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 ctx 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_keygen(3) 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()
associate an opaque, application-defined pointer with an EVP_PKEY_CTX
object.
This pointer is not interpreted by the library and is reserved entirely
for use by the application. It may be used to store arbitrary context or
state that needs to be accessible wherever the corresponding EVP_PKEY_CTX
is available.
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. The list of built-in curves can be obtained
programmatically using EC_get_builtin_curves(3), and their names can be
retrieved using OSSL_EC_curve_nid2name(3). If type is: "ED25519",
"ED448", "SM2", "X25519", "X448", "ML-DSA-44", "ML-DSA-65", "ML-DSA-87",
"ML-KEM-512", "ML-KEM-768", or "ML-KEM-1024" no further parameters are
needed. Other key types may be possible if they are supplied by the
loaded providers. EVP_PKEY_Q_keygen() may be usable with such key types
as long as they do not require further parameters.
RETURN VALUES
EVP_PKEY_keygen(3) 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(3) 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(3),
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 2006-2026 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>.
3.6.5 2026-09-29 EVP_PKEY_KEYGEN(3ossl)
openssl 3.6.5 - Generated Sat Oct 3 07:15:44 CDT 2026