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>

11 files changed, 69 insertions, 8 deletions

diff --git a/NEWS b/NEWS
index 22565ed6..79d19313 100644
--- a/NEWS
+++ b/NEWS
@@ -36,6 +36,7 @@ Noteworthy changes in version 1.7.0 (unreleased)
  gcry_cipher_set_sbox            NEW macro.
  GCRY_MD_GOSTR3411_CP            NEW.
  gcry_mpi_ec_sub                 NEW.
+ gcry_mpi_ec_decode_point        NEW.
  GCRY_CIPHER_MODE_OCB            NEW.
  GCRYCTL_SET_TAGLEN              NEW.
  gcry_cipher_final               NEW macro.
diff --git a/cipher/ecc-common.h b/cipher/ecc-common.h
index 4e528af8..748e6dba 100644
--- a/cipher/ecc-common.h
+++ b/cipher/ecc-common.h
@@ -89,13 +89,10 @@ elliptic_curve_t _gcry_ecc_curve_copy (elliptic_curve_t E);
 const char *_gcry_ecc_model2str (enum gcry_mpi_ec_models model);
 const char *_gcry_ecc_dialect2str (enum ecc_dialects dialect);
 gcry_mpi_t   _gcry_ecc_ec2os (gcry_mpi_t x, gcry_mpi_t y, gcry_mpi_t p);
-gcry_err_code_t _gcry_ecc_os2ec (mpi_point_t result, gcry_mpi_t value);
 
 mpi_point_t  _gcry_ecc_compute_public (mpi_point_t Q, mpi_ec_t ec,
                                        mpi_point_t G, gcry_mpi_t d);
 
-gpg_err_code_t _gcry_ecc_mont_decodepoint (gcry_mpi_t pk, mpi_ec_t ctx,
-                                           mpi_point_t result);
 
 /*-- ecc.c --*/
 
@@ -116,10 +113,8 @@ gpg_err_code_t _gcry_ecc_eddsa_encodepoint (mpi_point_t point, mpi_ec_t ctx,
                                             unsigned int *r_buflen);
 gpg_err_code_t _gcry_ecc_eddsa_ensure_compact (gcry_mpi_t value,
                                                unsigned int nbits);
-gpg_err_code_t _gcry_ecc_eddsa_decodepoint (gcry_mpi_t pk, mpi_ec_t ctx,
-                                            mpi_point_t result,
-                                            unsigned char **r_encpk,
-                                            unsigned int *r_encpklen);
+
+
 gpg_err_code_t _gcry_ecc_eddsa_compute_h_d (unsigned char **r_digest,
                                             gcry_mpi_t d, mpi_ec_t ec);
 
diff --git a/doc/gcrypt.texi b/doc/gcrypt.texi
index 39c7c9f5..bbaaac62 100644
--- a/doc/gcrypt.texi
+++ b/doc/gcrypt.texi
@@ -4882,6 +4882,19 @@ Valid names are the point parameters of an elliptic curve
 (@pxref{ecc_keyparam}).
 @end deftypefun
 
+@deftypefun gpg_err_code_t gcry_mpi_ec_decode_point ( @
+ @w{mpi_point_t @var{result}}, @w{gcry_mpi_t @var{value}}, @
+ @w{gcry_ctx_t @var{ctx}})
+
+Decode the point given as an MPI in @var{value} and store at
+@var{result}.  To decide which encoding is used the function takes a
+context @var{ctx} which can be created with @code{gcry_mpi_ec_new}.
+If @code{NULL} is given for the context the function assumes a 0x04
+prefixed uncompressed encoding.  On error an error code is returned
+and @var{result} might be changed.
+@end deftypefun
+
+
 @deftypefun int gcry_mpi_ec_get_affine ( @
  @w{gcry_mpi_t @var{x}}, @w{gcry_mpi_t @var{y}}, @
  @w{gcry_mpi_point_t @var{point}}, @w{gcry_ctx_t @var{ctx}})
diff --git a/mpi/ec.c b/mpi/ec.c
index 40e09bed..346e5f1e 100644
--- a/mpi/ec.c
+++ b/mpi/ec.c
@@ -589,6 +589,27 @@ _gcry_mpi_ec_set_point (const char *name, gcry_mpi_point_t newvalue,
 }
 
 
+/* Given an encoded point in the MPI VALUE and a context EC, decode
+ * the point according to the context and store it in RESULT.  On
+ * error an error code is return but RESULT might have been changed.
+ * If no context is given the function tries to decode VALUE by
+ * assuming a 0x04 prefixed uncompressed encoding.  */
+gpg_err_code_t
+_gcry_mpi_ec_decode_point (mpi_point_t result, gcry_mpi_t value, mpi_ec_t ec)
+{
+  gcry_err_code_t rc;
+
+  if (ec && ec->dialect == ECC_DIALECT_ED25519)
+    rc = _gcry_ecc_eddsa_decodepoint (value, ec, result, NULL, NULL);
+  else if (ec && ec->model == MPI_EC_MONTGOMERY)
+    rc = _gcry_ecc_mont_decodepoint (value, ec, result);
+  else
+    rc = _gcry_ecc_os2ec (result, value);
+
+  return rc;
+}
+
+
 /* Compute the affine coordinates from the projective coordinates in
    POINT.  Set them into X and Y.  If one coordinate is not required,
    X or Y may be passed as NULL.  CTX is the usual context. Returns: 0
diff --git a/src/ec-context.h b/src/ec-context.h
index c8f2ad0c..d74fb695 100644
--- a/src/ec-context.h
+++ b/src/ec-context.h
@@ -81,5 +81,17 @@ gpg_err_code_t   _gcry_ecc_set_mpi (const char *name,
 gpg_err_code_t   _gcry_ecc_set_point (const char *name,
                                       gcry_mpi_point_t newvalue, mpi_ec_t ec);
 
+/*-- cipher/ecc-misc.c --*/
+gcry_err_code_t _gcry_ecc_os2ec (mpi_point_t result, gcry_mpi_t value);
+gpg_err_code_t _gcry_ecc_mont_decodepoint (gcry_mpi_t pk, mpi_ec_t ctx,
+                                           mpi_point_t result);
+
+/*-- cipher/ecc-eddsa.c --*/
+gpg_err_code_t _gcry_ecc_eddsa_decodepoint (gcry_mpi_t pk, mpi_ec_t ctx,
+                                            mpi_point_t result,
+                                            unsigned char **r_encpk,
+                                            unsigned int *r_encpklen);
+
+
 
 #endif /*GCRY_EC_CONTEXT_H*/
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);
diff --git a/src/libgcrypt.def b/src/libgcrypt.def
index f3e074bd..067cb843 100644
--- a/src/libgcrypt.def
+++ b/src/libgcrypt.def
@@ -280,4 +280,6 @@ EXPORTS
 
       gcry_md_extract           @245
 
+      gcry_mpi_ec_decode_point  @246
+
 ;; end of file with public symbols for Windows.
diff --git a/src/libgcrypt.vers b/src/libgcrypt.vers
index 5b3d4192..785b8ed2 100644
--- a/src/libgcrypt.vers
+++ b/src/libgcrypt.vers
@@ -106,7 +106,7 @@ GCRYPT_1.6 {
     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_sub; gcry_mpi_ec_mul;
-    gcry_mpi_ec_curve_point;
+    gcry_mpi_ec_curve_point; gcry_mpi_ec_decode_point;
 
     gcry_log_debug;
     gcry_log_debughex; gcry_log_debugmpi; gcry_log_debugpnt; gcry_log_debugsxp;
diff --git a/src/mpi.h b/src/mpi.h
index 0d19f461..cd539f5c 100644
--- a/src/mpi.h
+++ b/src/mpi.h
@@ -307,6 +307,8 @@ gpg_err_code_t _gcry_mpi_ec_set_mpi (const char *name, gcry_mpi_t newvalue,
 gpg_err_code_t _gcry_mpi_ec_set_point (const char *name,
                                        gcry_mpi_point_t newvalue,
                                        gcry_ctx_t ctx);
+gpg_err_code_t _gcry_mpi_ec_decode_point (mpi_point_t result,
+                                          gcry_mpi_t value, mpi_ec_t ec);
 
 /*-- ecc-curves.c --*/
 gpg_err_code_t _gcry_mpi_ec_new (gcry_ctx_t *r_ctx,
diff --git a/src/visibility.c b/src/visibility.c
index 23a2705a..3abbd379 100644
--- a/src/visibility.c
+++ b/src/visibility.c
@@ -544,6 +544,15 @@ gcry_mpi_ec_set_point (const char *name, gcry_mpi_point_t newvalue,
   return gpg_error (_gcry_mpi_ec_set_point (name, newvalue, ctx));
 }
 
+gpg_error_t
+gcry_mpi_ec_decode_point (gcry_mpi_point_t result, gcry_mpi_t value,
+                          gcry_ctx_t ctx)
+{
+  return gpg_error (_gcry_mpi_ec_decode_point
+                    (result, value,
+                     ctx? _gcry_ctx_get_pointer (ctx, CONTEXT_TYPE_EC) : NULL));
+}
+
 int
 gcry_mpi_ec_get_affine (gcry_mpi_t x, gcry_mpi_t y, gcry_mpi_point_t point,
                         gcry_ctx_t ctx)
diff --git a/src/visibility.h b/src/visibility.h
index bb25de01..7ecd75e3 100644
--- a/src/visibility.h
+++ b/src/visibility.h
@@ -222,6 +222,7 @@ 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_decode_point)
 MARK_VISIBLEX (gcry_mpi_ec_get_affine)
 MARK_VISIBLEX (gcry_mpi_ec_mul)
 MARK_VISIBLEX (gcry_mpi_ec_new)
@@ -492,6 +493,7 @@ MARK_VISIBLEX (_gcry_mpi_get_const)
 #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_decode_point    _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_get_affine      _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_get_mpi         _gcry_USE_THE_UNDERSCORED_FUNCTION
 #define gcry_mpi_ec_get_point       _gcry_USE_THE_UNDERSCORED_FUNCTION