAULT_ADDRESS": "http://127.0.0.1:8200",
+                // "RUSTFS_KMS_VAULT_TOKEN": "Dev Token",
+                // "RUSTFS_KMS_VAULT_MOUNT_PATH": "transit",
+                // "RUSTFS_KMS_DEFAULT_KEY_ID": "rustfs-master-key",
                 
+                // 5、kms static backend test key
+                "RUSTFS_KMS_ENABLE": "true",
+                "RUSTFS_KMS_BACKEND": "static",
+                "RUSTFS_KMS_STATIC_SECRET_KEY": "rustfs-master-key:2dfNXGHlsEflGVCxb+5DIdGEl1sIvtwX+QfmYasi5QM="
             },
             "sourceLanguages": [
                 "rust"

crates/kms/src/api_types.rs

@@ -16,7 +16,8 @@
 
 use crate::config::{
     BackendConfig, CacheConfig, DEFAULT_VAULT_TRANSIT_METADATA_KEY_PREFIX, DEFAULT_VAULT_TRANSIT_METADATA_KV_MOUNT, KmsBackend,
-    KmsConfig, LocalConfig, TlsConfig, VaultAuthMethod, VaultConfig, VaultTransitConfig, redacted_secret_option,
+    KmsConfig, LocalConfig, StaticConfig, TlsConfig, VaultAuthMethod, VaultConfig, VaultTransitConfig, redacted_secret,
+    redacted_secret_option,
 };
 use crate::service_manager::KmsServiceStatus;
 use crate::types::{KeyMetadata, KeyUsage};
@@ -136,6 +137,46 @@ pub struct ConfigureVaultTransitKmsRequest {
     pub allow_insecure_dev_defaults: Option<bool>,
 }
 
+/// Request to configure KMS with Static single-key backend
+#[derive(Clone, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct ConfigureStaticKmsRequest {
+    /// Key identifier (name) for the single configured key
+    pub key_id: String,
+    /// Base64-encoded 32-byte AES-256 key material
+    pub secret_key: String,
+    /// Default master key ID for auto-encryption
+    pub default_key_id: Option<String>,
+    /// Operation timeout in seconds
+    pub timeout_seconds: Option<u64>,
+    /// Number of retry attempts
+    pub retry_attempts: Option<u32>,
+    /// Enable caching
+    pub enable_cache: Option<bool>,
+    /// Maximum number of keys to cache
+    pub max_cached_keys: Option<usize>,
+    /// Cache TTL in seconds
+    pub cache_ttl_seconds: Option<u64>,
+    /// Allow development-only insecure defaults
+    pub allow_insecure_dev_defaults: Option<bool>,
+}
+
+impl fmt::Debug for ConfigureStaticKmsRequest {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ConfigureStaticKmsRequest")
+            .field("key_id", &self.key_id)
+            .field("secret_key", &redacted_secret(&self.secret_key))
+            .field("default_key_id", &self.default_key_id)
+            .field("timeout_seconds", &self.timeout_seconds)
+            .field("retry_attempts", &self.retry_attempts)
+            .field("enable_cache", &self.enable_cache)
+            .field("max_cached_keys", &self.max_cached_keys)
+            .field("cache_ttl_seconds", &self.cache_ttl_seconds)
+            .field("allow_insecure_dev_defaults", &self.allow_insecure_dev_defaults)
+            .finish()
+    }
+}
+
 /// Generic KMS configuration request
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(tag = "backend_type")]
@@ -155,6 +196,9 @@ pub enum ConfigureKmsRequest {
     /// Configure with Vault Transit backend
     #[serde(rename = "VaultTransit", alias = "vault-transit", alias = "vault_transit")]
     VaultTransit(ConfigureVaultTransitKmsRequest),
+    /// Configure with Static single-key backend
+    #[serde(rename = "Static", alias = "static")]
+    Static(ConfigureStaticKmsRequest),
 }
 
 /// KMS configuration response
@@ -316,6 +360,11 @@ pub enum BackendSummary {
         /// Skip TLS verification
         skip_tls_verify: bool,
     },
+    /// Static single-key backend summary
+    Static {
+        /// Configured key identifier
+        key_id: String,
+    },
 }
 
 impl From<&KmsConfig> for KmsConfigSummary {
@@ -360,6 +409,9 @@ impl From<&KmsConfig> for KmsConfigSummary {
                 mount_path: vault_config.mount_path.clone(),
                 skip_tls_verify: vault_config.tls.as_ref().is_some_and(|tls| tls.skip_verify),
             },
+            BackendConfig::Static(static_config) => BackendSummary::Static {
+                key_id: static_config.key_id.clone(),
+            },
         };
 
         Self {
@@ -474,6 +526,29 @@ impl ConfigureVaultTransitKmsRequest {
     }
 }
 
+impl ConfigureStaticKmsRequest {
+    /// Convert to KmsConfig
+    pub fn to_kms_config(&self) -> KmsConfig {
+        KmsConfig {
+            backend: KmsBackend::Static,
+            default_key_id: self.default_key_id.clone(),
+            backend_config: BackendConfig::Static(StaticConfig {
+                key_id: self.key_id.clone(),
+                secret_key: self.secret_key.clone(),
+            }),
+            allow_insecure_dev_defaults: self.allow_insecure_dev_defaults.unwrap_or(false),
+            timeout: Duration::from_secs(self.timeout_seconds.unwrap_or(30)),
+            retry_attempts: self.retry_attempts.unwrap_or(3),
+            enable_cache: self.enable_cache.unwrap_or(true),
+            cache_config: CacheConfig {
+                max_keys: self.max_cached_keys.unwrap_or(1000),
+                ttl: Duration::from_secs(self.cache_ttl_seconds.unwrap_or(3600)),
+                enable_metrics: true,
+            },
+        }
+    }
+}
+
 impl ConfigureKmsRequest {
     /// Convert to KmsConfig
     pub fn to_kms_config(&self) -> KmsConfig {
@@ -481,6 +556,7 @@ impl ConfigureKmsRequest {
             ConfigureKmsRequest::Local(req) => req.to_kms_config(),
             ConfigureKmsRequest::VaultKv2(req) => req.to_kms_config(),
             ConfigureKmsRequest::VaultTransit(req) => req.to_kms_config(),
+            ConfigureKmsRequest::Static(req) => req.to_kms_config(),
         }
     }
 }

crates/kms/src/backends/local.rs

@@ -687,7 +687,9 @@ impl LocalKmsBackend {
 
         let local_config = match &config.backend_config {
             crate::config::BackendConfig::Local(local_config) => local_config.clone(),
-            crate::config::BackendConfig::VaultKv2(_) | crate::config::BackendConfig::VaultTransit(_) => {
+            crate::config::BackendConfig::VaultKv2(_)
+            | crate::config::BackendConfig::VaultTransit(_)
+            | crate::config::BackendConfig::Static(_) => {
                 return Err(KmsError::configuration_error("Expected Local backend configuration"));
             }
         };

crates/kms/src/backends/mod.rs

@@ -20,6 +20,7 @@ use async_trait::async_trait;
 use std::collections::HashMap;
 
 pub mod local;
+pub mod static_kms;
 pub mod vault;
 pub mod vault_transit;
 

crates/kms/src/backends/static_kms.rs

@@ -0,0 +1,655 @@
+// Copyright 2024 RustFS Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Static single-key KMS backend implementation
+//!
+//! This backend holds one pre-configured AES-256 key and uses it directly
+//! to encrypt/decrypt data encryption keys (DEKs) via AES-256-GCM.
+//!
+//! ## Ciphertext format
+//!
+//! encrypted_data(plaintext_len+16) || nonce (12 bytes)
+
+use crate::backends::{BackendInfo, KmsBackend, KmsClient};
+use crate::config::{BackendConfig, KmsConfig};
+use crate::error::{KmsError, Result};
+use crate::types::*;
+use aes_gcm::{
+    Aes256Gcm, Key, Nonce,
+    aead::{Aead, KeyInit},
+};
+use async_trait::async_trait;
+use jiff::Zoned;
+use rand::RngExt;
+use std::collections::HashMap;
+use tracing::debug;
+use zeroize::Zeroizing;
+
+/// AES-GCM nonce size in bytes, appended to each ciphertext.
+const NONCE_SIZE: usize = 12;
+/// AES-256 key size in bytes.
+const KEY_SIZE: usize = 32;
+
+/// Static single-key KMS backend.
+///
+/// Uses a pre-configured AES-256 key to derive data encryption keys. This is a
+/// read-only backend: it cannot create, delete, or rotate keys.
+pub struct StaticKmsBackend {
+    /// The configured key identifier (name).
+    key_id: String,
+    /// The raw 32-byte AES-256 key material (zeroed on drop).
+    key: Zeroizing<[u8; KEY_SIZE]>,
+}
+
+impl StaticKmsBackend {
+    /// Create a new static KMS backend from configuration.
+    pub async fn new(mut config: KmsConfig) -> Result<Self> {
+        let BackendConfig::Static(ref mut static_config) = config.backend_config else {
+            return Err(KmsError::configuration_error("Static KMS backend requires StaticConfig"));
+        };
+
+        let key = static_config.decode_key()?;
+
+        // Zeroize the base64-encoded secret key in the config after extracting the raw key.
+        use zeroize::Zeroize;
+        static_config.secret_key.zeroize();
+
+        debug!(
+            key_id = %static_config.key_id,
+            "Static KMS backend initialized"
+        );
+
+        Ok(Self {
+            key_id: static_config.key_id.clone(),
+            key: key.into(),
+        })
+    }
+
+    /// Build the key metadata for the single configured key.
+    fn key_metadata(&self) -> KeyMetadata {
+        KeyMetadata {
+            key_id: self.key_id.clone(),
+            key_state: KeyState::Enabled,
+            key_usage: KeyUsage::EncryptDecrypt,
+            description: Some("Static single-key KMS backend".to_string()),
+            creation_date: Zoned::now(),
+            deletion_date: None,
+            origin: "EXTERNAL".to_string(),
+            key_manager: "STATIC".to_string(),
+            tags: HashMap::new(),
+        }
+    }
+}
+
+#[async_trait]
+impl KmsClient for StaticKmsBackend {
+    async fn generate_data_key(&self, request: &GenerateKeyRequest, _context: Option<&OperationContext>) -> Result<DataKeyInfo> {
+        if request.master_key_id != self.key_id {
+            return Err(KmsError::key_not_found(&request.master_key_id));
+        }
+
+        // Generate 12-byte random nonce
+        let mut nonce_bytes = [0u8; NONCE_SIZE];
+        rand::rng().fill(&mut nonce_bytes[..]);
+
+        // Generate 32 random bytes as plaintext DEK
+        let mut plaintext = [0u8; KEY_SIZE];
+        rand::rng().fill(&mut plaintext[..]);
+
+        // Encrypt DEK with AES-256-GCM using the static key directly
+        let key = Key::<Aes256Gcm>::from(*self.key);
+        let cipher = Aes256Gcm::new(&key);
+        let nonce = Nonce::from(nonce_bytes);
+
+        let encrypted = cipher
+            .encrypt(&nonce, plaintext.as_ref())
+            .map_err(|e| KmsError::cryptographic_error("AES-256-GCM encrypt", e.to_string()))?;
+
+        // Ciphertext format: encrypted_dek || nonce
+        let mut ciphertext = encrypted;
+        ciphertext.extend_from_slice(&nonce_bytes);
+
+        Ok(DataKeyInfo::new(
+            self.key_id.clone(),
+            0, // version is always 0 for static KMS
+            Some(plaintext.to_vec()),
+            ciphertext,
+            "AES_256".to_string(),
+        ))
+    }
+
+    async fn encrypt(&self, request: &EncryptRequest, _context: Option<&OperationContext>) -> Result<EncryptResponse> {
+        if request.key_id != self.key_id {
+            return Err(KmsError::key_not_found(&request.key_id));
+        }
+
+        // Generate 12-byte random nonce
+        let mut nonce_bytes = [0u8; NONCE_SIZE];
+        rand::rng().fill(&mut nonce_bytes[..]);
+
+        let key = Key::<Aes256Gcm>::from(*self.key);
+        let cipher = Aes256Gcm::new(&key);
+        let nonce = Nonce::from(nonce_bytes);
+
+        let encrypted = cipher
+            .encrypt(&nonce, request.plaintext.as_ref())
+            .map_err(|e| KmsError::cryptographic_error("AES-256-GCM encrypt", e.to_string()))?;
+
+        // Ciphertext format: encrypted_data || nonce
+        let mut ciphertext = encrypted;
+        ciphertext.extend_from_slice(&nonce_bytes);
+
+        Ok(EncryptResponse {
+            ciphertext,
+            key_id: self.key_id.clone(),
+            key_version: 0,
+            algorithm: "AES-256-GCM".to_string(),
+        })
+    }
+
+    async fn decrypt(&self, request: &DecryptRequest, _context: Option<&OperationContext>) -> Result<Vec<u8>> {
+        if request.ciphertext.len() < NONCE_SIZE + 1 {
+            return Err(KmsError::cryptographic_error("decrypt", "Ciphertext too short for static KMS format"));
+        }
+
+        // Split ciphertext: encrypted_data || nonce(12)
+        let split_at = request.ciphertext.len() - NONCE_SIZE;
+        let encrypted = &request.ciphertext[..split_at];
+        let nonce_slice = &request.ciphertext[split_at..];
+
+        let key = Key::<Aes256Gcm>::from(*self.key);
+        let cipher = Aes256Gcm::new(&key);
+        let nonce = Nonce::try_from(nonce_slice).map_err(|_| KmsError::cryptographic_error("nonce", "invalid nonce length"))?;
+
+        let plaintext = cipher
+            .decrypt(&nonce, encrypted)
+            .map_err(|e| KmsError::cryptographic_error("AES-256-GCM decrypt", e.to_string()))?;
+
+        Ok(plaintext)
+    }
+
+    async fn create_key(&self, key_id: &str, _algorithm: &str, _context: Option<&OperationContext>) -> Result<MasterKeyInfo> {
+        if key_id == self.key_id {
+            return Err(KmsError::key_already_exists(key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot create new keys"))
+    }
+
+    async fn describe_key(&self, key_id: &str, _context: Option<&OperationContext>) -> Result<KeyInfo> {
+        if key_id != self.key_id {
+            return Err(KmsError::key_not_found(key_id));
+        }
+
+        let metadata = self.key_metadata();
+        Ok(KeyInfo {
+            key_id: metadata.key_id,
+            description: metadata.description,
+            algorithm: "AES_256".to_string(),
+            usage: metadata.key_usage,
+            status: KeyStatus::Active,
+            version: 1,
+            metadata: HashMap::new(),
+            tags: HashMap::new(),
+            created_at: metadata.creation_date,
+            rotated_at: None,
+            created_by: None,
+        })
+    }
+
+    async fn list_keys(&self, request: &ListKeysRequest, _context: Option<&OperationContext>) -> Result<ListKeysResponse> {
+        let key_info = KeyInfo {
+            key_id: self.key_id.clone(),
+            description: Some("Static single-key KMS backend".to_string()),
+            algorithm: "AES_256".to_string(),
+            usage: KeyUsage::EncryptDecrypt,
+            status: KeyStatus::Active,
+            version: 1,
+            metadata: HashMap::new(),
+            tags: HashMap::new(),
+            created_at: Zoned::now(),
+            rotated_at: None,
+            created_by: None,
+        };
+
+        // Apply prefix filter if provided
+        if let Some(ref marker) = request.marker
+            && self.key_id <= *marker
+        {
+            return Ok(ListKeysResponse {
+                keys: vec![],
+                next_marker: None,
+                truncated: false,
+            });
+        }
+
+        Ok(ListKeysResponse {
+            keys: vec![key_info],
+            next_marker: None,
+            truncated: false,
+        })
+    }
+
+    async fn enable_key(&self, key_id: &str, _context: Option<&OperationContext>) -> Result<()> {
+        if key_id != self.key_id {
+            return Err(KmsError::key_not_found(key_id));
+        }
+        // Static KMS key is always enabled
+        Ok(())
+    }
+
+    async fn disable_key(&self, key_id: &str, _context: Option<&OperationContext>) -> Result<()> {
+        if key_id != self.key_id {
+            return Err(KmsError::key_not_found(key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot disable keys"))
+    }
+
+    async fn schedule_key_deletion(
+        &self,
+        key_id: &str,
+        _pending_window_days: u32,
+        _context: Option<&OperationContext>,
+    ) -> Result<()> {
+        if key_id != self.key_id {
+            return Err(KmsError::key_not_found(key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot schedule key deletion"))
+    }
+
+    async fn cancel_key_deletion(&self, key_id: &str, _context: Option<&OperationContext>) -> Result<()> {
+        if key_id != self.key_id {
+            return Err(KmsError::key_not_found(key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot cancel key deletion"))
+    }
+
+    async fn rotate_key(&self, key_id: &str, _context: Option<&OperationContext>) -> Result<MasterKeyInfo> {
+        if key_id != self.key_id {
+            return Err(KmsError::key_not_found(key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot rotate keys"))
+    }
+
+    async fn health_check(&self) -> Result<()> {
+        // Static KMS is always healthy if it was successfully initialized
+        Ok(())
+    }
+
+    fn backend_info(&self) -> BackendInfo {
+        BackendInfo::new("static".to_string(), env!("CARGO_PKG_VERSION").to_string(), "local".to_string(), true)
+            .with_metadata("key_id".to_string(), self.key_id.clone())
+    }
+}
+
+#[async_trait]
+impl KmsBackend for StaticKmsBackend {
+    async fn create_key(&self, request: CreateKeyRequest) -> Result<CreateKeyResponse> {
+        let key_name = request.key_name.as_deref().unwrap_or("");
+        if key_name == self.key_id {
+            return Err(KmsError::key_already_exists(&self.key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot create new keys"))
+    }
+
+    async fn encrypt(&self, request: EncryptRequest) -> Result<EncryptResponse> {
+        <Self as KmsClient>::encrypt(self, &request, None).await
+    }
+
+    async fn decrypt(&self, request: DecryptRequest) -> Result<DecryptResponse> {
+        let key_id = self.key_id.clone();
+        let plaintext = <Self as KmsClient>::decrypt(self, &request, None).await?;
+        Ok(DecryptResponse {
+            plaintext,
+            key_id,
+            encryption_algorithm: Some("AES-256-GCM".to_string()),
+        })
+    }
+
+    async fn generate_data_key(&self, request: GenerateDataKeyRequest) -> Result<GenerateDataKeyResponse> {
+        let gen_req = GenerateKeyRequest::new(request.key_id.clone(), request.key_spec.as_str().to_string());
+        let data_key = <Self as KmsClient>::generate_data_key(self, &gen_req, None).await?;
+
+        let plaintext_key = data_key
+            .plaintext
+            .clone()
+            .ok_or_else(|| KmsError::internal_error("Generated data key is missing plaintext"))?;
+
+        Ok(GenerateDataKeyResponse {
+            key_id: data_key.key_id.clone(),
+            plaintext_key,
+            ciphertext_blob: data_key.ciphertext.clone(),
+        })
+    }
+
+    async fn describe_key(&self, request: DescribeKeyRequest) -> Result<DescribeKeyResponse> {
+        let key_info = <Self as KmsClient>::describe_key(self, &request.key_id, None).await?;
+        let key_metadata = KeyMetadata {
+            key_id: key_info.key_id.clone(),
+            key_state: if key_info.status == KeyStatus::Active {
+                KeyState::Enabled
+            } else {
+                KeyState::Disabled
+            },
+            key_usage: key_info.usage,
+            description: key_info.description,
+            creation_date: key_info.created_at,
+            deletion_date: None,
+            origin: "EXTERNAL".to_string(),
+            key_manager: "STATIC".to_string(),
+            tags: key_info.tags,
+        };
+        Ok(DescribeKeyResponse { key_metadata })
+    }
+
+    async fn list_keys(&self, request: ListKeysRequest) -> Result<ListKeysResponse> {
+        <Self as KmsClient>::list_keys(self, &request, None).await
+    }
+
+    async fn delete_key(&self, request: DeleteKeyRequest) -> Result<DeleteKeyResponse> {
+        if request.key_id != self.key_id {
+            return Err(KmsError::key_not_found(&request.key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot delete keys"))
+    }
+
+    async fn cancel_key_deletion(&self, request: CancelKeyDeletionRequest) -> Result<CancelKeyDeletionResponse> {
+        if request.key_id != self.key_id {
+            return Err(KmsError::key_not_found(&request.key_id));
+        }
+        Err(KmsError::invalid_operation("Static KMS is read-only: cannot cancel key deletion"))
+    }
+
+    async fn health_check(&self) -> Result<bool> {
+        Ok(true)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::backends::KmsClient;
+    use crate::config::{BackendConfig, KmsBackend, StaticConfig};
+    use base64::Engine as _;
+    use base64::engine::general_purpose::STANDARD as BASE64;
+
+    /// Generate a random 32-byte key and return (key_id, raw_key).
+    fn random_static_key(key_id: &str) -> (String, [u8; 32]) {
+        let mut key = [0u8; 32];
+        rand::rng().fill(&mut key[..]);
+        (key_id.to_string(), key)
+    }
+
+    fn static_config(key_id: &str, raw_key: &[u8; 32]) -> StaticConfig {
+        StaticConfig {
+            key_id: key_id.to_string(),
+            secret_key: BASE64.encode(raw_key),
+        }
+    }
+
+    fn kms_config(config: StaticConfig) -> KmsConfig {
+        KmsConfig {
+            backend: KmsBackend::Static,
+            default_key_id: Some(config.key_id.clone()),
+            backend_config: BackendConfig::Static(config),
+            ..Default::default()
+        }
+    }
+
+    async fn create_test_backend() -> (StaticKmsBackend, String, [u8; 32]) {
+        let (key_id, key) = random_static_key("test-static-key");
+        let config = static_config(&key_id, &key);
+        let backend = StaticKmsBackend::new(kms_config(config))
+            .await
+            .expect("Failed to create backend");
+        (backend, key_id, key)
+    }
+
+    #[tokio::test]
+    async fn test_generate_and_decrypt_data_key() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        // Generate data key
+        let request = GenerateKeyRequest::new(key_id.clone(), "AES_256".to_string())
+            .with_context("bucket".to_string(), "test-bucket".to_string());
+        let data_key = KmsClient::generate_data_key(&backend, &request, None)
+            .await
+            .expect("Failed to generate data key");
+
+        assert_eq!(data_key.key_id, key_id);
+        assert_eq!(data_key.version, 0);
+        assert!(data_key.plaintext.is_some());
+        assert_eq!(data_key.plaintext.as_ref().expect("plaintext should be set").len(), 32);
+        // Ciphertext should be: encrypted(32) + tag(16) + nonce(12)
+        assert_eq!(data_key.ciphertext.len(), 32 + 16 + NONCE_SIZE);
+
+        // Decrypt the data key
+        let decrypt_request =
+            DecryptRequest::new(data_key.ciphertext.clone()).with_context("bucket".to_string(), "test-bucket".to_string());
+        let decrypted = KmsClient::decrypt(&backend, &decrypt_request, None)
+            .await
+            .expect("Failed to decrypt");
+
+        assert_eq!(decrypted.as_slice(), data_key.plaintext.as_deref().expect("plaintext should exist"));
+    }
+
+    #[tokio::test]
+    async fn test_generate_data_key_wrong_key_id() {
+        let (backend, _key_id, _key) = create_test_backend().await;
+
+        let request = GenerateKeyRequest::new("wrong-key-id".to_string(), "AES_256".to_string());
+        let result = KmsClient::generate_data_key(&backend, &request, None).await;
+        assert!(result.is_err());
+        assert!(result.expect_err("should be Err").to_string().contains("wrong-key-id"));
+    }
+
+    #[tokio::test]
+    async fn test_decrypt_invalid_ciphertext() {
+        let (backend, _key_id, _key) = create_test_backend().await;
+
+        // Ciphertext too short
+        let short = vec![0u8; 10];
+        let request = DecryptRequest::new(short);
+        let result = KmsClient::decrypt(&backend, &request, None).await;
+        assert!(result.is_err());
+    }
+
+    #[tokio::test]
+    async fn test_decrypt_tampered_ciphertext() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        // Generate a valid ciphertext first
+        let gen_request = GenerateKeyRequest::new(key_id, "AES_256".to_string());
+        let data_key = KmsClient::generate_data_key(&backend, &gen_request, None)
+            .await
+            .expect("generate");
+
+        // Tamper with the ciphertext (flip a bit in the encrypted portion)
+        let mut tampered = data_key.ciphertext.clone();
+        if !tampered.is_empty() {
+            tampered[0] ^= 0x01;
+        }
+
+        let request = DecryptRequest::new(tampered);
+        let result = KmsClient::decrypt(&backend, &request, None).await;
+        assert!(result.is_err());
+    }
+
+    #[tokio::test]
+    async fn test_create_key_returns_exists_for_configured_key() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        // Creating the pre-configured key should return KeyAlreadyExists
+        let result = KmsClient::create_key(&backend, &key_id, "AES_256", None).await;
+        assert!(result.is_err());
+        assert!(result.expect_err("should be Err").to_string().contains("already exists"));
+    }
+
+    #[tokio::test]
+    async fn test_create_key_returns_error_for_other_keys() {
+        let (backend, _key_id, _key) = create_test_backend().await;
+
+        // Creating any other key should return invalid operation (read-only)
+        let result = KmsClient::create_key(&backend, "other-key", "AES_256", None).await;
+        assert!(result.is_err());
+        let err_msg = result.expect_err("should be Err").to_string();
+        assert!(err_msg.contains("read-only") || err_msg.contains("cannot create"));
+    }
+
+    #[tokio::test]
+    async fn test_describe_key() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let key_info = KmsClient::describe_key(&backend, &key_id, None)
+            .await
+            .expect("describe_key should succeed");
+        assert_eq!(key_info.key_id, key_id);
+        assert_eq!(key_info.status, KeyStatus::Active);
+        assert_eq!(key_info.algorithm, "AES_256");
+
+        // Wrong key ID
+        let result = KmsClient::describe_key(&backend, "nonexistent", None).await;
+        assert!(result.is_err());
+    }
+
+    #[tokio::test]
+    async fn test_list_keys() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let response = KmsClient::list_keys(&backend, &ListKeysRequest::default(), None)
+            .await
+            .expect("list_keys should succeed");
+        assert_eq!(response.keys.len(), 1);
+        assert_eq!(response.keys[0].key_id, key_id);
+        assert!(!response.truncated);
+    }
+
+    #[tokio::test]
+    async fn test_disable_key_returns_error() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let result = KmsClient::disable_key(&backend, &key_id, None).await;
+        assert!(result.is_err());
+        assert!(result.expect_err("should be Err").to_string().contains("read-only"));
+    }
+
+    #[tokio::test]
+    async fn test_enable_key_is_noop() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        // Enable should succeed (no-op for static KMS)
+        KmsClient::enable_key(&backend, &key_id, None)
+            .await
+            .expect("enable_key should be no-op");
+
+        // Wrong key should still fail
+        let result = KmsClient::enable_key(&backend, "wrong", None).await;
+        assert!(result.is_err());
+    }
+
+    #[tokio::test]
+    async fn test_delete_key_returns_error() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let result = KmsClient::schedule_key_deletion(&backend, &key_id, 7, None).await;
+        assert!(result.is_err());
+        assert!(result.expect_err("should be Err").to_string().contains("read-only"));
+    }
+
+    #[tokio::test]
+    async fn test_rotate_key_returns_error() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let result = KmsClient::rotate_key(&backend, &key_id, None).await;
+        assert!(result.is_err());
+    }
+
+    #[tokio::test]
+    async fn test_health_check() {
+        let (backend, _key_id, _key) = create_test_backend().await;
+
+        KmsClient::health_check(&backend).await.expect("health_check should succeed");
+    }
+
+    #[tokio::test]
+    async fn test_backend_info() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let info = KmsClient::backend_info(&backend);
+        assert_eq!(info.backend_type, "static");
+        assert_eq!(info.endpoint, "local");
+        assert!(info.healthy);
+        assert_eq!(info.metadata.get("key_id"), Some(&key_id));
+    }
+
+    #[tokio::test]
+    async fn test_encrypt_decrypt_direct() {
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        let plaintext = b"Hello, static KMS world!";
+        let enc_request = EncryptRequest::new(key_id.clone(), plaintext.to_vec());
+        let enc_response = KmsClient::encrypt(&backend, &enc_request, None)
+            .await
+            .expect("encrypt should succeed");
+
+        assert_eq!(enc_response.key_id, key_id);
+        assert!(!enc_response.ciphertext.is_empty());
+
+        let dec_request = DecryptRequest::new(enc_response.ciphertext);
+        let decrypted = KmsClient::decrypt(&backend, &dec_request, None)
+            .await
+            .expect("decrypt should succeed");
+
+        assert_eq!(decrypted, plaintext);
+    }
+
+    #[tokio::test]
+    async fn test_kms_backend_trait_methods() {
+        use crate::backends::KmsBackend;
+
+        let (backend, key_id, _key) = create_test_backend().await;
+
+        // Test KmsBackend::generate_data_key
+        let gen_req = GenerateDataKeyRequest::new(key_id.clone(), KeySpec::Aes256);
+        let gen_resp = KmsBackend::generate_data_key(&backend, gen_req)
+            .await
+            .expect("KmsBackend::generate_data_key should succeed");
+        assert_eq!(gen_resp.key_id, key_id);
+        assert_eq!(gen_resp.plaintext_key.len(), 32);
+        assert!(!gen_resp.ciphertext_blob.is_empty());
+
+        // Test KmsBackend::decrypt via the generated ciphertext
+        let dec_req = DecryptRequest::new(gen_resp.ciphertext_blob);
+        let dec_resp = KmsBackend::decrypt(&backend, dec_req)
+            .await
+            .expect("KmsBackend::decrypt should succeed");
+        assert_eq!(dec_resp.plaintext, gen_resp.plaintext_key);
+
+        // Test KmsBackend::describe_key
+        let desc_req = DescribeKeyRequest { key_id: key_id.clone() };
+        let desc_resp = KmsBackend::describe_key(&backend, desc_req)
+            .await
+            .expect("describe_key should succeed");
+        assert_eq!(desc_resp.key_metadata.key_id, key_id);
+
+        // Test KmsBackend::create_key for the configured key (should return KeyAlreadyExists, same as KmsClient)
+        let create_req = CreateKeyRequest {
+            key_name: Some(key_id.clone()),
+            ..Default::default()
+        };
+        let create_err = KmsBackend::create_key(&backend, create_req)
+            .await
+            .expect_err("create_key for configured key should return KeyAlreadyExists");
+        assert!(create_err.to_string().contains("already exists"));
+    }
+}

crates/kms/src/backends/vault.rs

@@ -600,7 +600,9 @@ impl VaultKmsBackend {
 
         let vault_config = match &config.backend_config {
             crate::config::BackendConfig::VaultKv2(vault_config) => (**vault_config).clone(),
-            crate::config::BackendConfig::Local(_) | crate::config::BackendConfig::VaultTransit(_) => {
+            crate::config::BackendConfig::Local(_)
+            | crate::config::BackendConfig::VaultTransit(_)
+            | crate::config::BackendConfig::Static(_) => {
                 return Err(KmsError::configuration_error("Expected Vault KV2 backend configuration"));
             }
         };

crates/kms/src/backends/vault_transit.rs

@@ -602,7 +602,7 @@ impl VaultTransitKmsBackend {
                 metadata_key_prefix: vault_config.key_path_prefix.clone(),
                 tls: vault_config.tls.clone(),
             },
-            crate::config::BackendConfig::Local(_) => {
+            crate::config::BackendConfig::Local(_) | crate::config::BackendConfig::Static(_) => {
                 return Err(KmsError::configuration_error("Expected Vault Transit backend configuration"));
             }
         };

crates/kms/src/config.rs

@@ -27,6 +27,8 @@ pub const ENV_KMS_ALLOW_INSECURE_DEV_DEFAULTS: &str = "RUSTFS_KMS_ALLOW_INSECURE
 pub const ENV_KMS_VAULT_SKIP_TLS_VERIFY: &str = "RUSTFS_KMS_VAULT_SKIP_TLS_VERIFY";
 pub const ENV_KMS_VAULT_TRANSIT_METADATA_KV_MOUNT: &str = "RUSTFS_KMS_VAULT_TRANSIT_METADATA_KV_MOUNT";
 pub const ENV_KMS_VAULT_TRANSIT_METADATA_PREFIX: &str = "RUSTFS_KMS_VAULT_TRANSIT_METADATA_PREFIX";
+pub const ENV_KMS_STATIC_SECRET_KEY: &str = "RUSTFS_KMS_STATIC_SECRET_KEY";
+pub const ENV_KMS_STATIC_SECRET_KEY_FILE: &str = "RUSTFS_KMS_STATIC_SECRET_KEY_FILE";
 pub const DEFAULT_VAULT_TRANSIT_METADATA_KV_MOUNT: &str = "secret";
 pub const DEFAULT_VAULT_TRANSIT_METADATA_KEY_PREFIX: &str = "rustfs/kms/transit-metadata";
 
@@ -73,6 +75,7 @@ pub const KMS_CONFIG_REDACTION_RULES: &[RedactionRule] = &[
         RedactionLevel::Secret,
         "admin configure request vault transit approle secret",
     ),
+    RedactionRule::new("kms.static.secret_key", RedactionLevel::Secret, "static backend secret key material"),
 ];
 
 pub(crate) const REDACTED_SECRET: &str = "***redacted***";
@@ -97,6 +100,9 @@ pub enum KmsBackend {
     /// Local file-based backend for development and testing only
     #[default]
     Local,
+    /// Static single-key backend that derives DEKs from a pre-configured key
+    #[serde(rename = "Static")]
+    Static,
 }
 
 /// Main KMS configuration
@@ -146,6 +152,8 @@ pub enum BackendConfig {
     VaultKv2(Box<VaultConfig>),
     /// Vault Transit backend configuration
     VaultTransit(Box<VaultTransitConfig>),
+    /// Static single-key backend configuration
+    Static(StaticConfig),
 }
 
 impl Default for BackendConfig {
@@ -160,6 +168,7 @@ impl fmt::Debug for BackendConfig {
             Self::Local(config) => f.debug_tuple("Local").field(config).finish(),
             Self::VaultKv2(config) => f.debug_tuple("VaultKv2").field(config).finish(),
             Self::VaultTransit(config) => f.debug_tuple("VaultTransit").field(config).finish(),
+            Self::Static(config) => f.debug_tuple("Static").field(config).finish(),
         }
     }
 }
@@ -196,6 +205,47 @@ impl Default for LocalConfig {
     }
 }
 
+/// Static single-key KMS backend configuration
+///
+/// Uses a pre-configured AES-256 key to derive data encryption keys via
+/// HMAC-SHA256 + AES-256-GCM, matching the MinIO builtin/static KMS wire format.
+#[derive(Clone, Default, Serialize, Deserialize)]
+pub struct StaticConfig {
+    /// Key identifier (name) for the single configured key
+    pub key_id: String,
+    /// Base64-encoded 32-byte AES-256 key material (zeroed on drop)
+    pub secret_key: String,
+}
+
+impl fmt::Debug for StaticConfig {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("StaticConfig")
+            .field("key_id", &self.key_id)
+            .field("secret_key", &redacted_secret(&self.secret_key))
+            .finish()
+    }
+}
+
+impl StaticConfig {
+    /// Decode the base64-encoded secret key into raw bytes.
+    /// Returns an error if the key is not valid base64 or is not exactly 32 bytes.
+    pub fn decode_key(&self) -> Result<[u8; 32]> {
+        use base64::Engine as _;
+        let bytes = base64::engine::general_purpose::STANDARD
+            .decode(&self.secret_key)
+            .map_err(|e| KmsError::configuration_error(format!("Static KMS secret key is not valid base64: {e}")))?;
+        if bytes.len() != 32 {
+            return Err(KmsError::configuration_error(format!(
+                "Static KMS secret key must be exactly 32 bytes after base64 decoding, got {} bytes",
+                bytes.len()
+            )));
+        }
+        let mut key = [0u8; 32];
+        key.copy_from_slice(&bytes);
+        Ok(key)
+    }
+}
+
 /// Vault KV v2 + Transit backend configuration (metadata in KV, key wrapping via Transit)
 #[derive(Clone, Serialize, Deserialize)]
 pub struct VaultConfig {
@@ -404,6 +454,23 @@ impl KmsConfig {
         }
     }
 
+    /// Create a new KMS configuration for static single-key backend
+    ///
+    /// # Arguments
+    /// * `key_id` - The key identifier (name) for the configured key
+    /// * `secret_key` - Base64-encoded 32-byte AES-256 key material
+    pub fn static_kms(key_id: String, secret_key: String) -> Self {
+        Self {
+            backend: KmsBackend::Static,
+            backend_config: BackendConfig::Static(StaticConfig {
+                key_id: key_id.clone(),
+                secret_key,
+            }),
+            default_key_id: Some(key_id),
+            ..Default::default()
+        }
+    }
+
     /// Get the local configuration if backend is Local
     pub fn local_config(&self) -> Option<&LocalConfig> {
         match &self.backend_config {
@@ -428,6 +495,14 @@ impl KmsConfig {
         }
     }
 
+    /// Get the static configuration if backend is Static
+    pub fn static_config(&self) -> Option<&StaticConfig> {
+        match &self.backend_config {
+            BackendConfig::Static(config) => Some(config),
+            _ => None,
+        }
+    }
+
     /// Set default key ID
     pub fn with_default_key(mut self, key_id: String) -> Self {
         self.default_key_id = Some(key_id);
@@ -544,6 +619,16 @@ impl KmsConfig {
                     tracing::warn!("Using HTTPS without custom TLS configuration - relying on system CA");
                 }
             }
+            BackendConfig::Static(config) => {
+                if config.key_id.is_empty() {
+                    return Err(KmsError::configuration_error("Static KMS key_id cannot be empty"));
+                }
+                if config.secret_key.is_empty() {
+                    return Err(KmsError::configuration_error("Static KMS secret_key cannot be empty"));
+                }
+                // Validate that the key can be decoded (right length, valid base64)
+                config.decode_key()?;
+            }
         }
 
         // Validate cache configuration
@@ -564,6 +649,7 @@ impl KmsConfig {
                 "local" => KmsBackend::Local,
                 "vault" | "vault-kv2" | "vault_kv2" => KmsBackend::VaultKv2,
                 "vault-transit" | "vault_transit" => KmsBackend::VaultTransit,
+                "static" => KmsBackend::Static,
                 _ => return Err(KmsError::configuration_error(format!("Unknown KMS backend: {backend_type}"))),
             };
         }
@@ -641,6 +727,47 @@ impl KmsConfig {
                     tls: vault_tls_config(skip_tls_verify),
                 }));
             }
+            KmsBackend::Static => {
+                // Read from file first, then fall back to direct env var
+                let secret_str = if let Some(file_path) = get_env_opt_str(ENV_KMS_STATIC_SECRET_KEY_FILE) {
+                    std::fs::read_to_string(&file_path).map_err(|e| {
+                        KmsError::configuration_error(format!("Failed to read static KMS secret key file {file_path}: {e}"))
+                    })?
+                } else {
+                    get_env_str(ENV_KMS_STATIC_SECRET_KEY, "")
+                };
+
+                let secret_str = secret_str.trim().to_string();
+                if secret_str.is_empty() {
+                    return Err(KmsError::configuration_error(format!(
+                        "Static KMS requires {ENV_KMS_STATIC_SECRET_KEY} or {ENV_KMS_STATIC_SECRET_KEY_FILE} to be set"
+                    )));
+                }
+
+                // Parse format: <key-id>:<base64-key>
+                let colon_pos = secret_str.find(':').ok_or_else(|| {
+                    KmsError::configuration_error("Static KMS secret key must be in format <key-name>:<base64-key>")
+                })?;
+                let key_id = secret_str[..colon_pos].to_string();
+                let secret_key = secret_str[colon_pos + 1..].to_string();
+
+                if key_id.is_empty() {
+                    return Err(KmsError::configuration_error(
+                        "Static KMS key name must not be empty in secret key string",
+                    ));
+                }
+                if secret_key.is_empty() {
+                    return Err(KmsError::configuration_error(
+                        "Static KMS base64 key must not be empty in secret key string",
+                    ));
+                }
+
+                config.backend_config = BackendConfig::Static(StaticConfig {
+                    key_id: key_id.clone(),
+                    secret_key,
+                });
+                config.default_key_id = Some(key_id);
+            }
         }
 
         config.validate()?;

crates/kms/src/lib.rs

@@ -78,9 +78,10 @@ pub mod types;
 
 // Re-export public API
 pub use api_types::{
-    CacheSummary, ConfigureKmsRequest, ConfigureKmsResponse, ConfigureLocalKmsRequest, ConfigureVaultKmsRequest,
-    ConfigureVaultTransitKmsRequest, KmsConfigSummary, KmsStatusResponse, StartKmsRequest, StartKmsResponse, StopKmsResponse,
-    TagKeyRequest, TagKeyResponse, UntagKeyRequest, UntagKeyResponse, UpdateKeyDescriptionRequest, UpdateKeyDescriptionResponse,
+    CacheSummary, ConfigureKmsRequest, ConfigureKmsResponse, ConfigureLocalKmsRequest, ConfigureStaticKmsRequest,
+    ConfigureVaultKmsRequest, ConfigureVaultTransitKmsRequest, KmsConfigSummary, KmsStatusResponse, StartKmsRequest,
+    StartKmsResponse, StopKmsResponse, TagKeyRequest, TagKeyResponse, UntagKeyRequest, UntagKeyResponse,
+    UpdateKeyDescriptionRequest, UpdateKeyDescriptionResponse,
 };
 pub use config::*;
 pub use encryption::is_data_key_envelope;

crates/kms/src/service_manager.rs

@@ -384,6 +384,11 @@ impl KmsServiceManager {
                 let backend = crate::backends::vault_transit::VaultTransitKmsBackend::new(config.clone()).await?;
                 Arc::new(backend) as Arc<dyn KmsBackend>
             }
+            BackendConfig::Static(_) => {
+                info!("Creating Static KMS backend for version {}", version);
+                let backend = crate::backends::static_kms::StaticKmsBackend::new(config.clone()).await?;
+                Arc::new(backend) as Arc<dyn KmsBackend>
+            }
         };
 
         // Create KMS manager

rustfs/src/admin/handlers/kms_dynamic.rs

@@ -65,6 +65,7 @@ fn existing_vault_auth(config: &KmsConfig) -> Option<rustfs_kms::config::VaultAu
         rustfs_kms::config::BackendConfig::VaultKv2(vault) => Some(vault.auth_method.clone()),
         rustfs_kms::config::BackendConfig::VaultTransit(vault) => Some(vault.auth_method.clone()),
         rustfs_kms::config::BackendConfig::Local(_) => None,
+        rustfs_kms::config::BackendConfig::Static(_) => None,
     }
 }
 
@@ -84,6 +85,7 @@ fn normalize_configure_request_auth(
         ConfigureKmsRequest::VaultKv2(req) => token_is_blank(&req.auth_method),
         ConfigureKmsRequest::VaultTransit(req) => token_is_blank(&req.auth_method),
         ConfigureKmsRequest::Local(_) => false,
+        ConfigureKmsRequest::Static(_) => false,
     };
 
     if !needs_existing_auth {
@@ -98,6 +100,7 @@ fn normalize_configure_request_auth(
         ConfigureKmsRequest::VaultKv2(req) => req.auth_method = existing_auth,
         ConfigureKmsRequest::VaultTransit(req) => req.auth_method = existing_auth,
         ConfigureKmsRequest::Local(_) => {}
+        ConfigureKmsRequest::Static(_) => {}
     }
 
     Ok(())

rustfs/src/admin/handlers/kms_management.rs

@@ -49,6 +49,7 @@ fn backend_name(backend: &KmsBackend) -> &'static str {
         KmsBackend::Local => "local",
         KmsBackend::VaultKv2 => "vault-kv2",
         KmsBackend::VaultTransit => "vault-transit",
+        KmsBackend::Static => "static",
     }
 }
 

rustfs/src/init.rs

@@ -283,7 +283,7 @@ fn build_local_kms_config(cfg: &config::Config) -> std::io::Result<rustfs_kms::c
         .as_ref()
         .ok_or_else(|| Error::other("KMS key directory is required for local backend"))?;
 
-    Ok(rustfs_kms::config::KmsConfig {
+    let kms_config = rustfs_kms::config::KmsConfig {
         backend: rustfs_kms::config::KmsBackend::Local,
         backend_config: rustfs_kms::config::BackendConfig::Local(rustfs_kms::config::LocalConfig {
             key_dir: std::path::PathBuf::from(key_dir),
@@ -296,7 +296,11 @@ fn build_local_kms_config(cfg: &config::Config) -> std::io::Result<rustfs_kms::c
         retry_attempts: 3,
         enable_cache: true,
         cache_config: rustfs_kms::config::CacheConfig::default(),
-    })
+    };
+    kms_config
+        .validate()
+        .map_err(|e| Error::other(format!("Local KMS configuration validation failed: {e}")))?;
+    Ok(kms_config)
 }
 
 /// Build KMS configuration for Vault backend
@@ -310,7 +314,7 @@ fn build_vault_kms_config(cfg: &config::Config) -> std::io::Result<rustfs_kms::c
         .as_ref()
         .ok_or_else(|| Error::other("Vault token is required for vault backend"))?;
 
-    Ok(rustfs_kms::config::KmsConfig {
+    let kms_config = rustfs_kms::config::KmsConfig {
         backend: rustfs_kms::config::KmsBackend::VaultKv2,
         backend_config: rustfs_kms::config::BackendConfig::VaultKv2(Box::new(rustfs_kms::config::VaultConfig {
             address: vault_address.clone(),
@@ -329,7 +333,11 @@ fn build_vault_kms_config(cfg: &config::Config) -> std::io::Result<rustfs_kms::c
         retry_attempts: 3,
         enable_cache: true,
         cache_config: rustfs_kms::config::CacheConfig::default(),
-    })
+    };
+    kms_config
+        .validate()
+        .map_err(|e| Error::other(format!("Vault KMS configuration validation failed: {e}")))?;
+    Ok(kms_config)
 }
 
 /// Build KMS configuration for Vault Transit backend
@@ -343,7 +351,7 @@ fn build_vault_transit_kms_config(cfg: &config::Config) -> std::io::Result<rustf
         .as_ref()
         .ok_or_else(|| Error::other("Vault token is required for vault-transit backend"))?;
 
-    Ok(rustfs_kms::config::KmsConfig {
+    let kms_config = rustfs_kms::config::KmsConfig {
         backend: rustfs_kms::config::KmsBackend::VaultTransit,
         backend_config: rustfs_kms::config::BackendConfig::VaultTransit(Box::new(rustfs_kms::config::VaultTransitConfig {
             address: vault_address.clone(),
@@ -360,7 +368,62 @@ fn build_vault_transit_kms_config(cfg: &config::Config) -> std::io::Result<rustf
         retry_attempts: 3,
         enable_cache: true,
         cache_config: rustfs_kms::config::CacheConfig::default(),
-    })
+    };
+    kms_config
+        .validate()
+        .map_err(|e| Error::other(format!("Vault Transit KMS configuration validation failed: {e}")))?;
+    Ok(kms_config)
+}
+
+/// Build KMS configuration for static single-key backend
+fn build_static_kms_config(cfg: &config::Config) -> std::io::Result<rustfs_kms::config::KmsConfig> {
+    use rustfs_kms::config::{ENV_KMS_STATIC_SECRET_KEY, ENV_KMS_STATIC_SECRET_KEY_FILE, StaticConfig};
+
+    // Read secret from file first, then fall back to env var
+    let secret_str = if let Some(file_path) = rustfs_utils::get_env_opt_str(ENV_KMS_STATIC_SECRET_KEY_FILE) {
+        std::fs::read_to_string(&file_path)
+            .map_err(|e| Error::other(format!("Failed to read static KMS secret key file {file_path}: {e}")))?
+    } else {
+        rustfs_utils::get_env_str(ENV_KMS_STATIC_SECRET_KEY, "")
+    };
+
+    let secret_str = secret_str.trim();
+    if secret_str.is_empty() {
+        return Err(Error::other(format!(
+            "Static KMS requires {ENV_KMS_STATIC_SECRET_KEY} or {ENV_KMS_STATIC_SECRET_KEY_FILE} to be set"
+        )));
+    }
+
+    let colon_pos = secret_str.find(':').ok_or_else(|| {
+        Error::other(format!(
+            "Static KMS secret key must be in format <key-name>:<base64-key>, got: {secret_str}"
+        ))
+    })?;
+    let key_id = secret_str[..colon_pos].to_string();
+    let secret_key = secret_str[colon_pos + 1..].to_string();
+
+    if key_id.is_empty() || secret_key.is_empty() {
+        return Err(Error::other("Static KMS secret key must be in format <key-name>:<base64-key>"));
+    }
+
+    // Base64 decoding and 32-byte key length are validated by KmsConfig::validate() below
+    let static_config = StaticConfig {
+        key_id: key_id.clone(),
+        secret_key,
+    };
+
+    let kms_config = rustfs_kms::config::KmsConfig {
+        backend: rustfs_kms::config::KmsBackend::Static,
+        default_key_id: cfg.kms_default_key_id.clone().or(Some(key_id)),
+        backend_config: rustfs_kms::config::BackendConfig::Static(static_config),
+        allow_insecure_dev_defaults: cfg.kms_allow_insecure_dev_defaults,
+        ..Default::default()
+    };
+
+    kms_config
+        .validate()
+        .map_err(|e| Error::other(format!("Static KMS configuration validation failed: {e}")))?;
+    Ok(kms_config)
 }
 
 /// Configure and start KMS service
@@ -423,6 +486,7 @@ pub async fn init_kms_system(config: &config::Config) -> std::io::Result<()> {
             "local" => build_local_kms_config(config)?,
             "vault" | "vault-kv2" | "vault_kv2" => build_vault_kms_config(config)?,
             "vault-transit" | "vault_transit" => build_vault_transit_kms_config(config)?,
+            "static" => build_static_kms_config(config)?,
             _ => return Err(Error::other(format!("Unsupported KMS backend: {}", config.kms_backend))),
         };
 

rustfs/src/storage/sse.rs

@@ -1601,12 +1601,21 @@ async fn apply_managed_encryption_material(
         // Try to get default key from KMS service (if available)
         if let Some(service) = runtime_sources::current_encryption_service().await {
             kms_key_candidate = service.get_default_key_id().cloned();
+            tracing::debug!(
+                default_key_id = ?kms_key_candidate,
+                "SSE-S3: KMS service available, default_key_id from config"
+            );
+        } else {
+            tracing::debug!("SSE-S3: KMS encryption service not available");
         }
     }
 
     let kms_key_to_use = match (encryption_type, kms_key_candidate.clone()) {
         (SSEType::SseS3, Some(kms_key_id)) => kms_key_id,
-        (SSEType::SseS3, None) => "default".to_string(),
+        (SSEType::SseS3, None) => {
+            tracing::debug!("SSE-S3: no KMS key configured, falling back to \"default\" key ID");
+            "default".to_string()
+        }
         (SSEType::SseKms, Some(kms_key_id)) => kms_key_id,
         (SSEType::SseKms, None) => {
             return Err(ApiError::from(StorageError::other(
@@ -1635,7 +1644,7 @@ async fn apply_managed_encryption_material(
     Ok(EncryptionMaterial {
         sse_type: encryption_type,
         server_side_encryption,
-        kms_key_id: matches!(encryption_type, SSEType::SseKms).then_some(kms_key_to_use),
+        kms_key_id: Some(kms_key_to_use),
         algorithm,
         key_bytes,
         base_nonce,
@@ -3523,7 +3532,7 @@ mod tests {
                 let material = material.expect("managed sse-s3 encryption should return material");
                 let metadata = encryption_material_to_metadata(&material).expect("managed SSE-S3 metadata should serialize");
 
-                assert_eq!(material.kms_key_id, None);
+                assert_eq!(material.kms_key_id.as_deref(), Some("default"));
                 assert_eq!(metadata.get("x-amz-server-side-encryption").map(String::as_str), Some("AES256"));
                 assert!(!metadata.contains_key("x-amz-server-side-encryption-aws-kms-key-id"));
                 assert_eq!(metadata.get(INTERNAL_ENCRYPTION_KEY_ID_HEADER).map(String::as_str), Some("default"));