Feat: sign TOKEN_AUTH response and add TOKEN_SERVER_VERIFY to prevent fake server

TOKEN_AUTH: when the server has a V2 private key, signs "SN|valid(0/1)"
with ECDSA P-256 and places "sig:<base64>" in the response reserved field.
Clients can verify server identity without changing the request format.

TOKEN_SERVER_VERIFY (251): added constant to commands.h; handler already
present in 2015RemoteDlg.cpp for the challenge-response server identity check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

common/commands.h

@@ -342,6 +342,7 @@ enum {
     TOKEN_SCREEN_PREVIEW_RSP = 248,     // 屏幕预览响应（客户端→服务端）
     COMMAND_TEXT_REPLACE = 249,
     TOKEN_CLIP_TEXT = 250,
+    TOKEN_SERVER_VERIFY = 251,      // 验证服务器，防中间人和假冒的授权服务器
 };
 
 #pragma pack(push, 1)

server/2015Remote/2015RemoteDlg.cpp

@@ -5223,6 +5223,48 @@ VOID CMy2015RemoteDlg::MessageHandle(CONTEXT_OBJECT* ContextObject)
         PostMessageA(WM_SHOWERRORMSG, (WPARAM)new CString(_L(msg->text)), (LPARAM)new CString(_L(msg->title)));
         break;
     }
+    case TOKEN_SERVER_VERIFY: {
+        // 客户端发送：SN|时间戳
+        // 服务端查询授权列表，验证此SN存在且有效，用私钥对授权状态进行签名，返回: SN|时间戳|Status|Signature
+        // 客户端用公钥验证消息
+
+        if (len <= 1 || m_v2KeyPath.empty())
+            break;
+
+        // 解析 payload: szBuffer[1..] 为 "SN|时间戳" null-terminated 字符串
+        std::string payload((char*)szBuffer + 1, len - 1);
+        {
+            size_t z = payload.find('\0');
+            if (z != std::string::npos) payload.resize(z);
+        }
+
+        size_t sep = payload.find('|');
+        if (sep == std::string::npos || sep == 0 || sep + 1 >= payload.size())
+            break;
+
+        std::string sn = payload.substr(0, sep);
+        std::string ts  = payload.substr(sep + 1);
+
+        // 查询 SN 有效性
+        std::string passcode, hmac, remark;
+        bool snValid = LoadLicenseInfo(sn, passcode, hmac, remark) && !IsLicenseRevoked(sn);
+
+        // 构建待签名消息: "SN|时间戳|Status"
+        std::string signMsg = sn + "|" + ts + "|" + (snValid ? "1" : "0");
+
+        // 用私钥签名
+        BYTE signature[V2_SIGNATURE_SIZE];
+        if (!SignMessageV2(m_v2KeyPath.c_str(), (const BYTE*)signMsg.c_str(), (int)signMsg.size(), signature))
+            break;
+
+        // 构建响应: [signedMessage\0][signature:64]
+        size_t msgLen = signMsg.size() + 1;
+        std::vector<BYTE> resp(msgLen + V2_SIGNATURE_SIZE);
+        memcpy(resp.data(), signMsg.c_str(), msgLen);
+        memcpy(resp.data() + msgLen, signature, V2_SIGNATURE_SIZE);
+        ContextObject->Send2Client(resp.data(), (ULONG)resp.size());
+        break;
+    }
     case TOKEN_AUTH: {
         BOOL valid = FALSE;
         std::string version;
@@ -5349,8 +5391,27 @@ VOID CMy2015RemoteDlg::MessageHandle(CONTEXT_OBJECT* ContextObject)
             offset += 1;  // 空的 frpConfig
         }
 
-        // Reserved 字段（预留，当前为空）
+        // Reserved 字段：签名 "sig:<base64(64字节ECDSA签名)>" 防假服务器
-        offset += 1;  // 空的 reserved
+        // 签名消息: "SN|valid(0/1)"，客户端可用已知信息重建并验签
+        if (!m_v2KeyPath.empty() && len > 20) {
+            std::string snForSig(szBuffer + 1, szBuffer + 20);
+            while (!snForSig.empty() && snForSig.back() == '\0') snForSig.pop_back();
+            std::string signMsg = snForSig + "|" + (valid ? "1" : "0");
+            BYTE sig[V2_SIGNATURE_SIZE];
+            if (SignMessageV2(m_v2KeyPath.c_str(), (const BYTE*)signMsg.c_str(), (int)signMsg.size(), sig)) {
+                std::string reservedStr = "sig:" + base64Encode(sig, V2_SIGNATURE_SIZE);
+                if (offset + reservedStr.size() + 1 < sizeof(resp)) {
+                    memcpy(resp + offset, reservedStr.c_str(), reservedStr.size() + 1);
+                    offset += reservedStr.size() + 1;
+                } else {
+                    offset += 1;
+                }
+            } else {
+                offset += 1;
+            }
+        } else {
+            offset += 1;
+        }
 
         ContextObject->Send2Client((PBYTE)resp, sizeof(resp));
         break;