=pod

=head1 NAME

provider-skeymgmt - The SKEYMGMT library E<lt>-E<gt> provider functions

=head1 SYNOPSIS

 #include <openssl/core_dispatch.h>

 /*
  * None of these are actual functions, but are displayed like this for
  * the function signatures for functions that are offered as function
  * pointers in OSSL_DISPATCH arrays.
  */

 /* Key object destruction */
 void OSSL_FUNC_skeymgmt_free(void *keydata);

 /* Key object import and export functions */
 void *OSSL_FUNC_skeymgmt_import(void *provctx, int selection,
                                 const OSSL_PARAM params[]);
 int OSSL_FUNC_skeymgmt_export(void *keydata, int selection,
                               OSSL_CALLBACK *param_cb, void *cbarg);
 void *OSSL_FUNC_skeymgmt_generate(void *provctx,
                                   const OSSL_PARAM params[]);
 const OSSL_PARAM *OSSL_FUNC_skeymgmt_gen_settable_params(void *provctx);
 const OSSL_PARAM *OSSL_FUNC_skeymgmt_imp_settable_params(void *provctx);
 const char *OSSL_FUNC_skeymgmt_get_key_id(void *keydata);

=head1 DESCRIPTION

The SKEYMGMT operation doesn't have much public visibility in the OpenSSL
libraries, rather it is an internal operation that is designed to work
with operations that use opaque symmetric keys objects.

The SKEYMGMT operation shares knowledge with the operations it works with,
therefore the SKEYMGMT and the algorithms which use it must belong to the same
provider.  The OpenSSL libraries will ensure that they do.

The primary responsibility of the SKEYMGMT operation is to hold the
provider side key data for the OpenSSL library EVP_SKEY structure.

All "functions" mentioned here are passed as function pointers between
F<libcrypto> and the provider in L<OSSL_DISPATCH(3)> arrays via
L<OSSL_ALGORITHM(3)> arrays that are returned by the provider's
provider_query_operation() function
(see L<provider-base(7)/Provider Functions>).

All these "functions" have a corresponding function type definition
named B<OSSL_FUNC_{name}_fn>, and a helper function to retrieve the
function pointer from a L<OSSL_DISPATCH(3)> element named
B<OSSL_FUNC_{name}>.

L<OSSL_DISPATCH(3)> arrays are indexed by numbers that are provided as
macros in L<openssl-core_dispatch.h(7)>, as follows:

 OSSL_FUNC_skeymgmt_free                 OSSL_FUNC_SKEYMGMT_FREE

 OSSL_FUNC_skeymgmt_import               OSSL_FUNC_SKEYMGMT_IMPORT
 OSSL_FUNC_skeymgmt_export               OSSL_FUNC_SKEYMGMT_EXPORT

 OSSL_FUNC_skeymgmt_generate             OSSL_FUNC_SKEYMGMT_GENERATE

 OSSL_FUNC_skeymgmt_get_key_id           OSSL_FUNC_SKEYMGMT_GET_KEY_ID
 OSSL_FUNC_skeymgmt_imp_settable_params  OSSL_FUNC_SKEYMGMT_IMP_SETTABLE_PARAMS
 OSSL_FUNC_skeymgmt_gen_settable_params  OSSL_FUNC_SKEYMGMT_GEN_SETTABLE_PARAMS

The SKEYMGMT management is inspired by KEYMGMT but is simpler.

=head2 Key Objects

A key object is a collection of data for an symmetric key, and is
represented as I<keydata> in this manual.

The exact contents of a key object are defined by the provider, and it
is assumed that different operations in one and the same provider use
the exact same structure to represent this collection of data, so that
for example, a key object that has been created using the SKEYMGMT
interface can be passed as is to other algorithms from the same provider
operations, such as OSSL_FUNC_mac_init_opaque() (see
L<provider-mac(7)>).

With the export SKEYMGMT function, it's possible to select a specific
subset of data to handle, governed by the bits in a I<selection>
indicator.  The bits are:

=over 4

=item B<OSSL_SKEYMGMT_SELECT_SECRET_KEY>

Indicating that the secret key raw bytes in a key object should be
included.

=item B<OSSL_SKEYMGMT_SELECT_PARAMETERS>

Indicating that the parameters in a key object should be
included.

=back

Combined selector bits are also defined for easier use:

=over 4

=item B<OSSL_SKEYMGMT_SELECT_ALL>

Indicating that everything in a key object should be included.

=back

The exact interpretation of those bits or how they combine is left to
each function where you can specify a selector.

=head2 Destructing Function

OSSL_FUNC_skeymgmt_free() should free the passed I<keydata>.

=head2 Key Object Import and Export Functions

OSSL_FUNC_skeymgmt_import() should import data into I<keydata> with values
taken from the L<OSSL_PARAM(3)> array I<params>. It allocates the I<keydata>
object (there is no separate allocation function).

OSSL_FUNC_skeymgmt_imp_settable_params() returns a list of parameters that can
be provided to the OSSL_FUNC_skeymgmt_import() function.

OSSL_FUNC_skeymgmt_export() should extract values indicated by I<selection>
from I<keydata>, create an L<OSSL_PARAM(3)> array with them and call
I<param_cb> with that array as well as the given I<cbarg>.
The passed L<OSSL_PARAM(3)> array is transient and is freed upon the return from I<param_cb>.

=head2 Key Object Generation Functions

OSSL_FUNC_skeymgmt_generate() creates a new key according to the values
taken from the L<OSSL_PARAM(3)> array I<params>. It allocates the I<keydata>
object.

OSSL_FUNC_skeymgmt_gen_settable_params() returns a list of parameters that can
be provided to the OSSL_FUNC_skeymgmt_generate() function.

=head2 Key Object Information functions

OSSL_FUNC_skeymgmt_get_key_id() returns a NUL-terminated string identifying the
particular key. The returned string will be freed by a call to EVP_SKEY_free()
so callers need to copy it themselves if they want to preserve the value past
the key lifetime.  The purpose of this function is providing a printable string
that can help users to access the specific key.  The content of this string is
provider-specific.

=head2 Common Import and Export Parameters

See L<OSSL_PARAM(3)> for further details on the parameters structure.

Common information parameters currently recognised by built-in
skeymgmt algorithms are as follows:

=over 4

=item "raw-bytes" (B<SKEY_PARAM_RAW_BYTES>) <octet string>

The value represents symmetric key as a byte array.

=item "key-length" (B<SKEY_PARAM_KEY_LENGTH>) <integer>

The value is the byte length of the given key.

=back

=head1 RETURN VALUES

OSSL_FUNC_skeymgmt_import() and OSSL_FUNC_skeymgmt_generate() return a pointer
to an allocated object on success and NULL on error.

OSSL_FUNC_skeymgmt_export() returns 1 for success or 0 on error.

OSSL_FUNC_skeymgmt_get_key_id() returns a pointer to a 0-terminated string or NULL.

OSSL_FUNC_skeymgmt_gen_settable_params() and OSSL_FUNC_skeymgmt_imp_settable_params()
return references to an array of B<OSSL_PARAM> which can be NULL if there are
no settable parameters.

=head1 SEE ALSO

L<provider(7)>, L<EVP_SKEY(3)>, L<EVP_KEYMGMT(3)>

=head1 HISTORY

The SKEYMGMT interface was introduced in OpenSSL 3.5.

=head1 COPYRIGHT

Copyright 2024-2025 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
L<https://www.openssl.org/source/license.html>.

=cut
