ecc: New API function gcry_mpi_ec_decode_point.

* mpi/ec.c (_gcry_mpi_ec_decode_point): New.
* cipher/ecc-common.h: Move two prototypes to ...
* src/ec-context.h: here.
* src/gcrypt.h.in (gcry_mpi_ec_decode_point): New.
* src/libgcrypt.def (gcry_mpi_ec_decode_point): New.
* src/libgcrypt.vers (gcry_mpi_ec_decode_point): New.
* src/visibility.c (gcry_mpi_ec_decode_point): New.
* src/visibility.h: Add new function.
--

This new function make the use of the gcry_mpi_ec_curve_point function
possible in many contexts.  Here is a code snippet which could be used
in gpg to check a point:

static gpg_error_t
check_point (PKT_public_key *pk, gcry_mpi_t m_point)
{
  gpg_error_t err;
  char *curve;
  gcry_ctx_t gctx = NULL;
  gcry_mpi_point_t point = NULL;

  /* Get the curve name from the first OpenPGP key parameter.  */
  curve = openpgp_oid_to_str (pk->pkey[0]);
  if (!curve)
    {
      err = gpg_error_from_syserror ();
      goto leave;
    }

  point = gcry_mpi_point_new (0);
  if (!point)
    {
      err = gpg_error_from_syserror ();
      goto leave;
    }

  err = gcry_mpi_ec_new (&gctx, NULL, curve);
  if (err)
    goto leave;

  err = gcry_mpi_ec_decode_point (point, m_point, gctx);
  if (err)
    goto leave;

  if (!gcry_mpi_ec_curve_point (point, gctx))
    err = gpg_error (GPG_ERR_BAD_DATA);

 leave:
  gcry_ctx_release (gctx);
  gcry_mpi_point_release (point);
  xfree (curve);
  return err;
}

Signed-off-by: Werner Koch <wk@gnupg.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/gcrypt.h.in b/src/gcrypt.h.in
index 93b1f43f..f48f04fb 100644
--- a/src/gcrypt.h.in
+++ b/src/gcrypt.h.in
@@ -694,6 +694,10 @@ gpg_error_t gcry_mpi_ec_set_mpi (const char *name, gcry_mpi_t newvalue,
 gpg_error_t gcry_mpi_ec_set_point (const char *name, gcry_mpi_point_t newvalue,
                                    gcry_ctx_t ctx);
 
+/* Decode and store VALUE into RESULT.  */
+gpg_error_t gcry_mpi_ec_decode_point (gcry_mpi_point_t result,
+                                      gcry_mpi_t value, gcry_ctx_t ctx);
+
 /* Store the affine coordinates of POINT into X and Y.  */
 int gcry_mpi_ec_get_affine (gcry_mpi_t x, gcry_mpi_t y, gcry_mpi_point_t point,
                             gcry_ctx_t ctx);