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NAME

EC_POINT_get_affine_coordinates, EC_POINT_set_affine_coordinates, EC_POINT_set_compressed_coordinates, EC_POINT_set_to_infinity, EC_POINT_get_affine_coordinates_GFp, EC_POINT_set_affine_coordinates_GFp, EC_POINT_set_compressed_coordinates_GFp — get and set coordinates of elliptic curve points

SYNOPSIS

#include <openssl/bn.h>
#include <openssl/ec.h>

int
EC_POINT_get_affine_coordinates(const EC_GROUP *group, const EC_POINT *point, BIGNUM *x, BIGNUM *y, BN_CTX *ctx);

int
EC_POINT_set_affine_coordinates(const EC_GROUP *group, EC_POINT *point, const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx);

int
EC_POINT_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *point, const BIGNUM *x, int y_bit, BN_CTX *ctx);

int
EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point);

Deprecated:

int
EC_POINT_get_affine_coordinates_GFp(const EC_GROUP *group, const EC_POINT *point, BIGNUM *x, BIGNUM *y, BN_CTX *ctx);

int
EC_POINT_set_affine_coordinates_GFp(const EC_GROUP *group, EC_POINT *point, const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx);

int
EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group, EC_POINT *point, const BIGNUM *x, int y_bit, BN_CTX *ctx);

DESCRIPTION

EC_POINT_get_affine_coordinates() assumes that point is a point on group, calculates its affine coordinates from its internal representation using the optional ctx, and copies them into the optional user-provided x and y.

EC_POINT_set_affine_coordinates() assumes that x and y are the affine coordinates of a point on group, converts them into internal representation and sets them on point using the optional ctx. The user-provided point should be the result of EC_POINT_new(3) with an argument of group. It then verifies using EC_POINT_is_on_curve(3) that x and y are indeed the affine coordinates of a point on group.

EC_POINT_set_compressed_coordinates() assumes that x is the x-coordinate and y_bit is the parity bit of a point on group and sets point to the corresponding point on group. It does this by solving the quadratic equation y^2 = x^3 + ax + b using BN_mod_sqrt(3) and the optional ctx, chooses the solution y with parity matching y_bit, and passes x and y to EC_POINT_set_affine_coordinates(). The user-provided point should be the result of EC_POINT_new() with argument group.

EC_POINT_set_to_infinity() sets point to the internal representation of the point at infinity on group.

EC_POINT_get_affine_coordinates_GFp() is a deprecated alias for EC_POINT_get_affine_coordinates(). Similarly for EC_POINT_set_affine_coordinates_GFp() and EC_POINT_set_compressed_coordinates_GFp().

RETURN VALUES

All these functions return 1 on success and 0 on error. Error conditions include memory allocation failure, that point is incompatible with group, and, for the coordinate setters, that the provided coordinates do not represent a point on group.

SEE ALSO

BN_CTX_new(3), BN_is_zero(3), BN_mod_sqrt(3), crypto(3), d2i_ECPKParameters(3), EC_GROUP_check(3), EC_GROUP_get_curve_name(3), EC_GROUP_new_by_curve_name(3), EC_GROUP_new_curve_GFp(3), EC_KEY_METHOD_new(3), EC_KEY_new(3), EC_POINT_add(3), EC_POINT_new(3), EC_POINT_point2oct(3), ECDH_compute_key(3), ECDSA_SIG_new(3)

HISTORY

EC_POINT_get_affine_coordinates_GFp(), EC_POINT_set_affine_coordinates_GFp(), EC_POINT_set_compressed_coordinates_GFp(), and EC_POINT_set_to_infinity() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.

EC_POINT_get_affine_coordinates(), EC_POINT_set_affine_coordinates(), and EC_POINT_set_compressed_coordinates() first appeared in OpenSSL 1.1.1 and have been available since OpenBSD 7.0.