fix_rpm_signature.py

# References:
# https://github.com/ashang/unar/blob/473488cc612c3f47e1c76f9baf92d268db259dc1/XADMaster/XADRPMParser.m
# https://refspecs.linuxbase.org/LSB_3.1.1/LSB-Core-generic/LSB-Core-generic/pkgformat.html

import os
import sys
import hashlib

with open(sys.argv[1], "r+b") as f:
	lead_header_bytes = f.read(4)
	if lead_header_bytes == b"\xED\xAB\xEE\xDB":
		f.seek(92, os.SEEK_CUR) # skip rest of lead
		signature_header_bytes = f.read(4)
		if signature_header_bytes == b"\x8E\xAD\xE8\x01":
			f.seek(4, os.SEEK_CUR)
			signature_entries = int.from_bytes(f.read(4), byteorder="big")
			signature_bytes = int.from_bytes(f.read(4), byteorder="big")
			signature_entries_bytes = f.read(signature_entries * 16)
			signature_bytes_start = f.tell()
			signature_bytes_bytes = f.read((signature_bytes + 7) & (7 ^ 0xffffffff))
			signature_entries_list = []
			for i in range(signature_entries):
				base = (i * 16)
				signature_entries_list.append(
					{
						"tag" : int.from_bytes(signature_entries_bytes[base + 0:base + 4], byteorder="big"),
						"type" : int.from_bytes(signature_entries_bytes[base + 4:base + 8], byteorder="big"),
						"offset" : int.from_bytes(signature_entries_bytes[base + 8:base + 12], byteorder="big"),
						"count" : int.from_bytes(signature_entries_bytes[base + 12:base + 16], byteorder="big"),
					}
				)
			for x in signature_entries_list:
				if x["type"] == 4:
					x["data"] = int.from_bytes(signature_bytes_bytes[x["offset"]:x["offset"] + (x["count"] * 4)], byteorder="big")
				if x["type"] == 7:
					x["data"] = signature_bytes_bytes[x["offset"]:x["offset"] + (x["count"] * 4)]

			data = f.read()
			data_len = len(data)
			data_md5 = hashlib.md5(data).digest()

			for x in signature_entries_list:
				if x["tag"] == 1000 and x["count"] == 1:
					f.seek(signature_bytes_start + x["offset"])
					f.write(data_len.to_bytes(byteorder="big", length=4))
				if x["tag"] == 1004 and x["count"] == 16:
					f.seek(signature_bytes_start + x["offset"])
					f.write(data_md5)