ecp_oct.c
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/*
* Copyright 2011-2018 The OpenSSL Project Authors. All Rights Reserved.
* Copyright (c) 2002, Oracle and/or its affiliates. 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
*/
#include <openssl/err.h>
#include <openssl/symhacks.h>
#include "ec_lcl.h"
int ec_GFp_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 *tmp1, *tmp2, *x, *y;
int ret = 0;
/* 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);
BN_CTX_start(ctx);
tmp1 = BN_CTX_get(ctx);
tmp2 = BN_CTX_get(ctx);
x = BN_CTX_get(ctx);
y = BN_CTX_get(ctx);
if (y == NULL)
goto err;
/*-
* Recover y. We have a Weierstrass equation
* y^2 = x^3 + a*x + b,
* so y is one of the square roots of x^3 + a*x + b.
*/
/* tmp1 := x^3 */
if (!BN_nnmod(x, x_, group->field, ctx))
goto err;
if (group->meth->field_decode == 0) {
/* field_{sqr,mul} work on standard representation */
if (!group->meth->field_sqr(group, tmp2, x_, ctx))
goto err;
if (!group->meth->field_mul(group, tmp1, tmp2, x_, ctx))
goto err;
} else {
if (!BN_mod_sqr(tmp2, x_, group->field, ctx))
goto err;
if (!BN_mod_mul(tmp1, tmp2, x_, group->field, ctx))
goto err;
}
/* tmp1 := tmp1 + a*x */
if (group->a_is_minus3) {
if (!BN_mod_lshift1_quick(tmp2, x, group->field))
goto err;
if (!BN_mod_add_quick(tmp2, tmp2, x, group->field))
goto err;
if (!BN_mod_sub_quick(tmp1, tmp1, tmp2, group->field))
goto err;
} else {
if (group->meth->field_decode) {
if (!group->meth->field_decode(group, tmp2, group->a, ctx))
goto err;
if (!BN_mod_mul(tmp2, tmp2, x, group->field, ctx))
goto err;
} else {
/* field_mul works on standard representation */
if (!group->meth->field_mul(group, tmp2, group->a, x, ctx))
goto err;
}
if (!BN_mod_add_quick(tmp1, tmp1, tmp2, group->field))
goto err;
}
/* tmp1 := tmp1 + b */
if (group->meth->field_decode) {
if (!group->meth->field_decode(group, tmp2, group->b, ctx))
goto err;
if (!BN_mod_add_quick(tmp1, tmp1, tmp2, group->field))
goto err;
} else {
if (!BN_mod_add_quick(tmp1, tmp1, group->b, group->field))
goto err;
}
if (!BN_mod_sqrt(y, tmp1, group->field, ctx)) {
unsigned long err = ERR_peek_last_error();
if (ERR_GET_LIB(err) == ERR_LIB_BN
&& ERR_GET_REASON(err) == BN_R_NOT_A_SQUARE) {
ERR_clear_error();
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
EC_R_INVALID_COMPRESSED_POINT);
} else
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
ERR_R_BN_LIB);
goto err;
}
if (y_bit != BN_is_odd(y)) {
if (BN_is_zero(y)) {
int kron;
kron = BN_kronecker(x, group->field, ctx);
if (kron == -2)
goto err;
if (kron == 1)
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
EC_R_INVALID_COMPRESSION_BIT);
else
/*
* BN_mod_sqrt() should have caught this error (not a square)
*/
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
EC_R_INVALID_COMPRESSED_POINT);
goto err;
}
if (!BN_usub(y, group->field, y))
goto err;
}
if (y_bit != BN_is_odd(y)) {
ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES,
ERR_R_INTERNAL_ERROR);
goto err;
}
if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
goto err;
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}
size_t ec_GFp_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;
size_t field_len, i, skip;
if ((form != POINT_CONVERSION_COMPRESSED)
&& (form != POINT_CONVERSION_UNCOMPRESSED)
&& (form != POINT_CONVERSION_HYBRID)) {
ECerr(EC_F_EC_GFP_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_GFP_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
return 0;
}
buf[0] = 0;
}
return 1;
}
/* ret := required output buffer length */
field_len = BN_num_bytes(group->field);
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_GFP_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);
if (y == NULL)
goto err;
if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
goto err;
if ((form == POINT_CONVERSION_COMPRESSED
|| form == POINT_CONVERSION_HYBRID) && BN_is_odd(y))
buf[0] = form + 1;
else
buf[0] = form;
i = 1;
skip = field_len - BN_num_bytes(x);
if (skip > field_len) {
ECerr(EC_F_EC_GFP_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_GFP_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_GFP_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_GFP_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;
}
int ec_GFp_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;
size_t field_len, enc_len;
int ret = 0;
if (len == 0) {
ECerr(EC_F_EC_GFP_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_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
if (form == 0) {
if (len != 1) {
ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
return 0;
}
return EC_POINT_set_to_infinity(group, point);
}
field_len = BN_num_bytes(group->field);
enc_len =
(form ==
POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
if (len != enc_len) {
ECerr(EC_F_EC_GFP_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);
if (y == NULL)
goto err;
if (!BN_bin2bn(buf + 1, field_len, x))
goto err;
if (BN_ucmp(x, group->field) >= 0) {
ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
goto err;
}
if (form == POINT_CONVERSION_COMPRESSED) {
if (!EC_POINT_set_compressed_coordinates(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_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
goto err;
}
if (form == POINT_CONVERSION_HYBRID) {
if (y_bit != BN_is_odd(y)) {
ECerr(EC_F_EC_GFP_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
goto err;
}
}
/*
* EC_POINT_set_affine_coordinates is responsible for checking that
* the point is on the curve.
*/
if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
goto err;
}
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
return ret;
}