From bac28f498c5fee10720c8ed71988434e05d9197f Mon Sep 17 00:00:00 2001
From: Kévin Le Gouguec <kevin.legouguec@airbus.com>
Date: Fri, 22 Mar 2019 10:38:19 +0100
Subject: [implem-python] Création d'un paquet "lilliput"
MIME-Version: 1.0
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---
 python/lilliput/lilliput_ae_2.py | 127 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 python/lilliput/lilliput_ae_2.py

(limited to 'python/lilliput/lilliput_ae_2.py')

diff --git a/python/lilliput/lilliput_ae_2.py b/python/lilliput/lilliput_ae_2.py
new file mode 100644
index 0000000..61aa86e
--- /dev/null
+++ b/python/lilliput/lilliput_ae_2.py
@@ -0,0 +1,127 @@
+"""
+    SCT 2 for lilliput ae 2
+"""
+
+from .constants import BLOCK_BYTES
+from .helpers import (
+    ArrayToBlockbytesMatrix,
+    BlockbytesMatrixToBytes,
+    BuildAuth,
+    Padding10LSB,
+    TagValidationError,
+    XorState
+)
+from . import tbc
+
+
+TWEAK_BITS = 128
+TWEAK_BYTES = TWEAK_BITS//8
+
+
+def TweakTag(j, padded):
+    tweak = [0 for byte in range(0, TWEAK_BYTES)]
+
+    tweak[TWEAK_BYTES - 1] |= ((j >> 120) & 0xf)
+    for byte in range(TWEAK_BYTES - 2, -1, -1):
+        tweak[byte] = (j >> (8 * byte)) & 0xff
+
+    if padded:
+        tweak[TWEAK_BYTES - 1] |= 0x40
+
+    return tweak
+
+
+def TweakTagEnd(N):
+    tweak = [0 for byte in range(0, TWEAK_BYTES)]
+
+    for byte in range(0, TWEAK_BYTES - 1):
+        tweak[byte] = N[byte]
+    tweak[TWEAK_BYTES - 1] = 0x10
+
+    return tweak
+
+
+def AddTagJ(tag, j):
+    array_j = [0 for byte in range(0, TWEAK_BYTES)]
+    for byte in range(0, TWEAK_BYTES):
+        array_j[byte] = (j >> (byte * 8))
+
+    xorr = XorState(tag, array_j)
+
+    xorr[TWEAK_BYTES - 1] |= 0x80
+
+    return xorr
+
+
+def MesssageAuthTag(M, N, Auth, key):
+    l = len(M)//BLOCK_BYTES
+    need_padding = len(M)%BLOCK_BYTES > 0
+
+    tag = list(Auth)
+    M = ArrayToBlockbytesMatrix(M)
+
+    for j in range(0, l):
+        tweak = TweakTag(j, False)
+        encryption = tbc.encrypt(tweak, key, M[j])
+        tag = XorState(tag, encryption)
+
+    if need_padding:
+        tweak = TweakTag(l, True)
+        m_padded = Padding10LSB(M[l])
+        encryption = tbc.encrypt(tweak, key, m_padded)
+        tag = XorState(tag, encryption)
+
+    tweak = TweakTagEnd(N)
+    encryption = tbc.encrypt(tweak, key, tag)
+    tag = encryption
+
+    return tag
+
+
+def MessageEncryption(M, N, tag, key):
+    l = len(M)//BLOCK_BYTES
+    need_padding = len(M)%BLOCK_BYTES > 0
+
+    M = ArrayToBlockbytesMatrix(M)
+    C = []
+
+    for j in range(0, l):
+        tweak = AddTagJ(tag, j)
+        padded_nonce = list(N) + [0x00]
+        encryption = tbc.encrypt(tweak, key, padded_nonce)
+        C.append(XorState(M[j], encryption))
+
+    if need_padding:
+        tweak = AddTagJ(tag, l)
+        padded_nonce = list(N) + [0x00]
+        encryption = tbc.encrypt(tweak, key, padded_nonce)
+        C.append(XorState(M[l], encryption))
+
+    return C
+
+
+################################################################################
+def encrypt(A, M, N, key):
+    K = list(key)
+
+    Auth = BuildAuth(TWEAK_BITS, A, K)
+    tag = MesssageAuthTag(M, N, Auth, K)
+    C = MessageEncryption(M, N, tag, K)
+
+    return BlockbytesMatrixToBytes(C), bytes(tag)
+
+
+def decrypt(A, C, N, tag, key):
+    K = list(key)
+    tag = list(tag)
+
+    M = BlockbytesMatrixToBytes(
+        MessageEncryption(C, N, tag, K)
+    )
+    Auth = BuildAuth(TWEAK_BITS, A, K)
+    tag2 = MesssageAuthTag(M, N, Auth, K)
+
+    if tag != tag2:
+        raise TagValidationError(tag, tag2)
+
+    return M
-- 
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