Rewrite ghash C implementation.

5 files changed, 62 insertions, 172 deletions

diff --git a/ChangeLog b/ChangeLog
index 67986932..f3e2f4bb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2023-04-07  Niels Möller  <nisse@lysator.liu.se>
+
+	* ghash-update.c (gcm_gf_mul): Rewrite to avoid side channel
+	leakage. Now processes message bits one at a time, using tabulated
+	values of the key premultiplied by appropriate powers of x, so
+	that the table is accessed in a fixed sequential order.
+	Performance penalty, on x86_64, is roughly 3 times.
+	(shift_table): Deleted table.
+	(gcm_gf_shift_8): Deleted function.
+
+	* ghash-set-key.c (_ghash_set_key): Rewrite table generation.
+
+	* gcmdata.c: Deleted.
+
 2023-04-03  Niels Möller  <nisse@lysator.liu.se>
 
 	From Mamone Tarsha:
diff --git a/Makefile.in b/Makefile.in
index 081337a8..2464e17e 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -250,7 +250,7 @@ INSTALL_HEADERS = $(HEADERS) version.h @IF_MINI_GMP@ mini-gmp.h
 SOURCES = $(nettle_SOURCES) $(hogweed_SOURCES) \
 	  $(getopt_SOURCES) $(internal_SOURCES) \
 	  $(OPT_SOURCES) \
-	  aesdata.c desdata.c twofishdata.c shadata.c gcmdata.c eccdata.c
+	  aesdata.c desdata.c twofishdata.c shadata.c eccdata.c
 
 # NOTE: This list must include all source files, with no duplicates,
 # independently of which source files are included in the build.
@@ -683,7 +683,6 @@ clean-here:
 		desdata$(EXEEXT_FOR_BUILD) \
 		twofishdata$(EXEEXT_FOR_BUILD) \
 		shadata$(EXEEXT_FOR_BUILD) \
-		gcmdata$(EXEEXT_FOR_BUILD) \
 		eccdata$(EXEEXT_FOR_BUILD) eccdata.stamp
 	-rm -rf .lib libnettle.stamp libhogweed.stamp
 
diff --git a/gcmdata.c b/gcmdata.c
deleted file mode 100644
index 2d57b46a..00000000
--- a/gcmdata.c
+++ /dev/null
@@ -1,84 +0,0 @@
-/* gcmdata.c
-
-   Galois counter mode, specified by NIST,
-   http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf
-
-   Generation of fixed multiplication tables.
-
-   Copyright (C) 2011 Niels Möller
-
-   This file is part of GNU Nettle.
-
-   GNU Nettle is free software: you can redistribute it and/or
-   modify it under the terms of either:
-
-     * the GNU Lesser General Public License as published by the Free
-       Software Foundation; either version 3 of the License, or (at your
-       option) any later version.
-
-   or
-
-     * the GNU General Public License as published by the Free
-       Software Foundation; either version 2 of the License, or (at your
-       option) any later version.
-
-   or both in parallel, as here.
-
-   GNU Nettle is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   General Public License for more details.
-
-   You should have received copies of the GNU General Public License and
-   the GNU Lesser General Public License along with this program.  If
-   not, see http://www.gnu.org/licenses/.
-*/
-
-#include <stdio.h>
-#include <stdlib.h>
-
-#define GHASH_POLYNOMIAL 0xE1
-
-
-/* When x is shifted out over the block edge, add multiples of the
-   defining polynomial to eliminate each bit. */
-static unsigned
-reduce(unsigned x)
-{
-  unsigned p = GHASH_POLYNOMIAL << 1;
-  unsigned y = 0;
-  for (; x; x >>= 1, p <<= 1)
-    if (x & 1)
-      y ^= p;
-  return y;
-}
-
-int
-main(int argc, char **argv)
-{
-  unsigned i;
-  printf("4-bit table:\n");
-  
-  for (i = 0; i<16; i++)
-    {
-      unsigned x;
-      if (i && !(i%8))
-	printf("\n");
-
-      x = reduce(i << 4);
-      printf("W(%02x,%02x),", x >> 8, x & 0xff);
-    }
-  printf("\n\n");
-  printf("8-bit table:\n");
-  for (i = 0; i<256; i++)
-    {
-      unsigned x;
-      if (i && !(i%8))
-	printf("\n");
-
-      x = reduce(i);
-      printf("W(%02x,%02x),", x >> 8, x & 0xff);
-    }
-  printf("\n");
-  return EXIT_SUCCESS;
-}
diff --git a/ghash-set-key.c b/ghash-set-key.c
index 0e91afcb..58ebb633 100644
--- a/ghash-set-key.c
+++ b/ghash-set-key.c
@@ -51,25 +51,43 @@ _nettle_ghash_set_key_c (struct gcm_key *ctx, const union nettle_block16 *key);
 #define _nettle_ghash_set_key _nettle_ghash_set_key_c
 #endif
 
+#if GCM_TABLE_BITS < 7
+# error Unsupported table size.
+#endif
+
 /* Implements a lookup table for processors without carryless-mul
    instruction. */
 void
 _ghash_set_key (struct gcm_key *ctx, const union nettle_block16 *key)
 {
-  /* Middle element if GCM_TABLE_BITS > 0, otherwise the first
-     element */
-  unsigned i = (1<<GCM_TABLE_BITS)/2;
-  block16_zero (&ctx->h[0]);
-  ctx->h[i] = *key;
-
-  /* Algorithm 3 from the gcm paper. First do powers of two, then do
-     the rest by adding. */
-  while (i /= 2)
-    block16_mulx_ghash (&ctx->h[i], &ctx->h[2*i]);
-  for (i = 2; i < 1<<GCM_TABLE_BITS; i *= 2)
-    {
-      unsigned j;
-      for (j = 1; j < i; j++)
-	block16_xor3 (&ctx->h[i+j], &ctx->h[i], &ctx->h[j]);
-    }
+  /* Table elements hold the key, premultiplied by all needed powers
+     of x. Element ordering follows the order bits are processed in
+     _ghash_update, first u64[0] bits, starting from the least
+     significant end, then the u64[1] bits, also from least
+     significant end. In the gcm bit order, bits (left to right)
+     correspond to x powers (the numbers) like
+
+       |0...7|8...15|...|56...63|64...71|72...79|...|120...127|
+
+     where | indicates the byte boundaries. On little endian, these
+     bits are in u64 like
+
+       u64[0]: | 56...63   48...55   40...47  32...39  24...31 16...23  8...15  0...7|
+       u64[1]: |120...127 112...129 104...111 96...103 88...95 80...87 72...79 64...71|
+
+     With big-endian, we instead get
+
+       u64[0]:  |0...63|
+       u64[1]: |64...127|
+  */
+#if WORDS_BIGENDIAN
+# define INDEX_PERMUTE 63
+#else
+# define INDEX_PERMUTE 7
+#endif
+  unsigned i;
+
+  block16_set (&ctx->h[INDEX_PERMUTE], key);
+  for (i = 1; i < 128; i++)
+    block16_mulx_ghash(&ctx->h[i ^ INDEX_PERMUTE], &ctx->h[(i-1) ^ INDEX_PERMUTE]);
 }
diff --git a/ghash-update.c b/ghash-update.c
index 6eb19d80..7cd19643 100644
--- a/ghash-update.c
+++ b/ghash-update.c
@@ -44,7 +44,7 @@
 #include "ghash-internal.h"
 #include "block-internal.h"
 
-#if GCM_TABLE_BITS != 8
+#if GCM_TABLE_BITS < 7
 # error Unsupported table size.
 #endif
 
@@ -54,83 +54,26 @@ const uint8_t *
 _nettle_ghash_update_c (const struct gcm_key *ctx, union nettle_block16 *state,
 			size_t blocks, const uint8_t *data);
 #define _nettle_ghash_update _nettle_ghash_update_c
-
-#endif
-#if WORDS_BIGENDIAN
-# define W(left,right) (0x##left##right)
-#else
-# define W(left,right) (0x##right##left)
 #endif
 
-static const uint16_t
-shift_table[0x100] = {
-  W(00,00),W(01,c2),W(03,84),W(02,46),W(07,08),W(06,ca),W(04,8c),W(05,4e),
-  W(0e,10),W(0f,d2),W(0d,94),W(0c,56),W(09,18),W(08,da),W(0a,9c),W(0b,5e),
-  W(1c,20),W(1d,e2),W(1f,a4),W(1e,66),W(1b,28),W(1a,ea),W(18,ac),W(19,6e),
-  W(12,30),W(13,f2),W(11,b4),W(10,76),W(15,38),W(14,fa),W(16,bc),W(17,7e),
-  W(38,40),W(39,82),W(3b,c4),W(3a,06),W(3f,48),W(3e,8a),W(3c,cc),W(3d,0e),
-  W(36,50),W(37,92),W(35,d4),W(34,16),W(31,58),W(30,9a),W(32,dc),W(33,1e),
-  W(24,60),W(25,a2),W(27,e4),W(26,26),W(23,68),W(22,aa),W(20,ec),W(21,2e),
-  W(2a,70),W(2b,b2),W(29,f4),W(28,36),W(2d,78),W(2c,ba),W(2e,fc),W(2f,3e),
-  W(70,80),W(71,42),W(73,04),W(72,c6),W(77,88),W(76,4a),W(74,0c),W(75,ce),
-  W(7e,90),W(7f,52),W(7d,14),W(7c,d6),W(79,98),W(78,5a),W(7a,1c),W(7b,de),
-  W(6c,a0),W(6d,62),W(6f,24),W(6e,e6),W(6b,a8),W(6a,6a),W(68,2c),W(69,ee),
-  W(62,b0),W(63,72),W(61,34),W(60,f6),W(65,b8),W(64,7a),W(66,3c),W(67,fe),
-  W(48,c0),W(49,02),W(4b,44),W(4a,86),W(4f,c8),W(4e,0a),W(4c,4c),W(4d,8e),
-  W(46,d0),W(47,12),W(45,54),W(44,96),W(41,d8),W(40,1a),W(42,5c),W(43,9e),
-  W(54,e0),W(55,22),W(57,64),W(56,a6),W(53,e8),W(52,2a),W(50,6c),W(51,ae),
-  W(5a,f0),W(5b,32),W(59,74),W(58,b6),W(5d,f8),W(5c,3a),W(5e,7c),W(5f,be),
-  W(e1,00),W(e0,c2),W(e2,84),W(e3,46),W(e6,08),W(e7,ca),W(e5,8c),W(e4,4e),
-  W(ef,10),W(ee,d2),W(ec,94),W(ed,56),W(e8,18),W(e9,da),W(eb,9c),W(ea,5e),
-  W(fd,20),W(fc,e2),W(fe,a4),W(ff,66),W(fa,28),W(fb,ea),W(f9,ac),W(f8,6e),
-  W(f3,30),W(f2,f2),W(f0,b4),W(f1,76),W(f4,38),W(f5,fa),W(f7,bc),W(f6,7e),
-  W(d9,40),W(d8,82),W(da,c4),W(db,06),W(de,48),W(df,8a),W(dd,cc),W(dc,0e),
-  W(d7,50),W(d6,92),W(d4,d4),W(d5,16),W(d0,58),W(d1,9a),W(d3,dc),W(d2,1e),
-  W(c5,60),W(c4,a2),W(c6,e4),W(c7,26),W(c2,68),W(c3,aa),W(c1,ec),W(c0,2e),
-  W(cb,70),W(ca,b2),W(c8,f4),W(c9,36),W(cc,78),W(cd,ba),W(cf,fc),W(ce,3e),
-  W(91,80),W(90,42),W(92,04),W(93,c6),W(96,88),W(97,4a),W(95,0c),W(94,ce),
-  W(9f,90),W(9e,52),W(9c,14),W(9d,d6),W(98,98),W(99,5a),W(9b,1c),W(9a,de),
-  W(8d,a0),W(8c,62),W(8e,24),W(8f,e6),W(8a,a8),W(8b,6a),W(89,2c),W(88,ee),
-  W(83,b0),W(82,72),W(80,34),W(81,f6),W(84,b8),W(85,7a),W(87,3c),W(86,fe),
-  W(a9,c0),W(a8,02),W(aa,44),W(ab,86),W(ae,c8),W(af,0a),W(ad,4c),W(ac,8e),
-  W(a7,d0),W(a6,12),W(a4,54),W(a5,96),W(a0,d8),W(a1,1a),W(a3,5c),W(a2,9e),
-  W(b5,e0),W(b4,22),W(b6,64),W(b7,a6),W(b2,e8),W(b3,2a),W(b1,6c),W(b0,ae),
-  W(bb,f0),W(ba,32),W(b8,74),W(b9,b6),W(bc,f8),W(bd,3a),W(bf,7c),W(be,be),
-};
-#undef W
-
-static void
-gcm_gf_shift_8(union nettle_block16 *x)
-{
-  uint64_t reduce;
-
-  /* Shift uses big-endian representation. */
-#if WORDS_BIGENDIAN
-  reduce = shift_table[x->u64[1] & 0xff];
-  x->u64[1] = (x->u64[1] >> 8) | ((x->u64[0] & 0xff) << 56);
-  x->u64[0] = (x->u64[0] >> 8) ^ (reduce << 48);
-#else /* ! WORDS_BIGENDIAN */
-  reduce = shift_table[(x->u64[1] >> 56) & 0xff];
-  x->u64[1] = (x->u64[1] << 8) | (x->u64[0] >> 56);
-  x->u64[0] = (x->u64[0] << 8) ^ reduce;
-#endif /* ! WORDS_BIGENDIAN */
-}
-
 static void
 gcm_gf_mul (union nettle_block16 *x, const union nettle_block16 *table)
 {
-  union nettle_block16 Z;
+  uint64_t x0 = x->u64[0];
+  uint64_t x1 = x->u64[1];
+  uint64_t r0 = 0;
+  uint64_t r1 = 0;
   unsigned i;
-
-  Z = table[x->b[GCM_BLOCK_SIZE-1]];
-
-  for (i = GCM_BLOCK_SIZE-2; i > 0; i--)
+  for (i = 0; i < 64; i++, x0 >>= 1, x1 >>= 1)
     {
-      gcm_gf_shift_8(&Z);
-      block16_xor(&Z, &table[x->b[i]]);
+      uint64_t m0 = -(x0 & 1);
+      uint64_t m1 = -(x1 & 1);
+      r0 ^= m0 & table[i].u64[0];
+      r1 ^= m0 & table[i].u64[1];
+      r0 ^= m1 & table[64+i].u64[0];
+      r1 ^= m1 & table[64+i].u64[1];
     }
-  gcm_gf_shift_8(&Z);
-  block16_xor3(x, &Z, &table[x->b[0]]);
+  x->u64[0] = r0; x->u64[1] = r1;
 }
 
 const uint8_t *