diff --git a/td/mtproto/CryptoStorer.h b/td/mtproto/CryptoStorer.h
index 08c12684..58010363 100644
--- a/td/mtproto/CryptoStorer.h
+++ b/td/mtproto/CryptoStorer.h
@@ -18,6 +18,7 @@
 
 namespace td {
 namespace mtproto {
+
 template <class Object, class ObjectStorer>
 class ObjectImpl {
  public:
@@ -329,5 +330,6 @@ class CryptoImpl {
   uint64 message_id_;
   int32 seq_no_;
 };
+
 }  // namespace mtproto
 }  // namespace td
diff --git a/td/mtproto/NoCryptoStorer.h b/td/mtproto/NoCryptoStorer.h
index 7836d734..913c658d 100644
--- a/td/mtproto/NoCryptoStorer.h
+++ b/td/mtproto/NoCryptoStorer.h
@@ -11,12 +11,12 @@
 
 namespace td {
 namespace mtproto {
+
 class NoCryptoImpl {
  public:
-  NoCryptoImpl(uint64 message_id, const Storer &data, bool need_pad = true) : message_id(message_id), data(data) {
+  NoCryptoImpl(uint64 message_id, const Storer &data, bool need_pad = true) : message_id_(message_id), data_(data) {
     if (need_pad) {
-      auto data_size = data.size();
-      auto pad_size = (data_size + 15) / 16 * 16 - data_size;
+      auto pad_size = -static_cast<int>(data_.size()) & 15;
       pad_size += 16 * (static_cast<size_t>(Random::secure_int32()) % 16);
       pad_.resize(pad_size);
       Random::secure_bytes(pad_);
@@ -24,16 +24,17 @@ class NoCryptoImpl {
   }
   template <class T>
   void do_store(T &storer) const {
-    storer.store_binary(message_id);
-    storer.store_binary(static_cast<int32>(data.size() + pad_.size()));
-    storer.store_storer(data);
+    storer.store_binary(message_id_);
+    storer.store_binary(static_cast<int32>(data_.size() + pad_.size()));
+    storer.store_storer(data_);
     storer.store_slice(pad_);
   }
 
  private:
-  uint64 message_id;
-  const Storer &data;
+  uint64 message_id_;
+  const Storer &data_;
   std::string pad_;
 };
+
 }  // namespace mtproto
 }  // namespace td
diff --git a/td/mtproto/TcpTransport.cpp b/td/mtproto/TcpTransport.cpp
index d3ab8146..5de248cd 100644
--- a/td/mtproto/TcpTransport.cpp
+++ b/td/mtproto/TcpTransport.cpp
@@ -151,7 +151,7 @@ void ObfuscatedTransport::init(ChainBufferReader *input, ChainBufferWriter *outp
     }
     auto first_int = as<uint32>(header.data());
     if (first_int == 0x44414548 || first_int == 0x54534f50 || first_int == 0x20544547 || first_int == 0x4954504f ||
-        first_int == 0xeeeeeeee) {
+        first_int == 0xdddddddd || first_int == 0xeeeeeeee) {
       continue;
     }
     auto second_int = as<uint32>(header.data() + sizeof(uint32));
diff --git a/td/mtproto/TcpTransport.h b/td/mtproto/TcpTransport.h
index 43c60105..2ffdaf8c 100644
--- a/td/mtproto/TcpTransport.h
+++ b/td/mtproto/TcpTransport.h
@@ -119,7 +119,8 @@ class OldTransport : public IStreamTransport {
 
 class ObfuscatedTransport : public IStreamTransport {
  public:
-  ObfuscatedTransport(int16 dc_id, std::string secret) : dc_id_(dc_id), secret_(std::move(secret)) {
+  ObfuscatedTransport(int16 dc_id, std::string secret)
+      : dc_id_(dc_id), secret_(std::move(secret)), impl_(secret_.size() >= 17) {
   }
   Result<size_t> read_next(BufferSlice *message, uint32 *quick_ack) override TD_WARN_UNUSED_RESULT {
     aes_ctr_byte_flow_.wakeup();
@@ -162,7 +163,7 @@ class ObfuscatedTransport : public IStreamTransport {
  private:
   int16 dc_id_;
   std::string secret_;
-  TransportImpl impl_{secret_.size() >= 17};
+  TransportImpl impl_;
   AesCtrByteFlow aes_ctr_byte_flow_;
   ByteFlowSink byte_flow_sink_;
   ChainBufferReader *input_;
diff --git a/td/telegram/net/ConnectionCreator.cpp b/td/telegram/net/ConnectionCreator.cpp
index 4d04ec1e..44d34fc9 100644
--- a/td/telegram/net/ConnectionCreator.cpp
+++ b/td/telegram/net/ConnectionCreator.cpp
@@ -279,6 +279,16 @@ void ConnectionCreator::add_proxy(string server, int32 port, bool enable,
     return promise.set_error(Status::Error(400, "Wrong port number"));
   }
 
+  auto is_secret_supported = [](Slice secret) {
+    if (secret.size() == 32) {
+      return true;
+    }
+    if (secret.size() == 34) {
+      return begins_with(secret, "dd");
+    }
+    return false;
+  };
+
   Proxy new_proxy;
   switch (proxy_type->get_id()) {
     case td_api::proxyTypeSocks5::ID: {
@@ -288,8 +298,11 @@ void ConnectionCreator::add_proxy(string server, int32 port, bool enable,
     }
     case td_api::proxyTypeMtproto::ID: {
       auto type = td_api::move_object_as<td_api::proxyTypeMtproto>(proxy_type);
-      if ((type->secret_.size() != 32 && type->secret_.size() != 34) || hex_decode(type->secret_).is_error()) {
-        return promise.set_error(Status::Error(400, "Wrong server secret"));
+      if (hex_decode(type->secret_).is_error()) {
+        return promise.set_error(Status::Error(400, "Wrong secret"));
+      }
+      if (!is_secret_supported(type->secret_)) {
+        return promise.set_error(Status::Error(400, "Unsupported secret"));
       }
       new_proxy = Proxy::mtproto(server, port, type->secret_);
       break;