[PATCH 5/8] mpi:ec: Resize when GCRYECC_FLAG_LEAST_LEAK.

NIIBE Yutaka via Gcrypt-devel <[email protected]> Thu, 27 Mar 2025 14:19:08 +0900

Newsgroups	gmane.comp.encryption.gpg.libgcrypt.devel
Message-ID	<794b8e7378e84c344a0629af61b1154f8830aca4.1743052412.git.gniibe@fsij.org>

* mpi/ec.c (ec_p_init): Also resize when GCRYECC_FLAG_LEAST_LEAK.

Signed-off-by: NIIBE Yutaka <[email protected]>
---
 mpi/ec.c     | 33 ++++++++++++++++++---------------
 src/cipher.h |  2 +-
 2 files changed, 19 insertions(+), 16 deletions(-)

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0005-mpi-ec-Resize-when-GCRYECC_FLAG_LEAST_LEAK.patch (text/x-patch, 1.9 KB)

diff --git a/mpi/ec.c b/mpi/ec.c
index 4e24d817..d13c0fd8 100644
--- a/mpi/ec.c
+++ b/mpi/ec.c
@@ -29,6 +29,7 @@
 #include "context.h"
 #include "ec-context.h"
 #include "ec-internal.h"
+#include "cipher.h" /* for GCRYECC_FLAG_LEAST_LEAK */
 
 extern void reverse_buffer (unsigned char *buffer, unsigned int length);
 
@@ -887,24 +888,26 @@ ec_p_init (mpi_ec_t ctx, enum gcry_mpi_ec_models model,
           ctx->mul2 = field_table[i].mul2 ? field_table[i].mul2 : ctx->mul2;
           ctx->pow2 = field_table[i].pow2 ? field_table[i].pow2 : ctx->pow2;
           ctx->mod = field_table[i].mod ? field_table[i].mod : ctx->mod;
+          break;
+        }
+    }
 
-	  if (ctx->a)
-	    {
-	      mpi_resize (ctx->a, ctx->p->nlimbs);
-	      ctx->a->nlimbs = ctx->p->nlimbs;
-	    }
-
-	  if (ctx->b)
-	    {
-	      mpi_resize (ctx->b, ctx->p->nlimbs);
-	      ctx->b->nlimbs = ctx->p->nlimbs;
-	    }
-
-          for (i=0; i< DIM(ctx->t.scratch) && ctx->t.scratch[i]; i++)
-            ctx->t.scratch[i]->nlimbs = ctx->p->nlimbs;
+  if (field_table[i].p || (flags & GCRYECC_FLAG_LEAST_LEAK))
+    {
+      if (ctx->a)
+        {
+          mpi_resize (ctx->a, ctx->p->nlimbs);
+          ctx->a->nlimbs = ctx->p->nlimbs;
+        }
 
-          break;
+      if (ctx->b)
+        {
+          mpi_resize (ctx->b, ctx->p->nlimbs);
+          ctx->b->nlimbs = ctx->p->nlimbs;
         }
+
+      for (i=0; i< DIM(ctx->t.scratch) && ctx->t.scratch[i]; i++)
+        ctx->t.scratch[i]->nlimbs = ctx->p->nlimbs;
     }
 
   /* Prepare for fast reduction.  */
diff --git a/src/cipher.h b/src/cipher.h
index 78a7c7ce..652bdd6f 100644
--- a/src/cipher.h
+++ b/src/cipher.h
@@ -48,7 +48,7 @@
  * The internal flag to select least leak implementation for ECC.
  * It needs to be a distinct value not covered by PUBKEY_* above.
  */
-#define GCRYECC_FLAG_LEAST_LEAK   (1 << 30)
+#define GCRYECC_FLAG_LEAST_LEAK    (1 << 30)
 
 
 enum pk_operation