crypto/ec/ec2_oct.c

   1 /*
   2  * Copyright 2011-2020 The OpenSSL Project Authors. All Rights Reserved.
   3  * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
   4  *
   5  * Licensed under the Apache License 2.0 (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 /*
  12  * ECDSA low level APIs are deprecated for public use, but still ok for
  13  * internal use.
  14  */
  15 #include "internal/deprecated.h"
  16
  17 #include <openssl/err.h>
  18
  19 #include "ec_local.h"
  20
  21 #ifndef OPENSSL_NO_EC2M
  22
  23 /*-
  24  * Calculates and sets the affine coordinates of an EC_POINT from the given
  25  * compressed coordinates.  Uses algorithm 2.3.4 of SEC 1.
  26  * Note that the simple implementation only uses affine coordinates.
  27  *
  28  * The method is from the following publication:
  29  *
  30  *     Harper, Menezes, Vanstone:
  31  *     "Public-Key Cryptosystems with Very Small Key Lengths",
  32  *     EUROCRYPT '92, Springer-Verlag LNCS 658,
  33  *     published February 1993
  34  *
  35  * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
  36  * the same method, but claim no priority date earlier than July 29, 1994
  37  * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
  38  */
  39 int ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group,
  40                                               EC_POINT *point,
  41                                               const BIGNUM *x_, int y_bit,
  42                                               BN_CTX *ctx)
  43 {
  44     BIGNUM *tmp, *x, *y, *z;
  45     int ret = 0, z0;
  46 #ifndef FIPS_MODULE
  47     BN_CTX *new_ctx = NULL;
  48
  49     /* clear error queue */
  50     ERR_clear_error();
  51
  52     if (ctx == NULL) {
  53         ctx = new_ctx = BN_CTX_new();
  54         if (ctx == NULL)
  55             return 0;
  56     }
  57 #endif
  58
  59     y_bit = (y_bit != 0) ? 1 : 0;
  60
  61     BN_CTX_start(ctx);
  62     tmp = BN_CTX_get(ctx);
  63     x = BN_CTX_get(ctx);
  64     y = BN_CTX_get(ctx);
  65     z = BN_CTX_get(ctx);
  66     if (z == NULL)
  67         goto err;
  68
  69     if (!BN_GF2m_mod_arr(x, x_, group->poly))
  70         goto err;
  71     if (BN_is_zero(x)) {
  72         if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))
  73             goto err;
  74     } else {
  75         if (!group->meth->field_sqr(group, tmp, x, ctx))
  76             goto err;
  77         if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))
  78             goto err;
  79         if (!BN_GF2m_add(tmp, group->a, tmp))
  80             goto err;
  81         if (!BN_GF2m_add(tmp, x, tmp))
  82             goto err;
  83         if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
  84 #ifndef FIPS_MODULE
  85             unsigned long err = ERR_peek_last_error();
  86
  87             if (ERR_GET_LIB(err) == ERR_LIB_BN
  88                 && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
  89                 ERR_clear_error();
  90                 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
  91                       EC_R_INVALID_COMPRESSED_POINT);
  92             } else
  93 #endif
  94             {
  95                 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
  96                       ERR_R_BN_LIB);
  97             }
  98             goto err;
  99         }
 100         z0 = (BN_is_odd(z)) ? 1 : 0;
 101         if (!group->meth->field_mul(group, y, x, z, ctx))
 102             goto err;
 103         if (z0 != y_bit) {
 104             if (!BN_GF2m_add(y, y, x))
 105                 goto err;
 106         }
 107     }
 108
 109     if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
 110         goto err;
 111
 112     ret = 1;
 113
 114  err:
 115     BN_CTX_end(ctx);
 116 #ifndef FIPS_MODULE
 117     BN_CTX_free(new_ctx);
 118 #endif
 119     return ret;
 120 }
 121
 122 /*
 123  * Converts an EC_POINT to an octet string. If buf is NULL, the encoded
 124  * length will be returned. If the length len of buf is smaller than required
 125  * an error will be returned.
 126  */
 127 size_t ec_GF2m_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
 128                                 point_conversion_form_t form,
 129                                 unsigned char *buf, size_t len, BN_CTX *ctx)
 130 {
 131     size_t ret;
 132     int used_ctx = 0;
 133     BIGNUM *x, *y, *yxi;
 134     size_t field_len, i, skip;
 135 #ifndef FIPS_MODULE
 136     BN_CTX *new_ctx = NULL;
 137 #endif
 138
 139     if ((form != POINT_CONVERSION_COMPRESSED)
 140         && (form != POINT_CONVERSION_UNCOMPRESSED)
 141         && (form != POINT_CONVERSION_HYBRID)) {
 142         ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
 143         goto err;
 144     }
 145
 146     if (EC_POINT_is_at_infinity(group, point)) {
 147         /* encodes to a single 0 octet */
 148         if (buf != NULL) {
 149             if (len < 1) {
 150                 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
 151                 return 0;
 152             }
 153             buf[0] = 0;
 154         }
 155         return 1;
 156     }
 157
 158     /* ret := required output buffer length */
 159     field_len = (EC_GROUP_get_degree(group) + 7) / 8;
 160     ret =
 161         (form ==
 162          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 163
 164     /* if 'buf' is NULL, just return required length */
 165     if (buf != NULL) {
 166         if (len < ret) {
 167             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
 168             goto err;
 169         }
 170
 171 #ifndef FIPS_MODULE
 172         if (ctx == NULL) {
 173             ctx = new_ctx = BN_CTX_new();
 174             if (ctx == NULL)
 175                 return 0;
 176         }
 177 #endif
 178
 179         BN_CTX_start(ctx);
 180         used_ctx = 1;
 181         x = BN_CTX_get(ctx);
 182         y = BN_CTX_get(ctx);
 183         yxi = BN_CTX_get(ctx);
 184         if (yxi == NULL)
 185             goto err;
 186
 187         if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
 188             goto err;
 189
 190         buf[0] = form;
 191         if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
 192             if (!group->meth->field_div(group, yxi, y, x, ctx))
 193                 goto err;
 194             if (BN_is_odd(yxi))
 195                 buf[0]++;
 196         }
 197
 198         i = 1;
 199
 200         skip = field_len - BN_num_bytes(x);
 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(x, buf + i);
 210         i += skip;
 211         if (i != 1 + field_len) {
 212             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 213             goto err;
 214         }
 215
 216         if (form == POINT_CONVERSION_UNCOMPRESSED
 217             || form == POINT_CONVERSION_HYBRID) {
 218             skip = field_len - BN_num_bytes(y);
 219             if (skip > field_len) {
 220                 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 221                 goto err;
 222             }
 223             while (skip > 0) {
 224                 buf[i++] = 0;
 225                 skip--;
 226             }
 227             skip = BN_bn2bin(y, buf + i);
 228             i += skip;
 229         }
 230
 231         if (i != ret) {
 232             ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
 233             goto err;
 234         }
 235     }
 236
 237     if (used_ctx)
 238         BN_CTX_end(ctx);
 239 #ifndef FIPS_MODULE
 240     BN_CTX_free(new_ctx);
 241 #endif
 242     return ret;
 243
 244  err:
 245     if (used_ctx)
 246         BN_CTX_end(ctx);
 247 #ifndef FIPS_MODULE
 248     BN_CTX_free(new_ctx);
 249 #endif
 250     return 0;
 251 }
 252
 253 /*
 254  * Converts an octet string representation to an EC_POINT. Note that the
 255  * simple implementation only uses affine coordinates.
 256  */
 257 int ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
 258                              const unsigned char *buf, size_t len,
 259                              BN_CTX *ctx)
 260 {
 261     point_conversion_form_t form;
 262     int y_bit, m;
 263     BIGNUM *x, *y, *yxi;
 264     size_t field_len, enc_len;
 265     int ret = 0;
 266 #ifndef FIPS_MODULE
 267     BN_CTX *new_ctx = NULL;
 268 #endif
 269
 270     if (len == 0) {
 271         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
 272         return 0;
 273     }
 274     form = buf[0];
 275     y_bit = form & 1;
 276     form = form & ~1U;
 277     if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
 278         && (form != POINT_CONVERSION_UNCOMPRESSED)
 279         && (form != POINT_CONVERSION_HYBRID)) {
 280         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 281         return 0;
 282     }
 283     if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
 284         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 285         return 0;
 286     }
 287
 288     if (form == 0) {
 289         if (len != 1) {
 290             ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 291             return 0;
 292         }
 293
 294         return EC_POINT_set_to_infinity(group, point);
 295     }
 296
 297     m = EC_GROUP_get_degree(group);
 298     field_len = (m + 7) / 8;
 299     enc_len =
 300         (form ==
 301          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 302
 303     if (len != enc_len) {
 304         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 305         return 0;
 306     }
 307
 308 #ifndef FIPS_MODULE
 309     if (ctx == NULL) {
 310         ctx = new_ctx = BN_CTX_new();
 311         if (ctx == NULL)
 312             return 0;
 313     }
 314 #endif
 315
 316     BN_CTX_start(ctx);
 317     x = BN_CTX_get(ctx);
 318     y = BN_CTX_get(ctx);
 319     yxi = BN_CTX_get(ctx);
 320     if (yxi == NULL)
 321         goto err;
 322
 323     if (!BN_bin2bn(buf + 1, field_len, x))
 324         goto err;
 325     if (BN_num_bits(x) > m) {
 326         ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 327         goto err;
 328     }
 329
 330     if (form == POINT_CONVERSION_COMPRESSED) {
 331         if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
 332             goto err;
 333     } else {
 334         if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
 335             goto err;
 336         if (BN_num_bits(y) > m) {
 337             ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 338             goto err;
 339         }
 340         if (form == POINT_CONVERSION_HYBRID) {
 341             if (!group->meth->field_div(group, yxi, y, x, ctx))
 342                 goto err;
 343             if (y_bit != BN_is_odd(yxi)) {
 344                 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
 345                 goto err;
 346             }
 347         }
 348
 349         /*
 350          * EC_POINT_set_affine_coordinates is responsible for checking that
 351          * the point is on the curve.
 352          */
 353         if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
 354             goto err;
 355     }
 356
 357     ret = 1;
 358
 359  err:
 360     BN_CTX_end(ctx);
 361 #ifndef FIPS_MODULE
 362     BN_CTX_free(new_ctx);
 363 #endif
 364     return ret;
 365 }
 366 #endif