crypto/ec/ec2_oct.c

   1 /*
   2  * Copyright 2011-2022 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 ossl_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     if (ctx == NULL) {
  50         ctx = new_ctx = BN_CTX_new();
  51         if (ctx == NULL)
  52             return 0;
  53     }
  54 #endif
  55
  56     y_bit = (y_bit != 0) ? 1 : 0;
  57
  58     BN_CTX_start(ctx);
  59     tmp = BN_CTX_get(ctx);
  60     x = BN_CTX_get(ctx);
  61     y = BN_CTX_get(ctx);
  62     z = BN_CTX_get(ctx);
  63     if (z == NULL)
  64         goto err;
  65
  66     if (!BN_GF2m_mod_arr(x, x_, group->poly))
  67         goto err;
  68     if (BN_is_zero(x)) {
  69         if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))
  70             goto err;
  71     } else {
  72         if (!group->meth->field_sqr(group, tmp, x, ctx))
  73             goto err;
  74         if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))
  75             goto err;
  76         if (!BN_GF2m_add(tmp, group->a, tmp))
  77             goto err;
  78         if (!BN_GF2m_add(tmp, x, tmp))
  79             goto err;
  80         ERR_set_mark();
  81         if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
  82 #ifndef FIPS_MODULE
  83             unsigned long err = ERR_peek_last_error();
  84
  85             if (ERR_GET_LIB(err) == ERR_LIB_BN
  86                 && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
  87                 ERR_pop_to_mark();
  88                 ERR_raise(ERR_LIB_EC, EC_R_INVALID_COMPRESSED_POINT);
  89             } else
  90 #endif
  91             {
  92                 ERR_clear_last_mark();
  93                 ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
  94             }
  95             goto err;
  96         }
  97         ERR_clear_last_mark();
  98         z0 = (BN_is_odd(z)) ? 1 : 0;
  99         if (!group->meth->field_mul(group, y, x, z, ctx))
 100             goto err;
 101         if (z0 != y_bit) {
 102             if (!BN_GF2m_add(y, y, x))
 103                 goto err;
 104         }
 105     }
 106
 107     if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
 108         goto err;
 109
 110     ret = 1;
 111
 112  err:
 113     BN_CTX_end(ctx);
 114 #ifndef FIPS_MODULE
 115     BN_CTX_free(new_ctx);
 116 #endif
 117     return ret;
 118 }
 119
 120 /*
 121  * Converts an EC_POINT to an octet string. If buf is NULL, the encoded
 122  * length will be returned. If the length len of buf is smaller than required
 123  * an error will be returned.
 124  */
 125 size_t ossl_ec_GF2m_simple_point2oct(const EC_GROUP *group,
 126                                      const EC_POINT *point,
 127                                      point_conversion_form_t form,
 128                                      unsigned char *buf, size_t len, BN_CTX *ctx)
 129 {
 130     size_t ret;
 131     int used_ctx = 0;
 132     BIGNUM *x, *y, *yxi;
 133     size_t field_len, i, skip;
 134 #ifndef FIPS_MODULE
 135     BN_CTX *new_ctx = NULL;
 136 #endif
 137
 138     if ((form != POINT_CONVERSION_COMPRESSED)
 139         && (form != POINT_CONVERSION_UNCOMPRESSED)
 140         && (form != POINT_CONVERSION_HYBRID)) {
 141         ERR_raise(ERR_LIB_EC, EC_R_INVALID_FORM);
 142         goto err;
 143     }
 144
 145     if (EC_POINT_is_at_infinity(group, point)) {
 146         /* encodes to a single 0 octet */
 147         if (buf != NULL) {
 148             if (len < 1) {
 149                 ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
 150                 return 0;
 151             }
 152             buf[0] = 0;
 153         }
 154         return 1;
 155     }
 156
 157     /* ret := required output buffer length */
 158     field_len = (EC_GROUP_get_degree(group) + 7) / 8;
 159     ret =
 160         (form ==
 161          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 162
 163     /* if 'buf' is NULL, just return required length */
 164     if (buf != NULL) {
 165         if (len < ret) {
 166             ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
 167             goto err;
 168         }
 169
 170 #ifndef FIPS_MODULE
 171         if (ctx == NULL) {
 172             ctx = new_ctx = BN_CTX_new();
 173             if (ctx == NULL)
 174                 return 0;
 175         }
 176 #endif
 177
 178         BN_CTX_start(ctx);
 179         used_ctx = 1;
 180         x = BN_CTX_get(ctx);
 181         y = BN_CTX_get(ctx);
 182         yxi = BN_CTX_get(ctx);
 183         if (yxi == NULL)
 184             goto err;
 185
 186         if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
 187             goto err;
 188
 189         buf[0] = form;
 190         if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
 191             if (!group->meth->field_div(group, yxi, y, x, ctx))
 192                 goto err;
 193             if (BN_is_odd(yxi))
 194                 buf[0]++;
 195         }
 196
 197         i = 1;
 198
 199         skip = field_len - BN_num_bytes(x);
 200         if (skip > field_len) {
 201             ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
 202             goto err;
 203         }
 204         while (skip > 0) {
 205             buf[i++] = 0;
 206             skip--;
 207         }
 208         skip = BN_bn2bin(x, buf + i);
 209         i += skip;
 210         if (i != 1 + field_len) {
 211             ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
 212             goto err;
 213         }
 214
 215         if (form == POINT_CONVERSION_UNCOMPRESSED
 216             || form == POINT_CONVERSION_HYBRID) {
 217             skip = field_len - BN_num_bytes(y);
 218             if (skip > field_len) {
 219                 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
 220                 goto err;
 221             }
 222             while (skip > 0) {
 223                 buf[i++] = 0;
 224                 skip--;
 225             }
 226             skip = BN_bn2bin(y, buf + i);
 227             i += skip;
 228         }
 229
 230         if (i != ret) {
 231             ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
 232             goto err;
 233         }
 234     }
 235
 236     if (used_ctx)
 237         BN_CTX_end(ctx);
 238 #ifndef FIPS_MODULE
 239     BN_CTX_free(new_ctx);
 240 #endif
 241     return ret;
 242
 243  err:
 244     if (used_ctx)
 245         BN_CTX_end(ctx);
 246 #ifndef FIPS_MODULE
 247     BN_CTX_free(new_ctx);
 248 #endif
 249     return 0;
 250 }
 251
 252 /*
 253  * Converts an octet string representation to an EC_POINT. Note that the
 254  * simple implementation only uses affine coordinates.
 255  */
 256 int ossl_ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
 257                                   const unsigned char *buf, size_t len,
 258                                   BN_CTX *ctx)
 259 {
 260     point_conversion_form_t form;
 261     int y_bit, m;
 262     BIGNUM *x, *y, *yxi;
 263     size_t field_len, enc_len;
 264     int ret = 0;
 265 #ifndef FIPS_MODULE
 266     BN_CTX *new_ctx = NULL;
 267 #endif
 268
 269     if (len == 0) {
 270         ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
 271         return 0;
 272     }
 273
 274     /*
 275      * The first octet is the point conversion octet PC, see X9.62, page 4
 276      * and section 4.4.2.  It must be:
 277      *     0x00          for the point at infinity
 278      *     0x02 or 0x03  for compressed form
 279      *     0x04          for uncompressed form
 280      *     0x06 or 0x07  for hybrid form.
 281      * For compressed or hybrid forms, we store the last bit of buf[0] as
 282      * y_bit and clear it from buf[0] so as to obtain a POINT_CONVERSION_*.
 283      * We error if buf[0] contains any but the above values.
 284      */
 285     y_bit = buf[0] & 1;
 286     form = buf[0] & ~1U;
 287
 288     if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
 289         && (form != POINT_CONVERSION_UNCOMPRESSED)
 290         && (form != POINT_CONVERSION_HYBRID)) {
 291         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 292         return 0;
 293     }
 294     if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
 295         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 296         return 0;
 297     }
 298
 299     /* The point at infinity is represented by a single zero octet. */
 300     if (form == 0) {
 301         if (len != 1) {
 302             ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 303             return 0;
 304         }
 305
 306         return EC_POINT_set_to_infinity(group, point);
 307     }
 308
 309     m = EC_GROUP_get_degree(group);
 310     field_len = (m + 7) / 8;
 311     enc_len =
 312         (form ==
 313          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
 314
 315     if (len != enc_len) {
 316         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 317         return 0;
 318     }
 319
 320 #ifndef FIPS_MODULE
 321     if (ctx == NULL) {
 322         ctx = new_ctx = BN_CTX_new();
 323         if (ctx == NULL)
 324             return 0;
 325     }
 326 #endif
 327
 328     BN_CTX_start(ctx);
 329     x = BN_CTX_get(ctx);
 330     y = BN_CTX_get(ctx);
 331     yxi = BN_CTX_get(ctx);
 332     if (yxi == NULL)
 333         goto err;
 334
 335     if (!BN_bin2bn(buf + 1, field_len, x))
 336         goto err;
 337     if (BN_num_bits(x) > m) {
 338         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 339         goto err;
 340     }
 341
 342     if (form == POINT_CONVERSION_COMPRESSED) {
 343         if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
 344             goto err;
 345     } else {
 346         if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
 347             goto err;
 348         if (BN_num_bits(y) > m) {
 349             ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 350             goto err;
 351         }
 352         if (form == POINT_CONVERSION_HYBRID) {
 353             /*
 354              * Check that the form in the encoding was set correctly
 355              * according to X9.62 4.4.2.a, 4(c), see also first paragraph
 356              * of X9.62, 4.4.1.b.
 357              */
 358             if (BN_is_zero(x)) {
 359                 if (y_bit != 0) {
 360                     ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 361                     goto err;
 362                 }
 363             } else {
 364                 if (!group->meth->field_div(group, yxi, y, x, ctx))
 365                     goto err;
 366                 if (y_bit != BN_is_odd(yxi)) {
 367                     ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
 368                     goto err;
 369                 }
 370             }
 371         }
 372
 373         /*
 374          * EC_POINT_set_affine_coordinates is responsible for checking that
 375          * the point is on the curve.
 376          */
 377         if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
 378             goto err;
 379     }
 380
 381     ret = 1;
 382
 383  err:
 384     BN_CTX_end(ctx);
 385 #ifndef FIPS_MODULE
 386     BN_CTX_free(new_ctx);
 387 #endif
 388     return ret;
 389 }
 390 #endif