NAME

       EVP_PKEY_keygen_init, EVP_PKEY_keygen, EVP_PKEY_paramgen_init, EVP_PKEY_paramgen,
       EVP_PKEY_CTX_set_cb, EVP_PKEY_CTX_get_cb, EVP_PKEY_CTX_get_keygen_info,
       EVP_PKEY_CTX_set_app_data, EVP_PKEY_CTX_get_app_data, EVP_PKEY_gen_cb, EVP_PKEY_check,
       EVP_PKEY_public_check, EVP_PKEY_param_check - key and parameter generation and check
       functions

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_PKEY_keygen_init(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_keygen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);
        int EVP_PKEY_paramgen_init(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_paramgen(EVP_PKEY_CTX *ctx, EVP_PKEY **ppkey);

        typedef int EVP_PKEY_gen_cb(EVP_PKEY_CTX *ctx);

        void EVP_PKEY_CTX_set_cb(EVP_PKEY_CTX *ctx, EVP_PKEY_gen_cb *cb);
        EVP_PKEY_gen_cb *EVP_PKEY_CTX_get_cb(EVP_PKEY_CTX *ctx);

        int EVP_PKEY_CTX_get_keygen_info(EVP_PKEY_CTX *ctx, int idx);

        void EVP_PKEY_CTX_set_app_data(EVP_PKEY_CTX *ctx, void *data);
        void *EVP_PKEY_CTX_get_app_data(EVP_PKEY_CTX *ctx);

        int EVP_PKEY_check(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_public_check(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_param_check(EVP_PKEY_CTX *ctx);

DESCRIPTION

       The EVP_PKEY_keygen_init() function initializes a public key algorithm context using key
       pkey for a key generation operation.

       The EVP_PKEY_keygen() function performs a key generation operation, the generated key is
       written to ppkey.

       The functions EVP_PKEY_paramgen_init() and EVP_PKEY_paramgen() are similar except
       parameters are generated.

       The function EVP_PKEY_set_cb() sets the key or parameter generation callback to cb. The
       function EVP_PKEY_CTX_get_cb() returns the key or parameter generation callback.

       The function EVP_PKEY_CTX_get_keygen_info() returns parameters associated with the
       generation operation. If idx is -1 the total number of parameters available is returned.
       Any non negative value returns the value of that parameter. EVP_PKEY_CTX_gen_keygen_info()
       with a non-negative value for idx should only be called within the generation callback.

       If the callback returns 0 then the key generation operation is aborted and an error
       occurs. This might occur during a time consuming operation where a user clicks on a
       "cancel" button.

       The functions EVP_PKEY_CTX_set_app_data() and EVP_PKEY_CTX_get_app_data() set and retrieve
       an opaque pointer. This can be used to set some application defined value which can be
       retrieved in the callback: for example a handle which is used to update a "progress
       dialog".

       EVP_PKEY_check() validates the key-pair given by ctx. This function first tries to use
       customized key check method in EVP_PKEY_METHOD if it's present; otherwise it calls a
       default one defined in EVP_PKEY_ASN1_METHOD.

       EVP_PKEY_public_check() validates the public component of the key-pair given by ctx.  This
       function first tries to use customized key check method in EVP_PKEY_METHOD if it's
       present; otherwise it calls a default one defined in EVP_PKEY_ASN1_METHOD.

       EVP_PKEY_param_check() validates the algorithm parameters of the key-pair given by ctx.
       This function first tries to use customized key check method in EVP_PKEY_METHOD if it's
       present; otherwise it calls a default one defined in EVP_PKEY_ASN1_METHOD.

NOTES

       After the call to EVP_PKEY_keygen_init() or EVP_PKEY_paramgen_init() algorithm specific
       control operations can be performed to set any appropriate parameters for the operation.

       The functions EVP_PKEY_keygen() and EVP_PKEY_paramgen() can be called more than once on
       the same context if several operations are performed using the same parameters.

       The meaning of the parameters passed to the callback will depend on the algorithm and the
       specific implementation of the algorithm. Some might not give any useful information at
       all during key or parameter generation. Others might not even call the callback.

       The operation performed by key or parameter generation depends on the algorithm used. In
       some cases (e.g. EC with a supplied named curve) the "generation" option merely sets the
       appropriate fields in an EVP_PKEY structure.

       In OpenSSL an EVP_PKEY structure containing a private key also contains the public key
       components and parameters (if any). An OpenSSL private key is equivalent to what some
       libraries call a "key pair". A private key can be used in functions which require the use
       of a public key or parameters.

RETURN VALUES

       EVP_PKEY_keygen_init(), EVP_PKEY_paramgen_init(), EVP_PKEY_keygen() and
       EVP_PKEY_paramgen() return 1 for success and 0 or a negative value for failure.  In
       particular a return value of -2 indicates the operation is not supported by the public key
       algorithm.

       EVP_PKEY_check(), EVP_PKEY_public_check() and EVP_PKEY_param_check() return 1 for success
       or others for failure. They return -2 if the operation is not supported for the specific
       algorithm.

EXAMPLES

       Generate a 2048 bit RSA key:

        #include <openssl/evp.h>
        #include <openssl/rsa.h>

        EVP_PKEY_CTX *ctx;
        EVP_PKEY *pkey = NULL;

        ctx = EVP_PKEY_CTX_new_id(EVP_PKEY_RSA, NULL);
        if (!ctx)
            /* Error occurred */
        if (EVP_PKEY_keygen_init(ctx) <= 0)
            /* Error */
        if (EVP_PKEY_CTX_set_rsa_keygen_bits(ctx, 2048) <= 0)
            /* Error */

        /* Generate key */
        if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
            /* Error */

       Generate a key from a set of parameters:

        #include <openssl/evp.h>
        #include <openssl/rsa.h>

        EVP_PKEY_CTX *ctx;
        ENGINE *eng;
        EVP_PKEY *pkey = NULL, *param;

        /* Assumed param, eng are set up already */
        ctx = EVP_PKEY_CTX_new(param, eng);
        if (!ctx)
            /* Error occurred */
        if (EVP_PKEY_keygen_init(ctx) <= 0)
            /* Error */

        /* Generate key */
        if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
            /* Error */

       Example of generation callback for OpenSSL public key implementations:

        /* Application data is a BIO to output status to */

        EVP_PKEY_CTX_set_app_data(ctx, status_bio);

        static int genpkey_cb(EVP_PKEY_CTX *ctx)
        {
            char c = '*';
            BIO *b = EVP_PKEY_CTX_get_app_data(ctx);
            int p = EVP_PKEY_CTX_get_keygen_info(ctx, 0);

            if (p == 0)
                c = '.';
            if (p == 1)
                c = '+';
            if (p == 2)
                c = '*';
            if (p == 3)
                c = '\n';
            BIO_write(b, &c, 1);
            (void)BIO_flush(b);
            return 1;
        }

SEE ALSO

       EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3), EVP_PKEY_sign(3),
       EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3), EVP_PKEY_derive(3)

HISTORY

       These functions were first added to OpenSSL 1.0.0.

       EVP_PKEY_check(), EVP_PKEY_public_check() and EVP_PKEY_param_check() were added in OpenSSL
       1.1.1.

COPYRIGHT

       Copyright 2006-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use this file except in
       compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.