36 lines
1.2 KiB
Python
36 lines
1.2 KiB
Python
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# Pyrogram - Telegram MTProto API Client Library for Python
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# Copyright (C) 2017 Dan Tès <https://github.com/delivrance>
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#
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# This file is part of Pyrogram.
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#
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# Pyrogram is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Lesser General Public License as published
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# by the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# Pyrogram is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public License
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# along with Pyrogram. If not, see <http://www.gnu.org/licenses/>.
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try:
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from pyaes import AESModeOfOperationCTR
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except ImportError:
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pass
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class CTR:
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def __init__(self, key: bytes, iv: bytes):
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self.ctr = AESModeOfOperationCTR(key)
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self.iv = iv
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def decrypt(self, data: bytes, offset: int) -> bytes:
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replace = int.to_bytes(offset // 16, byteorder="big", length=4)
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iv = self.iv[:-4] + replace
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self.ctr._counter._counter = list(iv)
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return self.ctr.decrypt(data)
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