.\" $OpenBSD: EVP_PKEY_keygen.3,v 1.14 2024/07/21 08:02:17 tb Exp $ .\" full merge up to: OpenSSL 24a535ea Sep 22 13:14:20 2020 +0100 .\" .\" This file is a derived work. .\" The changes are covered by the following Copyright and license: .\" .\" Copyright (c) 2023 Ingo Schwarze .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: July 21 2024 $ .Dt EVP_PKEY_KEYGEN 3 .Os .Sh NAME .Nm EVP_PKEY_keygen_init , .Nm EVP_PKEY_keygen , .Nm EVP_PKEY_paramgen_init , .Nm EVP_PKEY_paramgen , .Nm EVP_PKEY_gen_cb , .Nm EVP_PKEY_CTX_set_cb , .Nm EVP_PKEY_CTX_get_cb , .Nm EVP_PKEY_CTX_set0_keygen_info , .Nm EVP_PKEY_CTX_get_keygen_info , .Nm EVP_PKEY_CTX_set_app_data , .Nm EVP_PKEY_CTX_get_app_data .Nd key and parameter generation functions .Sh SYNOPSIS .In openssl/evp.h .Ft int .Fo EVP_PKEY_keygen_init .Fa "EVP_PKEY_CTX *ctx" .Fc .Ft int .Fo EVP_PKEY_keygen .Fa "EVP_PKEY_CTX *ctx" .Fa "EVP_PKEY **ppkey" .Fc .Ft int .Fo EVP_PKEY_paramgen_init .Fa "EVP_PKEY_CTX *ctx" .Fc .Ft int .Fo EVP_PKEY_paramgen .Fa "EVP_PKEY_CTX *ctx" .Fa "EVP_PKEY **ppkey" .Fc .Ft typedef int .Fo EVP_PKEY_gen_cb .Fa "EVP_PKEY_CTX *ctx" .Fc .Ft void .Fo EVP_PKEY_CTX_set_cb .Fa "EVP_PKEY_CTX *ctx" .Fa "EVP_PKEY_gen_cb *cb" .Fc .Ft EVP_PKEY_gen_cb * .Fo EVP_PKEY_CTX_get_cb .Fa "EVP_PKEY_CTX *ctx" .Fc .Ft void .Fo EVP_PKEY_CTX_set0_keygen_info .Fa "EVP_PKEY_CTX *ctx" .Fa "int *dat" .Fa "int datlen" .Fc .Ft int .Fo EVP_PKEY_CTX_get_keygen_info .Fa "EVP_PKEY_CTX *ctx" .Fa "int idx" .Fc .Ft void .Fo EVP_PKEY_CTX_set_app_data .Fa "EVP_PKEY_CTX *ctx" .Fa "void *data" .Fc .Ft void * .Fo EVP_PKEY_CTX_get_app_data .Fa "EVP_PKEY_CTX *ctx" .Fc .Sh DESCRIPTION The .Fn EVP_PKEY_keygen_init function initializes a public key algorithm context using key .Fa ctx->pkey for a key generation operation. .Pp The .Fn EVP_PKEY_keygen function performs a key generation operation. The generated key is written to .Fa ppkey . .Pp The functions .Fn EVP_PKEY_paramgen_init and .Fn EVP_PKEY_paramgen are similar except parameters are generated. .Pp The functions .Fn EVP_PKEY_CTX_set_cb and .Fn EVP_PKEY_CTX_get_cb set and retrieve the key or parameter generation callback, respectively. .Pp The function .Fn EVP_PKEY_CTX_set0_keygen_info sets the parameters associated with the generation operation to the array .Fa dat containing .Ft datlen integer parameters. The caller retains ownership of the .Fa dat array; it will never be freed by the library. .Pp The function .Fn EVP_PKEY_CTX_get_keygen_info returns parameters associated with the generation operation. If .Fa idx is -1, the total number of parameters available is returned. Any non-negative value returns the value of that parameter. .Fn EVP_PKEY_CTX_get_keygen_info with a non-negative value for .Fa idx should only be called within the generation callback. .Pp 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. .Pp The functions .Fn EVP_PKEY_CTX_set_app_data and .Fn 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". .Pp After the call to .Fn EVP_PKEY_keygen_init or .Fn EVP_PKEY_paramgen_init , algorithm specific control operations can be performed to set any appropriate parameters for the operation. .Pp The functions .Fn EVP_PKEY_keygen and .Fn EVP_PKEY_paramgen can be called more than once on the same context if several operations are performed using the same parameters. .Pp 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. .Pp 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 .Vt EVP_PKEY structure. .Pp In OpenSSL, an .Vt 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. .Sh RETURN VALUES .Fn EVP_PKEY_keygen_init , .Fn EVP_PKEY_paramgen_init , .Fn EVP_PKEY_keygen , and .Fn 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. .Pp Callback functions of the type .Fn EVP_PKEY_gen_cb are supposed to return 1 on success or 0 on error. .Pp .Fn EVP_PKEY_CTX_get_cb returns a function pointer to the currently installed callback function or .Dv NULL if no callback function is installed. .Pp .Fn EVP_PKEY_CTX_get_keygen_info returns the number of available parameters if .Fa idx is \-1, one of these parameters if .Fa idx is greater than or equal to zero but less than the number of available parameters, or 0 otherwise. .Sh EXAMPLES Generate a 2048-bit RSA key: .Bd -literal -offset indent #include #include 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 */ .Ed .Pp Generate a key from a set of parameters: .Bd -literal -offset indent #include #include EVP_PKEY_CTX *ctx; EVP_PKEY *pkey = NULL, *param; /* Assumes that param is already set up. */ ctx = EVP_PKEY_CTX_new(param, NULL); if (!ctx) /* Error occurred */ if (EVP_PKEY_keygen_init(ctx) <= 0) /* Error */ /* Generate key */ if (EVP_PKEY_keygen(ctx, &pkey) <= 0) /* Error */ .Ed .Pp Example of generation callback for OpenSSL public key implementations: .Bd -literal -offset indent /* 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; 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 = '\en'; BIO_write(b, &c, 1); (void)BIO_flush(b); return 1; } .Ed .Sh SEE ALSO .Xr EVP_PKEY_CTX_new 3 , .Xr EVP_PKEY_decrypt 3 , .Xr EVP_PKEY_derive 3 , .Xr EVP_PKEY_encrypt 3 , .Xr EVP_PKEY_meth_set_keygen 3 , .Xr EVP_PKEY_sign 3 , .Xr EVP_PKEY_verify 3 , .Xr EVP_PKEY_verify_recover 3 , .Xr X25519 3 .Sh HISTORY These functions first appeared in OpenSSL 1.0.0 and have been available since .Ox 4.9 .