EVP_PKEY_CTX_get_cb(3ossl)

1EVP_PKEY_KEYGEN(3ossl)              OpenSSL             EVP_PKEY_KEYGEN(3ossl)
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NAME

6       EVP_PKEY_Q_keygen, EVP_PKEY_keygen_init, EVP_PKEY_paramgen_init,
7       EVP_PKEY_generate, EVP_PKEY_CTX_set_cb, EVP_PKEY_CTX_get_cb,
8       EVP_PKEY_CTX_get_keygen_info, EVP_PKEY_CTX_set_app_data,
9       EVP_PKEY_CTX_get_app_data, EVP_PKEY_gen_cb, EVP_PKEY_paramgen,
10       EVP_PKEY_keygen - key and parameter generation and check functions
11

SYNOPSIS

13        #include <openssl/evp.h>
14
15        EVP_PKEY *EVP_PKEY_Q_keygen(OSSL_LIB_CTX *libctx, const char *propq,
16                                    const char *type, ...);
17
18        int EVP_PKEY_keygen_init(EVP_PKEY_CTX *ctx);
19        int EVP_PKEY_paramgen_init(EVP_PKEY_CTX *ctx);
20        int EVP_PKEY_generate(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
21        int EVP_PKEY_paramgen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
22        int EVP_PKEY_keygen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
23
24        typedef int EVP_PKEY_gen_cb(EVP_PKEY_CTX *ctx);
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26        void EVP_PKEY_CTX_set_cb(EVP_PKEY_CTX *ctx, EVP_PKEY_gen_cb *cb);
27        EVP_PKEY_gen_cb *EVP_PKEY_CTX_get_cb(EVP_PKEY_CTX *ctx);
28
29        int EVP_PKEY_CTX_get_keygen_info(EVP_PKEY_CTX *ctx, int idx);
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31        void EVP_PKEY_CTX_set_app_data(EVP_PKEY_CTX *ctx, void *data);
32        void *EVP_PKEY_CTX_get_app_data(EVP_PKEY_CTX *ctx);
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DESCRIPTION

35       Generating keys is sometimes straight forward, just generate the key's
36       numbers and be done with it.  However, there are certain key types that
37       need key parameters, often called domain parameters but not necessarily
38       limited to that, that also need to be generated.  In addition to this,
39       the caller may want to set user provided generation parameters that
40       further affect key parameter or key generation, such as the desired key
41       size.
42
43       To flexibly allow all that's just been described, key parameter and key
44       generation is divided into an initialization of a key algorithm
45       context, functions to set user provided parameters, and finally the key
46       parameter or key generation function itself.
47
48       The key algorithm context must be created using EVP_PKEY_CTX_new(3) or
49       variants thereof, see that manual for details.
50
51       EVP_PKEY_keygen_init() initializes a public key algorithm context ctx
52       for a key generation operation.
53
54       EVP_PKEY_paramgen_init() is similar to EVP_PKEY_keygen_init() except
55       key parameters are generated.
56
57       After initialization, generation parameters may be provided with
58       EVP_PKEY_CTX_ctrl(3) or EVP_PKEY_CTX_set_params(3), or any other
59       function described in those manuals.
60
61       EVP_PKEY_generate() performs the generation operation, the resulting
62       key parameters or key are written to *ppkey.  If *ppkey is NULL when
63       this function is called, it will be allocated, and should be freed by
64       the caller when no longer useful, using EVP_PKEY_free(3).
65
66       EVP_PKEY_paramgen() and EVP_PKEY_keygen() do exactly the same thing as
67       EVP_PKEY_generate(), after checking that the corresponding
68       EVP_PKEY_paramgen_init() or EVP_PKEY_keygen_init() was used to
69       initialize ctx.  These are older functions that are kept for backward
70       compatibility.  It is safe to use EVP_PKEY_generate() instead.
71
72       The function EVP_PKEY_set_cb() sets the key or parameter generation
73       callback to cb. The function EVP_PKEY_CTX_get_cb() returns the key or
74       parameter generation callback.
75
76       The function EVP_PKEY_CTX_get_keygen_info() returns parameters
77       associated with the generation operation. If idx is -1 the total number
78       of parameters available is returned. Any non negative value returns the
79       value of that parameter. EVP_PKEY_CTX_gen_keygen_info() with a
80       nonnegative value for idx should only be called within the generation
81       callback.
82
83       If the callback returns 0 then the key generation operation is aborted
84       and an error occurs. This might occur during a time consuming operation
85       where a user clicks on a "cancel" button.
86
87       The functions EVP_PKEY_CTX_set_app_data() and
88       EVP_PKEY_CTX_get_app_data() set and retrieve an opaque pointer. This
89       can be used to set some application defined value which can be
90       retrieved in the callback: for example a handle which is used to update
91       a "progress dialog".
92
93       EVP_PKEY_Q_keygen() abstracts from the explicit use of EVP_PKEY_CTX
94       while providing a 'quick' but limited way of generating a new
95       asymmetric key pair.  It provides shorthands for simple and common
96       cases of key generation.  As usual, the library context libctx and
97       property query propq can be given for fetching algorithms from
98       providers.  If type is "RSA", a size_t parameter must be given to
99       specify the size of the RSA key.  If type is "EC", a string parameter
100       must be given to specify the name of the EC curve.  If type is
101       "X25519", "X448", "ED25519", "ED448", or "SM2" no further parameter is
102       needed.
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RETURN VALUES

105       EVP_PKEY_keygen_init(), EVP_PKEY_paramgen_init(), EVP_PKEY_keygen() and
106       EVP_PKEY_paramgen() return 1 for success and 0 or a negative value for
107       failure.  In particular a return value of -2 indicates the operation is
108       not supported by the public key algorithm.
109
110       EVP_PKEY_Q_keygen() returns an EVP_PKEY, or NULL on failure.
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NOTES

113       After the call to EVP_PKEY_keygen_init() or EVP_PKEY_paramgen_init()
114       algorithm specific control operations can be performed to set any
115       appropriate parameters for the operation.
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117       The functions EVP_PKEY_keygen() and EVP_PKEY_paramgen() can be called
118       more than once on the same context if several operations are performed
119       using the same parameters.
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121       The meaning of the parameters passed to the callback will depend on the
122       algorithm and the specific implementation of the algorithm. Some might
123       not give any useful information at all during key or parameter
124       generation. Others might not even call the callback.
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126       The operation performed by key or parameter generation depends on the
127       algorithm used. In some cases (e.g. EC with a supplied named curve) the
128       "generation" option merely sets the appropriate fields in an EVP_PKEY
129       structure.
130
131       In OpenSSL an EVP_PKEY structure containing a private key also contains
132       the public key components and parameters (if any). An OpenSSL private
133       key is equivalent to what some libraries call a "key pair". A private
134       key can be used in functions which require the use of a public key or
135       parameters.
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EXAMPLES

138       Generate a 2048 bit RSA key:
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140        #include <openssl/evp.h>
141        #include <openssl/rsa.h>
142
143        EVP_PKEY_CTX *ctx;
144        EVP_PKEY *pkey = NULL;
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146        ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_RSA, NULL);
147        if (!ctx)
148            /* Error occurred */
149        if (EVP_PKEY_keygen_init(ctx) <= 0)
150            /* Error */
151        if (EVP_PKEY_CTX_set_rsa_keygen_bits(ctx, 2048) <= 0)
152            /* Error */
153
154        /* Generate key */
155        if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
156            /* Error */
157
158       Generate a key from a set of parameters:
159
160        #include <openssl/evp.h>
161        #include <openssl/rsa.h>
162
163        EVP_PKEY_CTX *ctx;
164        ENGINE *eng;
165        EVP_PKEY *pkey = NULL, *param;
166
167        /* Assumed param, eng are set up already */
168        ctx = EVP_PKEY_CTX_new(param, eng);
169        if (!ctx)
170            /* Error occurred */
171        if (EVP_PKEY_keygen_init(ctx) <= 0)
172            /* Error */
173
174        /* Generate key */
175        if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
176            /* Error */
177
178       Example of generation callback for OpenSSL public key implementations:
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180        /* Application data is a BIO to output status to */
181
182        EVP_PKEY_CTX_set_app_data(ctx, status_bio);
183
184        static int genpkey_cb(EVP_PKEY_CTX *ctx)
185        {
186            char c = '*';
187            BIO *b = EVP_PKEY_CTX_get_app_data(ctx);
188            int p = EVP_PKEY_CTX_get_keygen_info(ctx, 0);
189
190            if (p == 0)
191                c = '.';
192            if (p == 1)
193                c = '+';
194            if (p == 2)
195                c = '*';
196            if (p == 3)
197                c = '\n';
198            BIO_write(b, &c, 1);
199            (void)BIO_flush(b);
200            return 1;
201        }
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HISTORY

209       EVP_PKEY_keygen_init(), int EVP_PKEY_paramgen_init(),
210       EVP_PKEY_keygen(), EVP_PKEY_paramgen(), EVP_PKEY_gen_cb(),
211       EVP_PKEY_CTX_set_cb(), EVP_PKEY_CTX_get_cb(),
212       EVP_PKEY_CTX_get_keygen_info(), EVP_PKEY_CTX_set_app_data() and
213       EVP_PKEY_CTX_get_app_data() were added in OpenSSL 1.0.0.
214
215       EVP_PKEY_Q_keygen() and EVP_PKEY_generate() were added in OpenSSL 3.0.
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COPYRIGHT

218       Copyright 2006-2022 The OpenSSL Project Authors. All Rights Reserved.
219
220       Licensed under the Apache License 2.0 (the "License").  You may not use
221       this file except in compliance with the License.  You can obtain a copy
222       in the file LICENSE in the source distribution or at
223       <https://www.openssl.org/source/license.html>.
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2273.1.1                             2023-08-31            EVP_PKEY_KEYGEN(3ossl)