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>.