(un)pad_iso10126

[pygost.git] / pygost / gost3413.py

diff --git a/pygost/gost3413.py b/pygost/gost3413.py
index 93244da09d720a08d2f6ec573425e1b918f3f82d..27f0c30dc79a75de4e66f8e284455221474fa215 100644 (file)
--- a/pygost/gost3413.py
+++ b/pygost/gost3413.py
@@ -18,6 +18,8 @@
 This module currently includes only padding methods.
 """
 
+from os import urandom
+
 from pygost.utils import bytes2long
 from pygost.utils import long2bytes
 from pygost.utils import strxor
@@ -365,3 +367,26 @@ def mac_acpkm_master(algo_class, encrypter, key_section_size, section_size, bs,
         strxor(pad3(tail, bs), prev),
         k1 if len(tail) == bs else k2,
     ))
+
+
+def pad_iso10126(data, blocksize):
+    """ISO 10126 padding
+
+    Does not exist in 34.13, but added for convenience.
+    It uses urandom call for getting the randomness.
+    """
+    pad_len = blocksize - len(data) % blocksize
+    if pad_len == 0:
+        pad_len = blocksize
+    return b"".join((data, urandom(pad_len - 1), bytes((pad_len,))))
+
+
+def unpad_iso10126(data, blocksize):
+    """Unpad :py:func:`pygost.gost3413.pad_iso10126`
+    """
+    if len(data) % blocksize != 0:
+        raise ValueError("Data length is not multiple of blocksize")
+    pad_len = bytearray(data)[-1]
+    if pad_len > blocksize:
+        raise ValueError("Padding length is bigger than blocksize")
+    return data[:-pad_len]