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openssl/crypto/ec/ec2_oct.c
Emilia Kasper 1e2012b7ff RT 4242: reject invalid EC point coordinates 
We already test in EC_POINT_oct2point that points are on the curve. To
be on the safe side, move this check to
EC_POINT_set_affine_coordinates_* so as to also check point coordinates
received through some other method.

We do not check projective coordinates, though, as
- it's unlikely that applications would be receiving this primarily
  internal representation from untrusted sources, and
- it's possible that the projective setters are used in a setting where
  performance matters.

Reviewed-by: Rich Salz <rsalz@openssl.org>
2016-06-09 23:58:20 +02:00

352 lines
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/*
* Copyright 2011-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/* ====================================================================
* Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
*
* The Elliptic Curve Public-Key Crypto Library (ECC Code) included
* herein is developed by SUN MICROSYSTEMS, INC., and is contributed
* to the OpenSSL project.
*
* The ECC Code is licensed pursuant to the OpenSSL open source
* license provided below.
*
* The software is originally written by Sheueling Chang Shantz and
* Douglas Stebila of Sun Microsystems Laboratories.
*
*/
#include <openssl/err.h>
#include "ec_lcl.h"
#ifndef OPENSSL_NO_EC2M
/*-
* Calculates and sets the affine coordinates of an EC_POINT from the given
* compressed coordinates. Uses algorithm 2.3.4 of SEC 1.
* Note that the simple implementation only uses affine coordinates.
*
* The method is from the following publication:
*
* Harper, Menezes, Vanstone:
* "Public-Key Cryptosystems with Very Small Key Lengths",
* EUROCRYPT '92, Springer-Verlag LNCS 658,
* published February 1993
*
* US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
* the same method, but claim no priority date earlier than July 29, 1994
* (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
*/
int ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group,
EC_POINT *point,
const BIGNUM *x_, int y_bit,
BN_CTX *ctx)
{
BN_CTX *new_ctx = NULL;
BIGNUM *tmp, *x, *y, *z;
int ret = 0, z0;
/* clear error queue */
ERR_clear_error();
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL)
return 0;
}
y_bit = (y_bit != 0) ? 1 : 0;
BN_CTX_start(ctx);
tmp = BN_CTX_get(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
z = BN_CTX_get(ctx);
if (z == NULL)
goto err;
if (!BN_GF2m_mod_arr(x, x_, group->poly))
goto err;
if (BN_is_zero(x)) {
if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))
goto err;
} else {
if (!group->meth->field_sqr(group, tmp, x, ctx))
goto err;
if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))
goto err;
if (!BN_GF2m_add(tmp, group->a, tmp))
goto err;
if (!BN_GF2m_add(tmp, x, tmp))
goto err;
if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
unsigned long err = ERR_peek_last_error();
if (ERR_GET_LIB(err) == ERR_LIB_BN
&& ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
ERR_clear_error();
ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
EC_R_INVALID_COMPRESSED_POINT);
} else
ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES,
ERR_R_BN_LIB);
goto err;
}
z0 = (BN_is_odd(z)) ? 1 : 0;
if (!group->meth->field_mul(group, y, x, z, ctx))
goto err;
if (z0 != y_bit) {
if (!BN_GF2m_add(y, y, x))
goto err;
}
}
if (!EC_POINT_set_affine_coordinates_GF2m(group, point, x, y, ctx))
goto err;
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
/*
* Converts an EC_POINT to an octet string. If buf is NULL, the encoded
* length will be returned. If the length len of buf is smaller than required
* an error will be returned.
*/
size_t ec_GF2m_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
point_conversion_form_t form,
unsigned char *buf, size_t len, BN_CTX *ctx)
{
size_t ret;
BN_CTX *new_ctx = NULL;
int used_ctx = 0;
BIGNUM *x, *y, *yxi;
size_t field_len, i, skip;
if ((form != POINT_CONVERSION_COMPRESSED)
&& (form != POINT_CONVERSION_UNCOMPRESSED)
&& (form != POINT_CONVERSION_HYBRID)) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
goto err;
}
if (EC_POINT_is_at_infinity(group, point)) {
/* encodes to a single 0 octet */
if (buf != NULL) {
if (len < 1) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
return 0;
}
buf[0] = 0;
}
return 1;
}
/* ret := required output buffer length */
field_len = (EC_GROUP_get_degree(group) + 7) / 8;
ret =
(form ==
POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
/* if 'buf' is NULL, just return required length */
if (buf != NULL) {
if (len < ret) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
goto err;
}
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL)
return 0;
}
BN_CTX_start(ctx);
used_ctx = 1;
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
yxi = BN_CTX_get(ctx);
if (yxi == NULL)
goto err;
if (!EC_POINT_get_affine_coordinates_GF2m(group, point, x, y, ctx))
goto err;
buf[0] = form;
if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
if (!group->meth->field_div(group, yxi, y, x, ctx))
goto err;
if (BN_is_odd(yxi))
buf[0]++;
}
i = 1;
skip = field_len - BN_num_bytes(x);
if (skip > field_len) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
goto err;
}
while (skip > 0) {
buf[i++] = 0;
skip--;
}
skip = BN_bn2bin(x, buf + i);
i += skip;
if (i != 1 + field_len) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
goto err;
}
if (form == POINT_CONVERSION_UNCOMPRESSED
|| form == POINT_CONVERSION_HYBRID) {
skip = field_len - BN_num_bytes(y);
if (skip > field_len) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
goto err;
}
while (skip > 0) {
buf[i++] = 0;
skip--;
}
skip = BN_bn2bin(y, buf + i);
i += skip;
}
if (i != ret) {
ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
goto err;
}
}
if (used_ctx)
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
err:
if (used_ctx)
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return 0;
}
/*
* Converts an octet string representation to an EC_POINT. Note that the
* simple implementation only uses affine coordinates.
*/
int ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
const unsigned char *buf, size_t len,
BN_CTX *ctx)
{
point_conversion_form_t form;
int y_bit;
BN_CTX *new_ctx = NULL;
BIGNUM *x, *y, *yxi;
size_t field_len, enc_len;
int ret = 0;
if (len == 0) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
return 0;
}
form = buf[0];
y_bit = form & 1;
form = form & ~1U;
if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
&& (form != POINT_CONVERSION_UNCOMPRESSED)
&& (form != POINT_CONVERSION_HYBRID)) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
if (form == 0) {
if (len != 1) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
return EC_POINT_set_to_infinity(group, point);
}
field_len = (EC_GROUP_get_degree(group) + 7) / 8;
enc_len =
(form ==
POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
if (len != enc_len) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
if (ctx == NULL) {
ctx = new_ctx = BN_CTX_new();
if (ctx == NULL)
return 0;
}
BN_CTX_start(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
yxi = BN_CTX_get(ctx);
if (yxi == NULL)
goto err;
if (!BN_bin2bn(buf + 1, field_len, x))
goto err;
if (BN_ucmp(x, group->field) >= 0) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
goto err;
}
if (form == POINT_CONVERSION_COMPRESSED) {
if (!EC_POINT_set_compressed_coordinates_GF2m
(group, point, x, y_bit, ctx))
goto err;
} else {
if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
goto err;
if (BN_ucmp(y, group->field) >= 0) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
goto err;
}
if (form == POINT_CONVERSION_HYBRID) {
if (!group->meth->field_div(group, yxi, y, x, ctx))
goto err;
if (y_bit != BN_is_odd(yxi)) {
ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
goto err;
}
}
/*
* EC_POINT_set_affine_coordinates_GF2m is responsible for checking that
* the point is on the curve.
*/
if (!EC_POINT_set_affine_coordinates_GF2m(group, point, x, y, ctx))
goto err;
}
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
#endif
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