From 3bb63d96b61e9e17108320efd89088d1f08b495a Mon Sep 17 00:00:00 2001
From: Kévin Le Gouguec <kevin.legouguec@airbus.com>
Date: Tue, 30 Apr 2019 15:41:59 +0200
Subject: Homogénéisation de la gestion de l'index de bloc dans les tweaks
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- "block number" → "block index"

- "192" → "t"

- boucle de copie de l'index

- utilisation de size_t :

    - par  définition, aucune  implémentation ne  pourra traiter  plus
      d'octets que SIZE_MAX (donc pas plus de blocs),

    - pas de  raison de  forcer un  index de 64  bits sur  ces pauvres
      ATmega et MSP430.
---
 src/ref/lilliput-i.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

(limited to 'src/ref/lilliput-i.c')

diff --git a/src/ref/lilliput-i.c b/src/ref/lilliput-i.c
index 97c2117..3ba7ea2 100644
--- a/src/ref/lilliput-i.c
+++ b/src/ref/lilliput-i.c
@@ -35,32 +35,26 @@ static const uint8_t _0n[BLOCK_BYTES] = {
 static void _fill_msg_tweak(
     uint8_t       prefix,
     const uint8_t N[NONCE_BYTES],
-    uint64_t      block_nb,
+    size_t        block_index,
     uint8_t       tweak[TWEAK_BYTES]
 )
 {
-    /* The 192-bit tweak is filled as follows:
+    /* With an s-bit block index, the t-bit tweak is filled as follows:
      *
-     * - bits   1- 68: block number
-     *          1- 64: actual 64-bit block number
-     *         64- 68: 0-padding
-     * - bits  67-188: nonce
-     * - bits 189-192: constant 4-bit prefix
+     * - bits [      1, t-|N|-4]: block index
+     *        [      1,       s]: actual 64-bit block index
+     *        [    s+1, t-|N|-4]: 0-padding
+     * - bits [t-|N|-4,     t-4]: nonce
+     * - bits [    t-3,       t]: 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;
-    }
+    copy_block_index(block_index, tweak);
 
-    tweak[sizeof(block_nb)] = lower_nibble(N[0]) << 4;
+    tweak[sizeof(block_index)] = lower_nibble(N[0]) << 4;
 
     for (size_t i=1; i<NONCE_BYTES; i++)
     {
-        tweak[sizeof(block_nb)+i] = lower_nibble(N[i]) << 4 ^ upper_nibble(N[i-1]);
+        tweak[sizeof(block_index)+i] = lower_nibble(N[i]) << 4 ^ upper_nibble(N[i-1]);
     }
 
     tweak[TWEAK_BYTES-1] = prefix << 4 ^ upper_nibble(N[NONCE_BYTES-1]);
-- 
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