2 * Copyright 2011-2018 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
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
11 #include <openssl/err.h>
15 #ifndef OPENSSL_NO_EC2M
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.
22 * The method is from the following publication:
24 * Harper, Menezes, Vanstone:
25 * "Public-Key Cryptosystems with Very Small Key Lengths",
26 * EUROCRYPT '92, Springer-Verlag LNCS 658,
27 * published February 1993
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).
33 int ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group,
35 const BIGNUM *x_, int y_bit,
38 BIGNUM *tmp, *x, *y, *z;
41 BN_CTX *new_ctx = NULL;
43 /* clear error queue */
47 ctx = new_ctx = BN_CTX_new();
53 y_bit = (y_bit != 0) ? 1 : 0;
56 tmp = BN_CTX_get(ctx);
63 if (!BN_GF2m_mod_arr(x, x_, group->poly))
66 if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))
69 if (!group->meth->field_sqr(group, tmp, x, ctx))
71 if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))
73 if (!BN_GF2m_add(tmp, group->a, tmp))
75 if (!BN_GF2m_add(tmp, x, tmp))
77 if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
79 unsigned long err = ERR_peek_last_error();
81 if (ERR_GET_LIB(err) == ERR_LIB_BN
82 && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
84 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
85 EC_R_INVALID_COMPRESSED_POINT);
89 ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
94 z0 = (BN_is_odd(z)) ? 1 : 0;
95 if (!group->meth->field_mul(group, y, x, z, ctx))
98 if (!BN_GF2m_add(y, y, x))
103 if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
111 BN_CTX_free(new_ctx);
117 * Converts an EC_POINT to an octet string. If buf is NULL, the encoded
118 * length will be returned. If the length len of buf is smaller than required
119 * an error will be returned.
121 size_t ec_GF2m_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
122 point_conversion_form_t form,
123 unsigned char *buf, size_t len, BN_CTX *ctx)
128 size_t field_len, i, skip;
130 BN_CTX *new_ctx = NULL;
133 if ((form != POINT_CONVERSION_COMPRESSED)
134 && (form != POINT_CONVERSION_UNCOMPRESSED)
135 && (form != POINT_CONVERSION_HYBRID)) {
136 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
140 if (EC_POINT_is_at_infinity(group, point)) {
141 /* encodes to a single 0 octet */
144 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
152 /* ret := required output buffer length */
153 field_len = (EC_GROUP_get_degree(group) + 7) / 8;
156 POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
158 /* if 'buf' is NULL, just return required length */
161 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
167 ctx = new_ctx = BN_CTX_new();
177 yxi = BN_CTX_get(ctx);
181 if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
185 if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
186 if (!group->meth->field_div(group, yxi, y, x, ctx))
194 skip = field_len - BN_num_bytes(x);
195 if (skip > field_len) {
196 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
203 skip = BN_bn2bin(x, buf + i);
205 if (i != 1 + field_len) {
206 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
210 if (form == POINT_CONVERSION_UNCOMPRESSED
211 || form == POINT_CONVERSION_HYBRID) {
212 skip = field_len - BN_num_bytes(y);
213 if (skip > field_len) {
214 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
221 skip = BN_bn2bin(y, buf + i);
226 ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
234 BN_CTX_free(new_ctx);
242 BN_CTX_free(new_ctx);
248 * Converts an octet string representation to an EC_POINT. Note that the
249 * simple implementation only uses affine coordinates.
251 int ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
252 const unsigned char *buf, size_t len,
255 point_conversion_form_t form;
258 size_t field_len, enc_len;
261 BN_CTX *new_ctx = NULL;
265 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
271 if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
272 && (form != POINT_CONVERSION_UNCOMPRESSED)
273 && (form != POINT_CONVERSION_HYBRID)) {
274 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
277 if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
278 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
284 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
288 return EC_POINT_set_to_infinity(group, point);
291 m = EC_GROUP_get_degree(group);
292 field_len = (m + 7) / 8;
295 POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
297 if (len != enc_len) {
298 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
304 ctx = new_ctx = BN_CTX_new();
313 yxi = BN_CTX_get(ctx);
317 if (!BN_bin2bn(buf + 1, field_len, x))
319 if (BN_num_bits(x) > m) {
320 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
324 if (form == POINT_CONVERSION_COMPRESSED) {
325 if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
328 if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
330 if (BN_num_bits(y) > m) {
331 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
334 if (form == POINT_CONVERSION_HYBRID) {
335 if (!group->meth->field_div(group, yxi, y, x, ctx))
337 if (y_bit != BN_is_odd(yxi)) {
338 ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
344 * EC_POINT_set_affine_coordinates is responsible for checking that
345 * the point is on the curve.
347 if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
356 BN_CTX_free(new_ctx);