xref: /openssl/doc/man3/EC_GROUP_new.pod (revision da1c088f) 
1=pod
2
3=head1 NAME
4
5EC_GROUP_get_ecparameters,
6EC_GROUP_get_ecpkparameters,
7EC_GROUP_new_from_params,
8EC_GROUP_to_params,
9EC_GROUP_new_from_ecparameters,
10EC_GROUP_new_from_ecpkparameters,
11EC_GROUP_new,
12EC_GROUP_free,
13EC_GROUP_clear_free,
14EC_GROUP_new_curve_GFp,
15EC_GROUP_new_curve_GF2m,
16EC_GROUP_new_by_curve_name_ex,
17EC_GROUP_new_by_curve_name,
18EC_GROUP_set_curve,
19EC_GROUP_get_curve,
20EC_GROUP_set_curve_GFp,
21EC_GROUP_get_curve_GFp,
22EC_GROUP_set_curve_GF2m,
23EC_GROUP_get_curve_GF2m,
24EC_get_builtin_curves,
25OSSL_EC_curve_nid2name -
26Functions for creating and destroying EC_GROUP objects
27
28=head1 SYNOPSIS
29
30 #include <openssl/ec.h>
31
32 EC_GROUP *EC_GROUP_new_from_params(const OSSL_PARAM params[],
33                                    OSSL_LIB_CTX *libctx, const char *propq);
34 OSSL_PARAM *EC_GROUP_to_params(const EC_GROUP *group, OSSL_LIB_CTX *libctx,
35                                const char *propq, BN_CTX *bnctx);
36 EC_GROUP *EC_GROUP_new_from_ecparameters(const ECPARAMETERS *params);
37 EC_GROUP *EC_GROUP_new_from_ecpkparameters(const ECPKPARAMETERS *params);
38 void EC_GROUP_free(EC_GROUP *group);
39
40 EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a,
41                                  const BIGNUM *b, BN_CTX *ctx);
42 EC_GROUP *EC_GROUP_new_curve_GF2m(const BIGNUM *p, const BIGNUM *a,
43                                   const BIGNUM *b, BN_CTX *ctx);
44 EC_GROUP *EC_GROUP_new_by_curve_name_ex(OSSL_LIB_CTX *libctx, const char *propq,
45                                         int nid);
46 EC_GROUP *EC_GROUP_new_by_curve_name(int nid);
47
48 int EC_GROUP_set_curve(EC_GROUP *group, const BIGNUM *p, const BIGNUM *a,
49                        const BIGNUM *b, BN_CTX *ctx);
50 int EC_GROUP_get_curve(const EC_GROUP *group, BIGNUM *p, BIGNUM *a, BIGNUM *b,
51                        BN_CTX *ctx);
52
53 ECPARAMETERS *EC_GROUP_get_ecparameters(const EC_GROUP *group,
54                                         ECPARAMETERS *params);
55 ECPKPARAMETERS *EC_GROUP_get_ecpkparameters(const EC_GROUP *group,
56                                             ECPKPARAMETERS *params);
57
58 size_t EC_get_builtin_curves(EC_builtin_curve *r, size_t nitems);
59 const char *OSSL_EC_curve_nid2name(int nid);
60
61The following functions have been deprecated since OpenSSL 3.0, and can be
62hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
63see L<openssl_user_macros(7)>:
64
65 EC_GROUP *EC_GROUP_new(const EC_METHOD *meth);
66 void EC_GROUP_clear_free(EC_GROUP *group);
67
68 int EC_GROUP_set_curve_GFp(EC_GROUP *group, const BIGNUM *p,
69                            const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
70 int EC_GROUP_get_curve_GFp(const EC_GROUP *group, BIGNUM *p,
71                            BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
72 int EC_GROUP_set_curve_GF2m(EC_GROUP *group, const BIGNUM *p,
73                             const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
74 int EC_GROUP_get_curve_GF2m(const EC_GROUP *group, BIGNUM *p,
75                             BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
76
77=head1 DESCRIPTION
78
79Within the library there are two forms of elliptic curve that are of interest.
80The first form is those defined over the prime field Fp. The elements of Fp are
81the integers 0 to p-1, where p is a prime number. This gives us a revised
82elliptic curve equation as follows:
83
84y^2 mod p = x^3 +ax + b mod p
85
86The second form is those defined over a binary field F2^m where the elements of
87the field are integers of length at most m bits. For this form the elliptic
88curve equation is modified to:
89
90y^2 + xy = x^3 + ax^2 + b (where b != 0)
91
92Operations in a binary field are performed relative to an
93B<irreducible polynomial>. All such curves with OpenSSL use a trinomial or a
94pentanomial for this parameter.
95
96Although deprecated since OpenSSL 3.0 and should no longer be used,
97a new curve can be constructed by calling EC_GROUP_new(), using the
98implementation provided by I<meth> (see L<EC_GFp_simple_method(3)>) and
99associated with the library context I<ctx> (see L<OSSL_LIB_CTX(3)>).
100The I<ctx> parameter may be NULL in which case the default library context is
101used.
102It is then necessary to call EC_GROUP_set_curve() to set the curve parameters.
103Applications should instead use one of the other EC_GROUP_new_* constructors.
104
105EC_GROUP_new_from_params() creates a group with parameters specified by I<params>.
106The library context I<libctx> (see L<OSSL_LIB_CTX(3)>) and property query string
107I<propq> are used to fetch algorithms from providers.
108I<params> may be either a list of explicit params or a named group,
109The values for I<ctx> and I<propq> may be NULL.
110The I<params> that can be used are described in
111L<B<EVP_PKEY-EC>(7)|EVP_PKEY-EC(7)/Common EC parameters>.
112
113EC_GROUP_to_params creates an OSSL_PARAM array with the corresponding parameters
114describing the given EC_GROUP. The resulting parameters may contain parameters
115describing a named or explicit curve depending on the EC_GROUP.
116The library context I<libctx> (see L<OSSL_LIB_CTX(3)>) and property query string
117I<propq> are used to fetch algorithms from providers.
118I<bnctx> is an optional preallocated BN_CTX (to save the overhead of allocating
119and freeing the structure in a loop).
120The values for I<libctx>, I<propq> and I<bnctx> may be NULL.
121The caller is responsible for freeing the OSSL_PARAM pointer returned.
122
123EC_GROUP_new_from_ecparameters() will create a group from the
124specified I<params> and
125EC_GROUP_new_from_ecpkparameters() will create a group from the specific PK
126I<params>.
127
128EC_GROUP_set_curve() sets the curve parameters I<p>, I<a> and I<b>. For a curve
129over Fp I<p> is the prime for the field. For a curve over F2^m I<p> represents
130the irreducible polynomial - each bit represents a term in the polynomial.
131Therefore, there will either be three or five bits set dependent on whether the
132polynomial is a trinomial or a pentanomial.
133In either case, I<a> and I<b> represents the coefficients a and b from the
134relevant equation introduced above.
135
136EC_group_get_curve() obtains the previously set curve parameters.
137
138EC_GROUP_set_curve_GFp() and EC_GROUP_set_curve_GF2m() are synonyms for
139EC_GROUP_set_curve(). They are defined for backwards compatibility only and
140should not be used.
141
142EC_GROUP_get_curve_GFp() and EC_GROUP_get_curve_GF2m() are synonyms for
143EC_GROUP_get_curve(). They are defined for backwards compatibility only and
144should not be used.
145
146The functions EC_GROUP_new_curve_GFp() and EC_GROUP_new_curve_GF2m() are
147shortcuts for calling EC_GROUP_new() and then the EC_GROUP_set_curve() function.
148An appropriate default implementation method will be used.
149
150Whilst the library can be used to create any curve using the functions described
151above, there are also a number of predefined curves that are available. In order
152to obtain a list of all of the predefined curves, call the function
153EC_get_builtin_curves(). The parameter I<r> should be an array of
154EC_builtin_curve structures of size I<nitems>. The function will populate the
155I<r> array with information about the built-in curves. If I<nitems> is less than
156the total number of curves available, then the first I<nitems> curves will be
157returned. Otherwise the total number of curves will be provided. The return
158value is the total number of curves available (whether that number has been
159populated in I<r> or not). Passing a NULL I<r>, or setting I<nitems> to 0 will
160do nothing other than return the total number of curves available.
161The EC_builtin_curve structure is defined as follows:
162
163 typedef struct {
164        int nid;
165        const char *comment;
166        } EC_builtin_curve;
167
168Each EC_builtin_curve item has a unique integer id (I<nid>), and a human
169readable comment string describing the curve.
170
171In order to construct a built-in curve use the function
172EC_GROUP_new_by_curve_name_ex() and provide the I<nid> of the curve to
173be constructed, the associated library context to be used in I<ctx> (see
174L<OSSL_LIB_CTX(3)>) and any property query string in I<propq>. The I<ctx> value
175may be NULL in which case the default library context is used. The I<propq>
176value may also be NULL.
177
178EC_GROUP_new_by_curve_name() is the same as
179EC_GROUP_new_by_curve_name_ex() except that the default library context
180is always used along with a NULL property query string.
181
182EC_GROUP_free() frees the memory associated with the EC_GROUP.
183If I<group> is NULL nothing is done.
184
185EC_GROUP_clear_free() is deprecated: it was meant to destroy any sensitive data
186held within the EC_GROUP and then free its memory, but since all the data stored
187in the EC_GROUP is public anyway, this function is unnecessary.
188Its use can be safely replaced with EC_GROUP_free().
189If I<group> is NULL nothing is done.
190
191OSSL_EC_curve_nid2name() converts a curve I<nid> into the corresponding name.
192
193=head1 RETURN VALUES
194
195All EC_GROUP_new* functions return a pointer to the newly constructed group, or
196NULL on error.
197
198EC_get_builtin_curves() returns the number of built-in curves that are
199available.
200
201EC_GROUP_set_curve_GFp(), EC_GROUP_get_curve_GFp(), EC_GROUP_set_curve_GF2m(),
202EC_GROUP_get_curve_GF2m() return 1 on success or 0 on error.
203
204OSSL_EC_curve_nid2name() returns a character string constant, or NULL on error.
205
206=head1 SEE ALSO
207
208L<crypto(7)>, L<EC_GROUP_copy(3)>,
209L<EC_POINT_new(3)>, L<EC_POINT_add(3)>, L<EC_KEY_new(3)>,
210L<EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)>,
211L<OSSL_LIB_CTX(3)>, L<EVP_PKEY-EC(7)>
212
213=head1 HISTORY
214
215=over 2
216
217=item *
218
219EC_GROUP_new() was deprecated in OpenSSL 3.0.
220
221EC_GROUP_new_by_curve_name_ex() and EC_GROUP_new_from_params() were
222added in OpenSSL 3.0.
223
224=item *
225
226EC_GROUP_clear_free() was deprecated in OpenSSL 3.0; use EC_GROUP_free()
227instead.
228
229=item *
230
231 EC_GROUP_set_curve_GFp(), EC_GROUP_get_curve_GFp(),
232 EC_GROUP_set_curve_GF2m() and EC_GROUP_get_curve_GF2m() were deprecated in
233 OpenSSL 3.0; use EC_GROUP_set_curve() and EC_GROUP_get_curve() instead.
234
235=back
236
237=head1 COPYRIGHT
238
239Copyright 2013-2023 The OpenSSL Project Authors. All Rights Reserved.
240
241Licensed under the Apache License 2.0 (the "License").  You may not use
242this file except in compliance with the License.  You can obtain a copy
243in the file LICENSE in the source distribution or at
244L<https://www.openssl.org/source/license.html>.
245
246=cut
247