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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_GETTABLE_PARAMS 3ossl"
.TH EVP_PKEY_GETTABLE_PARAMS 3ossl "2023-09-19" "3.0.11" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_PKEY_gettable_params, EVP_PKEY_get_params,
EVP_PKEY_get_int_param, EVP_PKEY_get_size_t_param,
EVP_PKEY_get_bn_param, EVP_PKEY_get_utf8_string_param,
EVP_PKEY_get_octet_string_param
\&\- retrieve key parameters from a key
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& const OSSL_PARAM *EVP_PKEY_gettable_params(EVP_PKEY *pkey);
\& int EVP_PKEY_get_params(const EVP_PKEY *pkey, OSSL_PARAM params[]);
\& int EVP_PKEY_get_int_param(const EVP_PKEY *pkey, const char *key_name,
\&                            int *out);
\& int EVP_PKEY_get_size_t_param(const EVP_PKEY *pkey, const char *key_name,
\&                               size_t *out);
\& int EVP_PKEY_get_bn_param(const EVP_PKEY *pkey, const char *key_name,
\&                           BIGNUM **bn);
\& int EVP_PKEY_get_utf8_string_param(const EVP_PKEY *pkey, const char *key_name,
\&                                    char *str, size_t max_buf_sz,
\&                                    size_t *out_len);
\& int EVP_PKEY_get_octet_string_param(const EVP_PKEY *pkey, const char *key_name,
\&                                     unsigned char *buf, size_t max_buf_sz,
\&                                     size_t *out_len);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
See \s-1\fBOSSL_PARAM\s0\fR\|(3) for information about parameters.
.PP
\&\fBEVP_PKEY_get_params()\fR retrieves parameters from the key \fIpkey\fR, according to
the contents of \fIparams\fR.
.PP
\&\fBEVP_PKEY_gettable_params()\fR returns a constant list of \fIparams\fR indicating
the names and types of key parameters that can be retrieved.
.PP
An \s-1\fBOSSL_PARAM\s0\fR\|(3) of type \fB\s-1OSSL_PARAM_INTEGER\s0\fR or
\&\fB\s-1OSSL_PARAM_UNSIGNED_INTEGER\s0\fR is of arbitrary length. Such a parameter can be
obtained using any of the functions \fBEVP_PKEY_get_int_param()\fR,
\&\fBEVP_PKEY_get_size_t_param()\fR or \fBEVP_PKEY_get_bn_param()\fR. Attempting to
obtain an integer value that does not fit into a native C \fBint\fR type will cause
\&\fBEVP_PKEY_get_int_param()\fR to fail. Similarly attempting to obtain an integer
value that is negative or does not fit into a native C \fBsize_t\fR type using
\&\fBEVP_PKEY_get_size_t_param()\fR will also fail.
.PP
\&\fBEVP_PKEY_get_int_param()\fR retrieves a key \fIpkey\fR integer value \fI*out\fR
associated with a name of \fIkey_name\fR if it fits into \f(CW\*(C`int\*(C'\fR type. For
parameters that do not fit into \f(CW\*(C`int\*(C'\fR use \fBEVP_PKEY_get_bn_param()\fR.
.PP
\&\fBEVP_PKEY_get_size_t_param()\fR retrieves a key \fIpkey\fR size_t value \fI*out\fR
associated with a name of \fIkey_name\fR if it fits into \f(CW\*(C`size_t\*(C'\fR type. For
parameters that do not fit into \f(CW\*(C`size_t\*(C'\fR use \fBEVP_PKEY_get_bn_param()\fR.
.PP
\&\fBEVP_PKEY_get_bn_param()\fR retrieves a key \fIpkey\fR \s-1BIGNUM\s0 value \fI**bn\fR
associated with a name of \fIkey_name\fR. If \fI*bn\fR is \s-1NULL\s0 then the \s-1BIGNUM\s0
is allocated by the method.
.PP
\&\fBEVP_PKEY_get_utf8_string_param()\fR get a key \fIpkey\fR \s-1UTF8\s0 string value into a
buffer \fIstr\fR of maximum size \fImax_buf_sz\fR associated with a name of
\&\fIkey_name\fR.  The maximum size must be large enough to accommodate the string
value including a terminating \s-1NUL\s0 byte, or this function will fail.
If \fIout_len\fR is not \s-1NULL,\s0 \fI*out_len\fR is set to the length of the string
not including the terminating \s-1NUL\s0 byte. The required buffer size not including
the terminating \s-1NUL\s0 byte can be obtained from \fI*out_len\fR by calling the
function with \fIstr\fR set to \s-1NULL.\s0
.PP
\&\fBEVP_PKEY_get_octet_string_param()\fR get a key \fIpkey\fR's octet string value into a
buffer \fIbuf\fR of maximum size \fImax_buf_sz\fR associated with a name of \fIkey_name\fR.
If \fIout_len\fR is not \s-1NULL,\s0 \fI*out_len\fR is set to the length of the contents.
The required buffer size can be obtained from \fI*out_len\fR by calling the
function with \fIbuf\fR set to \s-1NULL.\s0
.SH "NOTES"
.IX Header "NOTES"
These functions only work for \fB\s-1EVP_PKEY\s0\fRs that contain a provider side key.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_gettable_params()\fR returns \s-1NULL\s0 on error or if it is not supported.
.PP
All other methods return 1 if a value associated with the key's \fIkey_name\fR was
successfully returned, or 0 if there was an error.
An error may be returned by methods \fBEVP_PKEY_get_utf8_string_param()\fR and
\&\fBEVP_PKEY_get_octet_string_param()\fR if \fImax_buf_sz\fR is not big enough to hold the
value.  If \fIout_len\fR is not \s-1NULL,\s0 \fI*out_len\fR will be assigned the required
buffer size to hold the value.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
.Vb 1
\& #include <openssl/evp.h>
\&
\& char curve_name[64];
\& unsigned char pub[256];
\& BIGNUM *bn_priv = NULL;
\&
\& /*
\&  * NB: assumes \*(Aqkey\*(Aq is set up before the next step. In this example the key
\&  * is an EC key.
\&  */
\&
\& if (!EVP_PKEY_get_utf8_string_param(key, OSSL_PKEY_PARAM_GROUP_NAME,
\&                                     curve_name, sizeof(curve_name), &len)) {
\&   /* Error */
\& }
\& if (!EVP_PKEY_get_octet_string_param(key, OSSL_PKEY_PARAM_PUB_KEY,
\&                                      pub, sizeof(pub), &len)) {
\&     /* Error */
\& }
\& if (!EVP_PKEY_get_bn_param(key, OSSL_PKEY_PARAM_PRIV_KEY, &bn_priv)) {
\&     /* Error */
\& }
\&
\& BN_clear_free(bn_priv);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3), \fBprovider\-keymgmt\fR\|(7), \s-1\fBOSSL_PARAM\s0\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
These functions were added in OpenSSL 3.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2020\-2023 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.