OSSL_ALGORITHM - OpenSSL Core type to define a fetchable algorithm

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       Licensed under the Apache License 2.0 (the "License").  You may not use this file  except  in  compliance
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3.5.0                                              2025-06-04                               OSSL_ALGORITHM(3SSL)

       The OSSL_ALGORITHM type is a publicstructure 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_ALGORITHMfieldsalgorithm_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.

OSSL_ALGORITHM was added in OpenSSL 3.0

       OSSL_ALGORITHM - OpenSSL Core type to define a fetchable algorithm

Onthesubjectofalgorithmnames
       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.

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

        #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;
        };