diff --git a/telethon/crypto/__init__.py b/telethon/crypto/__init__.py
index d151a96c..aa470adf 100644
--- a/telethon/crypto/__init__.py
+++ b/telethon/crypto/__init__.py
@@ -1,3 +1,8 @@
+"""
+This module contains several utilities regarding cryptographic purposes,
+such as the AES IGE mode used by Telegram, the authorization key bound with
+their data centers, and so on.
+"""
 from .aes import AES
 from .aes_ctr import AESModeCTR
 from .auth_key import AuthKey
diff --git a/telethon/crypto/aes.py b/telethon/crypto/aes.py
index c09add56..191cde15 100644
--- a/telethon/crypto/aes.py
+++ b/telethon/crypto/aes.py
@@ -1,3 +1,6 @@
+"""
+AES IGE implementation in Python. This module may use libssl if available.
+"""
 import os
 import pyaes
 from . import libssl
@@ -9,10 +12,15 @@ if libssl.AES is not None:
 else:
     # Fallback to a pure Python implementation
     class AES:
+        """
+        Class that servers as an interface to encrypt and decrypt
+        text through the AES IGE mode.
+        """
         @staticmethod
         def decrypt_ige(cipher_text, key, iv):
-            """Decrypts the given text in 16-bytes blocks by using the
-               given key and 32-bytes initialization vector
+            """
+            Decrypts the given text in 16-bytes blocks by using the
+            given key and 32-bytes initialization vector.
             """
             iv1 = iv[:len(iv) // 2]
             iv2 = iv[len(iv) // 2:]
@@ -42,8 +50,9 @@ else:
 
         @staticmethod
         def encrypt_ige(plain_text, key, iv):
-            """Encrypts the given text in 16-bytes blocks by using the
-               given key and 32-bytes initialization vector
+            """
+            Encrypts the given text in 16-bytes blocks by using the
+            given key and 32-bytes initialization vector.
             """
 
             # Add random padding iff it's not evenly divisible by 16 already
diff --git a/telethon/crypto/aes_ctr.py b/telethon/crypto/aes_ctr.py
index 7bd7b79a..34422904 100644
--- a/telethon/crypto/aes_ctr.py
+++ b/telethon/crypto/aes_ctr.py
@@ -1,3 +1,6 @@
+"""
+This module holds the AESModeCTR wrapper class.
+"""
 import pyaes
 
 
@@ -6,6 +9,12 @@ class AESModeCTR:
     # TODO Maybe make a pull request to pyaes to support iv on CTR
 
     def __init__(self, key, iv):
+        """
+        Initializes the AES CTR mode with the given key/iv pair.
+
+        :param key: the key to be used as bytes.
+        :param iv: the bytes initialization vector. Must have a length of 16.
+        """
         # TODO Use libssl if available
         assert isinstance(key, bytes)
         self._aes = pyaes.AESModeOfOperationCTR(key)
@@ -15,7 +24,19 @@ class AESModeCTR:
         self._aes._counter._counter = list(iv)
 
     def encrypt(self, data):
+        """
+        Encrypts the given plain text through AES CTR.
+
+        :param data: the plain text to be encrypted.
+        :return: the encrypted cipher text.
+        """
         return self._aes.encrypt(data)
 
     def decrypt(self, data):
+        """
+        Decrypts the given cipher text through AES CTR
+
+        :param data: the cipher text to be decrypted.
+        :return: the decrypted plain text.
+        """
         return self._aes.decrypt(data)
diff --git a/telethon/crypto/auth_key.py b/telethon/crypto/auth_key.py
index 17a7f8ca..679e62ff 100644
--- a/telethon/crypto/auth_key.py
+++ b/telethon/crypto/auth_key.py
@@ -1,3 +1,6 @@
+"""
+This module holds the AuthKey class.
+"""
 import struct
 from hashlib import sha1
 
@@ -6,7 +9,16 @@ from ..extensions import BinaryReader
 
 
 class AuthKey:
+    """
+    Represents an authorization key, used to encrypt and decrypt
+    messages sent to Telegram's data centers.
+    """
     def __init__(self, data):
+        """
+        Initializes a new authorization key.
+
+        :param data: the data in bytes that represent this auth key.
+        """
         self.key = data
 
         with BinaryReader(sha1(self.key).digest()) as reader:
@@ -15,8 +27,12 @@ class AuthKey:
             self.key_id = reader.read_long(signed=False)
 
     def calc_new_nonce_hash(self, new_nonce, number):
-        """Calculates the new nonce hash based on
-           the current class fields' values
+        """
+        Calculates the new nonce hash based on the current attributes.
+
+        :param new_nonce: the new nonce to be hashed.
+        :param number: number to prepend before the hash.
+        :return: the hash for the given new nonce.
         """
         new_nonce = new_nonce.to_bytes(32, 'little', signed=True)
         data = new_nonce + struct.pack('<BQ', number, self.aux_hash)
diff --git a/telethon/crypto/cdn_decrypter.py b/telethon/crypto/cdn_decrypter.py
index f4b0ef3e..24a4bb49 100644
--- a/telethon/crypto/cdn_decrypter.py
+++ b/telethon/crypto/cdn_decrypter.py
@@ -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()
diff --git a/telethon/crypto/factorization.py b/telethon/crypto/factorization.py
index 359887d3..75df4dd9 100644
--- a/telethon/crypto/factorization.py
+++ b/telethon/crypto/factorization.py
@@ -1,9 +1,21 @@
+"""
+This module holds a fast Factorization class.
+"""
 from random import randint
 
 
 class Factorization:
+    """
+    Simple module to factorize large numbers really quickly.
+    """
     @classmethod
     def factorize(cls, pq):
+        """
+        Factorizes the given large integer.
+
+        :param pq: the prime pair pq.
+        :return: a tuple containing the two factors p and q.
+        """
         if pq % 2 == 0:
             return 2, pq // 2
 
@@ -39,6 +51,13 @@ class Factorization:
 
     @staticmethod
     def gcd(a, b):
+        """
+        Calculates the Greatest Common Divisor.
+
+        :param a: the first number.
+        :param b: the second number.
+        :return: GCD(a, b)
+        """
         while b:
             a, b = b, a % b
 
diff --git a/telethon/crypto/libssl.py b/telethon/crypto/libssl.py
index f9917d71..b4735112 100644
--- a/telethon/crypto/libssl.py
+++ b/telethon/crypto/libssl.py
@@ -1,3 +1,6 @@
+"""
+This module holds an AES IGE class, if libssl is available on the system.
+"""
 import os
 import ctypes
 from ctypes.util import find_library
@@ -35,14 +38,23 @@ else:
     AES_DECRYPT = ctypes.c_int(0)
 
     class AES_KEY(ctypes.Structure):
+        """Helper class representing an AES key"""
         _fields_ = [
             ('rd_key', ctypes.c_uint32 * (4*(AES_MAXNR + 1))),
             ('rounds', ctypes.c_uint),
         ]
 
     class AES:
+        """
+        Class that servers as an interface to encrypt and decrypt
+        text through the AES IGE mode, using the system's libssl.
+        """
         @staticmethod
         def decrypt_ige(cipher_text, key, iv):
+            """
+            Decrypts the given text in 16-bytes blocks by using the
+            given key and 32-bytes initialization vector.
+            """
             aeskey = AES_KEY()
             ckey = (ctypes.c_ubyte * len(key))(*key)
             cklen = ctypes.c_int(len(key)*8)
@@ -65,6 +77,10 @@ else:
 
         @staticmethod
         def encrypt_ige(plain_text, key, iv):
+            """
+            Encrypts the given text in 16-bytes blocks by using the
+            given key and 32-bytes initialization vector.
+            """
             # Add random padding iff it's not evenly divisible by 16 already
             if len(plain_text) % 16 != 0:
                 padding_count = 16 - len(plain_text) % 16
diff --git a/telethon/crypto/rsa.py b/telethon/crypto/rsa.py
index 9abefc55..0303587b 100644
--- a/telethon/crypto/rsa.py
+++ b/telethon/crypto/rsa.py
@@ -1,3 +1,6 @@
+"""
+This module holds several utilities regarding RSA and server fingerprints.
+"""
 import os
 import struct
 from hashlib import sha1
@@ -32,8 +35,11 @@ def get_byte_array(integer):
 
 
 def _compute_fingerprint(key):
-    """For a given Crypto.RSA key, computes its 8-bytes-long fingerprint
-       in the same way that Telegram does.
+    """
+    Given a RSA key, computes its fingerprint like Telegram does.
+
+    :param key: the Crypto.RSA key.
+    :return: its 8-bytes-long fingerprint.
     """
     n = TLObject.serialize_bytes(get_byte_array(key.n))
     e = TLObject.serialize_bytes(get_byte_array(key.e))
@@ -49,8 +55,14 @@ def add_key(pub):
 
 
 def encrypt(fingerprint, data):
-    """Given the fingerprint of a previously added RSA key, encrypt its data
-       in the way Telegram requires us to do so (sha1(data) + data + padding)
+    """
+    Encrypts the given data known the fingerprint to be used
+    in the way Telegram requires us to do so (sha1(data) + data + padding)
+
+    :param fingerprint: the fingerprint of the RSA key.
+    :param data: the data to be encrypted.
+    :return:
+        the cipher text, or None if no key matching this fingerprint is found.
     """
     global _server_keys
     key = _server_keys.get(fingerprint, None)