feat: MeshSafe 文件摆渡安全卫士 v1.0 初始提交

核心功能:
- 6 层检测管线: L0 结构分析 → L1 ClamAV → L2 文档深度检测 → L3 关键词匹配 → L4 YARA → L5 PE/二进制
- FastAPI + PostgreSQL + Redis + Docker Compose 架构
- 客户端 HMAC-SHA256 签名鉴权 + 限流 + 幂等性
- 控制台 UI (登录/Dashboard/诊断中心/策略管理/任务列表/测试中心/产品介绍页)
- 三层诊断定时器 (error_scan 30s / db_aggregate 30s / container_check 5min)

并发与稳定性修复:
- 诊断定时器 Redis 时间槽位锁 (多 worker 同一槽位只有一个执行)
- JSONL 存储 fcntl 跨进程排他锁 + 容错解码 + 原子重写
- 移除 SQLite fallback, 统一 PostgreSQL
- API_CLIENTS 脱敏为环境变量, .env 已 .gitignore

app/security/crypto.py

@@ -0,0 +1,106 @@
+"""密码学基础工具：密钥派生、口令哈希、常数时间比较。"""
+
+from __future__ import annotations
+
+import base64
+import hashlib
+import hmac
+import os
+from typing import Tuple
+
+# 口令哈希迭代次数。等保三级要求存储口令不可逆，PBKDF2-HMAC-SHA256
+# 迭代 60 万次在现代 CPU 上约 0.3~0.6 秒，兼顾抗暴力破解与可用性。
+PBKDF2_ITERATIONS = 600_000
+PBKDF2_ALGORITHM = "sha256"
+SALT_BYTES = 16
+
+
+def derive_key(secret: str, salt: str, info: str, length: int = 32) -> bytes:
+    """使用 HKDF-SHA256 从调用方密钥派生用途隔离的子密钥。
+
+    不同用途使用不同 ``info`` 标签，使得请求签名密钥与响应签名密钥相互独立。
+    """
+    prk = hmac.new(
+        salt.encode("utf-8"), secret.encode("utf-8"), hashlib.sha256
+    ).digest()
+    okm = b""
+    block = b""
+    counter = 1
+    while len(okm) < length:
+        block = hmac.new(prk, block + info.encode("utf-8") + bytes([counter]), hashlib.sha256).digest()
+        okm += block
+        counter += 1
+    return okm[:length]
+
+
+def derive_client_signing_key(secret: str, client_id: str) -> bytes:
+    return derive_key(secret, client_id, "meshsafe/api/v1/request-signing")
+
+
+def derive_client_response_key(secret: str, client_id: str) -> bytes:
+    return derive_key(secret, client_id, "meshsafe/api/v1/response-signing")
+
+
+def hash_password(password: str) -> str:
+    """生成 ``pbkdf2_sha256$迭代次数$盐$哈希`` 格式的口令哈希。"""
+    salt = os.urandom(SALT_BYTES)
+    dk = hashlib.pbkdf2_hmac(
+        PBKDF2_ALGORITHM, password.encode("utf-8"), salt, PBKDF2_ITERATIONS
+    )
+    return "$".join(
+        [
+            "pbkdf2_sha256",
+            str(PBKDF2_ITERATIONS),
+            base64.b64encode(salt).decode("ascii"),
+            base64.b64encode(dk).decode("ascii"),
+        ]
+    )
+
+
+def verify_password(password: str, stored: str) -> bool:
+    """校验口令。格式非法时返回 False，不抛出异常。"""
+    try:
+        algo, iterations, salt_b64, hash_b64 = stored.split("$")
+        if algo != "pbkdf2_sha256":
+            return False
+        salt = base64.b64decode(salt_b64)
+        expected = base64.b64decode(hash_b64)
+        actual = hashlib.pbkdf2_hmac(
+            PBKDF2_ALGORITHM, password.encode("utf-8"), salt, int(iterations)
+        )
+        return hmac.compare_digest(actual, expected)
+    except Exception:  # noqa: BLE001
+        return False
+
+
+def needs_rehash(stored: str) -> bool:
+    """判断存量口令哈希是否需要按当前参数重新计算。"""
+    try:
+        algo, iterations, _, _ = stored.split("$")
+        return algo != "pbkdf2_sha256" or int(iterations) < PBKDF2_ITERATIONS
+    except Exception:  # noqa: BLE001
+        return True
+
+
+def sha256_bytes(data: bytes) -> str:
+    return hashlib.sha256(data).hexdigest()
+
+
+def sha256_file(path: str, chunk_size: int = 1024 * 1024) -> Tuple[str, int]:
+    """流式计算文件 SHA256 与 MD5，返回 (sha256, md5, size)。"""
+    sha = hashlib.sha256()
+    md5 = hashlib.md5()
+    size = 0
+    with open(path, "rb") as fh:
+        while True:
+            chunk = fh.read(chunk_size)
+            if not chunk:
+                break
+            sha.update(chunk)
+            md5.update(chunk)
+            size += len(chunk)
+    return sha.hexdigest(), md5.hexdigest(), size
+
+
+def constant_time_equals(a: str, b: str) -> bool:
+    return hmac.compare_digest(a.encode("utf-8"), b.encode("utf-8"))