mpi: Add gcry_mpi_ec_sub.

* NEWS (gcry_mpi_ec_sub): New.
* doc/gcrypt.texi (gcry_mpi_ec_sub): New.
* mpi/ec.c (_gcry_mpi_ec_sub, sub_points_edwards): New.
(sub_points_montgomery, sub_points_weierstrass): New stubs.
* src/gcrypt-int.h (_gcry_mpi_ec_sub): New.
* src/gcrypt.h.in (gcry_mpi_ec_sub): New.
* src/libgcrypt.def (gcry_mpi_ec_sub): New.
* src/libgcrypt.vers (gcry_mpi_ec_sub): New.
* src/mpi.h (_gcry_mpi_ec_sub_points): New.
* src/visibility.c (gcry_mpi_ec_sub): New.
* src/visibility.h (gcry_mpi_ec_sub): New.
--

This function subtracts two points on the curve. Only Twisted Edwards
curves are supported with this change.

Signed-off-by: Markus Teich <markus dot teich at stusta dot mhn dot de>

7 files changed, 22 insertions, 1 deletions

diff --git a/src/gcrypt-int.h b/src/gcrypt-int.h
index 8a6df840..918937b8 100644
--- a/src/gcrypt-int.h
+++ b/src/gcrypt-int.h
@@ -430,6 +430,8 @@ int _gcry_mpi_ec_get_affine (gcry_mpi_t x, gcry_mpi_t y, gcry_mpi_point_t point,
 void _gcry_mpi_ec_dup (gcry_mpi_point_t w, gcry_mpi_point_t u, gcry_ctx_t ctx);
 void _gcry_mpi_ec_add (gcry_mpi_point_t w,
                        gcry_mpi_point_t u, gcry_mpi_point_t v, mpi_ec_t ctx);
+void _gcry_mpi_ec_sub (gcry_mpi_point_t w,
+                       gcry_mpi_point_t u, gcry_mpi_point_t v, mpi_ec_t ctx);
 void _gcry_mpi_ec_mul (gcry_mpi_point_t w, gcry_mpi_t n, gcry_mpi_point_t u,
                        mpi_ec_t ctx);
 int _gcry_mpi_ec_curve_point (gcry_mpi_point_t w, mpi_ec_t ctx);
diff --git a/src/gcrypt.h.in b/src/gcrypt.h.in
index 65d9ef6a..f3207c96 100644
--- a/src/gcrypt.h.in
+++ b/src/gcrypt.h.in
@@ -704,6 +704,10 @@ void gcry_mpi_ec_dup (gcry_mpi_point_t w, gcry_mpi_point_t u, gcry_ctx_t ctx);
 void gcry_mpi_ec_add (gcry_mpi_point_t w,
                       gcry_mpi_point_t u, gcry_mpi_point_t v, gcry_ctx_t ctx);
 
+/* W = U - V.  */
+void gcry_mpi_ec_sub (gcry_mpi_point_t w,
+                      gcry_mpi_point_t u, gcry_mpi_point_t v, gcry_ctx_t ctx);
+
 /* W = N * U.  */
 void gcry_mpi_ec_mul (gcry_mpi_point_t w, gcry_mpi_t n, gcry_mpi_point_t u,
                       gcry_ctx_t ctx);
diff --git a/src/libgcrypt.def b/src/libgcrypt.def
index 57ed490e..924f17fe 100644
--- a/src/libgcrypt.def
+++ b/src/libgcrypt.def
@@ -276,5 +276,7 @@ EXPORTS
       gcry_mac_ctl              @242
       gcry_mac_get_algo         @243
 
+      gcry_mpi_ec_sub           @244
+
 
 ;; end of file with public symbols for Windows.
diff --git a/src/libgcrypt.vers b/src/libgcrypt.vers
index 7ee0541a..7e8df3f0 100644
--- a/src/libgcrypt.vers
+++ b/src/libgcrypt.vers
@@ -105,7 +105,7 @@ GCRYPT_1.6 {
     gcry_mpi_ec_get_mpi; gcry_mpi_ec_get_point;
     gcry_mpi_ec_set_mpi; gcry_mpi_ec_set_point;
     gcry_mpi_ec_get_affine;
-    gcry_mpi_ec_dup; gcry_mpi_ec_add; gcry_mpi_ec_mul;
+    gcry_mpi_ec_dup; gcry_mpi_ec_add; gcry_mpi_ec_sub; gcry_mpi_ec_mul;
     gcry_mpi_ec_curve_point;
 
     gcry_log_debug;
diff --git a/src/mpi.h b/src/mpi.h
index 7407b7fc..13b51175 100644
--- a/src/mpi.h
+++ b/src/mpi.h
@@ -286,6 +286,9 @@ void _gcry_mpi_ec_dup_point (mpi_point_t result,
 void _gcry_mpi_ec_add_points (mpi_point_t result,
                               mpi_point_t p1, mpi_point_t p2,
                               mpi_ec_t ctx);
+void _gcry_mpi_ec_sub_points (mpi_point_t result,
+                              mpi_point_t p1, mpi_point_t p2,
+                              mpi_ec_t ctx);
 void _gcry_mpi_ec_mul_point (mpi_point_t result,
                              gcry_mpi_t scalar, mpi_point_t point,
                              mpi_ec_t ctx);
diff --git a/src/visibility.c b/src/visibility.c
index 6ed57ca6..fa23e53c 100644
--- a/src/visibility.c
+++ b/src/visibility.c
@@ -567,6 +567,14 @@ gcry_mpi_ec_add (gcry_mpi_point_t w,
 }
 
 void
+gcry_mpi_ec_sub (gcry_mpi_point_t w,
+                 gcry_mpi_point_t u, gcry_mpi_point_t v, gcry_ctx_t ctx)
+{
+  _gcry_mpi_ec_sub_points (w, u, v,
+                           _gcry_ctx_get_pointer (ctx, CONTEXT_TYPE_EC));
+}
+
+void
 gcry_mpi_ec_mul (gcry_mpi_point_t w, gcry_mpi_t n, gcry_mpi_point_t u,
                  gcry_ctx_t ctx)
 {
diff --git a/src/visibility.h b/src/visibility.h
index 96b52355..fa3c7630 100644
--- a/src/visibility.h
+++ b/src/visibility.h
@@ -218,6 +218,7 @@ MARK_VISIBLEX (gcry_mpi_copy)
 MARK_VISIBLEX (gcry_mpi_div)
 MARK_VISIBLEX (gcry_mpi_dump)
 MARK_VISIBLEX (gcry_mpi_ec_add)
+MARK_VISIBLEX (gcry_mpi_ec_sub)
 MARK_VISIBLEX (gcry_mpi_ec_curve_point)
 MARK_VISIBLEX (gcry_mpi_ec_dup)
 MARK_VISIBLEX (gcry_mpi_ec_get_affine)
@@ -486,6 +487,7 @@ MARK_VISIBLEX (_gcry_mpi_get_const)
 
 #define gcry_mpi_abs                _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_add             _gcry_USE_THE_UNDERSCORED_FUNCTION
+#define gcry_mpi_ec_sub             _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_curve_point     _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_dup             _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_get_affine      _gcry_USE_THE_UNDERSCORED_FUNCTION