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OSSL_ALGORITHM(3)                   OpenSSL                  OSSL_ALGORITHM(3)



NAME
       OSSL_ALGORITHM - OpenSSL Core type to define a fetchable algorithm

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/core.h>

        typedef struct ossl_algorithm_st OSSL_ALGORITHM;
        struct ossl_algorithm_st {
            const char *algorithm_names;     /* key */
            const char *property_definition; /* key */
            const OSSL_DISPATCH *implementation;
            const char *algorithm_description;
        };

DESCRIPTION
       The OSSL_ALGORITHM type is a public structure that describes an
       algorithm that a provider(7) provides.  Arrays of this type are
       returned by providers on demand from 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 where
       algorithm_names is NULL.

       This type of array is typically returned by the provider's operation
       querying function, further described in "Provider Functions" in
       provider-base(7).

   OSSL_ALGORITHM fields
       algorithm_names
           This string is a colon separated set of names / identities, and is
           used by the appropriate fetching functionality (such as
           EVP_CIPHER_fetch(3), EVP_MD_fetch(3), etc) to find the desired
           algorithm.

           Multiple names / identities allow a specific algorithm
           implementation to be fetched multiple ways.  For example, the RSA
           algorithm has the following known identities:

           ⊕   "RSA"

           ⊕   "rsaEncryption"

               This is the name of the algorithm's OBJECT IDENTIFIER (OID), as
               given by the PKCS#1 RFC's ASN.1 module <https://www.rfc-
               editor.org/rfc/rfc8017#appendix-C>

           ⊕   1.2.840.113549.1.1.1

               This is the OID itself for "rsaEncryption", in canonical
               decimal text form.

           The resulting algorithm_names string would look like this:

            "RSA:rsaEncryption:1.2.840.113549.1.1.1"

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

           See the notes "On the subject of algorithm names" below for a more
           in depth discussion on algorithm_names and how that may interact
           with applications and libraries, including OpenSSL's.

       property_definition
           This string defines a set of properties associated with a
           particular algorithm implementation, and is used by the appropriate
           fetching functionality (such as EVP_CIPHER_fetch(3),
           EVP_MD_fetch(3), etc) for a finer grained lookup of an algorithm
           implementation, which is useful in case multiple implementations of
           the same algorithm are available.

           See property(7) for a further description of the contents of this
           string.

       implementation
           Pointer to an OSSL_DISPATCH(3) array, containing pointers to the
           functions of a particular algorithm implementation.

       algorithm_description
           A string with a short human-readable description of the algorithm.

NOTES
   On the subject of algorithm names
       Providers may find the need to register ASN.1 OIDs for algorithms using
       OBJ_create(3) (via the core_obj_create upcall described in
       provider-base(7), because some application or library -- possibly still
       the OpenSSL libraries, even -- use NIDs to look up algorithms.

       In that scenario, you must make sure that the corresponding
       OSSL_ALGORITHM's algorithm_names includes both the short and the long
       name.

       Most of the time, registering ASN.1 OIDs like this shouldn't be
       necessary, and applications and libraries are encouraged to use
       OBJ_obj2txt(3) to get a text representation of the OID, which may be a
       long or short name for OIDs that are registered, or the OID itself in
       canonical decimal text form if not (or if OBJ_obj2txt(3) is called with
       no_name = 1).

       It's recommended to make sure that the corresponding OSSL_ALGORITHM's
       algorithm_names include known names as well as the OID itself in
       canonical decimal text form.  That should cover all scenarios.

SEE ALSO
       crypto(7), provider-base(7), openssl-core.h(7),
       openssl-core_dispatch.h(7), OSSL_DISPATCH(3)

HISTORY
       OSSL_ALGORITHM was added in OpenSSL 3.0

COPYRIGHT
       Copyright 2022 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>.



3.0.12                            2023-05-07                 OSSL_ALGORITHM(3)