crypto/ec/ec2_oct.c

   1 /* crypto/ec/ec2_oct.c */
   2 /* ====================================================================
   3  * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
   4  *
   5  * The Elliptic Curve Public-Key Crypto Library (ECC Code) included
   6  * herein is developed by SUN MICROSYSTEMS, INC., and is contributed
   7  * to the OpenSSL project.
   8  *
   9  * The ECC Code is licensed pursuant to the OpenSSL open source
  10  * license provided below.
  11  *
  12  * The software is originally written by Sheueling Chang Shantz and
  13  * Douglas Stebila of Sun Microsystems Laboratories.
  14  *
  15  */
  16 /* ====================================================================
  17  * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.
  18  *
  19  * Redistribution and use in source and binary forms, with or without
  20  * modification, are permitted provided that the following conditions
  21  * are met:
  22  *
  23  * 1. Redistributions of source code must retain the above copyright
  24  *    notice, this list of conditions and the following disclaimer.
  25  *
  26  * 2. Redistributions in binary form must reproduce the above copyright
  27  *    notice, this list of conditions and the following disclaimer in
  28  *    the documentation and/or other materials provided with the
  29  *    distribution.
  30  *
  31  * 3. All advertising materials mentioning features or use of this
  32  *    software must display the following acknowledgment:
  33  *    "This product includes software developed by the OpenSSL Project
  34  *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
  35  *
  36  * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
  37  *    endorse or promote products derived from this software without
  38  *    prior written permission. For written permission, please contact
  39  *    openssl-core@openssl.org.
  40  *
  41  * 5. Products derived from this software may not be called "OpenSSL"
  42  *    nor may "OpenSSL" appear in their names without prior written
  43  *    permission of the OpenSSL Project.
  44  *
  45  * 6. Redistributions of any form whatsoever must retain the following
  46  *    acknowledgment:
  47  *    "This product includes software developed by the OpenSSL Project
  48  *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
  49  *
  50  * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
  51  * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  52  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  53  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
  54  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  55  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  56  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  57  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  58  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  59  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  60  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
  61  * OF THE POSSIBILITY OF SUCH DAMAGE.
  62  * ====================================================================
  63  *
  64  * This product includes cryptographic software written by Eric Young
  65  * (eay@cryptsoft.com).  This product includes software written by Tim
  66  * Hudson (tjh@cryptsoft.com).
  67  *
  68  */
  69
  70 #include <openssl/err.h>
  71
  72 #include "ec_lcl.h"
  73
  74 #ifndef OPENSSL_NO_EC2M
  75
  76 /*-
  77  * Calculates and sets the affine coordinates of an EC_POINT from the given
  78  * compressed coordinates.  Uses algorithm 2.3.4 of SEC 1.
  79  * Note that the simple implementation only uses affine coordinates.
  80  *
  81  * The method is from the following publication:
  82  *
  83  *     Harper, Menezes, Vanstone:
  84  *     "Public-Key Cryptosystems with Very Small Key Lengths",
  85  *     EUROCRYPT '92, Springer-Verlag LNCS 658,
  86  *     published February 1993
  87  *
  88  * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
  89  * the same method, but claim no priority date earlier than July 29, 1994
  90  * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
  91  */
  92 int ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group,
  93                                               EC_POINT *point,
  94                                               const BIGNUM *x_, int y_bit,
  95                                               BN_CTX *ctx)
  96 {
  97     BN_CTX *new_ctx = NULL;
  98     BIGNUM *tmp, *x, *y, *z;
  99     int ret = 0, z0;
 100
 101     /* clear error queue */
 102     ERR_clear_error();
 103
 104     if (ctx == NULL) {
 105         ctx = new_ctx = BN_CTX_new();
 106         if (ctx == NULL)
 107             return 0;
 108     }
 109
 110     y_bit = (y_bit != 0) ? 1 : 0;
 111
 112     BN_CTX_start(ctx);
 113     tmp = BN_CTX_get(ctx);
 114     x = BN_CTX_get(ctx);
 115     y = BN_CTX_get(ctx);
 116     z = BN_CTX_get(ctx);
 117     if (z == NULL)
 118         goto err;
 119
 120     if (!BN_GF2m_mod_arr(x, x_, group->poly))
 121         goto err;
 122     if (BN_is_zero(x)) {
 123         if (!BN_GF2m_mod_sqrt_arr(y, &group->b, group->poly, ctx))
 124             goto err;
 125     } else {
 126         if (!group->meth->field_sqr(group, tmp, x, ctx))
 127             goto err;
 128         if (!group->meth->field_div(group, tmp, &group->b, tmp, ctx))
 129             goto err;
 130         if (!BN_GF2m_add(tmp, &group->a, tmp))
 131             goto err;
 132         if (!BN_GF2m_add(tmp, x, tmp))
 133             goto err;
 134         if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
 135             unsigned long err = ERR_peek_last_error();
 136
 137             if (ERR_GET_LIB(err) == ERR_LIB_BN
 138                 && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
 139                 ERR_clear_error();
 140                 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
 141                       EC_R_INVALID_COMPRESSED_POINT);
 142             } else
 143                 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
 144                       ERR_R_BN_LIB);
 145             goto err;
 146         }
 147         z0 = (BN_is_odd(z)) ? 1 : 0;
 148         if (!group->meth->field_mul(group, y, x, z, ctx))
 149             goto err;
 150         if (z0 != y_bit) {
 151             if (!BN_GF2m_add(y, y, x))
 152                 goto err;
 153         }
 154     }
 155
 156     if (!EC_POINT_set_affine_coordinates_GF2m(group, point, x, y, ctx))
 157         goto err;
 158
 159     ret = 1;
 160
 161  err:
 162     BN_CTX_end(ctx);
 163     if (new_ctx != NULL)
 164         BN_CTX_free(new_ctx);
 165     return ret;
 166 }
 167
 168 /*
 169  * Converts an EC_POINT to an octet string. If buf is NULL, the encoded
 170  * length will be returned. If the length len of buf is smaller than required
 171  * an error will be returned.
 172  */
 173 size_t ec_GF2m_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
 174                                 point_conversion_form_t form,
 175                                 unsigned char *buf, size_t len, BN_CTX *ctx)
 176 {
 177     size_t ret;
 178     BN_CTX *new_ctx = NULL;
 179     int used_ctx = 0;
 180     BIGNUM *x, *y, *yxi;
 181     size_t field_len, i, skip;
 182
 183     if ((form != POINT_CONVERSION_COMPRESSED)
 184         && (form != POINT_CONVERSION_UNCOMPRESSED)
 185         && (form != POINT_CONVERSION_HYBRID)) {
 186         ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
 187         goto err;
 188     }
 189
 190     if (EC_POINT_is_at_infinity(group, point)) {
 191         /* encodes to a single 0 octet */
 192         if (buf != NULL) {
 193             if (len < 1) {
 194                 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
 195                 return 0;
 196             }
 197             buf[0] = 0;
 198         }
 199         return 1;
 200     }
 201
 202     /* ret := required output buffer length */
 203     field_len = (EC_GROUP_get_degree(group) + 7) / 8;
 204     ret =
 205         (form ==
 206          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 207
 208     /* if 'buf' is NULL, just return required length */
 209     if (buf != NULL) {
 210         if (len < ret) {
 211             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
 212             goto err;
 213         }
 214
 215         if (ctx == NULL) {
 216             ctx = new_ctx = BN_CTX_new();
 217             if (ctx == NULL)
 218                 return 0;
 219         }
 220
 221         BN_CTX_start(ctx);
 222         used_ctx = 1;
 223         x = BN_CTX_get(ctx);
 224         y = BN_CTX_get(ctx);
 225         yxi = BN_CTX_get(ctx);
 226         if (yxi == NULL)
 227             goto err;
 228
 229         if (!EC_POINT_get_affine_coordinates_GF2m(group, point, x, y, ctx))
 230             goto err;
 231
 232         buf[0] = form;
 233         if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
 234             if (!group->meth->field_div(group, yxi, y, x, ctx))
 235                 goto err;
 236             if (BN_is_odd(yxi))
 237                 buf[0]++;
 238         }
 239
 240         i = 1;
 241
 242         skip = field_len - BN_num_bytes(x);
 243         if (skip > field_len) {
 244             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 245             goto err;
 246         }
 247         while (skip > 0) {
 248             buf[i++] = 0;
 249             skip--;
 250         }
 251         skip = BN_bn2bin(x, buf + i);
 252         i += skip;
 253         if (i != 1 + field_len) {
 254             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 255             goto err;
 256         }
 257
 258         if (form == POINT_CONVERSION_UNCOMPRESSED
 259             || form == POINT_CONVERSION_HYBRID) {
 260             skip = field_len - BN_num_bytes(y);
 261             if (skip > field_len) {
 262                 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 263                 goto err;
 264             }
 265             while (skip > 0) {
 266                 buf[i++] = 0;
 267                 skip--;
 268             }
 269             skip = BN_bn2bin(y, buf + i);
 270             i += skip;
 271         }
 272
 273         if (i != ret) {
 274             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 275             goto err;
 276         }
 277     }
 278
 279     if (used_ctx)
 280         BN_CTX_end(ctx);
 281     if (new_ctx != NULL)
 282         BN_CTX_free(new_ctx);
 283     return ret;
 284
 285  err:
 286     if (used_ctx)
 287         BN_CTX_end(ctx);
 288     if (new_ctx != NULL)
 289         BN_CTX_free(new_ctx);
 290     return 0;
 291 }
 292
 293 /*
 294  * Converts an octet string representation to an EC_POINT. Note that the
 295  * simple implementation only uses affine coordinates.
 296  */
 297 int ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
 298                              const unsigned char *buf, size_t len,
 299                              BN_CTX *ctx)
 300 {
 301     point_conversion_form_t form;
 302     int y_bit;
 303     BN_CTX *new_ctx = NULL;
 304     BIGNUM *x, *y, *yxi;
 305     size_t field_len, enc_len;
 306     int ret = 0;
 307
 308     if (len == 0) {
 309         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
 310         return 0;
 311     }
 312     form = buf[0];
 313     y_bit = form & 1;
 314     form = form & ~1U;
 315     if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
 316         && (form != POINT_CONVERSION_UNCOMPRESSED)
 317         && (form != POINT_CONVERSION_HYBRID)) {
 318         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 319         return 0;
 320     }
 321     if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
 322         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 323         return 0;
 324     }
 325
 326     if (form == 0) {
 327         if (len != 1) {
 328             ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 329             return 0;
 330         }
 331
 332         return EC_POINT_set_to_infinity(group, point);
 333     }
 334
 335     field_len = (EC_GROUP_get_degree(group) + 7) / 8;
 336     enc_len =
 337         (form ==
 338          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 339
 340     if (len != enc_len) {
 341         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 342         return 0;
 343     }
 344
 345     if (ctx == NULL) {
 346         ctx = new_ctx = BN_CTX_new();
 347         if (ctx == NULL)
 348             return 0;
 349     }
 350
 351     BN_CTX_start(ctx);
 352     x = BN_CTX_get(ctx);
 353     y = BN_CTX_get(ctx);
 354     yxi = BN_CTX_get(ctx);
 355     if (yxi == NULL)
 356         goto err;
 357
 358     if (!BN_bin2bn(buf + 1, field_len, x))
 359         goto err;
 360     if (BN_ucmp(x, &group->field) >= 0) {
 361         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 362         goto err;
 363     }
 364
 365     if (form == POINT_CONVERSION_COMPRESSED) {
 366         if (!EC_POINT_set_compressed_coordinates_GF2m
 367             (group, point, x, y_bit, ctx))
 368             goto err;
 369     } else {
 370         if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
 371             goto err;
 372         if (BN_ucmp(y, &group->field) >= 0) {
 373             ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 374             goto err;
 375         }
 376         if (form == POINT_CONVERSION_HYBRID) {
 377             if (!group->meth->field_div(group, yxi, y, x, ctx))
 378                 goto err;
 379             if (y_bit != BN_is_odd(yxi)) {
 380                 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 381                 goto err;
 382             }
 383         }
 384
 385         if (!EC_POINT_set_affine_coordinates_GF2m(group, point, x, y, ctx))
 386             goto err;
 387     }
 388
 389     /* test required by X9.62 */
 390     if (EC_POINT_is_on_curve(group, point, ctx) <= 0) {
 391         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_POINT_IS_NOT_ON_CURVE);
 392         goto err;
 393     }
 394
 395     ret = 1;
 396
 397  err:
 398     BN_CTX_end(ctx);
 399     if (new_ctx != NULL)
 400         BN_CTX_free(new_ctx);
 401     return ret;
 402 }
 403 #endif