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3cc26f2eba
Add more explicit documentation about the relation between EC_POINT_point2oct(), EC_POINT_point2hex(), EC_POINT_point2bn() and their reverse. In particular highlight that EC_POINT_point2oct() and EC_POINT_oct2point() conform to, respectively, Sec. 2.3.3 and Sec. 2.3.4 of the SECG SEC 1 standard (which is the normative reference for the already mentioned RFC 5480), highlighting with a note how this affect the encoding/decoding of the point at infinity (which in contrast with any other valid generic point of a curve is assigned an exceptional fixed octet string encoding, i.e., 0x00). Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/10329)
254 lines
12 KiB
Plaintext
254 lines
12 KiB
Plaintext
=pod
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=head1 NAME
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EC_POINT_set_Jprojective_coordinates_GFp,
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EC_POINT_point2buf,
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EC_POINT_new,
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EC_POINT_free,
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EC_POINT_clear_free,
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EC_POINT_copy,
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EC_POINT_dup,
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EC_POINT_method_of,
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EC_POINT_set_to_infinity,
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EC_POINT_get_Jprojective_coordinates_GFp,
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EC_POINT_set_affine_coordinates,
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EC_POINT_get_affine_coordinates,
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EC_POINT_set_compressed_coordinates,
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EC_POINT_set_affine_coordinates_GFp,
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EC_POINT_get_affine_coordinates_GFp,
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EC_POINT_set_compressed_coordinates_GFp,
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EC_POINT_set_affine_coordinates_GF2m,
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EC_POINT_get_affine_coordinates_GF2m,
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EC_POINT_set_compressed_coordinates_GF2m,
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EC_POINT_point2oct,
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EC_POINT_oct2point,
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EC_POINT_point2bn,
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EC_POINT_bn2point,
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EC_POINT_point2hex,
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EC_POINT_hex2point
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- Functions for creating, destroying and manipulating EC_POINT objects
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=head1 SYNOPSIS
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#include <openssl/ec.h>
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EC_POINT *EC_POINT_new(const EC_GROUP *group);
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void EC_POINT_free(EC_POINT *point);
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void EC_POINT_clear_free(EC_POINT *point);
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int EC_POINT_copy(EC_POINT *dst, const EC_POINT *src);
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EC_POINT *EC_POINT_dup(const EC_POINT *src, const EC_GROUP *group);
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const EC_METHOD *EC_POINT_method_of(const EC_POINT *point);
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int EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point);
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int EC_POINT_set_Jprojective_coordinates_GFp(const EC_GROUP *group,
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EC_POINT *p,
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const BIGNUM *x, const BIGNUM *y,
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const BIGNUM *z, BN_CTX *ctx);
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int EC_POINT_get_Jprojective_coordinates_GFp(const EC_GROUP *group,
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const EC_POINT *p,
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BIGNUM *x, BIGNUM *y, BIGNUM *z,
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BN_CTX *ctx);
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int EC_POINT_set_affine_coordinates(const EC_GROUP *group, EC_POINT *p,
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const BIGNUM *x, const BIGNUM *y,
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BN_CTX *ctx);
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int EC_POINT_get_affine_coordinates(const EC_GROUP *group, const EC_POINT *p,
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BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
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int EC_POINT_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *p,
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const BIGNUM *x, int y_bit,
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BN_CTX *ctx);
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int EC_POINT_set_affine_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,
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const BIGNUM *x, const BIGNUM *y,
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BN_CTX *ctx);
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int EC_POINT_get_affine_coordinates_GFp(const EC_GROUP *group,
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const EC_POINT *p,
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BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
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int EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group,
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EC_POINT *p,
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const BIGNUM *x, int y_bit,
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BN_CTX *ctx);
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int EC_POINT_set_affine_coordinates_GF2m(const EC_GROUP *group, EC_POINT *p,
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const BIGNUM *x, const BIGNUM *y,
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BN_CTX *ctx);
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int EC_POINT_get_affine_coordinates_GF2m(const EC_GROUP *group,
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const EC_POINT *p,
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BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
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int EC_POINT_set_compressed_coordinates_GF2m(const EC_GROUP *group,
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EC_POINT *p,
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const BIGNUM *x, int y_bit,
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BN_CTX *ctx);
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size_t EC_POINT_point2oct(const EC_GROUP *group, const EC_POINT *p,
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point_conversion_form_t form,
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unsigned char *buf, size_t len, BN_CTX *ctx);
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size_t EC_POINT_point2buf(const EC_GROUP *group, const EC_POINT *point,
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point_conversion_form_t form,
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unsigned char **pbuf, BN_CTX *ctx);
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int EC_POINT_oct2point(const EC_GROUP *group, EC_POINT *p,
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const unsigned char *buf, size_t len, BN_CTX *ctx);
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BIGNUM *EC_POINT_point2bn(const EC_GROUP *group, const EC_POINT *p,
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point_conversion_form_t form, BIGNUM *bn,
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BN_CTX *ctx);
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EC_POINT *EC_POINT_bn2point(const EC_GROUP *group, const BIGNUM *bn,
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EC_POINT *p, BN_CTX *ctx);
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char *EC_POINT_point2hex(const EC_GROUP *group, const EC_POINT *p,
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point_conversion_form_t form, BN_CTX *ctx);
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EC_POINT *EC_POINT_hex2point(const EC_GROUP *group, const char *hex,
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EC_POINT *p, BN_CTX *ctx);
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=head1 DESCRIPTION
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An B<EC_POINT> structure represents a point on a curve. A new point is
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constructed by calling the function EC_POINT_new() and providing the
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B<group> object that the point relates to.
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EC_POINT_free() frees the memory associated with the B<EC_POINT>.
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if B<point> is NULL nothing is done.
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EC_POINT_clear_free() destroys any sensitive data held within the EC_POINT and
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then frees its memory. If B<point> is NULL nothing is done.
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EC_POINT_copy() copies the point B<src> into B<dst>. Both B<src> and B<dst>
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must use the same B<EC_METHOD>.
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EC_POINT_dup() creates a new B<EC_POINT> object and copies the content from
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B<src> to the newly created B<EC_POINT> object.
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EC_POINT_method_of() obtains the B<EC_METHOD> associated with B<point>.
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A valid point on a curve is the special point at infinity. A point is set to
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be at infinity by calling EC_POINT_set_to_infinity().
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The affine co-ordinates for a point describe a point in terms of its x and y
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position. The function EC_POINT_set_affine_coordinates() sets the B<x> and B<y>
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co-ordinates for the point B<p> defined over the curve given in B<group>. The
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function EC_POINT_get_affine_coordinates() sets B<x> and B<y>, either of which
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may be NULL, to the corresponding coordinates of B<p>.
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The functions EC_POINT_set_affine_coordinates_GFp() and
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EC_POINT_set_affine_coordinates_GF2m() are synonyms for
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EC_POINT_set_affine_coordinates(). They are defined for backwards compatibility
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only and should not be used.
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The functions EC_POINT_get_affine_coordinates_GFp() and
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EC_POINT_get_affine_coordinates_GF2m() are synonyms for
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EC_POINT_get_affine_coordinates(). They are defined for backwards compatibility
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only and should not be used.
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As well as the affine co-ordinates, a point can alternatively be described in
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terms of its Jacobian projective co-ordinates (for Fp curves only). Jacobian
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projective co-ordinates are expressed as three values x, y and z. Working in
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this co-ordinate system provides more efficient point multiplication
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operations. A mapping exists between Jacobian projective co-ordinates and
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affine co-ordinates. A Jacobian projective co-ordinate (x, y, z) can be written
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as an affine co-ordinate as (x/(z^2), y/(z^3)). Conversion to Jacobian
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projective from affine co-ordinates is simple. The co-ordinate (x, y) is mapped
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to (x, y, 1). To set or get the projective co-ordinates use
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EC_POINT_set_Jprojective_coordinates_GFp() and
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EC_POINT_get_Jprojective_coordinates_GFp() respectively.
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Points can also be described in terms of their compressed co-ordinates. For a
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point (x, y), for any given value for x such that the point is on the curve
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there will only ever be two possible values for y. Therefore a point can be set
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using the EC_POINT_set_compressed_coordinates() function where B<x> is the x
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co-ordinate and B<y_bit> is a value 0 or 1 to identify which of the two
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possible values for y should be used.
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The functions EC_POINT_set_compressed_coordinates_GFp() and
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EC_POINT_set_compressed_coordinates_GF2m() are synonyms for
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EC_POINT_set_compressed_coordinates(). They are defined for backwards
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compatibility only and should not be used.
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In addition B<EC_POINT> can be converted to and from various external
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representations. The octet form is the binary encoding of the B<ECPoint>
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structure (as defined in RFC5480 and used in certificates and TLS records):
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only the content octets are present, the B<OCTET STRING> tag and length are
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not included. B<BIGNUM> form is the octet form interpreted as a big endian
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integer converted to a B<BIGNUM> structure. Hexadecimal form is the octet
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form converted to a NULL terminated character string where each character
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is one of the printable values 0-9 or A-F (or a-f).
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The functions EC_POINT_point2oct(), EC_POINT_oct2point(), EC_POINT_point2bn(),
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EC_POINT_bn2point(), EC_POINT_point2hex() and EC_POINT_hex2point() convert from
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and to EC_POINTs for the formats: octet, BIGNUM and hexadecimal respectively.
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The function EC_POINT_point2oct() encodes the given curve point B<p> as an
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octet string into the buffer B<buf> of size B<len>, using the specified
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conversion form B<form>.
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The encoding conforms with Sec. 2.3.3 of the SECG SEC 1 ("Elliptic Curve
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Cryptography") standard.
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Similarly the function EC_POINT_oct2point() decodes a curve point into B<p> from
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the octet string contained in the given buffer B<buf> of size B<len>, conforming
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to Sec. 2.3.4 of the SECG SEC 1 ("Elliptic Curve Cryptography") standard.
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The functions EC_POINT_point2hex() and EC_POINT_point2bn() convert a point B<p>,
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respectively, to the hexadecimal or BIGNUM representation of the same
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encoding of the function EC_POINT_point2oct().
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Vice versa, similarly to the function EC_POINT_oct2point(), the functions
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EC_POINT_hex2point() and EC_POINT_point2bn() decode the hexadecimal or
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BIGNUM representation into the EC_POINT B<p>.
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Notice that, according to the standard, the octet string encoding of the point
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at infinity for a given curve is fixed to a single octet of value zero and that,
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vice versa, a single octet of size zero is decoded as the point at infinity.
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The function EC_POINT_point2oct() must be supplied with a buffer long enough to
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store the octet form. The return value provides the number of octets stored.
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Calling the function with a NULL buffer will not perform the conversion but
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will still return the required buffer length.
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The function EC_POINT_point2buf() allocates a buffer of suitable length and
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writes an EC_POINT to it in octet format. The allocated buffer is written to
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B<*pbuf> and its length is returned. The caller must free up the allocated
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buffer with a call to OPENSSL_free(). Since the allocated buffer value is
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written to B<*pbuf> the B<pbuf> parameter B<MUST NOT> be B<NULL>.
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The function EC_POINT_point2hex() will allocate sufficient memory to store the
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hexadecimal string. It is the caller's responsibility to free this memory with
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a subsequent call to OPENSSL_free().
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=head1 RETURN VALUES
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EC_POINT_new() and EC_POINT_dup() return the newly allocated EC_POINT or NULL
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on error.
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The following functions return 1 on success or 0 on error: EC_POINT_copy(),
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EC_POINT_set_to_infinity(), EC_POINT_set_Jprojective_coordinates_GFp(),
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EC_POINT_get_Jprojective_coordinates_GFp(),
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EC_POINT_set_affine_coordinates_GFp(), EC_POINT_get_affine_coordinates_GFp(),
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EC_POINT_set_compressed_coordinates_GFp(),
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EC_POINT_set_affine_coordinates_GF2m(), EC_POINT_get_affine_coordinates_GF2m(),
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EC_POINT_set_compressed_coordinates_GF2m() and EC_POINT_oct2point().
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EC_POINT_method_of returns the EC_METHOD associated with the supplied EC_POINT.
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EC_POINT_point2oct() and EC_POINT_point2buf() return the length of the required
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buffer or 0 on error.
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EC_POINT_point2bn() returns the pointer to the BIGNUM supplied, or NULL on
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error.
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EC_POINT_bn2point() returns the pointer to the EC_POINT supplied, or NULL on
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error.
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EC_POINT_point2hex() returns a pointer to the hex string, or NULL on error.
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EC_POINT_hex2point() returns the pointer to the EC_POINT supplied, or NULL on
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error.
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=head1 SEE ALSO
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L<crypto(7)>, L<EC_GROUP_new(3)>, L<EC_GROUP_copy(3)>,
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L<EC_POINT_add(3)>, L<EC_KEY_new(3)>,
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L<EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)>
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=head1 COPYRIGHT
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Copyright 2013-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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