implemented crypto module for client

setup.py

@@ -14,6 +14,7 @@ with open(path.join(here, 'steam/__init__.py'), encoding='utf-8') as f:
 install_requires = [
     'requests',
     'vdf',
+    'pycrypto',
 ]
 
 if sys.version_info < (3, 4):

steam/client/crypto.py

@@ -0,0 +1,35 @@
+from base64 import b64decode
+from Crypto import Random
+from Crypto.Cipher import PKCS1_OAEP, AES
+from Crypto.PublicKey import RSA
+
+public_key = """
+MIGdMA0GCSqGSIb3DQEBAQUAA4GLADCBhwKBgQDf7BrWLBBmLBc1OhSwfFkRf53T
+2Ct64+AVzRkeRuh7h3SiGEYxqQMUeYKO6UWiSRKpI2hzic9pobFhRr3Bvr/WARvY
+gdTckPv+T1JzZsuVcNfFjrocejN1oWI0Rrtgt4Bo+hOneoo3S57G9F1fOpn5nsQ6
+6WOiu4gZKODnFMBCiQIBEQ==
+"""
+
+BS = AES.block_size
+pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS)
+unpad = lambda s: s[0:-ord(s[-1])]
+
+
+def generate_session_key():
+    session_key = Random.new().read(32)
+    cipher = PKCS1_OAEP.new(RSA.importKey(b64decode(public_key)))
+    encrypted_session_key = cipher.encrypt(session_key)
+    return (session_key, encrypted_session_key)
+
+
+def encrypt(message, key):
+    iv = Random.new().read(BS)
+    encrypted_iv = AES.new(key, AES.MODE_ECB).encrypt(iv)
+    cyphertext = AES.new(key, AES.MODE_CBC, iv).encrypt(pad(message))
+    return encrypted_iv + cyphertext
+
+
+def decrypt(cyphertext, key):
+    iv = AES.new(key, AES.MODE_ECB).decrypt(cyphertext[:BS])
+    message = AES.new(key, AES.MODE_CBC, iv).decrypt(cyphertext[BS:])
+    return unpad(message)