Merge branch 'refactor-python-implem'

1 files changed, 104 insertions, 0 deletions

diff --git a/src/add_python/lilliput/ae_common.py b/src/add_python/lilliput/ae_common.py
new file mode 100644
index 0000000..b94be1b
--- /dev/null
+++ b/src/add_python/lilliput/ae_common.py
@@ -0,0 +1,104 @@
+# Implementation of the Lilliput-AE tweakable block cipher.
+#
+# Authors, hereby denoted as "the implementer":
+#     Kévin Le Gouguec,
+#     Léo Reynaud
+#     2019.
+#
+# For more information, feedback or questions, refer to our website:
+# https://paclido.fr/lilliput-ae
+#
+# To the extent possible under law, the implementer has waived all copyright
+# and related or neighboring rights to the source code in this file.
+# http://creativecommons.org/publicdomain/zero/1.0/
+
+"""Helper functions used in both Lilliput-I and Lilliput-II."""
+
+
+from .constants import BLOCK_BITS, BLOCK_BYTES
+from .helpers import xor
+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 pad10(X):
+    zeroes = [0] * (BLOCK_BYTES-len(X)-1)
+    return zeroes + [0b10000000] + X
+
+
+def integer_to_byte_array(i, n):
+    return list(i.to_bytes(n, 'little'))
+
+
+def _tweak_associated_data(t, i, padded):
+    tweak = integer_to_byte_array(i, t//8)
+
+    prefix = 0b0110 if padded else 0b0010
+
+    # Clear upper 4 bits and set them to prefix.
+    tweak[-1] &= 0b00001111
+    tweak[-1] = prefix << 4
+
+    return tweak
+
+
+def build_auth(t, A, key):
+    Auth = [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(l_a):
+        tweak = _tweak_associated_data(t, i, padded=False)
+        enc = tbc.encrypt(tweak, key, A[i])
+        Auth = xor(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(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