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Document the crypto/ module

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Lonami Exo
2017-11-26 16:57:40 +01:00
parent 74ec6391d9
commit a932fb6470
8 changed files with 142 additions and 21 deletions
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45
telethon/crypto/cdn_decrypter.py
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@@ -1,6 +1,8 @@
"""
This module holds the CdnDecrypter utility class.
"""
from hashlib import sha256
from ..tl import Session
from ..tl.functions.upload import GetCdnFileRequest, ReuploadCdnFileRequest
from ..tl.types.upload import CdnFileReuploadNeeded, CdnFile
from ..crypto import AESModeCTR
@@ -8,11 +10,20 @@ from ..errors import CdnFileTamperedError
class CdnDecrypter:
"""Used when downloading a file results in a 'FileCdnRedirect' to
both prepare the redirect, decrypt the file as it downloads, and
ensure the file hasn't been tampered. https://core.telegram.org/cdn
"""
Used when downloading a file results in a 'FileCdnRedirect' to
both prepare the redirect, decrypt the file as it downloads, and
ensure the file hasn't been tampered. https://core.telegram.org/cdn
"""
def __init__(self, cdn_client, file_token, cdn_aes, cdn_file_hashes):
"""
Initializes the CDN decrypter.
:param cdn_client: a client connected to a CDN.
:param file_token: the token of the file to be used.
:param cdn_aes: the AES CTR used to decrypt the file.
:param cdn_file_hashes: the hashes the decrypted file must match.
"""
self.client = cdn_client
self.file_token = file_token
self.cdn_aes = cdn_aes
@@ -20,10 +31,13 @@ class CdnDecrypter:
@staticmethod
def prepare_decrypter(client, cdn_client, cdn_redirect):
"""Prepares a CDN decrypter, returning (decrypter, file data).
'client' should be an existing client not connected to a CDN.
'cdn_client' should be an already-connected TelegramBareClient
with the auth key already created.
"""
Prepares a new CDN decrypter.
:param client: a TelegramClient connected to the main servers.
:param cdn_client: a new client connected to the CDN.
:param cdn_redirect: the redirect file object that caused this call.
:return: (CdnDecrypter, first chunk file data)
"""
cdn_aes = AESModeCTR(
key=cdn_redirect.encryption_key,
@@ -60,8 +74,11 @@ class CdnDecrypter:
return decrypter, cdn_file
def get_file(self):
"""Calls GetCdnFileRequest and decrypts its bytes.
Also ensures that the file hasn't been tampered.
"""
Calls GetCdnFileRequest and decrypts its bytes.
Also ensures that the file hasn't been tampered.
:return: the CdnFile result.
"""
if self.cdn_file_hashes:
cdn_hash = self.cdn_file_hashes.pop(0)
@@ -77,6 +94,12 @@ class CdnDecrypter:
@staticmethod
def check(data, cdn_hash):
"""Checks the integrity of the given data"""
"""
Checks the integrity of the given data.
Raises CdnFileTamperedError if the integrity check fails.
:param data: the data to be hashed.
:param cdn_hash: the expected hash.
"""
if sha256(data).digest() != cdn_hash.hash:
raise CdnFileTamperedError()