openssl/doc/crypto/EC_POINT_new.pod

=pod

=head1 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 B<EC_POINT> objects.

=head1 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 *);


=head1 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 B<group>
object that the point relates to.

EC_POINT_free frees the memory associated with the EC_POINT.
if B<point> is NULL nothing is done.

EC_POINT_clear_free destroys any sensitive data held within the EC_POINT and then frees its memory.
if B<point> is NULL nothing is done.

EC_POINT_copy copies the point B<src> into B<dst>. Both B<src> and B<dst> must use the same EC_METHOD.

EC_POINT_dup creates a new EC_POINT object and copies the content from B<src> to the newly created
EC_POINT object.

EC_POINT_method_of obtains the EC_METHOD associated with B<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 B<x> and B<y> co-ordinates for the point
B<p> defined over the curve given in B<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 B<x> is the x co-ordinate and B<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 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().

=head1 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.

=head1 SEE ALSO

L<crypto(3)>, L<ec(3)>, L<EC_GROUP_new(3)>, L<EC_GROUP_copy(3)>,
L<EC_POINT_add(3)>, L<EC_KEY_new(3)>,
L<EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)>

=cut