Make Files Non-Executable: Binary to ASCII

G5 Cyber Security

2 weeks ago

TL;DR

To prevent a file from running (make it non-executable), convert its binary data into plain text (ASCII). This removes the executable flags. We’ll use command-line tools like xxd and sed to achieve this, then reverse the process if needed.

How to Make a File Non-Executable

Backup your file: Always create a backup before modifying any file.
Convert Binary to Hexadecimal: Use xxd to convert the binary file into a hexadecimal representation.
```
xxd my_executable > my_executable.hex
```
This creates a new file, my_executable.hex, containing the hexadecimal data of your original file.
Remove Hexadecimal Formatting: The output from xxd includes offsets and other information we don’t need. Use sed to extract only the hexadecimal bytes.
```
sed 's/^[0-9a-fA-F ]*//g' my_executable.hex > my_executable.txt
```
This command removes all lines starting with numbers and spaces, leaving just the hex data in my_executable.txt.
Convert Hexadecimal to ASCII: Use xxd -r to convert the hexadecimal representation back into a text file.
```
xxd -r my_executable.txt > my_executable.ascii
```
This creates my_executable.ascii, which now contains the original file’s data as ASCII characters. Because binary data isn’t usually valid ASCII, this will likely result in many unprintable characters.
Verify Non-Executability: Attempt to execute the new file.
```
./my_executable.ascii
```
You should receive a “Permission denied” or similar error message indicating that the file is not executable.

How to Restore the File (ASCII back to Binary)

Convert ASCII to Hexadecimal: Use xxd to convert the ASCII file into hexadecimal representation.
```
xxd my_executable.ascii > my_executable.hex2
```
Remove Formatting (again): Remove the offset information from the hex file.
```
sed 's/^[0-9a-fA-F ]*//g' my_executable.hex2 > my_executable.txt2
```
Convert Hexadecimal back to Binary: Use xxd -r to convert the hexadecimal data back into binary.
```
xxd -r my_executable.txt2 > restored_executable
```
This creates a new file, restored_executable, which should be identical to your original my_executable.
Restore Executable Permissions: Make the restored file executable.
```
chmod +x restored_executable
```
Verify Restoration: Attempt to execute the restored file.
```
./restored_executable
```
It should now run as expected.

Important Considerations

File Size: Converting binary to ASCII will slightly increase the file size because each byte is represented by two hexadecimal characters.
Character Encoding: This method assumes a basic character encoding. If your original file contains specific encoding requirements, you may need to adjust the conversion process accordingly.
cyber security: While this prevents *direct* execution, it doesn’t protect against all cyber security threats. A determined attacker could still attempt to analyze and potentially exploit the ASCII representation of the data.