NAME

       openssl/core.h - OpenSSL Core types

SYNOPSIS

        #include <openssl/core.h>

DESCRIPTION

       The <openssl/core.h> header defines a number of public types that are used to communicate between the
       OpenSSL libraries and implementation providers.  These types are designed to minimise the need for
       intimate knowledge of internal structures between the OpenSSL libraries and the providers.

       The types are:

       OSSL_DISPATCH
           This  type  is  a  tuple  of  function identity and function pointer.  Arrays of this type are passed
           between the OpenSSL libraries and the providers to describe what functionality one side  provides  to
           the  other.   Arrays  of  this type must be terminated with a tuple having function identity zero and
           function pointer NULL.

           The  available  function  identities  and  corresponding   function   signatures   are   defined   in
           openssl-core_dispatch.h(7).

           Any  function  identity  not  recognised by the recipient of this type will be ignored.  This ensures
           that providers built with one OpenSSL version in mind will  work  together  with  any  other  OpenSSL
           version that supports this mechanism.

       OSSL_ITEM
           This  type  is a tuple of integer and pointer.  It's a generic type used as a generic descriptor, its
           exact meaning being defined by how it's used.  Arrays of this type are  passed  between  the  OpenSSL
           libraries  and  the  providers, and must be terminated with a tuple where the integer is zero and the
           pointer NULL.

       OSSL_ALGORITHM
           This type is a tuple of an algorithm name (string), a property definition  (string)  and  a  dispatch
           table  (array  of OSSL_DISPATCH).  Arrays of this type are passed on demand from the providers to the
           OpenSSL libraries to describe what algorithms the providers provide implementations of, and with what
           properties.  Arrays of this type must be terminated with a tuple having function  identity  zero  and
           function pointer NULL.

           The algorithm names and property definitions are defined by the providers.

           The  OpenSSL  libraries  use the first of the algorithm names as the main or canonical name, on a per
           algorithm implementation basis.

       OSSL_PARAM
           This type is a structure that allows passing arbitrary object data between two parties that  have  no
           or  very  little  shared  knowledge about their respective internal structures for that object.  It's
           normally passed in arrays, where the array is terminated with an element where all  fields  are  zero
           (for non-pointers) or NULL (for pointers).

           These  arrays  can  be used to set parameters for some object, to request parameters, and to describe
           parameters.

           OSSL_PARAM is further described in OSSL_PARAM(3)

       OSSL_CALLBACK
           This is a function type for a generic feedback callback function:

               typedef int (OSSL_CALLBACK)(const OSSL_PARAM params[], void *arg);

           A function that takes a pointer of this type should also take a pointer to caller data.  When calling
           this callback, the function is expected to build an OSSL_PARAM array of data it wants or is  expected
           to pass back, and pass that as params, as well as the caller data pointer it received, as arg.

       OSSL_PASSPHRASE_CALLBACK
           This is a function type for a generic pass phrase callback function:

               typedef int (OSSL_PASSPHRASE_CALLBACK)(char *pass, size_t pass_size,
                                                      size_t *pass_len,
                                                      const OSSL_PARAM params[],
                                                      void *arg);

           This  callback  can  be used to prompt the user for a passphrase.  When calling it, a buffer to store
           the pass phrase needs to be given with pass, and its size with pass_size.  The length of the prompted
           pass phrase will be given back in *pass_len.

           Additional parameters can be passed with the OSSL_PARAM array params.

           A function that takes a pointer of this type should also take a pointer to caller data, which  should
           be passed as arg to this callback.

SEE ALSO

       openssl-core_dispatch.h(7)

HISTORY

       The types described here were added in OpenSSL 3.0.

COPYRIGHT

       Copyright 2019-2021 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>.

3.0.2                                              2025-09-18                               OPENSSL-CORE.H(7SSL)