lilliput-ae-reference-implementation

commit 62cff183e2e9e67549db0461589a05138ce2ed00
parent 97db0c6e5dc3576cdcca339acf3bb33b698dccd0
Author: Kévin Le Gouguec <kevin.legouguec@gmail.com>
Date:   Sun, 24 Mar 2019 17:33:38 +0100

[implem-python] Remplacement de _low_part par du "tranchage" natif

Diffstat:
M
src/add_python/lilliput/ae_mode_1.py
 | 
28
++--------------------------

1 file changed, 2 insertions(+), 26 deletions(-)
diff --git a/src/add_python/lilliput/ae_mode_1.py b/src/add_python/lilliput/ae_mode_1.py
@@ -36,30 +36,6 @@ TWEAK_BITS = 192
 TWEAK_BYTES = TWEAK_BITS//8
 
 
-def _low_part(array, number_bits):
-    shifted = 0
-    for byte in range(0, len(array)):
-        shifted |= (array[byte] << (8 * byte))
-
-    mask = 0
-    for bit in range(0, number_bits):
-        mask |= (0x1 << bit)
-
-    lower_part = shifted & mask
-
-    will_pad = 0
-    if number_bits % 8 != 0:
-        will_pad = 1
-
-    lower_part_byte = []
-    nb_bytes = number_bits//8 + will_pad
-    for byte in range(nb_bytes):
-        lower_part_byte.append(lower_part & 0xff)
-        lower_part = lower_part >> 8
-
-    return lower_part_byte
-
-
 class _MessageTweak(Enum):
     BLOCK = 0b0000
     NO_PADDING = 0b0001
@@ -106,7 +82,7 @@ def _treat_message_enc(M, N, key):
         tweak = _tweak_message(N, l, _MessageTweak.PAD)
         pad = tbc.encrypt(tweak, key, [0 for byte in range(0, BLOCK_BYTES)])
 
-        lower_part = _low_part(pad, padding_bytes*8)
+        lower_part = pad[:padding_bytes]
         C.append(xor(M[l], lower_part))
         tweak_final = _tweak_message(N, l+1, _MessageTweak.FINAL)
         Final = tbc.encrypt(tweak_final, key, checksum)
@@ -135,7 +111,7 @@ def _treat_message_dec(C, N, key):
     else:
         tweak = _tweak_message(N, l, _MessageTweak.PAD)
         pad = tbc.encrypt(tweak, key, [0 for byte in range(0, BLOCK_BYTES)])
-        lower_part = _low_part(pad, padding_bytes*8)
+        lower_part = pad[:padding_bytes]
         M.append(xor(C[l], lower_part))
 
         m_padded = pad10(M[l])