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EVP_PKEY_KEYGEN(3ossl)		    OpenSSL		EVP_PKEY_KEYGEN(3ossl)

NAME
       EVP_PKEY_Q_keygen, EVP_PKEY_keygen_init,	EVP_PKEY_paramgen_init,
       EVP_PKEY_generate, 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_paramgen,
       EVP_PKEY_keygen - key and parameter generation and check	functions

SYNOPSIS
	#include <openssl/evp.h>

	EVP_PKEY *EVP_PKEY_Q_keygen(OSSL_LIB_CTX *libctx, const	char *propq,
				    const char *type, ...);

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

DESCRIPTION
       Generating keys is sometimes straight forward, just generate the	key's
       numbers and be done with	it.  However, there are	certain	key types that
       need key	parameters, often called domain	parameters but not necessarily
       limited to that,	that also need to be generated.	 In addition to	this,
       the caller may want to set user provided	generation parameters that
       further affect key parameter or key generation, such as the desired key
       size.

       To flexibly allow all that's just been described, key parameter and key
       generation is divided into an initialization of a key algorithm
       context,	functions to set user provided parameters, and finally the key
       parameter or key	generation function itself.

       The key algorithm context must be created using EVP_PKEY_CTX_new(3) or
       variants	thereof, see that manual for details.

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

       EVP_PKEY_paramgen_init()	is similar to EVP_PKEY_keygen_init() except
       key parameters are generated.

       After initialization, generation	parameters may be provided with
       EVP_PKEY_CTX_ctrl(3) or EVP_PKEY_CTX_set_params(3), or any other
       function	described in those manuals.

       EVP_PKEY_generate() performs the	generation operation, the resulting
       key parameters or key are written to *ppkey.  If	*ppkey is NULL when
       this function is	called,	it will	be allocated, and should be freed by
       the caller when no longer useful, using EVP_PKEY_free(3).

       EVP_PKEY_paramgen() and EVP_PKEY_keygen() do exactly the	same thing as
       EVP_PKEY_generate(), after checking that	the corresponding
       EVP_PKEY_paramgen_init()	or EVP_PKEY_keygen_init() was used to
       initialize ctx.	These are older	functions that are kept	for backward
       compatibility.  It is safe to use EVP_PKEY_generate() instead.

       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
       nonnegative 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_Q_keygen() abstracts from the explicit use of EVP_PKEY_CTX
       while providing a 'quick' but limited way of generating a new
       asymmetric key pair.  It	provides shorthands for	simple and common
       cases of	key generation.	 As usual, the library context libctx and
       property	query propq can	be given for fetching algorithms from
       providers.  If type is "RSA", a size_t parameter	must be	given to
       specify the size	of the RSA key.	 If type is "EC", a string parameter
       must be given to	specify	the name of the	EC curve.  If type is
       "X25519", "X448", "ED25519", or "ED448" no further parameter is needed.

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_Q_keygen() returns an EVP_PKEY,	or NULL	on failure.

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.

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_RSA_gen(3), EVP_EC_gen(3), 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
       EVP_PKEY_keygen_init(), int EVP_PKEY_paramgen_init(),
       EVP_PKEY_keygen(), EVP_PKEY_paramgen(), EVP_PKEY_gen_cb(),
       EVP_PKEY_CTX_set_cb(), EVP_PKEY_CTX_get_cb(),
       EVP_PKEY_CTX_get_keygen_info(), EVP_PKEY_CTX_set_app_data() and
       EVP_PKEY_CTX_get_app_data() were	added in OpenSSL 1.0.0.

       EVP_PKEY_Q_keygen() and EVP_PKEY_generate() were	added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2006-2021 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the Apache License 2.0 (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>.

3.0.0-beta1+quic		  2021-06-19		EVP_PKEY_KEYGEN(3ossl)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | NOTES | EXAMPLES | SEE ALSO | HISTORY | COPYRIGHT

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