xref: /freebsd/crypto/openssl/doc/man3/EC_POINT_new.pod (revision a8089ea5aee578e08acab2438e82fc9a9ae50ed8) 
1=pod
2
3=head1 NAME
4
5EC_POINT_set_Jprojective_coordinates_GFp,
6EC_POINT_point2buf,
7EC_POINT_new,
8EC_POINT_free,
9EC_POINT_clear_free,
10EC_POINT_copy,
11EC_POINT_dup,
12EC_POINT_method_of,
13EC_POINT_set_to_infinity,
14EC_POINT_get_Jprojective_coordinates_GFp,
15EC_POINT_set_affine_coordinates,
16EC_POINT_get_affine_coordinates,
17EC_POINT_set_compressed_coordinates,
18EC_POINT_set_affine_coordinates_GFp,
19EC_POINT_get_affine_coordinates_GFp,
20EC_POINT_set_compressed_coordinates_GFp,
21EC_POINT_set_affine_coordinates_GF2m,
22EC_POINT_get_affine_coordinates_GF2m,
23EC_POINT_set_compressed_coordinates_GF2m,
24EC_POINT_point2oct,
25EC_POINT_oct2point,
26EC_POINT_point2bn,
27EC_POINT_bn2point,
28EC_POINT_point2hex,
29EC_POINT_hex2point
30- Functions for creating, destroying and manipulating EC_POINT objects
31
32=head1 SYNOPSIS
33
34 #include <openssl/ec.h>
35
36 EC_POINT *EC_POINT_new(const EC_GROUP *group);
37 void EC_POINT_free(EC_POINT *point);
38 void EC_POINT_clear_free(EC_POINT *point);
39 int EC_POINT_copy(EC_POINT *dst, const EC_POINT *src);
40 EC_POINT *EC_POINT_dup(const EC_POINT *src, const EC_GROUP *group);
41 int EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point);
42 int EC_POINT_set_affine_coordinates(const EC_GROUP *group, EC_POINT *p,
43                                     const BIGNUM *x, const BIGNUM *y,
44                                     BN_CTX *ctx);
45 int EC_POINT_get_affine_coordinates(const EC_GROUP *group, const EC_POINT *p,
46                                     BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
47 int EC_POINT_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *p,
48                                         const BIGNUM *x, int y_bit,
49                                         BN_CTX *ctx);
50 size_t EC_POINT_point2oct(const EC_GROUP *group, const EC_POINT *p,
51                           point_conversion_form_t form,
52                           unsigned char *buf, size_t len, BN_CTX *ctx);
53 size_t EC_POINT_point2buf(const EC_GROUP *group, const EC_POINT *point,
54                           point_conversion_form_t form,
55                           unsigned char **pbuf, BN_CTX *ctx);
56 int EC_POINT_oct2point(const EC_GROUP *group, EC_POINT *p,
57                        const unsigned char *buf, size_t len, BN_CTX *ctx);
58 char *EC_POINT_point2hex(const EC_GROUP *group, const EC_POINT *p,
59                          point_conversion_form_t form, BN_CTX *ctx);
60 EC_POINT *EC_POINT_hex2point(const EC_GROUP *group, const char *hex,
61                              EC_POINT *p, BN_CTX *ctx);
62
63The following functions have been deprecated since OpenSSL 3.0, and can be
64hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
65see L<openssl_user_macros(7)>:
66
67 const EC_METHOD *EC_POINT_method_of(const EC_POINT *point);
68 int EC_POINT_set_Jprojective_coordinates_GFp(const EC_GROUP *group,
69                                              EC_POINT *p,
70                                              const BIGNUM *x, const BIGNUM *y,
71                                              const BIGNUM *z, BN_CTX *ctx);
72 int EC_POINT_get_Jprojective_coordinates_GFp(const EC_GROUP *group,
73                                              const EC_POINT *p,
74                                              BIGNUM *x, BIGNUM *y, BIGNUM *z,
75                                              BN_CTX *ctx);
76 int EC_POINT_set_affine_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,
77                                         const BIGNUM *x, const BIGNUM *y,
78                                         BN_CTX *ctx);
79 int EC_POINT_get_affine_coordinates_GFp(const EC_GROUP *group,
80                                         const EC_POINT *p,
81                                         BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
82 int EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group,
83                                             EC_POINT *p,
84                                             const BIGNUM *x, int y_bit,
85                                             BN_CTX *ctx);
86 int EC_POINT_set_affine_coordinates_GF2m(const EC_GROUP *group, EC_POINT *p,
87                                          const BIGNUM *x, const BIGNUM *y,
88                                          BN_CTX *ctx);
89 int EC_POINT_get_affine_coordinates_GF2m(const EC_GROUP *group,
90                                          const EC_POINT *p,
91                                          BIGNUM *x, BIGNUM *y, BN_CTX *ctx);
92 int EC_POINT_set_compressed_coordinates_GF2m(const EC_GROUP *group,
93                                              EC_POINT *p,
94                                              const BIGNUM *x, int y_bit,
95                                              BN_CTX *ctx);
96 BIGNUM *EC_POINT_point2bn(const EC_GROUP *group, const EC_POINT *p,
97                           point_conversion_form_t form, BIGNUM *bn,
98                           BN_CTX *ctx);
99 EC_POINT *EC_POINT_bn2point(const EC_GROUP *group, const BIGNUM *bn,
100                             EC_POINT *p, BN_CTX *ctx);
101
102=head1 DESCRIPTION
103
104An B<EC_POINT> structure represents a point on a curve. A new point is
105constructed by calling the function EC_POINT_new() and providing the
106B<group> object that the point relates to.
107
108EC_POINT_free() frees the memory associated with the B<EC_POINT>.
109if B<point> is NULL nothing is done.
110
111EC_POINT_clear_free() destroys any sensitive data held within the EC_POINT and
112then frees its memory. If B<point> is NULL nothing is done.
113
114EC_POINT_copy() copies the point B<src> into B<dst>. Both B<src> and B<dst>
115must use the same B<EC_METHOD>.
116
117EC_POINT_dup() creates a new B<EC_POINT> object and copies the content from
118B<src> to the newly created B<EC_POINT> object.
119
120EC_POINT_method_of() obtains the B<EC_METHOD> associated with B<point>.
121This function was deprecated in OpenSSL 3.0, since EC_METHOD is no longer a
122public concept.
123
124A valid point on a curve is the special point at infinity. A point is set to
125be at infinity by calling EC_POINT_set_to_infinity().
126
127The affine coordinates for a point describe a point in terms of its x and y
128position. The function EC_POINT_set_affine_coordinates() sets the B<x> and B<y>
129coordinates for the point B<p> defined over the curve given in B<group>. The
130function EC_POINT_get_affine_coordinates() sets B<x> and B<y>, either of which
131may be NULL, to the corresponding coordinates of B<p>.
132
133The functions EC_POINT_set_affine_coordinates_GFp() and
134EC_POINT_set_affine_coordinates_GF2m() are synonyms for
135EC_POINT_set_affine_coordinates(). They are defined for backwards compatibility
136only and should not be used.
137
138The functions EC_POINT_get_affine_coordinates_GFp() and
139EC_POINT_get_affine_coordinates_GF2m() are synonyms for
140EC_POINT_get_affine_coordinates(). They are defined for backwards compatibility
141only and should not be used.
142
143As well as the affine coordinates, a point can alternatively be described in
144terms of its Jacobian projective coordinates (for Fp curves only). Jacobian
145projective coordinates are expressed as three values x, y and z. Working in
146this coordinate system provides more efficient point multiplication
147operations.  A mapping exists between Jacobian projective coordinates and
148affine coordinates. A Jacobian projective coordinate (x, y, z) can be written
149as an affine coordinate as (x/(z^2), y/(z^3)). Conversion to Jacobian
150projective from affine coordinates is simple. The coordinate (x, y) is mapped
151to (x, y, 1). Although deprecated in OpenSSL 3.0 and should no longer be used,
152to set or get the projective coordinates in older versions use
153EC_POINT_set_Jprojective_coordinates_GFp() and
154EC_POINT_get_Jprojective_coordinates_GFp() respectively.
155Modern versions should instead use EC_POINT_set_affine_coordinates() and
156EC_POINT_get_affine_coordinates(), performing the conversion manually using the
157above maps in such rare circumstances.
158
159Points can also be described in terms of their compressed coordinates. For a
160point (x, y), for any given value for x such that the point is on the curve
161there will only ever be two possible values for y. Therefore, a point can be set
162using the EC_POINT_set_compressed_coordinates() function where B<x> is the x
163coordinate and B<y_bit> is a value 0 or 1 to identify which of the two
164possible values for y should be used.
165
166The functions EC_POINT_set_compressed_coordinates_GFp() and
167EC_POINT_set_compressed_coordinates_GF2m() are synonyms for
168EC_POINT_set_compressed_coordinates(). They are defined for backwards
169compatibility only and should not be used.
170
171In addition B<EC_POINT> can be converted to and from various external
172representations. The octet form is the binary encoding of the B<ECPoint>
173structure (as defined in RFC5480 and used in certificates and TLS records):
174only the content octets are present, the B<OCTET STRING> tag and length are
175not included. B<BIGNUM> form is the octet form interpreted as a big endian
176integer converted to a B<BIGNUM> structure. Hexadecimal form is the octet
177form converted to a NULL terminated character string where each character
178is one of the printable values 0-9 or A-F (or a-f).
179
180The functions EC_POINT_point2oct(), EC_POINT_oct2point(), EC_POINT_point2bn(),
181EC_POINT_bn2point(), EC_POINT_point2hex() and EC_POINT_hex2point() convert from
182and to EC_POINTs for the formats: octet, BIGNUM and hexadecimal respectively.
183
184The function EC_POINT_point2oct() encodes the given curve point B<p> as an
185octet string into the buffer B<buf> of size B<len>, using the specified
186conversion form B<form>.
187The encoding conforms with Sec. 2.3.3 of the SECG SEC 1 ("Elliptic Curve
188Cryptography") standard.
189Similarly the function EC_POINT_oct2point() decodes a curve point into B<p> from
190the octet string contained in the given buffer B<buf> of size B<len>, conforming
191to Sec. 2.3.4 of the SECG SEC 1 ("Elliptic Curve Cryptography") standard.
192
193The functions EC_POINT_point2hex() and EC_POINT_point2bn() convert a point B<p>,
194respectively, to the hexadecimal or BIGNUM representation of the same
195encoding of the function EC_POINT_point2oct().
196Vice versa, similarly to the function EC_POINT_oct2point(), the functions
197EC_POINT_hex2point() and EC_POINT_point2bn() decode the hexadecimal or
198BIGNUM representation into the EC_POINT B<p>.
199
200Notice that, according to the standard, the octet string encoding of the point
201at infinity for a given curve is fixed to a single octet of value zero and that,
202vice versa, a single octet of size zero is decoded as the point at infinity.
203
204The function EC_POINT_point2oct() must be supplied with a buffer long enough to
205store the octet form. The return value provides the number of octets stored.
206Calling the function with a NULL buffer will not perform the conversion but
207will still return the required buffer length.
208
209The function EC_POINT_point2buf() allocates a buffer of suitable length and
210writes an EC_POINT to it in octet format. The allocated buffer is written to
211B<*pbuf> and its length is returned. The caller must free up the allocated
212buffer with a call to OPENSSL_free(). Since the allocated buffer value is
213written to B<*pbuf> the B<pbuf> parameter B<MUST NOT> be B<NULL>.
214
215The function EC_POINT_point2hex() will allocate sufficient memory to store the
216hexadecimal string. It is the caller's responsibility to free this memory with
217a subsequent call to OPENSSL_free().
218
219=head1 RETURN VALUES
220
221EC_POINT_new() and EC_POINT_dup() return the newly allocated EC_POINT or NULL
222on error.
223
224The following functions return 1 on success or 0 on error: EC_POINT_copy(),
225EC_POINT_set_to_infinity(), EC_POINT_set_Jprojective_coordinates_GFp(),
226EC_POINT_get_Jprojective_coordinates_GFp(),
227EC_POINT_set_affine_coordinates_GFp(), EC_POINT_get_affine_coordinates_GFp(),
228EC_POINT_set_compressed_coordinates_GFp(),
229EC_POINT_set_affine_coordinates_GF2m(), EC_POINT_get_affine_coordinates_GF2m(),
230EC_POINT_set_compressed_coordinates_GF2m() and EC_POINT_oct2point().
231
232EC_POINT_method_of returns the EC_METHOD associated with the supplied EC_POINT.
233
234EC_POINT_point2oct() and EC_POINT_point2buf() return the length of the required
235buffer or 0 on error.
236
237EC_POINT_point2bn() returns the pointer to the BIGNUM supplied, or NULL on
238error.
239
240EC_POINT_bn2point() returns the pointer to the EC_POINT supplied, or NULL on
241error.
242
243EC_POINT_point2hex() returns a pointer to the hex string, or NULL on error.
244
245EC_POINT_hex2point() returns the pointer to the EC_POINT supplied, or NULL on
246error.
247
248=head1 SEE ALSO
249
250L<crypto(7)>, L<EC_GROUP_new(3)>, L<EC_GROUP_copy(3)>,
251L<EC_POINT_add(3)>, L<EC_KEY_new(3)>,
252L<EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)>
253
254=head1 HISTORY
255
256EC_POINT_method_of(),
257EC_POINT_set_Jprojective_coordinates_GFp(),
258EC_POINT_get_Jprojective_coordinates_GFp(),
259EC_POINT_set_affine_coordinates_GFp(), EC_POINT_get_affine_coordinates_GFp(),
260EC_POINT_set_compressed_coordinates_GFp(),
261EC_POINT_set_affine_coordinates_GF2m(), EC_POINT_get_affine_coordinates_GF2m(),
262EC_POINT_set_compressed_coordinates_GF2m(),
263EC_POINT_point2bn(), and EC_POINT_bn2point() were deprecated in OpenSSL 3.0.
264
265
266B<EC_POINT_set_affine_coordinates>, B<EC_POINT_get_affine_coordinates>,
267and B<EC_POINT_set_compressed_coordinates> were
268added in OpenSSL 1.1.1.
269
270=head1 COPYRIGHT
271
272Copyright 2013-2023 The OpenSSL Project Authors. All Rights Reserved.
273
274Licensed under the Apache License 2.0 (the "License").  You may not use
275this file except in compliance with the License.  You can obtain a copy
276in the file LICENSE in the source distribution or at
277L<https://www.openssl.org/source/license.html>.
278
279=cut
280