feat(core): DEK 缓存 + 密钥轮换管理端点

- erp-core/crypto/key_manager: DashMap LRU DEK 缓存 (TTL 5min, 100条)
- DekManager: get_or_create_dek, generate_new_dek, invalidate
- PiiCrypto 集成 DekManager
- POST /api/v1/admin/tenants/:id/rotate-key: 生成新 DEK + 缓存失效
- 权限: tenant.manage (仅超级管理员)

crates/erp-core/src/crypto/key_manager.rs

@@ -0,0 +1,120 @@
+use std::sync::Arc;
+use std::time::Instant;
+
+use dashmap::DashMap;
+use uuid::Uuid;
+
+use crate::error::{AppError, AppResult};
+
+use super::engine;
+
+/// DEK 缓存条目
+#[derive(Clone)]
+struct CachedDek {
+    dek: [u8; 32],
+    version: u32,
+    loaded_at: Instant,
+}
+
+/// DEK 缓存管理 — 每租户独立 DEK，LRU + TTL
+#[derive(Clone)]
+pub struct DekManager {
+    cache: DashMap<Uuid, CachedDek>,
+    ttl_secs: u64,
+    max_entries: usize,
+}
+
+impl DekManager {
+    pub fn new(ttl_secs: u64, max_entries: usize) -> Self {
+        Self {
+            cache: DashMap::new(),
+            ttl_secs,
+            max_entries,
+        }
+    }
+
+    /// 获取或创建租户的 DEK
+    pub fn get_or_create_dek(
+        &self,
+        tenant_id: Uuid,
+        encrypted_dek: Option<&str>,
+        kek: &[u8; 32],
+    ) -> AppResult<([u8; 32], u32)> {
+        // 检查缓存
+        if let Some(entry) = self.cache.get(&tenant_id) {
+            if entry.loaded_at.elapsed().as_secs() < self.ttl_secs {
+                return Ok((entry.dek, entry.version));
+            }
+        }
+
+        // 从加密 DEK 解密
+        if let Some(enc_dek) = encrypted_dek {
+            let dek_hex = engine::decrypt(kek, enc_dek).map_err(|e| AppError::Internal(e))?;
+            let dek_bytes = hex::decode(&dek_hex).map_err(|e| AppError::Internal(e.to_string()))?;
+            if dek_bytes.len() != 32 {
+                return Err(AppError::Internal("DEK must be 32 bytes".into()));
+            }
+            let mut dek = [0u8; 32];
+            dek.copy_from_slice(&dek_bytes);
+
+            // 缓存（版本从外部传入时无法确定，使用默认值 1）
+            self.evict_if_full();
+            self.cache.insert(tenant_id, CachedDek {
+                dek,
+                version: 1,
+                loaded_at: Instant::now(),
+            });
+            return Ok((dek, 1));
+        }
+
+        // 无现有 DEK → 生成新的
+        let dek = Self::generate_dek();
+        self.evict_if_full();
+        self.cache.insert(tenant_id, CachedDek {
+            dek,
+            version: 1,
+            loaded_at: Instant::now(),
+        });
+        Ok((dek, 1))
+    }
+
+    /// 使用 KEK 加密 DEK 以便存储
+    pub fn encrypt_dek_for_storage(dek: &[u8; 32], kek: &[u8; 32]) -> AppResult<String> {
+        let dek_hex = hex::encode(dek);
+        engine::encrypt(kek, &dek_hex).map_err(|e| AppError::Internal(e))
+    }
+
+    /// 生成新 DEK 并用 KEK 加密，返回 (新 DEK, 加密后的 DEK)
+    pub fn generate_new_dek(kek: &[u8; 32]) -> AppResult<([u8; 32], String)> {
+        let dek = Self::generate_dek();
+        let encrypted = Self::encrypt_dek_for_storage(&dek, kek)?;
+        Ok((dek, encrypted))
+    }
+
+    /// 使缓存失效（轮换后调用）
+    pub fn invalidate(&self, tenant_id: Uuid) {
+        self.cache.remove(&tenant_id);
+    }
+
+    fn generate_dek() -> [u8; 32] {
+        use rand::RngCore;
+        let mut dek = [0u8; 32];
+        rand::thread_rng().fill_bytes(&mut dek);
+        dek
+    }
+
+    fn evict_if_full(&self) {
+        if self.cache.len() >= self.max_entries {
+            // 简单策略：移除最早加载的一半
+            let to_remove: Vec<Uuid> = self.cache
+                .iter()
+                .filter(|e| e.loaded_at.elapsed().as_secs() > self.ttl_secs / 2)
+                .map(|e| *e.key())
+                .take(self.max_entries / 2)
+                .collect();
+            for id in to_remove {
+                self.cache.remove(&id);
+            }
+        }
+    }
+}