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/* ecc-misc.c - Elliptic Curve miscellaneous functions
* Copyright (C) 2007, 2008, 2010, 2011 Free Software Foundation, Inc.
* Copyright (C) 2013 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 <http://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "g10lib.h"
#include "mpi.h"
#include "context.h"
#include "ec-context.h"
#include "ecc-common.h"
/*
* Release a curve object.
*/
void
_gcry_ecc_curve_free (elliptic_curve_t *E)
{
mpi_free (E->p); E->p = NULL;
mpi_free (E->a); E->a = NULL;
mpi_free (E->b); E->b = NULL;
_gcry_mpi_point_free_parts (&E->G);
mpi_free (E->n); E->n = NULL;
}
/*
* Return a copy of a curve object.
*/
elliptic_curve_t
_gcry_ecc_curve_copy (elliptic_curve_t E)
{
elliptic_curve_t R;
R.model = E.model;
R.dialect = E.dialect;
R.p = mpi_copy (E.p);
R.a = mpi_copy (E.a);
R.b = mpi_copy (E.b);
_gcry_mpi_point_init (&R.G);
point_set (&R.G, &E.G);
R.n = mpi_copy (E.n);
return R;
}
/*
* Return a description of the curve model.
*/
const char *
_gcry_ecc_model2str (enum gcry_mpi_ec_models model)
{
const char *str = "?";
switch (model)
{
case MPI_EC_WEIERSTRASS: str = "Weierstrass"; break;
case MPI_EC_MONTGOMERY: str = "Montgomery"; break;
case MPI_EC_TWISTEDEDWARDS: str = "Twisted Edwards"; break;
}
return str;
}
/*
* Return a description of the curve dialect.
*/
const char *
_gcry_ecc_dialect2str (enum ecc_dialects dialect)
{
const char *str = "?";
switch (dialect)
{
case ECC_DIALECT_STANDARD: str = "Standard"; break;
case ECC_DIALECT_ED25519: str = "Ed25519"; break;
}
return str;
}
gcry_mpi_t
_gcry_ecc_ec2os (gcry_mpi_t x, gcry_mpi_t y, gcry_mpi_t p)
{
gpg_error_t err;
int pbytes = (mpi_get_nbits (p)+7)/8;
size_t n;
unsigned char *buf, *ptr;
gcry_mpi_t result;
buf = gcry_xmalloc ( 1 + 2*pbytes );
*buf = 04; /* Uncompressed point. */
ptr = buf+1;
err = gcry_mpi_print (GCRYMPI_FMT_USG, ptr, pbytes, &n, x);
if (err)
log_fatal ("mpi_print failed: %s\n", gpg_strerror (err));
if (n < pbytes)
{
memmove (ptr+(pbytes-n), ptr, n);
memset (ptr, 0, (pbytes-n));
}
ptr += pbytes;
err = gcry_mpi_print (GCRYMPI_FMT_USG, ptr, pbytes, &n, y);
if (err)
log_fatal ("mpi_print failed: %s\n", gpg_strerror (err));
if (n < pbytes)
{
memmove (ptr+(pbytes-n), ptr, n);
memset (ptr, 0, (pbytes-n));
}
err = gcry_mpi_scan (&result, GCRYMPI_FMT_USG, buf, 1+2*pbytes, NULL);
if (err)
log_fatal ("mpi_scan failed: %s\n", gpg_strerror (err));
gcry_free (buf);
return result;
}
/* Convert POINT into affine coordinates using the context CTX and
return a newly allocated MPI. If the conversion is not possible
NULL is returned. This function won't print an error message. */
gcry_mpi_t
_gcry_mpi_ec_ec2os (gcry_mpi_point_t point, mpi_ec_t ectx)
{
gcry_mpi_t g_x, g_y, result;
g_x = mpi_new (0);
g_y = mpi_new (0);
if (_gcry_mpi_ec_get_affine (g_x, g_y, point, ectx))
result = NULL;
else
result = _gcry_ecc_ec2os (g_x, g_y, ectx->p);
mpi_free (g_x);
mpi_free (g_y);
return result;
}
/* RESULT must have been initialized and is set on success to the
point given by VALUE. */
gcry_error_t
_gcry_ecc_os2ec (mpi_point_t result, gcry_mpi_t value)
{
gcry_error_t err;
size_t n;
const unsigned char *buf;
unsigned char *buf_memory;
gcry_mpi_t x, y;
if (mpi_is_opaque (value))
{
unsigned int nbits;
buf = gcry_mpi_get_opaque (value, &nbits);
if (!buf)
return GPG_ERR_INV_OBJ;
n = (nbits + 7)/8;
buf_memory = NULL;
}
else
{
n = (mpi_get_nbits (value)+7)/8;
buf_memory= gcry_xmalloc (n);
err = gcry_mpi_print (GCRYMPI_FMT_USG, buf_memory, n, &n, value);
if (err)
{
gcry_free (buf_memory);
return err;
}
buf = buf_memory;
}
if (n < 1)
{
gcry_free (buf_memory);
return GPG_ERR_INV_OBJ;
}
if (*buf != 4)
{
gcry_free (buf_memory);
return GPG_ERR_NOT_IMPLEMENTED; /* No support for point compression. */
}
if ( ((n-1)%2) )
{
gcry_free (buf_memory);
return GPG_ERR_INV_OBJ;
}
n = (n-1)/2;
err = gcry_mpi_scan (&x, GCRYMPI_FMT_USG, buf+1, n, NULL);
if (err)
{
gcry_free (buf_memory);
return err;
}
err = gcry_mpi_scan (&y, GCRYMPI_FMT_USG, buf+1+n, n, NULL);
gcry_free (buf_memory);
if (err)
{
mpi_free (x);
return err;
}
mpi_set (result->x, x);
mpi_set (result->y, y);
mpi_set_ui (result->z, 1);
mpi_free (x);
mpi_free (y);
return 0;
}
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