From 4fefe35fd63842b827016acecfadae891d0da953 Mon Sep 17 00:00:00 2001
From: Kévin Le Gouguec <kevin.legouguec@airbus.com>
Date: Tue, 27 Nov 2018 10:37:56 +0100
Subject: Extraction du traitement des données authentifiées
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Commun à ΘCB3 et SCT-2.
---
 src/ae-common.h | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)

(limited to 'src/ae-common.h')

diff --git a/src/ae-common.h b/src/ae-common.h
index 6343f98..da5d04d 100644
--- a/src/ae-common.h
+++ b/src/ae-common.h
@@ -65,5 +65,66 @@ static inline void pad10(size_t X_len, const uint8_t X[X_len], uint8_t padded[BL
     }
 }
 
+static inline void _fill_ad_tweak(
+    uint8_t  prefix,
+    uint64_t block_nb,
+    uint8_t  tweak[TWEAK_BYTES]
+)
+{
+    /* The t-bit tweak is filled as follows:
+     *
+     * - bits [  1, t-4]: block number
+     *        [  1,  64]: actual 64-bit block number
+     *        [ 65, t-4]: 0-padding
+     * - bits [t-3,   t]: constant 4-bit prefix
+     */
+
+    for (size_t i=0; i<sizeof(block_nb); i++)
+    {
+        uint64_t mask = (uint64_t)0xff << 8*i;
+        uint8_t b = (mask & block_nb) >> 8*i;
+
+        tweak[i] = b;
+    }
+
+    /* Assume padding bytes have already been memset to 0. */
+
+    tweak[TWEAK_BYTES-1] |= prefix << 4;
+}
+
+static void process_associated_data(
+    const uint8_t key[KEY_BYTES],
+    size_t        A_len,
+    const uint8_t A[A_len],
+    uint8_t       Auth[BLOCK_BYTES]
+)
+{
+    uint8_t Ek_Ai[BLOCK_BYTES];
+    uint8_t tweak[TWEAK_BYTES];
+
+    memset(tweak, 0, TWEAK_BYTES);
+    memset(Auth, 0, BLOCK_BYTES);
+
+    size_t l_a = A_len / BLOCK_BYTES;
+    size_t rest = A_len % BLOCK_BYTES;
+
+    for (size_t i=0; i<l_a; i++)
+    {
+        _fill_ad_tweak(0x2, i, tweak);
+        encrypt(key, tweak, &A[i*BLOCK_BYTES], Ek_Ai);
+        xor_into(Auth, Ek_Ai);
+    }
+
+    if (rest != 0)
+    {
+        uint8_t A_rest[BLOCK_BYTES];
+        pad10(rest, &A[l_a*BLOCK_BYTES], A_rest);
+        _fill_ad_tweak(0x6, l_a, tweak);
+        encrypt(key, tweak, A_rest, Ek_Ai);
+        xor_into(Auth, Ek_Ai);
+    }
+}
+
+
 
 #endif /* AE_COMMON_H */
-- 
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