Use PKCS#7 for encryption

Closes #156

jrnl/Journal.py

@@ -66,10 +66,18 @@ class Journal(object):
         except ValueError:
             util.prompt("ERROR: Your journal file seems to be corrupted. You do have a backup, don't you?")
             sys.exit(1)
-        padding = " ".encode("utf-8")
+
-        if not plain.endswith(padding):  # Journals are always padded
+        padding_length = ord(plain[-1])
+        if padding_length > AES.block_size and padding_length != 32:
+            # 32 is the space character and is kept for backwards compatibility
+            return None
+        elif padding_length == 32:
+            plain = plain.strip()
+        elif plain[-padding_length:] != util.int2byte(padding_length) * padding_length:
+            # Invalid padding!
             return None
         else:
+            plain = plain[:-padding_length]
         return plain.decode("utf-8")
 
     def _encrypt(self, plain):
@@ -80,7 +88,8 @@ class Journal(object):
         iv = Random.new().read(AES.block_size)
         crypto = AES.new(self.key, AES.MODE_CBC, iv)
         plain = plain.encode("utf-8")
-        plain += b" " * (AES.block_size - len(plain) % AES.block_size)
+        padding_length = AES.block_size - len(plain) % AES.block_size
+        plain += util.int2byte(padding_length) * padding_length
         return iv + crypto.encrypt(plain)
 
     def make_key(self, password):

jrnl/util.py

@@ -141,3 +141,7 @@ def slugify(string):
     slug = re.sub(r'[-\s]+', '-', no_punctuation)
     return u(slug)
 
+def int2byte(i):
+    """Converts an integer to a byte.
+    This is equivalent to chr() in Python 2 and bytes((i,)) in Python 3."""
+    return chr(i) if PY2 else bytes((i,))