1 files changed, 6 insertions, 17 deletions
diff --git a/python/helpers.py b/python/helpers.py
index 07affa9..be4b406 100644
--- a/python/helpers.py
+++ b/python/helpers.py
@@ -32,19 +32,9 @@ def XorState(state1, state2):
     return [s1^s2 for (s1, s2) in zip(state1, state2)]
 
 
-def Padding10LSB(array, number_bits):
-    shifted = 0
-    for byte in range(0, len(array)):
-        shifted |= (array[byte] << (8 * byte))
-    shifted = (shifted << (BLOCK_BITS - number_bits)) & 0xffffffffffffffffffffffffffffffff
-
-    padded = shifted | (0x1 << (BLOCK_BITS - number_bits - 1))
-
-    array_padded = [0 for byte in range(0, BLOCK_BYTES)]
-    for byte in range(0, BLOCK_BYTES):
-        array_padded[byte] = (padded & (0xff << (8 * byte))) >> (8 * byte)
-
-    return array_padded
+def Padding10LSB(X):
+    zeroes = [0] * (BLOCK_BYTES-len(X)-1)
+    return zeroes + [0b10000000] + X
 
 
 def _tweakAssociatedData(t, i, padded):
@@ -69,8 +59,7 @@ def _tweakAssociatedData(t, i, padded):
 def BuildAuth(t, A, key):
     Auth = [0 for byte in range(0, BLOCK_BYTES)]
     l_a = len(A)//BLOCK_BYTES
-
-    padding_bytes = len(A)%BLOCK_BYTES
+    need_padding = len(A)%BLOCK_BYTES > 0
 
     A = ArrayToBlockbytesMatrix(A)
 
@@ -79,11 +68,11 @@ def BuildAuth(t, A, key):
         enc = LilliputTBCEnc(tweak, key, A[i])
         Auth = XorState(Auth, enc)
 
-    if padding_bytes == 0:
+    if not need_padding:
         return Auth
 
     tweak = _tweakAssociatedData(t, l_a, padded=True)
-    ad_padded = Padding10LSB(A[l_a], padding_bytes*8)
+    ad_padded = Padding10LSB(A[l_a])
     enc = LilliputTBCEnc(tweak, key, ad_padded)
     Auth = XorState(Auth, enc)