1=pod
2
3=head1 NAME
4
5EC_GROUP_get_ecparameters,
6EC_GROUP_get_ecpkparameters,
7EC_GROUP_new_from_params,
8EC_GROUP_new_from_ecparameters,
9EC_GROUP_new_from_ecpkparameters,
10EC_GROUP_new,
11EC_GROUP_free,
12EC_GROUP_clear_free,
13EC_GROUP_new_curve_GFp,
14EC_GROUP_new_curve_GF2m,
15EC_GROUP_new_by_curve_name_ex,
16EC_GROUP_new_by_curve_name,
17EC_GROUP_set_curve,
18EC_GROUP_get_curve,
19EC_GROUP_set_curve_GFp,
20EC_GROUP_get_curve_GFp,
21EC_GROUP_set_curve_GF2m,
22EC_GROUP_get_curve_GF2m,
23EC_get_builtin_curves,
24OSSL_EC_curve_nid2name -
25Functions for creating and destroying EC_GROUP objects
26
27=head1 SYNOPSIS
28
29 #include <openssl/ec.h>
30
31 EC_GROUP *EC_GROUP_new_from_params(const OSSL_PARAM params[],
32                                    OSSL_LIB_CTX *libctx, const char *propq);
33 EC_GROUP *EC_GROUP_new_from_ecparameters(const ECPARAMETERS *params);
34 EC_GROUP *EC_GROUP_new_from_ecpkparameters(const ECPKPARAMETERS *params);
35 void EC_GROUP_free(EC_GROUP *group);
36
37 EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a,
38                                  const BIGNUM *b, BN_CTX *ctx);
39 EC_GROUP *EC_GROUP_new_curve_GF2m(const BIGNUM *p, const BIGNUM *a,
40                                   const BIGNUM *b, BN_CTX *ctx);
41 EC_GROUP *EC_GROUP_new_by_curve_name_ex(OSSL_LIB_CTX *libctx, const char *propq,
42                                         int nid);
43 EC_GROUP *EC_GROUP_new_by_curve_name(int nid);
44
45 int EC_GROUP_set_curve(EC_GROUP *group, const BIGNUM *p, const BIGNUM *a,
46                        const BIGNUM *b, BN_CTX *ctx);
47 int EC_GROUP_get_curve(const EC_GROUP *group, BIGNUM *p, BIGNUM *a, BIGNUM *b,
48                        BN_CTX *ctx);
49
50 ECPARAMETERS *EC_GROUP_get_ecparameters(const EC_GROUP *group,
51                                         ECPARAMETERS *params);
52 ECPKPARAMETERS *EC_GROUP_get_ecpkparameters(const EC_GROUP *group,
53                                             ECPKPARAMETERS *params);
54
55 size_t EC_get_builtin_curves(EC_builtin_curve *r, size_t nitems);
56 const char *OSSL_EC_curve_nid2name(int nid);
57
58The following functions have been deprecated since OpenSSL 3.0, and can be
59hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
60see L<openssl_user_macros(7)>:
61
62 EC_GROUP *EC_GROUP_new(const EC_METHOD *meth);
63 void EC_GROUP_clear_free(EC_GROUP *group);
64
65 int EC_GROUP_set_curve_GFp(EC_GROUP *group, const BIGNUM *p,
66                            const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
67 int EC_GROUP_get_curve_GFp(const EC_GROUP *group, BIGNUM *p,
68                            BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
69 int EC_GROUP_set_curve_GF2m(EC_GROUP *group, const BIGNUM *p,
70                             const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
71 int EC_GROUP_get_curve_GF2m(const EC_GROUP *group, BIGNUM *p,
72                             BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
73
74=head1 DESCRIPTION
75
76Within the library there are two forms of elliptic curve that are of interest.
77The first form is those defined over the prime field Fp. The elements of Fp are
78the integers 0 to p-1, where p is a prime number. This gives us a revised
79elliptic curve equation as follows:
80
81y^2 mod p = x^3 +ax + b mod p
82
83The second form is those defined over a binary field F2^m where the elements of
84the field are integers of length at most m bits. For this form the elliptic
85curve equation is modified to:
86
87y^2 + xy = x^3 + ax^2 + b (where b != 0)
88
89Operations in a binary field are performed relative to an
90B<irreducible polynomial>. All such curves with OpenSSL use a trinomial or a
91pentanomial for this parameter.
92
93Although deprecated since OpenSSL 3.0 and should no longer be used,
94a new curve can be constructed by calling EC_GROUP_new(), using the
95implementation provided by I<meth> (see L<EC_GFp_simple_method(3)>) and
96associated with the library context I<ctx> (see L<OSSL_LIB_CTX(3)>).
97The I<ctx> parameter may be NULL in which case the default library context is
98used.
99It is then necessary to call EC_GROUP_set_curve() to set the curve parameters.
100Applications should instead use one of the other EC_GROUP_new_* constructors.
101
102EC_GROUP_new_from_params() creates a group with parameters specified by I<params>.
103The library context I<libctx> (see L<OSSL_LIB_CTX(3)>) and property query string
104I<propq> are used to fetch algorithms from providers.
105I<params> may be either a list of explicit params or a named group,
106The values for I<ctx> and I<propq> may be NULL.
107The I<params> that can be used are described in
108L<B<EVP_PKEY-EC>(7)|EVP_PKEY-EC(7)/Common EC parameters>.
109
110EC_GROUP_new_from_ecparameters() will create a group from the
111specified I<params> and
112EC_GROUP_new_from_ecpkparameters() will create a group from the specific PK
113I<params>.
114
115EC_GROUP_set_curve() sets the curve parameters I<p>, I<a> and I<b>. For a curve
116over Fp I<p> is the prime for the field. For a curve over F2^m I<p> represents
117the irreducible polynomial - each bit represents a term in the polynomial.
118Therefore, there will either be three or five bits set dependent on whether the
119polynomial is a trinomial or a pentanomial.
120In either case, I<a> and I<b> represents the coefficients a and b from the
121relevant equation introduced above.
122
123EC_group_get_curve() obtains the previously set curve parameters.
124
125EC_GROUP_set_curve_GFp() and EC_GROUP_set_curve_GF2m() are synonyms for
126EC_GROUP_set_curve(). They are defined for backwards compatibility only and
127should not be used.
128
129EC_GROUP_get_curve_GFp() and EC_GROUP_get_curve_GF2m() are synonyms for
130EC_GROUP_get_curve(). They are defined for backwards compatibility only and
131should not be used.
132
133The functions EC_GROUP_new_curve_GFp() and EC_GROUP_new_curve_GF2m() are
134shortcuts for calling EC_GROUP_new() and then the EC_GROUP_set_curve() function.
135An appropriate default implementation method will be used.
136
137Whilst the library can be used to create any curve using the functions described
138above, there are also a number of predefined curves that are available. In order
139to obtain a list of all of the predefined curves, call the function
140EC_get_builtin_curves(). The parameter I<r> should be an array of
141EC_builtin_curve structures of size I<nitems>. The function will populate the
142I<r> array with information about the built-in curves. If I<nitems> is less than
143the total number of curves available, then the first I<nitems> curves will be
144returned. Otherwise the total number of curves will be provided. The return
145value is the total number of curves available (whether that number has been
146populated in I<r> or not). Passing a NULL I<r>, or setting I<nitems> to 0 will
147do nothing other than return the total number of curves available.
148The EC_builtin_curve structure is defined as follows:
149
150 typedef struct {
151        int nid;
152        const char *comment;
153        } EC_builtin_curve;
154
155Each EC_builtin_curve item has a unique integer id (I<nid>), and a human
156readable comment string describing the curve.
157
158In order to construct a built-in curve use the function
159EC_GROUP_new_by_curve_name_ex() and provide the I<nid> of the curve to
160be constructed, the associated library context to be used in I<ctx> (see
161L<OSSL_LIB_CTX(3)>) and any property query string in I<propq>. The I<ctx> value
162may be NULL in which case the default library context is used. The I<propq>
163value may also be NULL.
164
165EC_GROUP_new_by_curve_name() is the same as
166EC_GROUP_new_by_curve_name_ex() except that the default library context
167is always used along with a NULL property query string.
168
169EC_GROUP_free() frees the memory associated with the EC_GROUP.
170If I<group> is NULL nothing is done.
171
172EC_GROUP_clear_free() is deprecated: it was meant to destroy any sensitive data
173held within the EC_GROUP and then free its memory, but since all the data stored
174in the EC_GROUP is public anyway, this function is unnecessary.
175Its use can be safely replaced with EC_GROUP_free().
176If I<group> is NULL nothing is done.
177
178OSSL_EC_curve_nid2name() converts a curve I<nid> into the corresponding name.
179
180=head1 RETURN VALUES
181
182All EC_GROUP_new* functions return a pointer to the newly constructed group, or
183NULL on error.
184
185EC_get_builtin_curves() returns the number of built-in curves that are
186available.
187
188EC_GROUP_set_curve_GFp(), EC_GROUP_get_curve_GFp(), EC_GROUP_set_curve_GF2m(),
189EC_GROUP_get_curve_GF2m() return 1 on success or 0 on error.
190
191OSSL_EC_curve_nid2name() returns a character string constant, or NULL on error.
192
193=head1 SEE ALSO
194
195L<crypto(7)>, L<EC_GROUP_copy(3)>,
196L<EC_POINT_new(3)>, L<EC_POINT_add(3)>, L<EC_KEY_new(3)>,
197L<EC_GFp_simple_method(3)>, L<d2i_ECPKParameters(3)>,
198L<OSSL_LIB_CTX(3)>, L<EVP_PKEY-EC(7)>
199
200=head1 HISTORY
201
202=over 2
203
204=item *
205
206EC_GROUP_new() was deprecated in OpenSSL 3.0.
207
208EC_GROUP_new_by_curve_name_ex() and EC_GROUP_new_from_params() were
209added in OpenSSL 3.0.
210
211=item *
212
213EC_GROUP_clear_free() was deprecated in OpenSSL 3.0; use EC_GROUP_free()
214instead.
215
216=item *
217
218 EC_GROUP_set_curve_GFp(), EC_GROUP_get_curve_GFp(),
219 EC_GROUP_set_curve_GF2m() and EC_GROUP_get_curve_GF2m() were deprecated in
220 OpenSSL 3.0; use EC_GROUP_set_curve() and EC_GROUP_get_curve() instead.
221
222=back
223
224=head1 COPYRIGHT
225
226Copyright 2013-2021 The OpenSSL Project Authors. All Rights Reserved.
227
228Licensed under the Apache License 2.0 (the "License").  You may not use
229this file except in compliance with the License.  You can obtain a copy
230in the file LICENSE in the source distribution or at
231L<https://www.openssl.org/source/license.html>.
232
233=cut
234