mirror of
https://github.com/Leseratte10/acsm-calibre-plugin.git
synced 2024-06-29 07:07:28 +06:00
49 lines
1.5 KiB
Python
49 lines
1.5 KiB
Python
#!/usr/bin/env python3
|
|
# -*- coding: utf-8 -*-
|
|
|
|
'''
|
|
Use my own small RSA code so we don't have to include the huge
|
|
python3-rsa just for these small bits.
|
|
The original code used blinding and this one doesn't,
|
|
but we don't really care about side-channel attacks ...
|
|
'''
|
|
|
|
class CustomRSA:
|
|
|
|
def byte_size(number: int):
|
|
return (number.bit_length() + 7) // 8
|
|
|
|
def pad_message(message: bytes, target_len: int) -> bytes:
|
|
# Padding always uses 0xFF
|
|
# Returns: 00 01 PADDING 00 MESSAGE
|
|
|
|
max_message_length = target_len - 11
|
|
message_length = len(message)
|
|
|
|
if message_length > max_message_length:
|
|
raise OverflowError("Message too long, has %d bytes but only space for %d" % (message_length, max_message_length))
|
|
|
|
padding_len = target_len - message_length - 3
|
|
|
|
return b"".join([b"\x00\x01", padding_len * b"\xff", b"\x00", message])
|
|
|
|
def normal_encrypt(key, message: int):
|
|
|
|
if message < 0 or message > key.n:
|
|
raise ValueError("Invalid message")
|
|
|
|
encrypted = pow(message, key.d, key.n)
|
|
return encrypted
|
|
|
|
def transform_bytes2int(raw_bytes: bytes):
|
|
return int.from_bytes(raw_bytes, "big", signed=False)
|
|
|
|
def transform_int2bytes(number: int, fill_size: int = 0):
|
|
if number < 0:
|
|
raise ValueError("Negative number")
|
|
|
|
if fill_size > 0:
|
|
return number.to_bytes(fill_size, "big")
|
|
|
|
bytes_needed = max(1, CustomRSA.byte_size(number))
|
|
return number.to_bytes(bytes_needed, "big") |