OSSL_ALGORITHM(3SSL) OpenSSL OSSL_ALGORITHM(3SSL)
NAME
OSSL_ALGORITHM - OpenSSL Core type to define a fetchable algorithm
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>.
3.5.7 2026-06-09 OSSL_ALGORITHM(3SSL)
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