/* $OpenBSD: ecp_oct.c,v 1.28 2024/10/24 05:57:25 tb Exp $ */ /* Includes code written by Lenka Fibikova * for the OpenSSL project. * Includes code written by Bodo Moeller for the OpenSSL project. */ /* ==================================================================== * Copyright (c) 1998-2002 The OpenSSL Project. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. All advertising materials mentioning features or use of this * software must display the following acknowledgment: * "This product includes software developed by the OpenSSL Project * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" * * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to * endorse or promote products derived from this software without * prior written permission. For written permission, please contact * openssl-core@openssl.org. * * 5. Products derived from this software may not be called "OpenSSL" * nor may "OpenSSL" appear in their names without prior written * permission of the OpenSSL Project. * * 6. Redistributions of any form whatsoever must retain the following * acknowledgment: * "This product includes software developed by the OpenSSL Project * for use in the OpenSSL Toolkit (http://www.openssl.org/)" * * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED * OF THE POSSIBILITY OF SUCH DAMAGE. * ==================================================================== * * This product includes cryptographic software written by Eric Young * (eay@cryptsoft.com). This product includes software written by Tim * Hudson (tjh@cryptsoft.com). * */ /* ==================================================================== * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED. * Portions of this software developed by SUN MICROSYSTEMS, INC., * and contributed to the OpenSSL project. */ #include #include #include #include #include #include "ec_local.h" #include "bytestring.h" int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *point, const BIGNUM *x_, int y_bit, BN_CTX *ctx) { BIGNUM *tmp1, *tmp2, *x, *y; int ret = 0; /* clear error queue */ ERR_clear_error(); y_bit = (y_bit != 0); BN_CTX_start(ctx); if ((tmp1 = BN_CTX_get(ctx)) == NULL) goto err; if ((tmp2 = BN_CTX_get(ctx)) == NULL) goto err; if ((x = BN_CTX_get(ctx)) == NULL) goto err; if ((y = BN_CTX_get(ctx)) == 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 == NULL) { /* 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 != NULL) { 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(); ECerror(EC_R_INVALID_COMPRESSED_POINT); } else ECerror(ERR_R_BN_LIB); goto err; } if (y_bit != BN_is_odd(y)) { if (BN_is_zero(y)) { ECerror(EC_R_INVALID_COMPRESSION_BIT); goto err; } if (!BN_usub(y, &group->field, y)) goto err; if (y_bit != BN_is_odd(y)) { ECerror(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); return ret; } /* * Only the last three bits of the leading octet of a point should be set. * Bits 3 and 2 encode the conversion form for all points except the point * at infinity. In compressed and hybrid form bit 1 indicates if the even * or the odd solution of the quadratic equation for y should be used. * * The public point_conversion_t enum lacks the point at infinity, so we * ignore it except at the API boundary. */ #define EC_OCT_YBIT 0x01 #define EC_OCT_POINT_AT_INFINITY 0x00 #define EC_OCT_POINT_COMPRESSED 0x02 #define EC_OCT_POINT_UNCOMPRESSED 0x04 #define EC_OCT_POINT_HYBRID 0x06 #define EC_OCT_POINT_CONVERSION_MASK 0x06 static int ec_oct_conversion_form_is_valid(uint8_t form) { return (form & EC_OCT_POINT_CONVERSION_MASK) == form; } static int ec_oct_check_hybrid_ybit_is_consistent(uint8_t form, int ybit, const BIGNUM *y) { if (form == EC_OCT_POINT_HYBRID && ybit != BN_is_odd(y)) { ECerror(EC_R_INVALID_ENCODING); return 0; } return 1; } /* Nonzero y-bit only makes sense with compressed or hybrid encoding. */ static int ec_oct_nonzero_ybit_allowed(uint8_t form) { return form == EC_OCT_POINT_COMPRESSED || form == EC_OCT_POINT_HYBRID; } static int ec_oct_add_leading_octet_cbb(CBB *cbb, uint8_t form, int ybit) { if (ec_oct_nonzero_ybit_allowed(form) && ybit != 0) form |= EC_OCT_YBIT; return CBB_add_u8(cbb, form); } static int ec_oct_get_leading_octet_cbs(CBS *cbs, uint8_t *out_form, int *out_ybit) { uint8_t octet; if (!CBS_get_u8(cbs, &octet)) { ECerror(EC_R_BUFFER_TOO_SMALL); return 0; } *out_ybit = octet & EC_OCT_YBIT; *out_form = octet & ~EC_OCT_YBIT; if (!ec_oct_conversion_form_is_valid(*out_form)) { ECerror(EC_R_INVALID_ENCODING); return 0; } if (*out_ybit != 0 && !ec_oct_nonzero_ybit_allowed(*out_form)) { ECerror(EC_R_INVALID_ENCODING); return 0; } return 1; } static int ec_oct_encoded_length(const EC_GROUP *group, uint8_t form, size_t *out_len) { switch (form) { case EC_OCT_POINT_AT_INFINITY: *out_len = 1; return 1; case EC_OCT_POINT_COMPRESSED: *out_len = 1 + BN_num_bytes(&group->field); return 1; case EC_OCT_POINT_UNCOMPRESSED: case EC_OCT_POINT_HYBRID: *out_len = 1 + 2 * BN_num_bytes(&group->field); return 1; default: return 0; } } static int ec_oct_field_element_is_valid(const EC_GROUP *group, const BIGNUM *bn) { /* Ensure bn is in the range [0, field). */ return !BN_is_negative(bn) && BN_cmp(&group->field, bn) > 0; } static int ec_oct_add_field_element_cbb(CBB *cbb, const EC_GROUP *group, const BIGNUM *bn) { uint8_t *buf = NULL; int buf_len = BN_num_bytes(&group->field); if (!ec_oct_field_element_is_valid(group, bn)) { ECerror(EC_R_BIGNUM_OUT_OF_RANGE); return 0; } if (!CBB_add_space(cbb, &buf, buf_len)) { ECerror(ERR_R_MALLOC_FAILURE); return 0; } if (BN_bn2binpad(bn, buf, buf_len) != buf_len) { ECerror(ERR_R_MALLOC_FAILURE); return 0; } return 1; } static int ec_oct_get_field_element_cbs(CBS *cbs, const EC_GROUP *group, BIGNUM *bn) { CBS field_element; if (!CBS_get_bytes(cbs, &field_element, BN_num_bytes(&group->field))) { ECerror(EC_R_INVALID_ENCODING); return 0; } if (!BN_bin2bn(CBS_data(&field_element), CBS_len(&field_element), bn)) { ECerror(ERR_R_MALLOC_FAILURE); return 0; } if (!ec_oct_field_element_is_valid(group, bn)) { ECerror(EC_R_BIGNUM_OUT_OF_RANGE); return 0; } return 1; } size_t ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conversion_form_t conversion_form, unsigned char *buf, size_t len, BN_CTX *ctx) { CBB cbb; uint8_t form; BIGNUM *x, *y; size_t encoded_length; size_t ret = 0; if (conversion_form > UINT8_MAX) { ECerror(EC_R_INVALID_FORM); return 0; } form = conversion_form; /* * Established behavior is to reject a request for the form 0 for the * point at infinity even if it is valid. */ if (form == 0 || !ec_oct_conversion_form_is_valid(form)) { ECerror(EC_R_INVALID_FORM); return 0; } if (EC_POINT_is_at_infinity(group, point)) form = EC_OCT_POINT_AT_INFINITY; if (!ec_oct_encoded_length(group, form, &encoded_length)) { ECerror(EC_R_INVALID_FORM); return 0; } if (buf == NULL) return encoded_length; if (len < encoded_length) { ECerror(EC_R_BUFFER_TOO_SMALL); return 0; } BN_CTX_start(ctx); if (!CBB_init_fixed(&cbb, buf, len)) goto err; if (form == EC_OCT_POINT_AT_INFINITY) { if (!ec_oct_add_leading_octet_cbb(&cbb, form, 0)) goto err; goto done; } if ((x = BN_CTX_get(ctx)) == NULL) goto err; if ((y = BN_CTX_get(ctx)) == NULL) goto err; if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx)) goto err; if (!ec_oct_add_leading_octet_cbb(&cbb, form, BN_is_odd(y))) goto err; if (form == EC_OCT_POINT_COMPRESSED) { if (!ec_oct_add_field_element_cbb(&cbb, group, x)) goto err; } else { if (!ec_oct_add_field_element_cbb(&cbb, group, x)) goto err; if (!ec_oct_add_field_element_cbb(&cbb, group, y)) goto err; } done: if (!CBB_finish(&cbb, NULL, &ret)) goto err; if (ret != encoded_length) { ret = 0; goto err; } err: CBB_cleanup(&cbb); BN_CTX_end(ctx); return ret; } int ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point, const unsigned char *buf, size_t len, BN_CTX *ctx) { CBS cbs; uint8_t form; int ybit; BIGNUM *x, *y; int ret = 0; BN_CTX_start(ctx); CBS_init(&cbs, buf, len); if ((x = BN_CTX_get(ctx)) == NULL) goto err; if ((y = BN_CTX_get(ctx)) == NULL) goto err; if (!ec_oct_get_leading_octet_cbs(&cbs, &form, &ybit)) goto err; if (form == EC_OCT_POINT_AT_INFINITY) { if (!EC_POINT_set_to_infinity(group, point)) goto err; } else if (form == EC_OCT_POINT_COMPRESSED) { if (!ec_oct_get_field_element_cbs(&cbs, group, x)) goto err; if (!EC_POINT_set_compressed_coordinates(group, point, x, ybit, ctx)) goto err; } else { if (!ec_oct_get_field_element_cbs(&cbs, group, x)) goto err; if (!ec_oct_get_field_element_cbs(&cbs, group, y)) goto err; if (!ec_oct_check_hybrid_ybit_is_consistent(form, ybit, y)) goto err; if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx)) goto err; } if (CBS_len(&cbs) > 0) { ECerror(EC_R_INVALID_ENCODING); goto err; } ret = 1; err: BN_CTX_end(ctx); return ret; }