Move crypto stuff to separate file, clean code up

2017-10-05 00:30:11 -06:00
parent 7f96f1a6b6
commit ec6de719ab
3 changed files with 110 additions and 126 deletions
@@ -0,0 +1,105 @@
+import hashlib, hmac, json
+from base64 import b64encode, b64decode
+from binascii import hexlify, unhexlify
+from Crypto.Cipher import AES
+from Crypto.Random import random
+from copy import deepcopy
+
+class EncryptionHelper:
+    def pure_generatePasswordAndKey(self, password, pw_salt, pw_cost):
+        output = hashlib.pbkdf2_hmac('sha512', password.encode(), pw_salt.encode(), pw_cost, dklen=96)
+        output = hexlify(output).decode()
+
+        output_length = len(output)
+        split_length = output_length // 3
+        pw = output[0 : split_length]
+        mk = output[split_length : split_length * 2]
+        ak = output[split_length * 2 : split_length * 3]
+        return dict(pw=pw, mk=mk, ak=ak)
+
+    def encryptDirtyItems(self, dirty_items, keys):
+        return [self.pure_encryptItem(item, keys) for item in dirty_items]
+
+    def decryptResponseItems(self, response_items, keys):
+        return [self.pure_decryptItem(item, keys) for item in response_items]
+
+    def pure_encryptItem(self, item, keys):
+        uuid = item['uuid']
+        content = json.dumps(item['content'])
+
+        item_key = hex(random.getrandbits(512))
+        item_key = item_key[2:].rjust(128, '0') # remove '0x', pad to 128
+        item_key_length = len(item_key)
+        item_ek = item_key[:item_key_length//2]
+        item_ak = item_key[item_key_length//2:]
+
+        enc_item = deepcopy(item)
+        enc_item['content'] = self.pure_encryptString002(content, item_ek, item_ak, uuid)
+        enc_item['enc_item_key'] = self.pure_encryptString002(item_key, keys['mk'], keys['ak'], uuid)
+        return enc_item
+
+    def pure_decryptItem(self, item, keys):
+        uuid = item['uuid']
+        content = item['content']
+        enc_item_key = item['enc_item_key']
+
+        if not content:
+            return item
+
+        if content[:3] == '002':
+            item_key = self.pure_decryptString002(enc_item_key, keys['mk'], keys['ak'], uuid)
+            item_key_length = len(item_key)
+            item_ek = item_key[:item_key_length//2]
+            item_ak = item_key[item_key_length//2:]
+
+            dec_content = self.pure_decryptString002(content, item_ek, item_ak, uuid)
+        else:
+            print('Invalid protocol version.')
+
+        dec_item = deepcopy(item)
+        dec_item['content'] = json.loads(dec_content)
+        return dec_item
+
+    def pure_encryptString002(self, string_to_encrypt, encryption_key, auth_key, uuid):
+        IV = hex(random.getrandbits(128))
+        IV = IV[2:].rjust(32, '0') # remove '0x', pad to 32
+
+        cipher = AES.new(unhexlify(encryption_key), AES.MODE_CBC, unhexlify(IV))
+        pt = string_to_encrypt.encode()
+        pad = 16 - len(pt) % 16
+        padded_pt = pt + pad * bytes([pad])
+        ciphertext = b64encode(cipher.encrypt(padded_pt)).decode()
+
+        string_to_auth = ':'.join(['002', uuid, IV, ciphertext])
+        auth_hash = hmac.new(unhexlify(auth_key), string_to_auth.encode(), 'sha256').digest()
+        auth_hash = hexlify(auth_hash).decode()
+
+        result = ':'.join(['002', auth_hash, uuid, IV, ciphertext])
+
+        return result
+
+    def pure_decryptString002(self, string_to_decrypt, encryption_key, auth_key, uuid):
+        components = string_to_decrypt.split(':')
+        version = components[0]
+        auth_hash = components[1]
+        local_uuid = components[2]
+        IV = components[3]
+        ciphertext = components[4]
+
+        if local_uuid != uuid:
+            print('UUID does not match.')
+            return
+
+        string_to_auth = ':'.join([version, uuid, IV, ciphertext])
+        local_auth_hash = hmac.new(unhexlify(auth_key), string_to_auth.encode(), 'sha256').digest()
+        local_auth_hash = hexlify(local_auth_hash).decode()
+
+        if local_auth_hash != auth_hash:
+            print('Message has been tampered with.')
+            return
+
+        cipher = AES.new(unhexlify(encryption_key), AES.MODE_CBC, unhexlify(IV))
+        result = cipher.decrypt(b64decode(ciphertext))
+        result = result[:-result[-1]] # remove PKCS#7 padding
+
+        return result.decode()