nc3ctf2017 - fragfs

fragfs.py

#!/usr/bin/env python
import os
f = open("three.dd","rb")
fragfs = bytearray(f.read());
f.close();

def createPath(path):
    dir = os.path.dirname(path)
    if not os.path.exists(dir):
        os.makedirs(dir)

sectorSize = 4096
dataStart = sectorSize * 20

sectors = [bytearray(fragfs[i:i + sectorSize]) for i in xrange(0, len(fragfs), sectorSize)]

headerSeperator = bytearray.fromhex(u"00 ff  ff 00 ff 00")
headersPathTable, headersOffsetTable = fragfs[512:dataStart].split(headerSeperator)

headerPathPairSeperator = bytearray.fromhex(u"00 FF FF")
headersPathTable = [(x[0:32], x[33:]) for x in headersPathTable.split(headerPathPairSeperator)]

headersOffsetPairSeperator = bytearray.fromhex(u"00 FF")
headersOffsetSeperator = bytearray.fromhex(u"00")
headersOffsetTable = [(x.split(headersOffsetSeperator)) for x in headersOffsetTable.split(headersOffsetPairSeperator)]

allFiles = dict()
for fileID, filePATH in headersPathTable:
	allFiles[fileID.decode("utf-8")] = {"filePath": filePATH.decode("utf-8")}

for file in headersOffsetTable:
	if file[0].decode("utf-8") != u"":
		allFiles[file[0].decode("utf-8")]["offsets"] = [int(x) for x in file[1].decode("utf-8").split(" ")]

for key in allFiles:
	path = allFiles[key]["filePath"]
	frame = bytearray()
	for offset in allFiles[key]["offsets"]:
		sector = sectors[offset]
		frame.extend(sector)
	createPath(path)
	file = open(path, "wb")
	file.write(frame)