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.\" $OpenBSD: EC_POINT_get_affine_coordinates.3,v 1.1 2025/04/25 19:57:12 tb Exp $
.\"
.\" Copyright (c) 2025 Theo Buehler <tb@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: April 25 2025 $
.Dt EC_POINT_GET_AFFINE_COORDINATES 3
.Os
.Sh NAME
.Nm EC_POINT_get_affine_coordinates ,
.Nm EC_POINT_set_affine_coordinates ,
.Nm EC_POINT_set_compressed_coordinates ,
.Nm EC_POINT_set_to_infinity ,
.Nm EC_POINT_get_affine_coordinates_GFp ,
.Nm EC_POINT_set_affine_coordinates_GFp ,
.Nm EC_POINT_set_compressed_coordinates_GFp
.Nd get and set coordinates of elliptic curve points
.Sh SYNOPSIS
.In openssl/bn.h
.In openssl/ec.h
.Pp
.Ft int
.Fo EC_POINT_get_affine_coordinates
.Fa "const EC_GROUP *group"
.Fa "const EC_POINT *point"
.Fa "BIGNUM *x"
.Fa "BIGNUM *y"
.Fa "BN_CTX *ctx"
.Fc
.Ft int
.Fo EC_POINT_set_affine_coordinates
.Fa "const EC_GROUP *group"
.Fa "EC_POINT *point"
.Fa "const BIGNUM *x"
.Fa "const BIGNUM *y"
.Fa "BN_CTX *ctx"
.Fc
.Ft int
.Fo EC_POINT_set_compressed_coordinates
.Fa "const EC_GROUP *group"
.Fa "EC_POINT *point"
.Fa "const BIGNUM *x"
.Fa "int y_bit"
.Fa "BN_CTX *ctx"
.Fc
.Ft int
.Fo EC_POINT_set_to_infinity
.Fa "const EC_GROUP *group"
.Fa "EC_POINT *point"
.Fc
.Pp
Deprecated:
.Pp
.Ft int
.Fo EC_POINT_get_affine_coordinates_GFp
.Fa "const EC_GROUP *group"
.Fa "const EC_POINT *point"
.Fa "BIGNUM *x"
.Fa "BIGNUM *y"
.Fa "BN_CTX *ctx"
.Fc
.Ft int
.Fo EC_POINT_set_affine_coordinates_GFp
.Fa "const EC_GROUP *group"
.Fa "EC_POINT *point"
.Fa "const BIGNUM *x"
.Fa "const BIGNUM *y"
.Fa "BN_CTX *ctx"
.Fc
.Ft int
.Fo EC_POINT_set_compressed_coordinates_GFp
.Fa "const EC_GROUP *group"
.Fa "EC_POINT *point"
.Fa "const BIGNUM *x"
.Fa "int y_bit"
.Fa "BN_CTX *ctx"
.Fc
.Sh DESCRIPTION
.Fn EC_POINT_get_affine_coordinates
assumes that
.Fa point
is a point on
.Fa group ,
calculates its affine coordinates from its internal representation
using the optional
.Fa ctx ,
and copies them into the optional user-provided
.Fa x
and
.Fa y .
.Pp
.Fn EC_POINT_set_affine_coordinates
assumes that
.Fa x
and
.Fa y
are the affine coordinates of a point on
.Fa group ,
converts them into internal representation and sets them on
.Fa point
using the optional
.Fa ctx .
The user-provided
.Fa point
should be the result of
.Fn EC_POINT_new 3
with an argument of
.Fa group .
It then verifies using
.Xr EC_POINT_is_on_curve 3
that
.Fa x
and
.Fa y
are indeed the affine coordinates of a point on
.Fa group .
.Pp
.Fn EC_POINT_set_compressed_coordinates
assumes that
.Fa x
is the x-coordinate and
.Fa y_bit
is the parity bit of a point on
.Fa group
and sets
.Fa point
to the corresponding point on
.Fa group .
It does this by solving the quadratic equation y^2 = x^3 + ax + b using
.Xr BN_mod_sqrt 3
and the optional
.Fa ctx ,
chooses the solution
.Fa y
with parity matching
.Fa y_bit ,
and passes
.Fa x
and
.Fa y
to
.Fn EC_POINT_set_affine_coordinates .
The user-provided
.Fa point
should be the result of
.Fn EC_POINT_new
with argument
.Fa group .
.Pp
.Fn EC_POINT_set_to_infinity
sets
.Fa point
to the internal representation of the point at infinity on
.Fa group .
.Pp
.Fn EC_POINT_get_affine_coordinates_GFp
is a deprecated alias for
.Fn EC_POINT_get_affine_coordinates .
Similarly for
.Fn EC_POINT_set_affine_coordinates_GFp
and
.Fn EC_POINT_set_compressed_coordinates_GFp .
.Sh RETURN VALUES
All these functions return 1 on success and 0 on error.
Error conditions include memory allocation failure,
that
.Fa point
is incompatible with
.Fa group ,
and, for the coordinate setters, that the provided coordinates
do not represent a point on
.Fa group .
.Sh SEE ALSO
.Xr BN_CTX_new 3 ,
.Xr BN_is_zero 3 ,
.Xr BN_mod_sqrt 3 ,
.Xr crypto 3 ,
.Xr d2i_ECPKParameters 3 ,
.Xr EC_GROUP_check 3 ,
.Xr EC_GROUP_get_curve_name 3 ,
.Xr EC_GROUP_new_by_curve_name 3 ,
.Xr EC_GROUP_new_curve_GFp 3 ,
.Xr EC_KEY_METHOD_new 3 ,
.Xr EC_KEY_new 3 ,
.Xr EC_POINT_add 3 ,
.Xr EC_POINT_new 3 ,
.Xr EC_POINT_point2oct 3 ,
.Xr ECDH_compute_key 3 ,
.Xr ECDSA_SIG_new 3
.Sh HISTORY
.Fn EC_POINT_get_affine_coordinates_GFp ,
.Fn EC_POINT_set_affine_coordinates_GFp ,
.Fn EC_POINT_set_compressed_coordinates_GFp ,
and
.Fn EC_POINT_set_to_infinity
first appeared in OpenSSL 0.9.7 and have been available since
.Ox 3.2 .
.Pp
.Fn EC_POINT_get_affine_coordinates ,
.Fn EC_POINT_set_affine_coordinates ,
and
.Fn EC_POINT_set_compressed_coordinates
first appeared in OpenSSL 1.1.1 and have been available since
.Ox 7.0 .
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