libgcrypt/libgcrypt-1.10.0-marvin.patch

From a611e3a25d61505698e2bb38ec2db38bc6a74820 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Tue, 10 May 2022 15:44:19 +0900
Subject: [PATCH] mpi: Fix for 64-bit for _gcry_mpih_cmp_ui.

* mpi/mpih-const-time.c (_gcry_mpih_cmp_ui): Compare 64-bit
value correctly.

--

Reported-by: Guido Vranken <guidovranken@gmail.com>
GnuPG-bug-id: 5970
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 mpi/mpih-const-time.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index b527ad79..9d74d190 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -204,6 +204,13 @@ _gcry_mpih_cmp_ui (mpi_ptr_t up, mpi_size_t usize, unsigned long v)
     is_all_zero &= (up[i] == 0);
 
   if (is_all_zero)
-    return up[0] - v;
+    {
+      if (up[0] < v)
+        return -1;
+      else if (up[0] > v)
+        return 1;
+      else
+        return 0;
+    }
   return 1;
 }
-- 
2.44.0

From 34c20427926010d6fa95b1666e4b1b60f60a8742 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Fri, 27 Oct 2023 14:03:40 +0900
Subject: [PATCH] rsa: Fix decoding of PKCS#1 v1.5 and OAEP padding.

* src/Makefile.am (libgcrypt_la_SOURCES): Add const-time.h and
const-time.c.
* src/const-time.h (ct_not_equal_byte, sexp_null_cond): New.
(ct_memequal): New from NetBSD, modified return type and name.
* src/const-time.c: New.
* cipher/rsa-common.c (_gcry_rsa_pkcs1_decode_for_enc): Examine whole
sequence of the byte-array.  Use N0 to find the separator position, with
ct_not_equal_byte.  Return the MPI even when the case of an error.
* cipher/rsa-common.c (_gcry_rsa_oaep_decode): Use ct_memequal to
check LHASH.  Examine all the sequence of the byte-array.  Use N1 to
find the separator of 0x01.  Return the MPI even when the case of an
error.
* cipher/rsa.c (rsa_decrypt): Always build a SEXP.

--

Note: For architecture(s) which may result branch in comparison of
byte, configure script should emit POSSIBLE_BRANCH_IN_BYTE_COMPARISON.

Reported-by: Hubert Kario <hkario@redhat.com>
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 cipher/rsa-common.c | 72 +++++++++++++++++++++------------------------
 cipher/rsa.c        | 15 +++++++---
 src/Makefile.am     |  2 +-
 src/const-time.c    | 51 ++++++++++++++++++++++++++++++++
 src/const-time.h    | 53 +++++++++++++++++++++++++++++++++
 5 files changed, 149 insertions(+), 44 deletions(-)
 create mode 100644 src/const-time.c
 create mode 100644 src/const-time.h

diff --git a/cipher/rsa-common.c b/cipher/rsa-common.c
index dd654c39..bd6d4bd6 100644
--- a/cipher/rsa-common.c
+++ b/cipher/rsa-common.c
@@ -27,6 +27,7 @@
 #include "mpi.h"
 #include "cipher.h"
 #include "pubkey-internal.h"
+#include "const-time.h"
 
 
 /* Turn VALUE into an octet string and store it in an allocated buffer
@@ -172,7 +173,9 @@ _gcry_rsa_pkcs1_decode_for_enc (unsigned char **r_result, size_t *r_resultlen,
   gcry_error_t err;
   unsigned char *frame = NULL;
   size_t nframe = (nbits+7) / 8;
-  size_t n;
+  size_t n, n0;
+  unsigned int failed = 0;
+  unsigned int not_found = 1;
 
   *r_result = NULL;
 
@@ -203,33 +206,31 @@ _gcry_rsa_pkcs1_decode_for_enc (unsigned char **r_result, size_t *r_resultlen,
   n = 0;
   if (!frame[0])
     n++;
-  if (frame[n++] != 0x02)
-    {
-      xfree (frame);
-      return GPG_ERR_ENCODING_PROBLEM;  /* Wrong block type.  */
-    }
+  failed |= ct_not_equal_byte (frame[n++], 0x02);
 
-  /* Skip the non-zero random bytes and the terminating zero byte.  */
-  for (; n < nframe && frame[n] != 0x00; n++)
-    ;
-  if (n+1 >= nframe)
+  /* Find the terminating zero byte.  */
+  n0 = n;
+  for (; n < nframe; n++)
     {
-      xfree (frame);
-      return GPG_ERR_ENCODING_PROBLEM; /* No zero byte.  */
+      not_found &= ct_not_equal_byte (frame[n], 0x00);
+      n0 += not_found;
     }
-  n++; /* Skip the zero byte.  */
+
+  failed |= not_found;
+  n0 += !not_found; /* Skip the zero byte.  */
 
   /* To avoid an extra allocation we reuse the frame buffer.  The only
      caller of this function will anyway free the result soon.  */
-  memmove (frame, frame + n, nframe - n);
+  memmove (frame, frame + n0, nframe - n0);
+
   *r_result = frame;
-  *r_resultlen = nframe - n;
+  *r_resultlen = nframe - n0;
 
   if (DBG_CIPHER)
     log_printhex ("value extracted from PKCS#1 block type 2 encoded data",
                   *r_result, *r_resultlen);
 
-  return 0;
+  return (0U - failed) & GPG_ERR_ENCODING_PROBLEM;
 }
 
 
@@ -616,7 +617,8 @@ _gcry_rsa_oaep_decode (unsigned char **r_result, size_t *r_resultlen,
   size_t db_len;               /* Length of DB and masked_db.  */
   size_t nkey = (nbits+7)/8;   /* Length of the key in bytes.  */
   int failed = 0;              /* Error indicator.  */
-  size_t n;
+  size_t n, n1;
+  unsigned int not_found = 1;
 
   *r_result = NULL;
 
@@ -688,51 +690,43 @@ _gcry_rsa_oaep_decode (unsigned char **r_result, size_t *r_resultlen,
   db_len      = nframe - 1 - hlen;
 
   /* Step 3c and 3d: seed = maskedSeed ^ mgf(maskedDB, hlen).  */
-  if (mgf1 (seed, hlen, masked_db, db_len, algo))
-    failed = 1;
+  failed |= (mgf1 (seed, hlen, masked_db, db_len, algo) != 0);
   for (n = 0; n < hlen; n++)
     seed[n] ^= masked_seed[n];
 
   /* Step 3e and 3f: db = maskedDB ^ mgf(seed, db_len).  */
-  if (mgf1 (db, db_len, seed, hlen, algo))
-    failed = 1;
+  failed |= (mgf1 (db, db_len, seed, hlen, algo) != 0);
   for (n = 0; n < db_len; n++)
     db[n] ^= masked_db[n];
 
   /* Step 3g: Check lhash, an possible empty padding string terminated
      by 0x01 and the first byte of EM being 0.  */
-  if (memcmp (lhash, db, hlen))
-    failed = 1;
-  for (n = hlen; n < db_len; n++)
-    if (db[n] == 0x01)
-      break;
-  if (n == db_len)
-    failed = 1;
-  if (frame[0])
-    failed = 1;
+  failed |= !ct_memequal (lhash, db, hlen);
+  for (n = n1 = hlen; n < db_len; n++)
+    {
+      not_found &= ct_not_equal_byte (db[n], 0x01);
+      n1 += not_found;
+    }
+  failed |= not_found;
+  failed |= ct_not_equal_byte (frame[0], 0x00);
 
   xfree (lhash);
   xfree (frame);
-  if (failed)
-    {
-      xfree (seed);
-      return GPG_ERR_ENCODING_PROBLEM;
-    }
 
   /* Step 4: Output M.  */
   /* To avoid an extra allocation we reuse the seed buffer.  The only
      caller of this function will anyway free the result soon.  */
-  n++;
-  memmove (seed, db + n, db_len - n);
+  n1 += !not_found;
+  memmove (seed, db + n1, db_len - n1);
   *r_result = seed;
-  *r_resultlen = db_len - n;
+  *r_resultlen = db_len - n1;
   seed = NULL;
 
   if (DBG_CIPHER)
     log_printhex ("value extracted from OAEP encoded data",
                   *r_result, *r_resultlen);
 
-  return 0;
+  return (0U - failed) & GPG_ERR_ENCODING_PROBLEM;
 }
 
 
diff --git a/cipher/rsa.c b/cipher/rsa.c
index 45523e6b..ffa1aabd 100644
--- a/cipher/rsa.c
+++ b/cipher/rsa.c
@@ -33,6 +33,7 @@
 #include "mpi.h"
 #include "cipher.h"
 #include "pubkey-internal.h"
+#include "const-time.h"
 
 
 typedef struct
@@ -1444,6 +1445,8 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
   unsigned char *unpad = NULL;
   size_t unpadlen = 0;
   unsigned int nbits = rsa_get_nbits (keyparms);
+  gcry_sexp_t result = NULL;
+  gcry_sexp_t dummy = NULL;
 
   rc = rsa_check_keysize (nbits);
   if (rc)
@@ -1512,8 +1515,10 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
       rc = _gcry_rsa_pkcs1_decode_for_enc (&unpad, &unpadlen, nbits, plain);
       mpi_free (plain);
       plain = NULL;
-      if (!rc)
-        rc = sexp_build (r_plain, NULL, "(value %b)", (int)unpadlen, unpad);
+      sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
+      *r_plain = sexp_null_cond (result, !!rc);
+      dummy = sexp_null_cond (result, !rc);
+      sexp_release (dummy);
       break;
 
     case PUBKEY_ENC_OAEP:
@@ -1522,8 +1527,10 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
                                   plain, ctx.label, ctx.labellen);
       mpi_free (plain);
       plain = NULL;
-      if (!rc)
-        rc = sexp_build (r_plain, NULL, "(value %b)", (int)unpadlen, unpad);
+      sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
+      *r_plain = sexp_null_cond (result, !!rc);
+      dummy = sexp_null_cond (result,!rc);
+      sexp_release (dummy);
       break;
 
     default:
diff --git a/src/Makefile.am b/src/Makefile.am
index 5e003bf0..f6191bc8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -63,7 +63,7 @@ libgcrypt_la_SOURCES = \
 	misc.c global.c sexp.c hwfeatures.c hwf-common.h \
 	stdmem.c stdmem.h secmem.c secmem.h \
 	mpi.h missing-string.c fips.c \
-	context.c context.h \
+	context.c context.h const-time.h const-time.c \
 	ec-context.h
 
 EXTRA_libgcrypt_la_SOURCES = hwf-x86.c hwf-arm.c hwf-ppc.c hwf-s390x.c
diff --git a/src/const-time.c b/src/const-time.c
new file mode 100644
index 00000000..7e56f210
--- /dev/null
+++ b/src/const-time.c
@@ -0,0 +1,51 @@
+/* const-time.c  -  Constant-time functions
+ *      Copyright (C) 2023  g10 Code GmbH
+ *
+ * This file is part of Libgcrypt.
+ *
+ * Libgcrypt is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * Libgcrypt 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "g10lib.h"
+
+/* Originally in NetBSD.
+ *
+ * Written by Matthias Drochner <drochner@NetBSD.org>.
+ * Public domain.
+ *
+ * Modified the function name and return type to unsigned.
+ */
+unsigned int
+ct_memequal (const void *b1, const void *b2, size_t len)
+{
+	const unsigned char *c1 = b1, *c2 = b2;
+	unsigned int res = 0;
+
+	while (len--)
+		res |= *c1++ ^ *c2++;
+
+	/*
+	 * Map 0 to 1 and [1, 256) to 0 using only constant-time
+	 * arithmetic.
+	 *
+	 * This is not simply `!res' because although many CPUs support
+	 * branchless conditional moves and many compilers will take
+	 * advantage of them, certain compilers generate branches on
+	 * certain CPUs for `!res'.
+	 */
+	return (1 & ((res - 1) >> 8));
+}
diff --git a/src/const-time.h b/src/const-time.h
new file mode 100644
index 00000000..2055ef16
--- /dev/null
+++ b/src/const-time.h
@@ -0,0 +1,53 @@
+/* const-time.h  -  Constant-time functions
+ *      Copyright (C) 2023  g10 Code GmbH
+ *
+ * This file is part of Libgcrypt.
+ *
+ * Libgcrypt is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * Libgcrypt 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, see <https://www.gnu.org/licenses/>.
+ */
+
+/*
+ * Return 1 if it's not same, 0 if same.
+ */
+static inline unsigned int
+ct_not_equal_byte (unsigned char b0, unsigned char b1)
+{
+#ifdef POSSIBLE_BRANCH_IN_BYTE_COMPARISON
+  unsigned int diff;
+
+  diff = b0;
+  diff ^= b1;
+
+  return (0U - diff) >> (sizeof (unsigned int)*8 - 1);
+#else
+  return b0 != b1;
+#endif
+}
+
+/*
+ *  Return NULL when OP_ENABLED=1
+ *  otherwise, return W
+ */
+static inline gcry_sexp_t
+sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
+{
+  static volatile uintptr_t vone = 1;
+  size_t mask = (uintptr_t)op_enable - vone;
+
+  return (gcry_sexp_t)(void *)((uintptr_t)w & mask);
+}
+
+/* Compare byte-arrays of length LEN, return 1 if it's same, 0 otherwise.
+   We use pointer of void *, so that it can be used with any structure.  */
+unsigned int ct_memequal (const void *b1, const void *b2, size_t len);
-- 
2.44.0

From c848459e512615c1865a23cf24debb3ad4a1e85b Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Mon, 30 Oct 2023 10:28:28 +0900
Subject: [PATCH] build: Check if arch is VAX or compiler is MSVC.

* configure.ac (AH_BOTTOM): Add check for VAX and MSVC.
* src/const-time.h (POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON):
Rename.

--

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 configure.ac     | 5 +++++
 src/const-time.h | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 4f7c3a52..09c93289 100644
--- a/configure.ac
+++ b/configure.ac
@@ -121,6 +121,11 @@ AH_BOTTOM([
    properly prefixed.  */
 #define CAMELLIA_EXT_SYM_PREFIX _gcry_
 
+/* For some architectures or a specific compiler vendor, we need
+   to care about possible conditional branch in byte comparison.  */
+#if defined(__vax__) || defined(_MSC_VER)
+# define POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON 1
+#endif
 #endif /*_GCRYPT_CONFIG_H_INCLUDED*/
 ])
 
diff --git a/src/const-time.h b/src/const-time.h
index 2055ef16..9fc19779 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -23,7 +23,7 @@
 static inline unsigned int
 ct_not_equal_byte (unsigned char b0, unsigned char b1)
 {
-#ifdef POSSIBLE_BRANCH_IN_BYTE_COMPARISON
+#ifdef POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON
   unsigned int diff;
 
   diff = b0;
-- 
2.44.0

From c31b70b2660c3d24bd54ee08c255c36d867fdea7 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Mon, 30 Oct 2023 14:02:42 +0900
Subject: [PATCH] const-time: Use ct_not_memequal, instead.  Tested with AVR.

* cipher/rsa-common.c (_gcry_rsa_oaep_decode): Use ct_not_memequal.
* src/const-time.c (ct_not_memequal): Use ct_not_equal_byte.
* src/const-time.h (ct_not_memequal): Rename from ct_memequal.

--

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 cipher/rsa-common.c |  2 +-
 configure.ac        |  2 +-
 src/const-time.c    | 35 ++++++++++++++++-------------------
 src/const-time.h    |  7 ++++---
 4 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/cipher/rsa-common.c b/cipher/rsa-common.c
index bd6d4bd6..24f90e01 100644
--- a/cipher/rsa-common.c
+++ b/cipher/rsa-common.c
@@ -701,7 +701,7 @@ _gcry_rsa_oaep_decode (unsigned char **r_result, size_t *r_resultlen,
 
   /* Step 3g: Check lhash, an possible empty padding string terminated
      by 0x01 and the first byte of EM being 0.  */
-  failed |= !ct_memequal (lhash, db, hlen);
+  failed |= ct_not_memequal (lhash, db, hlen);
   for (n = n1 = hlen; n < db_len; n++)
     {
       not_found &= ct_not_equal_byte (db[n], 0x01);
diff --git a/configure.ac b/configure.ac
index 09c93289..aead8347 100644
--- a/configure.ac
+++ b/configure.ac
@@ -123,7 +123,7 @@ AH_BOTTOM([
 
 /* For some architectures or a specific compiler vendor, we need
    to care about possible conditional branch in byte comparison.  */
-#if defined(__vax__) || defined(_MSC_VER)
+#if defined(__vax__) || defined(AVR) || defined(_MSC_VER)
 # define POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON 1
 #endif
 #endif /*_GCRYPT_CONFIG_H_INCLUDED*/
diff --git a/src/const-time.c b/src/const-time.c
index 7e56f210..e66fee92 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -21,31 +21,28 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "g10lib.h"
+#include "const-time.h"
 
-/* Originally in NetBSD.
+/*
+ * Compare byte arrays of length LEN, return 1 if it's not same,
+ * 0, otherwise.
  *
- * Written by Matthias Drochner <drochner@NetBSD.org>.
- * Public domain.
+ * Originally in NetBSD as "consttime_memequal" which is:
  *
- * Modified the function name and return type to unsigned.
+ *   Written by Matthias Drochner <drochner@NetBSD.org>.
+ *   Public domain.
+ *
+ * Modified the function name, return type to unsigned,
+ * and return value (0 <-> 1).
  */
 unsigned int
-ct_memequal (const void *b1, const void *b2, size_t len)
+ct_not_memequal (const void *b1, const void *b2, size_t len)
 {
-	const unsigned char *c1 = b1, *c2 = b2;
-	unsigned int res = 0;
+  const unsigned char *c1 = b1, *c2 = b2;
+  unsigned int res = 0;
 
-	while (len--)
-		res |= *c1++ ^ *c2++;
+  while (len--)
+    res |= *c1++ ^ *c2++;
 
-	/*
-	 * Map 0 to 1 and [1, 256) to 0 using only constant-time
-	 * arithmetic.
-	 *
-	 * This is not simply `!res' because although many CPUs support
-	 * branchless conditional moves and many compilers will take
-	 * advantage of them, certain compilers generate branches on
-	 * certain CPUs for `!res'.
-	 */
-	return (1 & ((res - 1) >> 8));
+  return ct_not_equal_byte (res, 0);
 }
diff --git a/src/const-time.h b/src/const-time.h
index 9fc19779..b8add29d 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -48,6 +48,7 @@ sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
   return (gcry_sexp_t)(void *)((uintptr_t)w & mask);
 }
 
-/* Compare byte-arrays of length LEN, return 1 if it's same, 0 otherwise.
-   We use pointer of void *, so that it can be used with any structure.  */
-unsigned int ct_memequal (const void *b1, const void *b2, size_t len);
+/* Compare byte-arrays of length LEN, return 1 if it's not same, 0
+   otherwise.  We use pointer of void *, so that it can be used with
+   any structure.  */
+unsigned int ct_not_memequal (const void *b1, const void *b2, size_t len);
-- 
2.44.0

From bd08357436a9559766cd458d25781ee4f94012a2 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Tue, 31 Oct 2023 13:43:29 +0900
Subject: [PATCH] const-time: Add ct_memmov_cond, fix _gcry_mpih_set_cond.

* src/const-time.c (ct_memmov_cond): New.
* src/const-time.h (ct_memmov_cond): New.
* mpi/mpih-const-time.c (_gcry_mpih_set_cond): Use XOR and a MASK.

--

ct_memmov_cond is like memcpy, but it allows use with overlapping
memory area when DST <= SRC.  It's not like memmove because it doesn't
allow overlapping memory area when DST > SRC.

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 mpi/mpih-const-time.c |  7 ++-----
 src/const-time.c      | 19 +++++++++++++++++++
 src/const-time.h      | 16 ++++++++++++----
 3 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 9d74d190..3f0440a9 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -40,13 +40,10 @@ _gcry_mpih_set_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
   mpi_size_t i;
-  mpi_limb_t mask1 = vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - vone;
+  mpi_limb_t mask = vzero - op_enable;
 
   for (i = 0; i < usize; i++)
-    {
-      wp[i] = (wp[i] & mask2) | (up[i] & mask1);
-    }
+    wp[i] ^= mask & (wp[i] ^ up[i]);
 }
 
 
diff --git a/src/const-time.c b/src/const-time.c
index e66fee92..400af993 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -46,3 +46,22 @@ ct_not_memequal (const void *b1, const void *b2, size_t len)
 
   return ct_not_equal_byte (res, 0);
 }
+
+/*
+ * Copy LEN bytes from memory area SRC to memory area DST, when
+ * OP_ENABLED=1.  When DST <= SRC, the memory areas may overlap.  When
+ * DST > SRC, the memory areas must not overlap.
+ */
+void
+ct_memmov_cond (void *dst, const void *src, size_t len,
+                unsigned long op_enable)
+{
+  size_t i;
+  unsigned char mask;
+  unsigned char *b_dst = dst;
+  const unsigned char *b_src = src;
+
+  mask = -(unsigned char)op_enable;
+  for (i = 0; i < len; i++)
+    b_dst[i] ^= mask & (b_dst[i] ^ b_src[i]);
+}
diff --git a/src/const-time.h b/src/const-time.h
index b8add29d..53d7dd2a 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -35,6 +35,11 @@ ct_not_equal_byte (unsigned char b0, unsigned char b1)
 #endif
 }
 
+/* Compare byte-arrays of length LEN, return 1 if it's not same, 0
+   otherwise.  We use pointer of void *, so that it can be used with
+   any structure.  */
+unsigned int ct_not_memequal (const void *b1, const void *b2, size_t len);
+
 /*
  *  Return NULL when OP_ENABLED=1
  *  otherwise, return W
@@ -48,7 +53,10 @@ sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
   return (gcry_sexp_t)(void *)((uintptr_t)w & mask);
 }
 
-/* Compare byte-arrays of length LEN, return 1 if it's not same, 0
-   otherwise.  We use pointer of void *, so that it can be used with
-   any structure.  */
-unsigned int ct_not_memequal (const void *b1, const void *b2, size_t len);
+/*
+ * Copy LEN bytes from memory area SRC to memory area DST, when
+ * OP_ENABLED=1.  When DST <= SRC, the memory areas may overlap.  When
+ * DST > SRC, the memory areas must not overlap.
+ */
+void ct_memmov_cond (void *dst, const void *src, size_t len,
+                     unsigned long op_enable);
-- 
2.44.0

From 58b62be844549ad3d57c507d834027f1e2756567 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Tue, 31 Oct 2023 14:46:42 +0900
Subject: [PATCH] rsa: Use memmov_independently when unpadding.

* cipher/rsa-common.c (memmov_independently): New.
(_gcry_rsa_pkcs1_decode_for_enc): Use memmov_independently.
(_gcry_rsa_oaep_decode): Use memmov_independently.

--

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 cipher/rsa-common.c | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/cipher/rsa-common.c b/cipher/rsa-common.c
index 24f90e01..74eb6341 100644
--- a/cipher/rsa-common.c
+++ b/cipher/rsa-common.c
@@ -162,6 +162,35 @@ _gcry_rsa_pkcs1_encode_for_enc (gcry_mpi_t *r_result, unsigned int nbits,
 }
 
 
+/*
+ *                    <--len-->
+ * DST-------v       v-------------SRC
+ *           [.................]
+ *            <---- buflen --->
+ *
+ * Copy the memory area SRC with LEN into another memory area DST.
+ * Conditions met:
+ *         the address SRC > DST
+ *         DST + BUFLEN == SRC + LEN.
+ *
+ * Memory access doesn't depends on LEN, but always done independently,
+ * sliding memory area by 1, 2, 4 ... until done.
+ */
+static void
+memmov_independently (void *dst, const void *src, size_t len, size_t buflen)
+{
+  size_t offset = (size_t)((char *)src - (char *)dst);
+  size_t shift;
+
+  (void)len; /* No dependency.  */
+  for (shift = 1; shift < buflen; shift <<= 1)
+    {
+      ct_memmov_cond (dst, (char *)dst + shift, buflen - shift, (offset&1));
+      offset >>= 1;
+    }
+}
+
+
 /* Decode a plaintext in VALUE assuming pkcs#1 block type 2 padding.
    NBITS is the size of the secret key.  On success the result is
    stored as a newly allocated buffer at R_RESULT and its valid length at
@@ -221,7 +250,7 @@ _gcry_rsa_pkcs1_decode_for_enc (unsigned char **r_result, size_t *r_resultlen,
 
   /* To avoid an extra allocation we reuse the frame buffer.  The only
      caller of this function will anyway free the result soon.  */
-  memmove (frame, frame + n0, nframe - n0);
+  memmov_independently (frame, frame + n0, nframe - n0, nframe);
 
   *r_result = frame;
   *r_resultlen = nframe - n0;
@@ -717,7 +746,7 @@ _gcry_rsa_oaep_decode (unsigned char **r_result, size_t *r_resultlen,
   /* To avoid an extra allocation we reuse the seed buffer.  The only
      caller of this function will anyway free the result soon.  */
   n1 += !not_found;
-  memmove (seed, db + n1, db_len - n1);
+  memmov_independently (seed, db + n1, db_len - n1, nframe - 1);
   *r_result = seed;
   *r_resultlen = db_len - n1;
   seed = NULL;
-- 
2.44.0

From 6d1d50ba3aad1850975f717adbedb4cb8b236fa7 Mon Sep 17 00:00:00 2001
From: NIIBE Yutaka <gniibe@fsij.org>
Date: Tue, 31 Oct 2023 15:09:25 +0900
Subject: [PATCH] cipher: Fix ElGamal decryption.

* cipher/elgamal.c (elg_decrypt): Call sexp_build always.
* cipher/rsa.c (rsa_decrypt): Return an error code of sexp_build
when RC != 0.

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
---
 cipher/elgamal.c | 21 ++++++++++++++++-----
 cipher/rsa.c     | 10 +++++++---
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/cipher/elgamal.c b/cipher/elgamal.c
index eead4502..06881cb6 100644
--- a/cipher/elgamal.c
+++ b/cipher/elgamal.c
@@ -31,6 +31,7 @@
 #include "mpi.h"
 #include "cipher.h"
 #include "pubkey-internal.h"
+#include "const-time.h"
 
 
 /* Blinding is used to mitigate side-channel attacks.  You may undef
@@ -872,7 +873,7 @@ elg_encrypt (gcry_sexp_t *r_ciph, gcry_sexp_t s_data, gcry_sexp_t keyparms)
 static gcry_err_code_t
 elg_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
 {
-  gpg_err_code_t rc;
+  gpg_err_code_t rc, rc_sexp;
   struct pk_encoding_ctx ctx;
   gcry_sexp_t l1 = NULL;
   gcry_mpi_t data_a = NULL;
@@ -881,6 +882,8 @@ elg_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
   gcry_mpi_t plain = NULL;
   unsigned char *unpad = NULL;
   size_t unpadlen = 0;
+  gcry_sexp_t result = NULL;
+  gcry_sexp_t dummy = NULL;
 
   _gcry_pk_util_init_encoding_ctx (&ctx, PUBKEY_OP_DECRYPT,
                                    elg_get_nbits (keyparms));
@@ -929,8 +932,12 @@ elg_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
     case PUBKEY_ENC_PKCS1:
       rc = _gcry_rsa_pkcs1_decode_for_enc (&unpad, &unpadlen, ctx.nbits, plain);
       mpi_free (plain); plain = NULL;
-      if (!rc)
-        rc = sexp_build (r_plain, NULL, "(value %b)", (int)unpadlen, unpad);
+      rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
+      *r_plain = sexp_null_cond (result, !!rc);
+      dummy = sexp_null_cond (result, !rc);
+      sexp_release (dummy);
+      if (!rc && rc_sexp)
+        rc = rc_sexp;
       break;
 
     case PUBKEY_ENC_OAEP:
@@ -938,8 +945,12 @@ elg_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
                                   ctx.nbits, ctx.hash_algo, plain,
                                   ctx.label, ctx.labellen);
       mpi_free (plain); plain = NULL;
-      if (!rc)
-        rc = sexp_build (r_plain, NULL, "(value %b)", (int)unpadlen, unpad);
+      rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
+      *r_plain = sexp_null_cond (result, !!rc);
+      dummy = sexp_null_cond (result, !rc);
+      sexp_release (dummy);
+      if (!rc && rc_sexp)
+        rc = rc_sexp;
       break;
 
     default:
diff --git a/cipher/rsa.c b/cipher/rsa.c
index ffa1aabd..383e2474 100644
--- a/cipher/rsa.c
+++ b/cipher/rsa.c
@@ -1436,7 +1436,7 @@ static gcry_err_code_t
 rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
 
 {
-  gpg_err_code_t rc;
+  gpg_err_code_t rc, rc_sexp;
   struct pk_encoding_ctx ctx;
   gcry_sexp_t l1 = NULL;
   gcry_mpi_t data = NULL;
@@ -1515,10 +1515,12 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
       rc = _gcry_rsa_pkcs1_decode_for_enc (&unpad, &unpadlen, nbits, plain);
       mpi_free (plain);
       plain = NULL;
-      sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
+      rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
       *r_plain = sexp_null_cond (result, !!rc);
       dummy = sexp_null_cond (result, !rc);
       sexp_release (dummy);
+      if (!rc && rc_sexp)
+        rc = rc_sexp;
       break;
 
     case PUBKEY_ENC_OAEP:
@@ -1527,10 +1529,12 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
                                   plain, ctx.label, ctx.labellen);
       mpi_free (plain);
       plain = NULL;
-      sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
+      rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
       *r_plain = sexp_null_cond (result, !!rc);
       dummy = sexp_null_cond (result,!rc);
       sexp_release (dummy);
+      if (!rc && rc_sexp)
+        rc = rc_sexp;
       break;
 
     default:
-- 
2.44.0

From 1e9ddbd65c4627235611d75c3198c4ec197c9a05 Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Mon, 30 Oct 2023 21:05:24 +0200
Subject: [PATCH] Use single constant-time memory comparison implementation

* src/const-time.c (ct_not_memequal): Use original 'buf_eq_const'
implementation here.
(ct_memequal): New.
* cipher/bufhelp.h (buf_eq_const): Call to 'ct_memequal'.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 cipher/bufhelp.h | 19 +++----------------
 src/const-time.c | 36 +++++++++++++++++++++++-------------
 src/const-time.h | 13 +++++++++++++
 3 files changed, 39 insertions(+), 29 deletions(-)

diff --git a/cipher/bufhelp.h b/cipher/bufhelp.h
index fa5b2e8e..6dcc622a 100644
--- a/cipher/bufhelp.h
+++ b/cipher/bufhelp.h
@@ -22,6 +22,7 @@
 
 #include "g10lib.h"
 #include "bithelp.h"
+#include "const-time.h"
 
 
 #undef BUFHELP_UNALIGNED_ACCESS
@@ -362,23 +363,9 @@ buf_xor_n_copy(void *_dst_xor, void *_srcdst_cpy, const void *_src, size_t len)
 /* Constant-time compare of two buffers.  Returns 1 if buffers are equal,
    and 0 if buffers differ.  */
 static inline int
-buf_eq_const(const void *_a, const void *_b, size_t len)
+buf_eq_const(const void *a, const void *b, size_t len)
 {
-  const byte *a = _a;
-  const byte *b = _b;
-  int ab, ba;
-  size_t i;
-
-  /* Constant-time compare. */
-  for (i = 0, ab = 0, ba = 0; i < len; i++)
-    {
-      /* If a[i] != b[i], either ab or ba will be negative. */
-      ab |= a[i] - b[i];
-      ba |= b[i] - a[i];
-    }
-
-  /* 'ab | ba' is negative when buffers are not equal. */
-  return (ab | ba) >= 0;
+  return ct_memequal (a, b, len);
 }
 
 
diff --git a/src/const-time.c b/src/const-time.c
index 400af993..fb787a02 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -26,25 +26,35 @@
 /*
  * Compare byte arrays of length LEN, return 1 if it's not same,
  * 0, otherwise.
- *
- * Originally in NetBSD as "consttime_memequal" which is:
- *
- *   Written by Matthias Drochner <drochner@NetBSD.org>.
- *   Public domain.
- *
- * Modified the function name, return type to unsigned,
- * and return value (0 <-> 1).
  */
 unsigned int
 ct_not_memequal (const void *b1, const void *b2, size_t len)
 {
-  const unsigned char *c1 = b1, *c2 = b2;
-  unsigned int res = 0;
+  const byte *a = b1;
+  const byte *b = b2;
+  int ab, ba;
+  size_t i;
+
+  /* Constant-time compare. */
+  for (i = 0, ab = 0, ba = 0; i < len; i++)
+    {
+      /* If a[i] != b[i], either ab or ba will be negative. */
+      ab |= a[i] - b[i];
+      ba |= b[i] - a[i];
+    }
 
-  while (len--)
-    res |= *c1++ ^ *c2++;
+  /* 'ab | ba' is negative when buffers are not equal, extract sign bit.  */
+  return ((unsigned int)(ab | ba) >> (sizeof(unsigned int) * 8 - 1)) & 1;
+}
 
-  return ct_not_equal_byte (res, 0);
+/*
+ * Compare byte arrays of length LEN, return 0 if it's not same,
+ * 1, otherwise.
+ */
+unsigned int
+ct_memequal (const void *b1, const void *b2, size_t len)
+{
+  return ct_not_memequal (b1, b2, len) ^ 1;
 }
 
 /*
diff --git a/src/const-time.h b/src/const-time.h
index 53d7dd2a..defe5ff4 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -17,6 +17,12 @@
  * License along with this program; if not, see <https://www.gnu.org/licenses/>.
  */
 
+#ifndef GCRY_CONST_TIME_H
+#define GCRY_CONST_TIME_H
+
+#include "types.h"
+
+
 /*
  * Return 1 if it's not same, 0 if same.
  */
@@ -40,6 +46,11 @@ ct_not_equal_byte (unsigned char b0, unsigned char b1)
    any structure.  */
 unsigned int ct_not_memequal (const void *b1, const void *b2, size_t len);
 
+/* Compare byte-arrays of length LEN, return 0 if it's not same, 1
+   otherwise.  We use pointer of void *, so that it can be used with
+   any structure.  */
+unsigned int ct_memequal (const void *b1, const void *b2, size_t len);
+
 /*
  *  Return NULL when OP_ENABLED=1
  *  otherwise, return W
@@ -60,3 +71,5 @@ sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
  */
 void ct_memmov_cond (void *dst, const void *src, size_t len,
                      unsigned long op_enable);
+
+#endif /*GCRY_CONST_TIME_H*/
-- 
2.44.0

From 137e35ad47ee8734d0f3ffb6af1d1669c4621e0b Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Mon, 30 Oct 2023 20:17:09 +0200
Subject: [PATCH] const-time: always avoid comparison operator for byte
 comparison

* configure.ac: Remove POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON
macro.
* src/const-time.h (ct_not_equal_byte): Remove
POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON ifdef.
--

Performance impact of avoiding comparison is negligible, so
remove the option for using comparison to make this easier
maintain (tested on every arch).

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 configure.ac     | 5 -----
 src/const-time.h | 4 ----
 2 files changed, 9 deletions(-)

diff --git a/configure.ac b/configure.ac
index aead8347..4f7c3a52 100644
--- a/configure.ac
+++ b/configure.ac
@@ -121,11 +121,6 @@ AH_BOTTOM([
    properly prefixed.  */
 #define CAMELLIA_EXT_SYM_PREFIX _gcry_
 
-/* For some architectures or a specific compiler vendor, we need
-   to care about possible conditional branch in byte comparison.  */
-#if defined(__vax__) || defined(AVR) || defined(_MSC_VER)
-# define POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON 1
-#endif
 #endif /*_GCRYPT_CONFIG_H_INCLUDED*/
 ])
 
diff --git a/src/const-time.h b/src/const-time.h
index defe5ff4..4f14f86b 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -29,16 +29,12 @@
 static inline unsigned int
 ct_not_equal_byte (unsigned char b0, unsigned char b1)
 {
-#ifdef POSSIBLE_CONDITIONAL_BRANCH_IN_BYTE_COMPARISON
   unsigned int diff;
 
   diff = b0;
   diff ^= b1;
 
   return (0U - diff) >> (sizeof (unsigned int)*8 - 1);
-#else
-  return b0 != b1;
-#endif
 }
 
 /* Compare byte-arrays of length LEN, return 1 if it's not same, 0
-- 
2.44.0

From 84f934c09afac18b3f4351646c0fe6f93aede277 Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Mon, 30 Oct 2023 20:15:05 +0200
Subject: [PATCH] rsa, elgamal: avoid logical not operator in constant-time
 code

* cipher/elgamal.c (elg_decrypt): Replace ! operator with calls to
ct_is_not_zero/ct_is_zero/ct_ulong_select.
* cipher/rsa-common.c (_gcry_rsa_pkcs1_decode_for_enc): Replace !
operator with call to ct_is_zero.
* cipher/rsa.c (rsa_decrypt): Replace ! operator with calls to
ct_is_not_zero/ct_is_zero/ct_ulong_select.
* src/const-time.c (_gcry_ct_vzero, _gcry_ct_vone): New.
* src/const-time.h (_gcry_ct_vzero, _gcry_ct_vone): New.
(ct_is_not_zero, ct_is_zero, DEFINE_CT_TYPE_SELECT_FUNC)
(ct_uintptr_select, ct_ulong_select): New.
(sexp_null_cond): Use ct_uintptr_select.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 cipher/elgamal.c    | 22 +++++++++++---------
 cipher/rsa-common.c |  2 +-
 cipher/rsa.c        | 16 +++++++--------
 src/const-time.c    |  8 ++++++++
 src/const-time.h    | 49 +++++++++++++++++++++++++++++++++++++++++----
 5 files changed, 74 insertions(+), 23 deletions(-)

diff --git a/cipher/elgamal.c b/cipher/elgamal.c
index 06881cb6..540ecb02 100644
--- a/cipher/elgamal.c
+++ b/cipher/elgamal.c
@@ -931,26 +931,28 @@ elg_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
     {
     case PUBKEY_ENC_PKCS1:
       rc = _gcry_rsa_pkcs1_decode_for_enc (&unpad, &unpadlen, ctx.nbits, plain);
-      mpi_free (plain); plain = NULL;
+      mpi_free (plain);
+      plain = NULL;
       rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
-      *r_plain = sexp_null_cond (result, !!rc);
-      dummy = sexp_null_cond (result, !rc);
+      *r_plain = sexp_null_cond (result, ct_is_not_zero (rc));
+      dummy = sexp_null_cond (result, ct_is_zero (rc));
       sexp_release (dummy);
-      if (!rc && rc_sexp)
-        rc = rc_sexp;
+      rc = ct_ulong_select (rc_sexp, rc,
+			    ct_is_zero (rc) & ct_is_not_zero (rc_sexp));
       break;
 
     case PUBKEY_ENC_OAEP:
       rc = _gcry_rsa_oaep_decode (&unpad, &unpadlen,
                                   ctx.nbits, ctx.hash_algo, plain,
                                   ctx.label, ctx.labellen);
-      mpi_free (plain); plain = NULL;
+      mpi_free (plain);
+      plain = NULL;
       rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
-      *r_plain = sexp_null_cond (result, !!rc);
-      dummy = sexp_null_cond (result, !rc);
+      *r_plain = sexp_null_cond (result, ct_is_not_zero (rc));
+      dummy = sexp_null_cond (result, ct_is_zero (rc));
       sexp_release (dummy);
-      if (!rc && rc_sexp)
-        rc = rc_sexp;
+      rc = ct_ulong_select (rc_sexp, rc,
+			    ct_is_zero (rc) & ct_is_not_zero (rc_sexp));
       break;
 
     default:
diff --git a/cipher/rsa-common.c b/cipher/rsa-common.c
index 74eb6341..1920eedd 100644
--- a/cipher/rsa-common.c
+++ b/cipher/rsa-common.c
@@ -246,7 +246,7 @@ _gcry_rsa_pkcs1_decode_for_enc (unsigned char **r_result, size_t *r_resultlen,
     }
 
   failed |= not_found;
-  n0 += !not_found; /* Skip the zero byte.  */
+  n0 += ct_is_zero (not_found); /* Skip the zero byte.  */
 
   /* To avoid an extra allocation we reuse the frame buffer.  The only
      caller of this function will anyway free the result soon.  */
diff --git a/cipher/rsa.c b/cipher/rsa.c
index 383e2474..c7a809f4 100644
--- a/cipher/rsa.c
+++ b/cipher/rsa.c
@@ -1516,11 +1516,11 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
       mpi_free (plain);
       plain = NULL;
       rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
-      *r_plain = sexp_null_cond (result, !!rc);
-      dummy = sexp_null_cond (result, !rc);
+      *r_plain = sexp_null_cond (result, ct_is_not_zero (rc));
+      dummy = sexp_null_cond (result, ct_is_zero (rc));
       sexp_release (dummy);
-      if (!rc && rc_sexp)
-        rc = rc_sexp;
+      rc = ct_ulong_select (rc_sexp, rc,
+			    ct_is_zero (rc) & ct_is_not_zero (rc_sexp));
       break;
 
     case PUBKEY_ENC_OAEP:
@@ -1530,11 +1530,11 @@ rsa_decrypt (gcry_sexp_t *r_plain, gcry_sexp_t s_data, gcry_sexp_t keyparms)
       mpi_free (plain);
       plain = NULL;
       rc_sexp = sexp_build (&result, NULL, "(value %b)", (int)unpadlen, unpad);
-      *r_plain = sexp_null_cond (result, !!rc);
-      dummy = sexp_null_cond (result,!rc);
+      *r_plain = sexp_null_cond (result, ct_is_not_zero (rc));
+      dummy = sexp_null_cond (result, ct_is_zero (rc));
       sexp_release (dummy);
-      if (!rc && rc_sexp)
-        rc = rc_sexp;
+      rc = ct_ulong_select (rc_sexp, rc,
+			    ct_is_zero (rc) & ct_is_not_zero (rc_sexp));
       break;
 
     default:
diff --git a/src/const-time.c b/src/const-time.c
index fb787a02..908c0ee9 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -23,6 +23,14 @@
 #include "g10lib.h"
 #include "const-time.h"
 
+
+/* These variables are used to generate masks from conditional operation
+ * flag parameters.  Use of volatile prevents compiler optimizations from
+ * converting AND-masking to conditional branches.  */
+volatile unsigned int _gcry_ct_vzero = 0;
+volatile unsigned int _gcry_ct_vone = 1;
+
+
 /*
  * Compare byte arrays of length LEN, return 1 if it's not same,
  * 0, otherwise.
diff --git a/src/const-time.h b/src/const-time.h
index 4f14f86b..3a229ddb 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -23,6 +23,34 @@
 #include "types.h"
 
 
+extern volatile unsigned int _gcry_ct_vzero;
+extern volatile unsigned int _gcry_ct_vone;
+
+
+/*
+ * Return 0 if A is 0 and return 1 otherwise.
+ */
+static inline unsigned int
+ct_is_not_zero (unsigned int a)
+{
+  /* Sign bit set if A != 0. */
+  a = a | (-a);
+
+  return a >> (sizeof(unsigned int) * 8 - 1);
+}
+
+/*
+ * Return 1 if A is 0 and return 0 otherwise.
+ */
+static inline unsigned int
+ct_is_zero (unsigned int a)
+{
+  /* Sign bit set if A == 0. */
+  a = ~a & ~(-a);
+
+  return a >> (sizeof(unsigned int) * 8 - 1);
+}
+
 /*
  * Return 1 if it's not same, 0 if same.
  */
@@ -47,6 +75,21 @@ unsigned int ct_not_memequal (const void *b1, const void *b2, size_t len);
    any structure.  */
 unsigned int ct_memequal (const void *b1, const void *b2, size_t len);
 
+/*
+ *  Return A when OP_ENABLED=1
+ *  otherwise, return B
+ */
+#define DEFINE_CT_TYPE_SELECT_FUNC(name, type) \
+  static inline type \
+  ct_##name##_select (type a, type b, unsigned long op_enable) \
+  { \
+    type mask_b = (type)op_enable - (type)_gcry_ct_vone; \
+    type mask_a = (type)_gcry_ct_vzero - (type)op_enable; \
+    return (mask_a & a) | (mask_b & b); \
+  }
+DEFINE_CT_TYPE_SELECT_FUNC(uintptr, uintptr_t)
+DEFINE_CT_TYPE_SELECT_FUNC(ulong, unsigned long)
+
 /*
  *  Return NULL when OP_ENABLED=1
  *  otherwise, return W
@@ -54,10 +97,8 @@ unsigned int ct_memequal (const void *b1, const void *b2, size_t len);
 static inline gcry_sexp_t
 sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
 {
-  static volatile uintptr_t vone = 1;
-  size_t mask = (uintptr_t)op_enable - vone;
-
-  return (gcry_sexp_t)(void *)((uintptr_t)w & mask);
+  uintptr_t o = ct_uintptr_select((uintptr_t)NULL, (uintptr_t)w, op_enable);
+  return (gcry_sexp_t)(void *)o;
 }
 
 /*
-- 
2.44.0

From 0c6ec6bbe788b8c4a6982b2128d442b51323c898 Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 21:08:49 +0200
Subject: [PATCH] mpih_set_cond: restore EM leakage mitigation

* mpi/mpih-const-time.c (_gcry_mpih_set_cond): Replace single mask + XOR
with dual mask + AND/OR; Add comment about reason for dual mask usage.
(_gcry_mpih_add_n_cond, _gcry_mpih_sub_n_cond, _gcry_mpih_swap_cond)
(_gcry_mpih_abs_cond): Add comment about reason for dual mask usage.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/mpih-const-time.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 3f0440a9..388d2a91 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -39,11 +39,15 @@ void
 _gcry_mpih_set_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
+  mpi_limb_t mask1 = vzero - op_enable;
+  mpi_limb_t mask2 = op_enable - vone;
   mpi_size_t i;
-  mpi_limb_t mask = vzero - op_enable;
 
   for (i = 0; i < usize; i++)
-    wp[i] ^= mask & (wp[i] ^ up[i]);
+    {
+      wp[i] = (wp[i] & mask2) | (up[i] & mask1);
+    }
 }
 
 
@@ -55,10 +59,11 @@ mpi_limb_t
 _gcry_mpih_add_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
                        mpi_size_t usize, unsigned long op_enable)
 {
-  mpi_size_t i;
-  mpi_limb_t cy;
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
   mpi_limb_t mask1 = vzero - op_enable;
   mpi_limb_t mask2 = op_enable - vone;
+  mpi_size_t i;
+  mpi_limb_t cy;
 
   cy = 0;
   for (i = 0; i < usize; i++)
@@ -86,10 +91,11 @@ mpi_limb_t
 _gcry_mpih_sub_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
                        mpi_size_t usize, unsigned long op_enable)
 {
-  mpi_size_t i;
-  mpi_limb_t cy;
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
   mpi_limb_t mask1 = vzero - op_enable;
   mpi_limb_t mask2 = op_enable - vone;
+  mpi_size_t i;
+  mpi_limb_t cy;
 
   cy = 0;
   for (i = 0; i < usize; i++)
@@ -117,9 +123,10 @@ void
 _gcry_mpih_swap_cond (mpi_ptr_t up, mpi_ptr_t vp, mpi_size_t usize,
                       unsigned long op_enable)
 {
-  mpi_size_t i;
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
   mpi_limb_t mask1 = vzero - op_enable;
   mpi_limb_t mask2 = op_enable - vone;
+  mpi_size_t i;
 
   for (i = 0; i < usize; i++)
     {
@@ -139,10 +146,11 @@ void
 _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
-  mpi_size_t i;
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
   mpi_limb_t mask1 = vzero - op_enable;
   mpi_limb_t mask2 = op_enable - vone;
   mpi_limb_t cy = op_enable;
+  mpi_size_t i;
 
   for (i = 0; i < usize; i++)
     {
-- 
2.44.0

From 22dde5150ee2be01651410ed9756601ba6a29c93 Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 21:31:02 +0200
Subject: [PATCH] const-time: prefix global symbols with _gcry_

* cipher/const-time.c (ct_not_memequal, ct_memequal)
(ct_memmov_cond): Rename these to ...
(_gcry_ct_not_memequal, _gcry_ct_memequal)
(_gcry_ct_memmov_cond): ... these.
* cipher/const-time.h (ct_not_memequal, ct_memequal)
(ct_memmov_cond): Rename these to ...
(_gcry_ct_not_memequal, _gcry_ct_memequal)
(_gcry_ct_memmov_cond): ... these.
(ct_not_memequal, ct_memequal, ct_memmov_cond): New macros.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 src/const-time.c | 10 +++++-----
 src/const-time.h | 13 +++++++++----
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/src/const-time.c b/src/const-time.c
index 908c0ee9..2066d48d 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -36,7 +36,7 @@ volatile unsigned int _gcry_ct_vone = 1;
  * 0, otherwise.
  */
 unsigned int
-ct_not_memequal (const void *b1, const void *b2, size_t len)
+_gcry_ct_not_memequal (const void *b1, const void *b2, size_t len)
 {
   const byte *a = b1;
   const byte *b = b2;
@@ -60,9 +60,9 @@ ct_not_memequal (const void *b1, const void *b2, size_t len)
  * 1, otherwise.
  */
 unsigned int
-ct_memequal (const void *b1, const void *b2, size_t len)
+_gcry_ct_memequal (const void *b1, const void *b2, size_t len)
 {
-  return ct_not_memequal (b1, b2, len) ^ 1;
+  return _gcry_ct_not_memequal (b1, b2, len) ^ 1;
 }
 
 /*
@@ -71,8 +71,8 @@ ct_memequal (const void *b1, const void *b2, size_t len)
  * DST > SRC, the memory areas must not overlap.
  */
 void
-ct_memmov_cond (void *dst, const void *src, size_t len,
-                unsigned long op_enable)
+_gcry_ct_memmov_cond (void *dst, const void *src, size_t len,
+		      unsigned long op_enable)
 {
   size_t i;
   unsigned char mask;
diff --git a/src/const-time.h b/src/const-time.h
index 3a229ddb..e324dcb7 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -23,6 +23,11 @@
 #include "types.h"
 
 
+#define ct_not_memequal _gcry_ct_not_memequal
+#define ct_memequal _gcry_ct_memequal
+#define ct_memmov_cond _gcry_ct_memmov_cond
+
+
 extern volatile unsigned int _gcry_ct_vzero;
 extern volatile unsigned int _gcry_ct_vone;
 
@@ -68,12 +73,12 @@ ct_not_equal_byte (unsigned char b0, unsigned char b1)
 /* Compare byte-arrays of length LEN, return 1 if it's not same, 0
    otherwise.  We use pointer of void *, so that it can be used with
    any structure.  */
-unsigned int ct_not_memequal (const void *b1, const void *b2, size_t len);
+unsigned int _gcry_ct_not_memequal (const void *b1, const void *b2, size_t len);
 
 /* Compare byte-arrays of length LEN, return 0 if it's not same, 1
    otherwise.  We use pointer of void *, so that it can be used with
    any structure.  */
-unsigned int ct_memequal (const void *b1, const void *b2, size_t len);
+unsigned int _gcry_ct_memequal (const void *b1, const void *b2, size_t len);
 
 /*
  *  Return A when OP_ENABLED=1
@@ -106,7 +111,7 @@ sexp_null_cond (gcry_sexp_t w, unsigned long op_enable)
  * OP_ENABLED=1.  When DST <= SRC, the memory areas may overlap.  When
  * DST > SRC, the memory areas must not overlap.
  */
-void ct_memmov_cond (void *dst, const void *src, size_t len,
-                     unsigned long op_enable);
+void _gcry_ct_memmov_cond (void *dst, const void *src, size_t len,
+			   unsigned long op_enable);
 
 #endif /*GCRY_CONST_TIME_H*/
-- 
2.44.0

From 4d3e0e30b98b2acb90acb2792b8327c26824a66f Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 21:34:58 +0200
Subject: [PATCH] const-time: ct_memmov_cond: switch to use dual mask approach

* src/const-time.c (_gcry_ct_memmov_cond): Use dual mask + AND/OR
instead of single mask + XOR.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 src/const-time.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/const-time.c b/src/const-time.c
index 2066d48d..73bf8b40 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -74,12 +74,13 @@ void
 _gcry_ct_memmov_cond (void *dst, const void *src, size_t len,
 		      unsigned long op_enable)
 {
-  size_t i;
-  unsigned char mask;
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
+  unsigned char mask1 = _gcry_ct_vzero - op_enable;
+  unsigned char mask2 = op_enable - _gcry_ct_vone;
   unsigned char *b_dst = dst;
   const unsigned char *b_src = src;
+  size_t i;
 
-  mask = -(unsigned char)op_enable;
   for (i = 0; i < len; i++)
-    b_dst[i] ^= mask & (b_dst[i] ^ b_src[i]);
+    b_dst[i] = (b_dst[i] & mask2) | (b_src[i] & mask1);
 }
-- 
2.44.0

From 179df341162c74da312f76363a0ff1f2f303aa78 Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 21:43:36 +0200
Subject: [PATCH] mpih-const-time: use global vzero/vone variable

* mpi/mpih-const-time.c (vzero, vone): Remove.
(_gcry_mpih_set_cond, _gcry_mpih_add_n_cond, _gcry_mpih_sub_n_cond)
(_gcry_mpih_swap_cond, _gcry_mpih_abs_cond): Use _gcry_ct_vzero and
_gcry_ct_vone.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/mpih-const-time.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 388d2a91..85dba389 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -22,14 +22,10 @@
 #include <stdlib.h>
 #include "mpi-internal.h"
 #include "g10lib.h"
+#include "const-time.h"
 
 #define A_LIMB_1 ((mpi_limb_t)1)
 
-/* These variables are used to generate masks from conditional operation
- * flag parameters.  Use of volatile prevents compiler optimizations from
- * converting AND-masking to conditional branches.  */
-static volatile mpi_limb_t vzero = 0;
-static volatile mpi_limb_t vone = 1;
 
 /*
  *  W = U when OP_ENABLED=1
@@ -40,8 +36,8 @@ _gcry_mpih_set_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - vone;
+  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
+  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
   mpi_size_t i;
 
   for (i = 0; i < usize; i++)
@@ -60,8 +56,8 @@ _gcry_mpih_add_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
                        mpi_size_t usize, unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - vone;
+  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
+  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
   mpi_size_t i;
   mpi_limb_t cy;
 
@@ -92,8 +88,8 @@ _gcry_mpih_sub_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
                        mpi_size_t usize, unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - vone;
+  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
+  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
   mpi_size_t i;
   mpi_limb_t cy;
 
@@ -124,8 +120,8 @@ _gcry_mpih_swap_cond (mpi_ptr_t up, mpi_ptr_t vp, mpi_size_t usize,
                       unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - vone;
+  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
+  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
   mpi_size_t i;
 
   for (i = 0; i < usize; i++)
@@ -147,8 +143,8 @@ _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - vone;
+  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
+  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
   mpi_limb_t cy = op_enable;
   mpi_size_t i;
 
-- 
2.44.0

From d4aee9ace9a904446b987dddc2999119c4d62dae Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 22:11:35 +0200
Subject: [PATCH] mpiutil: use global vone and vzero

* mpi/mpiutil.c (_gcry_mpi_set_cond, _gcry_mpi_swap_cond): Use
_gcry_ct_vzero and _gcry_ct_vone.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/mpiutil.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mpi/mpiutil.c b/mpi/mpiutil.c
index d5a1b8a8..f7506718 100644
--- a/mpi/mpiutil.c
+++ b/mpi/mpiutil.c
@@ -27,6 +27,7 @@
 #include "g10lib.h"
 #include "mpi-internal.h"
 #include "mod-source-info.h"
+#include "const-time.h"
 
 
 #if SIZEOF_UNSIGNED_INT == 2
@@ -46,12 +47,6 @@
 /* Constants allocated right away at startup.  */
 static gcry_mpi_t constants[MPI_NUMBER_OF_CONSTANTS];
 
-/* These variables are used to generate masks from conditional operation
- * flag parameters.  Use of volatile prevents compiler optimizations from
- * converting AND-masking to conditional branches.  */
-static volatile mpi_limb_t vzero = 0;
-static volatile mpi_limb_t vone = 1;
-
 
 const char *
 _gcry_mpi_get_hw_config (void)
@@ -513,10 +508,11 @@ _gcry_mpi_set (gcry_mpi_t w, gcry_mpi_t u)
 gcry_mpi_t
 _gcry_mpi_set_cond (gcry_mpi_t w, const gcry_mpi_t u, unsigned long set)
 {
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
+  mpi_limb_t mask1 = _gcry_ct_vzero - set;
+  mpi_limb_t mask2 = set - _gcry_ct_vone;
   mpi_size_t i;
   mpi_size_t nlimbs = u->alloced;
-  mpi_limb_t mask1 = vzero - set;
-  mpi_limb_t mask2 = set - vone;
   mpi_limb_t xu;
   mpi_limb_t xw;
   mpi_limb_t *uu = u->d;
@@ -614,10 +610,11 @@ _gcry_mpi_swap (gcry_mpi_t a, gcry_mpi_t b)
 void
 _gcry_mpi_swap_cond (gcry_mpi_t a, gcry_mpi_t b, unsigned long swap)
 {
+  /* Note: dual mask with AND/OR used for EM leakage mitigation */
+  mpi_limb_t mask1 = _gcry_ct_vzero - swap;
+  mpi_limb_t mask2 = swap - _gcry_ct_vone;
   mpi_size_t i;
   mpi_size_t nlimbs;
-  mpi_limb_t mask1 = vzero - swap;
-  mpi_limb_t mask2 = swap - vone;
   mpi_limb_t *ua = a->d;
   mpi_limb_t *ub = b->d;
   mpi_limb_t xa;
-- 
2.44.0

From aab6a42d5f44724b73a02598546a5e7d8b33298e Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 21:45:05 +0200
Subject: [PATCH] mpih_cmp_ui: avoid unintentional conditional branch

* mpi/mpi-internal.h (mpih_limb_is_zero): New.
* mpi/mpih-const-time.c (_gcry_mpih_cmp_ui): Use mpih_limb_is_zero
instead of comparison.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/mpi-internal.h    | 9 +++++++++
 mpi/mpih-const-time.c | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/mpi/mpi-internal.h b/mpi/mpi-internal.h
index 79a6cce7..bb12e86c 100644
--- a/mpi/mpi-internal.h
+++ b/mpi/mpi-internal.h
@@ -267,6 +267,15 @@ mpi_limb_t _gcry_mpih_rshift( mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
 #define mpih_abs_cond(w,u,s,o) _gcry_mpih_abs_cond ((w),(u),(s),(o))
 #define mpih_mod(v,vs,u,us) _gcry_mpih_mod ((v),(vs),(u),(us))
 
+static inline int
+mpih_limb_is_zero (mpi_limb_t a)
+{
+  /* Sign bit set if A == 0. */
+  a = ~a & ~(-a);
+
+  return a >> (BITS_PER_MPI_LIMB - 1);
+}
+
 void _gcry_mpih_set_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                           unsigned long op_enable);
 mpi_limb_t _gcry_mpih_add_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 85dba389..3d854e8c 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -202,7 +202,7 @@ _gcry_mpih_cmp_ui (mpi_ptr_t up, mpi_size_t usize, unsigned long v)
   mpi_size_t i;
 
   for (i = 1; i < usize; i++)
-    is_all_zero &= (up[i] == 0);
+    is_all_zero &= mpih_limb_is_zero (up[i]);
 
   if (is_all_zero)
     {
-- 
2.44.0

From 5c5ba1ec2b505726ee1311339ac9e8b5c62cac4a Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Wed, 1 Nov 2023 22:02:44 +0200
Subject: [PATCH] ec-nist: use global vone and vzero

* mpi/ec-nist.c (vzero, vone): Remove.
(_gcry_mpi_ec_nist192_mod, _gcry_mpi_ec_nist224_mod)
(_gcry_mpi_ec_nist256_mod, _gcry_mpi_ec_nist384_mod): Use _gcry_ct_vzero
and _gcry_ct_vone.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/ec-nist.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/mpi/ec-nist.c b/mpi/ec-nist.c
index 14e3c3ab..a822af76 100644
--- a/mpi/ec-nist.c
+++ b/mpi/ec-nist.c
@@ -32,13 +32,7 @@
 #include "context.h"
 #include "ec-context.h"
 #include "ec-inline.h"
-
-
-/* These variables are used to generate masks from conditional operation
- * flag parameters.  Use of volatile prevents compiler optimizations from
- * converting AND-masking to conditional branches.  */
-static volatile mpi_limb_t vzero = 0;
-static volatile mpi_limb_t vone = 1;
+#include "const-time.h"
 
 
 static inline
@@ -147,8 +141,8 @@ _gcry_mpi_ec_nist192_mod (gcry_mpi_t w, mpi_ec_t ctx)
 
   s_is_negative = LO32_LIMB64(s[3]) >> 31;
 
-  mask2 = vzero - s_is_negative;
-  mask1 = s_is_negative - vone;
+  mask2 = _gcry_ct_vzero - s_is_negative;
+  mask1 = s_is_negative - _gcry_ct_vone;
 
   STORE64_COND(wp, 0, mask2, o[0], mask1, s[0]);
   STORE64_COND(wp, 1, mask2, o[1], mask1, s[1]);
@@ -270,8 +264,8 @@ _gcry_mpi_ec_nist224_mod (gcry_mpi_t w, mpi_ec_t ctx)
 
   s_is_negative = (HI32_LIMB64(s[3]) >> 31);
 
-  mask2 = vzero - s_is_negative;
-  mask1 = s_is_negative - vone;
+  mask2 = _gcry_ct_vzero - s_is_negative;
+  mask1 = s_is_negative - _gcry_ct_vone;
 
   STORE64_COND(wp, 0, mask2, d[0], mask1, s[0]);
   STORE64_COND(wp, 1, mask2, d[1], mask1, s[1]);
@@ -499,9 +493,9 @@ _gcry_mpi_ec_nist256_mod (gcry_mpi_t w, mpi_ec_t ctx)
 
   s_is_negative = LO32_LIMB64(s[4]) >> 31;
   d_is_negative = LO32_LIMB64(d[4]) >> 31;
-  mask3 = vzero - d_is_negative;
-  mask2 = (vzero - s_is_negative) & ~mask3;
-  mask1 = (s_is_negative - vone) & ~mask3;
+  mask3 = _gcry_ct_vzero - d_is_negative;
+  mask2 = (_gcry_ct_vzero - s_is_negative) & ~mask3;
+  mask1 = (s_is_negative - _gcry_ct_vone) & ~mask3;
 
   s[0] = LIMB_OR64(MASK_AND64(mask2, d[0]), MASK_AND64(mask1, s[0]));
   s[1] = LIMB_OR64(MASK_AND64(mask2, d[1]), MASK_AND64(mask1, s[1]));
@@ -770,8 +764,8 @@ _gcry_mpi_ec_nist384_mod (gcry_mpi_t w, mpi_ec_t ctx)
 	       p_mult[0 + 3][1], p_mult[0 + 3][0]);
 
   s_is_negative = LO32_LIMB64(s[6]) >> 31;
-  mask2 = vzero - s_is_negative;
-  mask1 = s_is_negative - vone;
+  mask2 = _gcry_ct_vzero - s_is_negative;
+  mask1 = s_is_negative - _gcry_ct_vone;
 
   STORE64_COND(wp, 0, mask2, d[0], mask1, s[0]);
   STORE64_COND(wp, 1, mask2, d[1], mask1, s[1]);
-- 
2.44.0

From cf757cf90e9ae966b95dcebfd2f31b9212697f0c Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Thu, 2 Nov 2023 20:38:04 +0200
Subject: [PATCH] const-time: add functions for generating masks from 0/1 input

* mpi/ec-nist.c (_gcry_mpi_ec_nist192_mod, _gcry_mpi_ec_nist224_mod)
(_gcry_mpi_ec_nist256_mod, _gcry_mpi_ec_nist384_mod): Use mask generating
functions.
* mpi/mpi-internal.h (ct_limb_gen_mask, ct_limb_gen_inv_mask): New.
* mpi/mpih-const-time.c (_gcry_mpih_set_cond, _gcry_mpih_add_n_cond)
(_gcry_mpih_sub_n_cond, _gcry_mpih_sub_n_cond, _gcry_mpih_swap_cond): Use
mask generating functions.
* mpi/mpiutil.c (_gcry_mpi_set_cond, _gcry_mpi_swap_cond): Use mask
generating functions.
* src/const-time.h (DEFINE_CT_TYPE_GEN_MASK, ct_uintptr_gen_mask)
(ct_ulong_gen_mask, DEFINE_CT_TYPE_GEN_INV_MASK, ct_uintptr_gen_inv_mask)
(ct_ulong_gen_inv_mask): New.
(DEFINE_CT_TYPE_SELECT_FUNC): Use mask generating functions.
* src/const-time.c (_gcry_ct_memmov_cond): Use mask generating functions.
--

Provide functions for generating mask for constant time operations.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/ec-nist.c         | 18 +++++++--------
 mpi/mpi-internal.h    |  4 ++++
 mpi/mpih-const-time.c | 20 ++++++++--------
 mpi/mpiutil.c         |  8 +++----
 src/const-time.c      |  6 +++--
 src/const-time.h      | 54 +++++++++++++++++++++++++++++++++++++++++--
 6 files changed, 83 insertions(+), 27 deletions(-)

diff --git a/mpi/ec-nist.c b/mpi/ec-nist.c
index 6dfaa1da..3213f9df 100644
--- a/mpi/ec-nist.c
+++ b/mpi/ec-nist.c
@@ -141,8 +141,8 @@ _gcry_mpi_ec_nist192_mod (gcry_mpi_t w, mpi_ec_t ctx)
 
   s_is_negative = LO32_LIMB64(s[3]) >> 31;
 
-  mask2 = _gcry_ct_vzero - s_is_negative;
-  mask1 = s_is_negative - _gcry_ct_vone;
+  mask2 = ct_limb_gen_mask(s_is_negative);
+  mask1 = ct_limb_gen_inv_mask(s_is_negative);
 
   STORE64_COND(wp, 0, mask2, o[0], mask1, s[0]);
   STORE64_COND(wp, 1, mask2, o[1], mask1, s[1]);
@@ -264,8 +264,8 @@ _gcry_mpi_ec_nist224_mod (gcry_mpi_t w, mpi_ec_t ctx)
 
   s_is_negative = (HI32_LIMB64(s[3]) >> 31);
 
-  mask2 = _gcry_ct_vzero - s_is_negative;
-  mask1 = s_is_negative - _gcry_ct_vone;
+  mask2 = ct_limb_gen_mask(s_is_negative);
+  mask1 = ct_limb_gen_inv_mask(s_is_negative);
 
   STORE64_COND(wp, 0, mask2, d[0], mask1, s[0]);
   STORE64_COND(wp, 1, mask2, d[1], mask1, s[1]);
@@ -493,9 +493,9 @@ _gcry_mpi_ec_nist256_mod (gcry_mpi_t w, mpi_ec_t ctx)
 
   s_is_negative = LO32_LIMB64(s[4]) >> 31;
   d_is_negative = LO32_LIMB64(d[4]) >> 31;
-  mask3 = _gcry_ct_vzero - d_is_negative;
-  mask2 = (_gcry_ct_vzero - s_is_negative) & ~mask3;
-  mask1 = (s_is_negative - _gcry_ct_vone) & ~mask3;
+  mask3 = ct_limb_gen_mask(d_is_negative);
+  mask2 = ct_limb_gen_mask(s_is_negative) & ~mask3;
+  mask1 = ct_limb_gen_inv_mask(s_is_negative) & ~mask3;
 
   s[0] = LIMB_OR64(MASK_AND64(mask2, d[0]), MASK_AND64(mask1, s[0]));
   s[1] = LIMB_OR64(MASK_AND64(mask2, d[1]), MASK_AND64(mask1, s[1]));
@@ -764,8 +764,8 @@ _gcry_mpi_ec_nist384_mod (gcry_mpi_t w, mpi_ec_t ctx)
 	       p_mult[0 + 3][1], p_mult[0 + 3][0]);
 
   s_is_negative = LO32_LIMB64(s[6]) >> 31;
-  mask2 = _gcry_ct_vzero - s_is_negative;
-  mask1 = s_is_negative - _gcry_ct_vone;
+  mask2 = ct_limb_gen_mask(s_is_negative);
+  mask1 = ct_limb_gen_inv_mask(s_is_negative);
 
   STORE64_COND(wp, 0, mask2, d[0], mask1, s[0]);
   STORE64_COND(wp, 1, mask2, d[1], mask1, s[1]);
diff --git a/mpi/mpi-internal.h b/mpi/mpi-internal.h
index 70045037..935bf3e1 100644
--- a/mpi/mpi-internal.h
+++ b/mpi/mpi-internal.h
@@ -50,6 +50,7 @@
 #endif /*BITS_PER_MPI_LIMB*/
 
 #include "mpi.h"
+#include "const-time.h"
 
 /* If KARATSUBA_THRESHOLD is not already defined, define it to a
  * value which is good on most machines.  */
@@ -267,6 +268,9 @@ mpi_limb_t _gcry_mpih_rshift( mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
 #define mpih_abs_cond(w,u,s,o) _gcry_mpih_abs_cond ((w),(u),(s),(o))
 #define mpih_mod(v,vs,u,us) _gcry_mpih_mod ((v),(vs),(u),(us))
 
+DEFINE_CT_TYPE_GEN_MASK(limb, mpi_limb_t)
+DEFINE_CT_TYPE_GEN_INV_MASK(limb, mpi_limb_t)
+
 static inline int
 mpih_limb_is_zero (mpi_limb_t a)
 {
diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 3d854e8c..4f563cb8 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -36,8 +36,8 @@ _gcry_mpih_set_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(op_enable);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(op_enable);
   mpi_size_t i;
 
   for (i = 0; i < usize; i++)
@@ -56,8 +56,8 @@ _gcry_mpih_add_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
                        mpi_size_t usize, unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(op_enable);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(op_enable);
   mpi_size_t i;
   mpi_limb_t cy;
 
@@ -88,8 +88,8 @@ _gcry_mpih_sub_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
                        mpi_size_t usize, unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(op_enable);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(op_enable);
   mpi_size_t i;
   mpi_limb_t cy;
 
@@ -120,8 +120,8 @@ _gcry_mpih_swap_cond (mpi_ptr_t up, mpi_ptr_t vp, mpi_size_t usize,
                       unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(op_enable);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(op_enable);
   mpi_size_t i;
 
   for (i = 0; i < usize; i++)
@@ -143,8 +143,8 @@ _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
                      unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - op_enable;
-  mpi_limb_t mask2 = op_enable - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(op_enable);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(op_enable);
   mpi_limb_t cy = op_enable;
   mpi_size_t i;
 
diff --git a/mpi/mpiutil.c b/mpi/mpiutil.c
index f7506718..07cef257 100644
--- a/mpi/mpiutil.c
+++ b/mpi/mpiutil.c
@@ -509,8 +509,8 @@ gcry_mpi_t
 _gcry_mpi_set_cond (gcry_mpi_t w, const gcry_mpi_t u, unsigned long set)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - set;
-  mpi_limb_t mask2 = set - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(set);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(set);
   mpi_size_t i;
   mpi_size_t nlimbs = u->alloced;
   mpi_limb_t xu;
@@ -611,8 +611,8 @@ void
 _gcry_mpi_swap_cond (gcry_mpi_t a, gcry_mpi_t b, unsigned long swap)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  mpi_limb_t mask1 = _gcry_ct_vzero - swap;
-  mpi_limb_t mask2 = swap - _gcry_ct_vone;
+  mpi_limb_t mask1 = ct_limb_gen_mask(swap);
+  mpi_limb_t mask2 = ct_limb_gen_inv_mask(swap);
   mpi_size_t i;
   mpi_size_t nlimbs;
   mpi_limb_t *ua = a->d;
diff --git a/src/const-time.c b/src/const-time.c
index 73bf8b40..0fb53a07 100644
--- a/src/const-time.c
+++ b/src/const-time.c
@@ -24,11 +24,13 @@
 #include "const-time.h"
 
 
+#ifndef HAVE_GCC_ASM_VOLATILE_MEMORY
 /* These variables are used to generate masks from conditional operation
  * flag parameters.  Use of volatile prevents compiler optimizations from
  * converting AND-masking to conditional branches.  */
 volatile unsigned int _gcry_ct_vzero = 0;
 volatile unsigned int _gcry_ct_vone = 1;
+#endif
 
 
 /*
@@ -75,8 +77,8 @@ _gcry_ct_memmov_cond (void *dst, const void *src, size_t len,
 		      unsigned long op_enable)
 {
   /* Note: dual mask with AND/OR used for EM leakage mitigation */
-  unsigned char mask1 = _gcry_ct_vzero - op_enable;
-  unsigned char mask2 = op_enable - _gcry_ct_vone;
+  unsigned char mask1 = ct_ulong_gen_mask(op_enable);
+  unsigned char mask2 = ct_ulong_gen_inv_mask(op_enable);
   unsigned char *b_dst = dst;
   const unsigned char *b_src = src;
   size_t i;
diff --git a/src/const-time.h b/src/const-time.h
index e324dcb7..fe07cc7a 100644
--- a/src/const-time.h
+++ b/src/const-time.h
@@ -28,8 +28,10 @@
 #define ct_memmov_cond _gcry_ct_memmov_cond
 
 
+#ifndef HAVE_GCC_ASM_VOLATILE_MEMORY
 extern volatile unsigned int _gcry_ct_vzero;
 extern volatile unsigned int _gcry_ct_vone;
+#endif
 
 
 /*
@@ -80,6 +82,54 @@ unsigned int _gcry_ct_not_memequal (const void *b1, const void *b2, size_t len);
    any structure.  */
 unsigned int _gcry_ct_memequal (const void *b1, const void *b2, size_t len);
 
+/*
+ * Return all bits set if A is 1 and return 0 otherwise.
+ */
+#ifdef HAVE_GCC_ASM_VOLATILE_MEMORY
+#  define DEFINE_CT_TYPE_GEN_MASK(name, type) \
+     static inline type \
+     ct_##name##_gen_mask (unsigned long op_enable) \
+     { \
+       type mask = -(type)op_enable; \
+       asm volatile ("\n" : "+r" (mask) :: "memory"); \
+       return mask; \
+     }
+#else
+#  define DEFINE_CT_TYPE_GEN_MASK(name, type) \
+     static inline type \
+     ct_##name##_gen_mask (unsigned long op_enable) \
+     { \
+       type mask = (type)_gcry_ct_vzero - (type)op_enable; \
+       return mask; \
+     }
+#endif
+DEFINE_CT_TYPE_GEN_MASK(uintptr, uintptr_t)
+DEFINE_CT_TYPE_GEN_MASK(ulong, unsigned long)
+
+/*
+ * Return all bits set if A is 0 and return 1 otherwise.
+ */
+#ifdef HAVE_GCC_ASM_VOLATILE_MEMORY
+#  define DEFINE_CT_TYPE_GEN_INV_MASK(name, type) \
+     static inline type \
+     ct_##name##_gen_inv_mask (unsigned long op_enable) \
+     { \
+       type mask = (type)op_enable - (type)1; \
+       asm volatile ("\n" : "+r" (mask) :: "memory"); \
+       return mask; \
+     }
+#else
+#  define DEFINE_CT_TYPE_GEN_INV_MASK(name, type) \
+     static inline type \
+     ct_##name##_gen_inv_mask (unsigned long op_enable) \
+     { \
+       type mask = (type)op_enable - (type)_gcry_ct_vone; \
+       return mask; \
+     }
+#endif
+DEFINE_CT_TYPE_GEN_INV_MASK(uintptr, uintptr_t)
+DEFINE_CT_TYPE_GEN_INV_MASK(ulong, unsigned long)
+
 /*
  *  Return A when OP_ENABLED=1
  *  otherwise, return B
@@ -88,8 +138,8 @@ unsigned int _gcry_ct_memequal (const void *b1, const void *b2, size_t len);
   static inline type \
   ct_##name##_select (type a, type b, unsigned long op_enable) \
   { \
-    type mask_b = (type)op_enable - (type)_gcry_ct_vone; \
-    type mask_a = (type)_gcry_ct_vzero - (type)op_enable; \
+    type mask_b = ct_##name##_gen_inv_mask(op_enable); \
+    type mask_a = ct_##name##_gen_mask(op_enable); \
     return (mask_a & a) | (mask_b & b); \
   }
 DEFINE_CT_TYPE_SELECT_FUNC(uintptr, uintptr_t)
-- 
2.44.0
From c419a04d529af7b5fb43732ec2b4304166c2579a Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Thu, 2 Nov 2023 20:59:24 +0200
Subject: [PATCH] mpih-const-time: use constant-time comparisons conditional
 add/sub/abs

* mpi/mpih-const-time.c (mpih_ct_limb_greater_than)
(mpih_ct_limb_less_than): New.
(_gcry_mpih_add_n_cond, _gcry_mpih_sub_n_cond, _gcry_mpih_abs_cond): Use
mpih_ct_limb_greater_than and mpih_ct_limb_less_than for comparisons.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/mpih-const-time.c | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 4f563cb8..26dc2d09 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -23,10 +23,33 @@
 #include "mpi-internal.h"
 #include "g10lib.h"
 #include "const-time.h"
+#include "longlong.h"
 
 #define A_LIMB_1 ((mpi_limb_t)1)
 
 
+/*
+ * Return 1 if X > Y and otherwise return 0.
+ */
+static inline mpi_limb_t
+mpih_ct_limb_greater_than (mpi_limb_t x, mpi_limb_t y)
+{
+  mpi_limb_t diff_hi, diff_lo;
+  sub_ddmmss (diff_hi, diff_lo, 0, y, 0, x);
+  return diff_hi >> (BITS_PER_MPI_LIMB - 1);
+}
+
+
+/*
+ * Return 1 if X < Y and otherwise return 0.
+ */
+static inline mpi_limb_t
+mpih_ct_limb_less_than (mpi_limb_t x, mpi_limb_t y)
+{
+  return mpih_ct_limb_greater_than (y, x);
+}
+
+
 /*
  *  W = U when OP_ENABLED=1
  *  otherwise, W keeps old value
@@ -66,11 +89,11 @@ _gcry_mpih_add_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
     {
       mpi_limb_t u = up[i];
       mpi_limb_t x = u + vp[i];
-      mpi_limb_t cy1 = x < u;
+      mpi_limb_t cy1 = mpih_ct_limb_less_than(x, u);
       mpi_limb_t cy2;
 
       x = x + cy;
-      cy2 = x < cy;
+      cy2 = mpih_ct_limb_less_than(x, cy);
       cy = cy1 | cy2;
       wp[i] = (u & mask2) | (x & mask1);
     }
@@ -98,10 +121,10 @@ _gcry_mpih_sub_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
     {
       mpi_limb_t u = up[i];
       mpi_limb_t x = u - vp[i];
-      mpi_limb_t cy1 = x > u;
+      mpi_limb_t cy1 = mpih_ct_limb_greater_than(x, u);
       mpi_limb_t cy2;
 
-      cy2 = x < cy;
+      cy2 = mpih_ct_limb_less_than(x, cy);
       x = x - cy;
       cy = cy1 | cy2;
       wp[i] = (u & mask2) | (x & mask1);
@@ -153,7 +176,7 @@ _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
       mpi_limb_t u = up[i];
       mpi_limb_t x = ~u + cy;
 
-      cy = (x < ~u);
+      cy = mpih_ct_limb_less_than(x, ~u);
       wp[i] = (u & mask2) | (x & mask1);
     }
 }
-- 
2.44.0

From 39d5364a9557d6f423de117601cb1e6414814f47 Mon Sep 17 00:00:00 2001
From: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Date: Fri, 3 Nov 2023 21:31:08 +0200
Subject: [PATCH] mpih_mod: avoid unintentional conditional branch

* mpi/mpih-const-time.c (_gcry_mpih_mod): Avoid conditional branch
on the_bit extraction.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
 mpi/mpih-const-time.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 26dc2d09..e5422409 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -204,7 +204,7 @@ _gcry_mpih_mod (mpi_ptr_t vp, mpi_size_t vsize,
       unsigned int limbno = j / BITS_PER_MPI_LIMB;
       unsigned int bitno = j % BITS_PER_MPI_LIMB;
       mpi_limb_t limb = vp[limbno];
-      unsigned int the_bit = ((limb & (A_LIMB_1 << bitno)) ? 1 : 0);
+      unsigned int the_bit = (limb >> bitno) & 1;
       mpi_limb_t underflow;
       mpi_limb_t overflow;
 
-- 
2.44.0