[implem-python] Réécriture de certains range() dans tbc.py

IME, itérer sur un range() est rarement la façon la plus expressive de
faire les choses ; les alternatives imposent une structure qui rendent
l'intention  plus claire.  E.g. quand  on voit  une compréhension,  on
comprend que l'auteur cherche à  filtrer et/ou transformer ce sur quoi
il itère.

Réutilisation  de  xor_state(),  renommé  xor()  puisqu'il  sert  dans
plusieurs situations.

Séparation  de   ce  xor()  et   des  fonctions  communes   aux  modes
authentifiés pour éviter un import circulaire.

1 files changed, 2 insertions, 92 deletions

diff --git a/src/add_python/lilliput/helpers.py b/src/add_python/lilliput/helpers.py
index 65989d0..048aac7 100644
--- a/src/add_python/lilliput/helpers.py
+++ b/src/add_python/lilliput/helpers.py
@@ -1,92 +1,2 @@
-from .constants import BLOCK_BITS, BLOCK_BYTES
-from . import tbc
-
-
-def bytes_to_block_matrix(array):
-    vector = list(array)
-
-    blocks_nb = len(vector)//BLOCK_BYTES
-
-    block_starts = (
-        i*BLOCK_BYTES for i in range(blocks_nb)
-    )
-
-    matrix = [
-        vector[start:start+BLOCK_BYTES] for start in block_starts
-    ]
-
-    padding_len = len(vector)%BLOCK_BYTES
-
-    if padding_len > 0:
-        padding = vector[-padding_len:]
-        matrix.append(padding)
-
-    return matrix
-
-
-def block_matrix_to_bytes(matrix):
-    return bytes(byte for block in matrix for byte in block)
-
-
-def xor_state(state1, state2):
-    return [s1^s2 for (s1, s2) in zip(state1, state2)]
-
-
-def pad10(X):
-    zeroes = [0] * (BLOCK_BYTES-len(X)-1)
-    return zeroes + [0b10000000] + X
-
-
-def _tweak_associated_data(t, i, padded):
-    t_bytes = t//8
-    tweak = [0]*(t_bytes)
-
-    mask = 0xff
-    for byte in range(t_bytes-1):
-        tweak[byte] = (i & mask) >> (byte * 8)
-        mask = mask << 8
-
-    mask = (0xf << (8 * t_bytes-1))
-    tweak[-1] = (i & mask) >> ((t_bytes-1)*8)
-    if not padded:
-        tweak[-1] |= 0x20
-    else:
-        tweak[-1] |= 0x60
-
-    return tweak
-
-
-def build_auth(t, A, key):
-    Auth = [0 for byte in range(0, BLOCK_BYTES)]
-    l_a = len(A)//BLOCK_BYTES
-    need_padding = len(A)%BLOCK_BYTES > 0
-
-    A = bytes_to_block_matrix(A)
-
-    for i in range(0, l_a):
-        tweak = _tweak_associated_data(t, i, padded=False)
-        enc = tbc.encrypt(tweak, key, A[i])
-        Auth = xor_state(Auth, enc)
-
-    if not need_padding:
-        return Auth
-
-    tweak = _tweak_associated_data(t, l_a, padded=True)
-    ad_padded = pad10(A[l_a])
-    enc = tbc.encrypt(tweak, key, ad_padded)
-    Auth = xor_state(Auth, enc)
-
-    return Auth
-
-
-class TagValidationError(Exception):
-    def __init__(self, announced, computed):
-        msg = '\n'.join((
-            'Invalid tag:',
-            announced.hex().upper()+' (announced)',
-            computed.hex().upper()+' (computed)'
-        ))
-
-        super().__init__(msg)
-        self._announced = announced
-        self._computed = computed
+def xor(array1, array2):
+    return [a1^a2 for (a1, a2) in zip(array1, array2)]