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✏️ Editing: EVP_PKEVP_PKEY_CTX_set_app_data.3

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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_keygen 3"
.TH EVP_PKEY_keygen 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "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_PKEVP_PKEY_CTX_set_app_data, EVP_PKEY_CTX_get_app_data \- key and parameter generation functions
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBEVP_PKEY_keygen_init()\fR function initializes a public key algorithm
context using key \fBpkey\fR for a key genration operation.
.PP
The \fBEVP_PKEY_keygen()\fR function performs a key generation operation, the 
generated key is written to \fBppkey\fR.
.PP
The functions \fBEVP_PKEY_paramgen_init()\fR and \fBEVP_PKEY_paramgen()\fR are similar
except parameters are generated.
.PP
The function \fBEVP_PKEY_set_cb()\fR sets the key or parameter generation callback
to \fBcb\fR. The function \fBEVP_PKEY_CTX_get_cb()\fR returns the key or parameter
generation callback.
.PP
The function \fBEVP_PKEY_CTX_get_keygen_info()\fR returns parameters associated
with the generation operation. If \fBidx\fR is \-1 the total number of
parameters available is returned. Any non negative value returns the value of
that parameter. \fBEVP_PKEY_CTX_gen_keygen_info()\fR with a non-negative value for
\&\fBidx\fR should only be called within the generation callback.
.PP
If the callback returns 0 then the key genration operation is aborted and an
error occurs. This might occur during a time consuming operation where
a user clicks on a \*(L"cancel\*(R" button.
.PP
The functions \fBEVP_PKEY_CTX_set_app_data()\fR and \fBEVP_PKEY_CTX_get_app_data()\fR 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 \*(L"progress dialog\*(R".
.SH "NOTES"
.IX Header "NOTES"
After the call to \fBEVP_PKEY_keygen_init()\fR or \fBEVP_PKEY_paramgen_init()\fR algorithm
specific control operations can be performed to set any appropriate parameters
for the operation.
.PP
The functions \fBEVP_PKEY_keygen()\fR and \fBEVP_PKEY_paramgen()\fR 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 specifiic 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. \s-1EC\s0 with a supplied named curve) the \*(L"generation\*(R"
option merely sets the appropriate fields in an \s-1EVP_PKEY\s0 structure.
.PP
In OpenSSL an \s-1EVP_PKEY\s0 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 \*(L"key pair\*(R". A private key can be used
in functions which require the use of a public key or parameters.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_keygen_init()\fR, \fBEVP_PKEY_paramgen_init()\fR, \fBEVP_PKEY_keygen()\fR and
\&\fBEVP_PKEY_paramgen()\fR 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.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Generate a 2048 bit \s-1RSA\s0 key:
.PP
.Vb 2
\& #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 */
.Ve
.PP
Generate a key from a set of parameters:
.PP
.Vb 2
\& #include <openssl/evp.h>
\& #include <openssl/rsa.h>
\&
\& EVP_PKEY_CTX *ctx;
\& EVP_PKEY *pkey = NULL, *param;
\& /* Assumed param is set up already */
\& ctx = EVP_PKEY_CTX_new(param);
\& if (!ctx)
\&        /* Error occurred */
\& if (EVP_PKEY_keygen_init(ctx) <= 0)
\&        /* Error */
\&
\& /* Generate key */
\& if (EVP_PKEY_keygen(ctx, &pkey) <= 0)
\&        /* Error */
.Ve
.PP
Example of generation callback for OpenSSL public key implementations:
.PP
.Vb 1
\& /* 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=\*(Aq*\*(Aq;
\&        BIO *b = EVP_PKEY_CTX_get_app_data(ctx);
\&        int p;
\&        p = EVP_PKEY_CTX_get_keygen_info(ctx, 0);
\&        if (p == 0) c=\*(Aq.\*(Aq;
\&        if (p == 1) c=\*(Aq+\*(Aq;
\&        if (p == 2) c=\*(Aq*\*(Aq;
\&        if (p == 3) c=\*(Aq\en\*(Aq;
\&        BIO_write(b,&c,1);
\&        (void)BIO_flush(b);
\&        return 1;
\&        }
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_encrypt\fR\|(3),
\&\fBEVP_PKEY_decrypt\fR\|(3),
\&\fBEVP_PKEY_sign\fR\|(3),
\&\fBEVP_PKEY_verify\fR\|(3),
\&\fBEVP_PKEY_verify_recover\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
These functions were first added to OpenSSL 1.0.0.

MR SKB