Homogénéisation de la gestion de l'index de bloc dans les tweaks

- "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.

1 files changed, 14 insertions, 13 deletions

diff --git a/src/ref/lilliput-ii.c b/src/ref/lilliput-ii.c
index a371521..6811d49 100644
--- a/src/ref/lilliput-ii.c
+++ b/src/ref/lilliput-ii.c
@@ -28,37 +28,38 @@ This file implements Lilliput-AE's nonce-misuse-resistant mode based on SCT-2.
 
 static void _init_msg_tweak(const uint8_t tag[TAG_BYTES], uint8_t tweak[TWEAK_BYTES])
 {
-    /* The t-bit tweak is filled as follows:
+    /* With an s-bit block index, the t-bit tweak is filled as follows:
      *
      * - bits [  1, t-1]: tag + block index
-     *        [  1,  64]: tag[ 1.. 64] XOR block index
-     *        [ 65, t-1]: tag[65..t-1]
+     *        [  1,   s]: tag[1..s] XOR block index
+     *        [s+1, t-1]: tag[s+1..t-1]
      * - bit t: 1
      *
-     * This function sets bits 65 to t once and for all.
+     * This function sets bits s+1 to t once and for all.
      */
 
-    memcpy(tweak+sizeof(uint64_t), tag+sizeof(uint64_t), TAG_BYTES-sizeof(uint64_t));
+    memcpy(tweak+sizeof(size_t), tag+sizeof(size_t), TAG_BYTES-sizeof(size_t));
     tweak[TWEAK_BYTES-1] |= 0x80;
 }
 
-static void _fill_msg_tweak(const uint8_t tag[TAG_BYTES], uint64_t block_index, uint8_t tweak[TWEAK_BYTES])
+static void _fill_msg_tweak(const uint8_t tag[TAG_BYTES], size_t block_index, uint8_t tweak[TWEAK_BYTES])
 {
-    /* The t-bit tweak is filled as follows:
+    /* With an s-bit block index, the t-bit tweak is filled as follows:
      *
      * - bits [  1, t-1]: tag + block index
-     *        [  1,  64]: tag[ 1.. 64] XOR block index
-     *        [ 65, t-1]: tag[65..t-1]
+     *        [  1,   s]: tag[1..s] XOR block index
+     *        [s+1, t-1]: tag[s+1..t-1]
      * - bit t: 1
      *
-     * This function assumes bits 65 to t have already been set, and
-     * only sets bits 1 to 64.
+     * This function assumes bits s+1 to t have already been set, and
+     * only sets bits 1 to s.
      */
 
+    copy_block_index(block_index, tweak);
+
     for (size_t i=0; i<sizeof(block_index); i++)
     {
-        uint8_t index_i = block_index >> i*8 & 0xff;
-        tweak[i] = tag[i] ^ index_i;
+        tweak[i] ^= tag[i];
     }
 }