EC_POINT_new(3) LibreSSL EC_POINT_new(3)NAME
EC_POINT_new, EC_POINT_free, EC_POINT_clear_free, EC_POINT_copy,
EC_POINT_dup, EC_POINT_method_of, EC_POINT_set_to_infinity,
EC_POINT_set_Jprojective_coordinates,
EC_POINT_get_Jprojective_coordinates_GFp,
EC_POINT_set_affine_coordinates_GFp,
EC_POINT_get_affine_coordinates_GFp,
EC_POINT_set_compressed_coordinates_GFp,
EC_POINT_set_affine_coordinates_GF2m,
EC_POINT_get_affine_coordinates_GF2m,
EC_POINT_set_compressed_coordinates_GF2m, EC_POINT_point2oct,
EC_POINT_oct2point, EC_POINT_point2bn, EC_POINT_bn2point,
EC_POINT_point2hex, EC_POINT_hex2point - Functions for creating,
destroying and manipulating EC_POINT objects.
SYNOPSIS
#include <openssl/ec.h>
#include <openssl/bn.h>
EC_POINT *EC_POINT_new(const EC_GROUP *group);
void EC_POINT_free(EC_POINT *point);
void EC_POINT_clear_free(EC_POINT *point);
int EC_POINT_copy(EC_POINT *dst, const EC_POINT *src);
EC_POINT *EC_POINT_dup(const EC_POINT *src, const EC_GROUP *group);
const EC_METHOD *EC_POINT_method_of(const EC_POINT *point);
int EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point);
int EC_POINT_set_Jprojective_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,
const BIGNUM *x, const BIGNUM *y, const BIGNUM *z, BN_CTX *ctx);
int EC_POINT_get_Jprojective_coordinates_GFp(const EC_GROUP *group,
const EC_POINT *p, BIGNUM *x, BIGNUM *y, BIGNUM *z, BN_CTX *ctx);
int EC_POINT_set_affine_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,
const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx);
int EC_POINT_get_affine_coordinates_GFp(const EC_GROUP *group,
const EC_POINT *p, BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
int EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,
const BIGNUM *x, int y_bit, BN_CTX *ctx);
int EC_POINT_set_affine_coordinates_GF2m(const EC_GROUP *group, EC_POINT *p,
const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx);
int EC_POINT_get_affine_coordinates_GF2m(const EC_GROUP *group,
const EC_POINT *p, BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
int EC_POINT_set_compressed_coordinates_GF2m(const EC_GROUP *group, EC_POINT *p,
const BIGNUM *x, int y_bit, BN_CTX *ctx);
size_t EC_POINT_point2oct(const EC_GROUP *group, const EC_POINT *p,
point_conversion_form_t form,
unsigned char *buf, size_t len, BN_CTX *ctx);
int EC_POINT_oct2point(const EC_GROUP *group, EC_POINT *p,
const unsigned char *buf, size_t len, BN_CTX *ctx);
BIGNUM *EC_POINT_point2bn(const EC_GROUP *, const EC_POINT *,
point_conversion_form_t form, BIGNUM *, BN_CTX *);
EC_POINT *EC_POINT_bn2point(const EC_GROUP *, const BIGNUM *,
EC_POINT *, BN_CTX *);
char *EC_POINT_point2hex(const EC_GROUP *, const EC_POINT *,
point_conversion_form_t form, BN_CTX *);
EC_POINT *EC_POINT_hex2point(const EC_GROUP *, const char *,
EC_POINT *, BN_CTX *);
DESCRIPTION
An EC_POINT represents a point on a curve. A new point is constructed
by calling the function EC_POINT_new and providing the group object
that the point relates to.
EC_POINT_free frees the memory associated with the EC_POINT.
EC_POINT_clear_free destroys any sensitive data held within the
EC_POINT and then frees its memory.
EC_POINT_copy copies the point src into dst. Both src and dst must use
the same EC_METHOD.
EC_POINT_dup creates a new EC_POINT object and copies the content from
src to the newly created EC_POINT object.
EC_POINT_method_of obtains the EC_METHOD associated with point.
A valid point on a curve is the special point at infinity. A point is
set to be at infinity by calling EC_POINT_set_to_infinity.
The affine co-ordinates for a point describe a point in terms of its x
and y position. The functions EC_POINT_set_affine_coordinates_GFp and
EC_POINT_set_affine_coordinates_GF2m set the x and y co-ordinates for
the point p defined over the curve given in group.
As well as the affine co-ordinates, a point can alternatively be
described in terms of its Jacobian projective co-ordinates (for Fp
curves only). Jacobian projective co-ordinates are expressed as three
values x, y and z. Working in this co-ordinate system provides more
efficient point multiplication operations. A mapping exists between
Jacobian projective co-ordinates and affine co-ordinates. A Jacobian
projective co-ordinate (x, y, z) can be written as an affine co-
ordinate as (x/(z^2), y/(z^3)). Conversion to Jacobian projective to
affine co-ordinates is simple. The co-ordinate (x, y) is mapped to (x,
y, 1). To set or get the projective co-ordinates use
EC_POINT_set_Jprojective_coordinates_GFp and
EC_POINT_get_Jprojective_coordinates_GFp respectively.
Points can also be described in terms of their compressed co-ordinates.
For a point (x, y), for any given value for x such that the point is on
the curve there will only ever be two possible values for y. Therefore
a point can be set using the EC_POINT_set_compressed_coordinates_GFp
and EC_POINT_set_compressed_coordinates_GF2m functions where x is the x
co-ordinate and y_bit is a value 0 or 1 to identify which of the two
possible values for y should be used.
In addition EC_POINTs can be converted to and from various external
representations. Supported representations are octet strings, BIGNUMs
and hexadecimal. The format of the external representation is described
by the point_conversion_form. See EC_GROUP_copy(3) for a description of
point_conversion_form. Octet strings are stored in a buffer along with
an associated buffer length. A point held in a BIGNUM is calculated by
converting the point to an octet string and then converting that octet
string into a BIGNUM integer. Points in hexadecimal format are stored
in a NULL terminated character string where each character is one of
the printable values 0-9 or A-F (or a-f).
The functions EC_POINT_point2oct, EC_POINT_oct2point,
EC_POINT_point2bn, EC_POINT_bn2point, EC_POINT_point2hex and
EC_POINT_hex2point convert from and to EC_POINTs for the formats: octet
string, BIGNUM and hexadecimal respectively.
The function EC_POINT_point2oct must be supplied with a buffer long
enough to store the octet string. The return value provides the number
of octets stored. Calling the function with a NULL buffer will not
perform the conversion but will still return the required buffer
length.
The function EC_POINT_point2hex will allocate sufficient memory to
store the hexadecimal string. It is the caller's responsibility to free
this memory with a subsequent call to free().
RETURN VALUESEC_POINT_new and EC_POINT_dup return the newly allocated EC_POINT or
NULL on error.
The following functions return 1 on success or 0 on error:
EC_POINT_copy, EC_POINT_set_to_infinity,
EC_POINT_set_Jprojective_coordinates_GFp,
EC_POINT_get_Jprojective_coordinates_GFp,
EC_POINT_set_affine_coordinates_GFp,
EC_POINT_get_affine_coordinates_GFp,
EC_POINT_set_compressed_coordinates_GFp,
EC_POINT_set_affine_coordinates_GF2m,
EC_POINT_get_affine_coordinates_GF2m,
EC_POINT_set_compressed_coordinates_GF2m and EC_POINT_oct2point.
EC_POINT_method_of returns the EC_METHOD associated with the supplied
EC_POINT.
EC_POINT_point2oct returns the length of the required buffer, or 0 on
error.
EC_POINT_point2bn returns the pointer to the BIGNUM supplied, or NULL
on error.
EC_POINT_bn2point returns the pointer to the EC_POINT supplied, or NULL
on error.
EC_POINT_point2hex returns a pointer to the hex string, or NULL on
error.
EC_POINT_hex2point returns the pointer to the EC_POINT supplied, or
NULL on error.
SEE ALSOcrypto(3), ec(3), EC_GROUP_new(3), EC_GROUP_copy(3), EC_POINT_add(3),
EC_KEY_new(3), EC_GFp_simple_method(3), d2i_ECPKParameters(3)LibreSSL 2015-12-05 EC_POINT_new(3)
