cIMG extraction

cIMG_extraction.py

import struct
import subprocess

def read_header(f):
    """Read and parse the cIMG header"""
    magic = f.read(4)
    if magic != b"cIMG":
        raise ValueError("Invalid magic number")
    
    version, width, height, num_directives = struct.unpack("<HBBI", f.read(8))
    return version, width, height, num_directives

def process_directives(f, width, height, num_directives):
    """Process all directives in the file and return final frame"""
    canvas = [[32] * width for _ in range(height)]
    
    for _ in range(num_directives):
        directive_type = struct.unpack("<H", f.read(2))[0]
        
        if directive_type == 2:
            x, y, w, h, r, g, b, char = struct.unpack("<BBBBBBBB", f.read(8))
            canvas[y][x] = char
        elif directive_type == 6:
            f.read(1)
            continue
        elif directive_type == 7:
            f.read(4)
            continue
        else:
            raise ValueError(f"Unknown directive type: {directive_type}")
    
    return '\n'.join(''.join(chr(c) for c in row).rstrip() for row in canvas)

def extract_flag(filename):
    """Extract flag from animated cIMG file"""
    subprocess.run(["/challenge/generate_flag_image"])
    
    with open(filename, "rb") as f:
        version, width, height, num_directives = read_header(f)
        final_frame = process_directives(f, width, height, num_directives)
        print(final_frame)

if __name__ == "__main__":
    extract_flag("/challenge/flag.cimg")