EC_POINT_point2bn(3)
EC_POINT_new(3) OpenSSL 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>
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EC_POINT_new(3) OpenSSL EC_POINT_new(3)
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.
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EC_POINT_new(3) OpenSSL EC_POINT_new(3)
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. 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
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EC_POINT_new(3) OpenSSL EC_POINT_new(3)
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
OPENSSL_free().
RETURN VALUES
EC_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 ALSO
crypto(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)
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