crypto/ec/ec2_oct.c

   1 /*
   2  * Copyright 2011-2016 The OpenSSL Project Authors. All Rights Reserved.
   3  * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
   4  *
   5  * Licensed under the OpenSSL license (the "License").  You may not use
   6  * this file except in compliance with the License.  You can obtain a copy
   7  * in the file LICENSE in the source distribution or at
   8  * https://www.openssl.org/source/license.html
   9  */
  10
  11 #include <openssl/err.h>
  12
  13 #include "ec_lcl.h"
  14
  15 #ifndef OPENSSL_NO_EC2M
  16
  17 /*-
  18  * Calculates and sets the affine coordinates of an EC_POINT from the given
  19  * compressed coordinates.  Uses algorithm 2.3.4 of SEC 1.
  20  * Note that the simple implementation only uses affine coordinates.
  21  *
  22  * The method is from the following publication:
  23  *
  24  *     Harper, Menezes, Vanstone:
  25  *     "Public-Key Cryptosystems with Very Small Key Lengths",
  26  *     EUROCRYPT '92, Springer-Verlag LNCS 658,
  27  *     published February 1993
  28  *
  29  * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
  30  * the same method, but claim no priority date earlier than July 29, 1994
  31  * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
  32  */
  33 int ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group,
  34                                               EC_POINT *point,
  35                                               const BIGNUM *x_, int y_bit,
  36                                               BN_CTX *ctx)
  37 {
  38     BN_CTX *new_ctx = NULL;
  39     BIGNUM *tmp, *x, *y, *z;
  40     int ret = 0, z0;
  41
  42     /* clear error queue */
  43     ERR_clear_error();
  44
  45     if (ctx == NULL) {
  46         ctx = new_ctx = BN_CTX_new();
  47         if (ctx == NULL)
  48             return 0;
  49     }
  50
  51     y_bit = (y_bit != 0) ? 1 : 0;
  52
  53     BN_CTX_start(ctx);
  54     tmp = BN_CTX_get(ctx);
  55     x = BN_CTX_get(ctx);
  56     y = BN_CTX_get(ctx);
  57     z = BN_CTX_get(ctx);
  58     if (z == NULL)
  59         goto err;
  60
  61     if (!BN_GF2m_mod_arr(x, x_, group->poly))
  62         goto err;
  63     if (BN_is_zero(x)) {
  64         if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))
  65             goto err;
  66     } else {
  67         if (!group->meth->field_sqr(group, tmp, x, ctx))
  68             goto err;
  69         if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))
  70             goto err;
  71         if (!BN_GF2m_add(tmp, group->a, tmp))
  72             goto err;
  73         if (!BN_GF2m_add(tmp, x, tmp))
  74             goto err;
  75         if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
  76             unsigned long err = ERR_peek_last_error();
  77
  78             if (ERR_GET_LIB(err) == ERR_LIB_BN
  79                 && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
  80                 ERR_clear_error();
  81                 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
  82                       EC_R_INVALID_COMPRESSED_POINT);
  83             } else
  84                 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
  85                       ERR_R_BN_LIB);
  86             goto err;
  87         }
  88         z0 = (BN_is_odd(z)) ? 1 : 0;
  89         if (!group->meth->field_mul(group, y, x, z, ctx))
  90             goto err;
  91         if (z0 != y_bit) {
  92             if (!BN_GF2m_add(y, y, x))
  93                 goto err;
  94         }
  95     }
  96
  97     if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
  98         goto err;
  99
 100     ret = 1;
 101
 102  err:
 103     BN_CTX_end(ctx);
 104     BN_CTX_free(new_ctx);
 105     return ret;
 106 }
 107
 108 /*
 109  * Converts an EC_POINT to an octet string. If buf is NULL, the encoded
 110  * length will be returned. If the length len of buf is smaller than required
 111  * an error will be returned.
 112  */
 113 size_t ec_GF2m_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
 114                                 point_conversion_form_t form,
 115                                 unsigned char *buf, size_t len, BN_CTX *ctx)
 116 {
 117     size_t ret;
 118     BN_CTX *new_ctx = NULL;
 119     int used_ctx = 0;
 120     BIGNUM *x, *y, *yxi;
 121     size_t field_len, i, skip;
 122
 123     if ((form != POINT_CONVERSION_COMPRESSED)
 124         && (form != POINT_CONVERSION_UNCOMPRESSED)
 125         && (form != POINT_CONVERSION_HYBRID)) {
 126         ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
 127         goto err;
 128     }
 129
 130     if (EC_POINT_is_at_infinity(group, point)) {
 131         /* encodes to a single 0 octet */
 132         if (buf != NULL) {
 133             if (len < 1) {
 134                 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
 135                 return 0;
 136             }
 137             buf[0] = 0;
 138         }
 139         return 1;
 140     }
 141
 142     /* ret := required output buffer length */
 143     field_len = (EC_GROUP_get_degree(group) + 7) / 8;
 144     ret =
 145         (form ==
 146          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 147
 148     /* if 'buf' is NULL, just return required length */
 149     if (buf != NULL) {
 150         if (len < ret) {
 151             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
 152             goto err;
 153         }
 154
 155         if (ctx == NULL) {
 156             ctx = new_ctx = BN_CTX_new();
 157             if (ctx == NULL)
 158                 return 0;
 159         }
 160
 161         BN_CTX_start(ctx);
 162         used_ctx = 1;
 163         x = BN_CTX_get(ctx);
 164         y = BN_CTX_get(ctx);
 165         yxi = BN_CTX_get(ctx);
 166         if (yxi == NULL)
 167             goto err;
 168
 169         if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
 170             goto err;
 171
 172         buf[0] = form;
 173         if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
 174             if (!group->meth->field_div(group, yxi, y, x, ctx))
 175                 goto err;
 176             if (BN_is_odd(yxi))
 177                 buf[0]++;
 178         }
 179
 180         i = 1;
 181
 182         skip = field_len - BN_num_bytes(x);
 183         if (skip > field_len) {
 184             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 185             goto err;
 186         }
 187         while (skip > 0) {
 188             buf[i++] = 0;
 189             skip--;
 190         }
 191         skip = BN_bn2bin(x, buf + i);
 192         i += skip;
 193         if (i != 1 + field_len) {
 194             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 195             goto err;
 196         }
 197
 198         if (form == POINT_CONVERSION_UNCOMPRESSED
 199             || form == POINT_CONVERSION_HYBRID) {
 200             skip = field_len - BN_num_bytes(y);
 201             if (skip > field_len) {
 202                 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 203                 goto err;
 204             }
 205             while (skip > 0) {
 206                 buf[i++] = 0;
 207                 skip--;
 208             }
 209             skip = BN_bn2bin(y, buf + i);
 210             i += skip;
 211         }
 212
 213         if (i != ret) {
 214             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 215             goto err;
 216         }
 217     }
 218
 219     if (used_ctx)
 220         BN_CTX_end(ctx);
 221     BN_CTX_free(new_ctx);
 222     return ret;
 223
 224  err:
 225     if (used_ctx)
 226         BN_CTX_end(ctx);
 227     BN_CTX_free(new_ctx);
 228     return 0;
 229 }
 230
 231 /*
 232  * Converts an octet string representation to an EC_POINT. Note that the
 233  * simple implementation only uses affine coordinates.
 234  */
 235 int ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
 236                              const unsigned char *buf, size_t len,
 237                              BN_CTX *ctx)
 238 {
 239     point_conversion_form_t form;
 240     int y_bit;
 241     BN_CTX *new_ctx = NULL;
 242     BIGNUM *x, *y, *yxi;
 243     size_t field_len, enc_len;
 244     int ret = 0;
 245
 246     if (len == 0) {
 247         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
 248         return 0;
 249     }
 250     form = buf[0];
 251     y_bit = form & 1;
 252     form = form & ~1U;
 253     if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
 254         && (form != POINT_CONVERSION_UNCOMPRESSED)
 255         && (form != POINT_CONVERSION_HYBRID)) {
 256         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 257         return 0;
 258     }
 259     if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
 260         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 261         return 0;
 262     }
 263
 264     if (form == 0) {
 265         if (len != 1) {
 266             ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 267             return 0;
 268         }
 269
 270         return EC_POINT_set_to_infinity(group, point);
 271     }
 272
 273     field_len = (EC_GROUP_get_degree(group) + 7) / 8;
 274     enc_len =
 275         (form ==
 276          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 277
 278     if (len != enc_len) {
 279         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 280         return 0;
 281     }
 282
 283     if (ctx == NULL) {
 284         ctx = new_ctx = BN_CTX_new();
 285         if (ctx == NULL)
 286             return 0;
 287     }
 288
 289     BN_CTX_start(ctx);
 290     x = BN_CTX_get(ctx);
 291     y = BN_CTX_get(ctx);
 292     yxi = BN_CTX_get(ctx);
 293     if (yxi == NULL)
 294         goto err;
 295
 296     if (!BN_bin2bn(buf + 1, field_len, x))
 297         goto err;
 298     if (BN_ucmp(x, group->field) >= 0) {
 299         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 300         goto err;
 301     }
 302
 303     if (form == POINT_CONVERSION_COMPRESSED) {
 304         if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
 305             goto err;
 306     } else {
 307         if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
 308             goto err;
 309         if (BN_ucmp(y, group->field) >= 0) {
 310             ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 311             goto err;
 312         }
 313         if (form == POINT_CONVERSION_HYBRID) {
 314             if (!group->meth->field_div(group, yxi, y, x, ctx))
 315                 goto err;
 316             if (y_bit != BN_is_odd(yxi)) {
 317                 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 318                 goto err;
 319             }
 320         }
 321
 322         /*
 323          * EC_POINT_set_affine_coordinates is responsible for checking that
 324          * the point is on the curve.
 325          */
 326         if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
 327             goto err;
 328     }
 329
 330     ret = 1;
 331
 332  err:
 333     BN_CTX_end(ctx);
 334     BN_CTX_free(new_ctx);
 335     return ret;
 336 }
 337 #endif