xref: /openssl/doc/man3/EVP_PKEY_keygen.pod (revision a57c6f84) 
1=pod
2
3=head1 NAME
4
5EVP_PKEY_Q_keygen,
6EVP_PKEY_keygen_init, EVP_PKEY_paramgen_init, EVP_PKEY_generate,
7EVP_PKEY_CTX_set_cb, EVP_PKEY_CTX_get_cb,
8EVP_PKEY_CTX_get_keygen_info, EVP_PKEY_CTX_set_app_data,
9EVP_PKEY_CTX_get_app_data,
10EVP_PKEY_gen_cb,
11EVP_PKEY_paramgen, EVP_PKEY_keygen
12- key and parameter generation and check functions
13
14=head1 SYNOPSIS
15
16 #include <openssl/evp.h>
17
18 EVP_PKEY *EVP_PKEY_Q_keygen(OSSL_LIB_CTX *libctx, const char *propq,
19                             const char *type, ...);
20
21 int EVP_PKEY_keygen_init(EVP_PKEY_CTX *ctx);
22 int EVP_PKEY_paramgen_init(EVP_PKEY_CTX *ctx);
23 int EVP_PKEY_generate(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
24 int EVP_PKEY_paramgen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
25 int EVP_PKEY_keygen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
26
27 typedef int EVP_PKEY_gen_cb(EVP_PKEY_CTX *ctx);
28
29 void EVP_PKEY_CTX_set_cb(EVP_PKEY_CTX *ctx, EVP_PKEY_gen_cb *cb);
30 EVP_PKEY_gen_cb *EVP_PKEY_CTX_get_cb(EVP_PKEY_CTX *ctx);
31
32 int EVP_PKEY_CTX_get_keygen_info(EVP_PKEY_CTX *ctx, int idx);
33
34 void EVP_PKEY_CTX_set_app_data(EVP_PKEY_CTX *ctx, void *data);
35 void *EVP_PKEY_CTX_get_app_data(EVP_PKEY_CTX *ctx);
36
37=head1 DESCRIPTION
38
39Generating keys is sometimes straight forward, just generate the key's
40numbers and be done with it.  However, there are certain key types that need
41key parameters, often called domain parameters but not necessarily limited
42to that, that also need to be generated.  In addition to this, the caller
43may want to set user provided generation parameters that further affect key
44parameter or key generation, such as the desired key size.
45
46To flexibly allow all that's just been described, key parameter and key
47generation is divided into an initialization of a key algorithm context,
48functions to set user provided parameters, and finally the key parameter or
49key generation function itself.
50
51The key algorithm context must be created using L<EVP_PKEY_CTX_new(3)> or
52variants thereof, see that manual for details.
53
54EVP_PKEY_keygen_init() initializes a public key algorithm context I<ctx>
55for a key generation operation.
56
57EVP_PKEY_paramgen_init() is similar to EVP_PKEY_keygen_init() except key
58parameters are generated.
59
60After initialization, generation parameters may be provided with
61L<EVP_PKEY_CTX_ctrl(3)> or L<EVP_PKEY_CTX_set_params(3)>, or any other
62function described in those manuals.
63
64EVP_PKEY_generate() performs the generation operation, the resulting key
65parameters or key are written to I<*ppkey>.  If I<*ppkey> is NULL when this
66function is called, it will be allocated, and should be freed by the caller
67when no longer useful, using L<EVP_PKEY_free(3)>.
68
69EVP_PKEY_paramgen() and EVP_PKEY_keygen() do exactly the same thing as
70EVP_PKEY_generate(), after checking that the corresponding EVP_PKEY_paramgen_init()
71or EVP_PKEY_keygen_init() was used to initialize I<ctx>.
72These are older functions that are kept for backward compatibility.
73It is safe to use EVP_PKEY_generate() instead.
74
75The function EVP_PKEY_set_cb() sets the key or parameter generation callback
76to I<cb>. The function EVP_PKEY_CTX_get_cb() returns the key or parameter
77generation callback.
78
79The function EVP_PKEY_CTX_get_keygen_info() returns parameters associated
80with the generation operation. If I<idx> is -1 the total number of
81parameters available is returned. Any non negative value returns the value of
82that parameter. EVP_PKEY_CTX_gen_keygen_info() with a nonnegative value for
83I<idx> should only be called within the generation callback.
84
85If the callback returns 0 then the key generation operation is aborted and an
86error occurs. This might occur during a time consuming operation where
87a user clicks on a "cancel" button.
88
89The functions EVP_PKEY_CTX_set_app_data() and EVP_PKEY_CTX_get_app_data() set
90and retrieve an opaque pointer. This can be used to set some application
91defined value which can be retrieved in the callback: for example a handle
92which is used to update a "progress dialog".
93
94EVP_PKEY_Q_keygen() abstracts from the explicit use of B<EVP_PKEY_CTX> while
95providing a 'quick' but limited way of generating a new asymmetric key pair.
96It provides shorthands for simple and common cases of key generation.
97As usual, the library context I<libctx> and property query I<propq>
98can be given for fetching algorithms from providers.
99If I<type> is C<RSA>,
100a B<size_t> parameter must be given to specify the size of the RSA key.
101If I<type> is C<EC>,
102a string parameter must be given to specify the name of the EC curve.
103If I<type> is C<X25519>, C<X448>, C<ED25519>, C<ED448>, or C<SM2>
104no further parameter is needed. Other key types may be possible if they are
105supplied by the loaded providers. EVP_PKEY_Q_keygen() may be usable with such
106key types as long as they do not require further parameters.
107
108=head1 RETURN VALUES
109
110EVP_PKEY_keygen_init(), EVP_PKEY_paramgen_init(), EVP_PKEY_keygen() and
111EVP_PKEY_paramgen() return 1 for success and 0 or a negative value for failure.
112In particular a return value of -2 indicates the operation is not supported by
113the public key algorithm.
114
115EVP_PKEY_Q_keygen() returns an B<EVP_PKEY>, or NULL on failure.
116
117=head1 NOTES
118
119After the call to EVP_PKEY_keygen_init() or EVP_PKEY_paramgen_init() algorithm
120specific control operations can be performed to set any appropriate parameters
121for the operation.
122
123The functions EVP_PKEY_keygen() and EVP_PKEY_paramgen() can be called more than
124once on the same context if several operations are performed using the same
125parameters.
126
127The meaning of the parameters passed to the callback will depend on the
128algorithm and the specific implementation of the algorithm. Some might not
129give any useful information at all during key or parameter generation. Others
130might not even call the callback.
131
132The operation performed by key or parameter generation depends on the algorithm
133used. In some cases (e.g. EC with a supplied named curve) the "generation"
134option merely sets the appropriate fields in an EVP_PKEY structure.
135
136In OpenSSL an EVP_PKEY structure containing a private key also contains the
137public key components and parameters (if any). An OpenSSL private key is
138equivalent to what some libraries call a "key pair". A private key can be used
139in functions which require the use of a public key or parameters.
140
141=head1 EXAMPLES
142
143Generate a 2048 bit RSA key:
144
145 #include <openssl/evp.h>
146 #include <openssl/rsa.h>
147
148 EVP_PKEY_CTX *ctx;
149 EVP_PKEY *pkey = NULL;
150
151 ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_RSA, NULL);
152 if (!ctx)
153     /* Error occurred */
154 if (EVP_PKEY_keygen_init(ctx) <= 0)
155     /* Error */
156 if (EVP_PKEY_CTX_set_rsa_keygen_bits(ctx, 2048) <= 0)
157     /* Error */
158
159 /* Generate key */
160 if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
161     /* Error */
162
163Generate a key from a set of parameters:
164
165 #include <openssl/evp.h>
166 #include <openssl/rsa.h>
167
168 EVP_PKEY_CTX *ctx;
169 ENGINE *eng;
170 EVP_PKEY *pkey = NULL, *param;
171
172 /* Assumed param, eng are set up already */
173 ctx = EVP_PKEY_CTX_new(param, eng);
174 if (!ctx)
175     /* Error occurred */
176 if (EVP_PKEY_keygen_init(ctx) <= 0)
177     /* Error */
178
179 /* Generate key */
180 if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
181     /* Error */
182
183Example of generation callback for OpenSSL public key implementations:
184
185 /* Application data is a BIO to output status to */
186
187 EVP_PKEY_CTX_set_app_data(ctx, status_bio);
188
189 static int genpkey_cb(EVP_PKEY_CTX *ctx)
190 {
191     char c = '*';
192     BIO *b = EVP_PKEY_CTX_get_app_data(ctx);
193     int p = EVP_PKEY_CTX_get_keygen_info(ctx, 0);
194
195     if (p == 0)
196         c = '.';
197     if (p == 1)
198         c = '+';
199     if (p == 2)
200         c = '*';
201     if (p == 3)
202         c = '\n';
203     BIO_write(b, &c, 1);
204     (void)BIO_flush(b);
205     return 1;
206 }
207
208=head1 SEE ALSO
209
210L<EVP_RSA_gen(3)>, L<EVP_EC_gen(3)>,
211L<EVP_PKEY_CTX_new(3)>,
212L<EVP_PKEY_encrypt(3)>,
213L<EVP_PKEY_decrypt(3)>,
214L<EVP_PKEY_sign(3)>,
215L<EVP_PKEY_verify(3)>,
216L<EVP_PKEY_verify_recover(3)>,
217L<EVP_PKEY_derive(3)>
218
219=head1 HISTORY
220
221EVP_PKEY_keygen_init(), int EVP_PKEY_paramgen_init(), EVP_PKEY_keygen(),
222EVP_PKEY_paramgen(), EVP_PKEY_gen_cb(), EVP_PKEY_CTX_set_cb(),
223EVP_PKEY_CTX_get_cb(), EVP_PKEY_CTX_get_keygen_info(),
224EVP_PKEY_CTX_set_app_data() and EVP_PKEY_CTX_get_app_data() were added in
225OpenSSL 1.0.0.
226
227EVP_PKEY_Q_keygen() and EVP_PKEY_generate() were added in OpenSSL 3.0.
228
229=head1 COPYRIGHT
230
231Copyright 2006-2021 The OpenSSL Project Authors. All Rights Reserved.
232
233Licensed under the Apache License 2.0 (the "License").  You may not use
234this file except in compliance with the License.  You can obtain a copy
235in the file LICENSE in the source distribution or at
236L<https://www.openssl.org/source/license.html>.
237
238=cut
239