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