1OSSL_ALGORITHM(3ossl)               OpenSSL              OSSL_ALGORITHM(3ossl)
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NAME

6       OSSL_ALGORITHM - OpenSSL Core type to define a fetchable algorithm
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SYNOPSIS

9        #include <openssl/core.h>
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11        typedef struct ossl_algorithm_st OSSL_ALGORITHM;
12        struct ossl_algorithm_st {
13            const char *algorithm_names;     /* key */
14            const char *property_definition; /* key */
15            const OSSL_DISPATCH *implementation;
16            const char *algorithm_description;
17        };
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DESCRIPTION

20       The OSSL_ALGORITHM type is a public structure that describes an
21       algorithm that a provider(7) provides.  Arrays of this type are
22       returned by providers on demand from the OpenSSL libraries to describe
23       what algorithms the providers provide implementations of, and with what
24       properties.
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26       Arrays of this type must be terminated with a tuple where
27       algorithm_names is NULL.
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29       This type of array is typically returned by the provider's operation
30       querying function, further described in "Provider Functions" in
31       provider-base(7).
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33   OSSL_ALGORITHM fields
34       algorithm_names
35           This string is a colon separated set of names / identities, and is
36           used by the appropriate fetching functionality (such as
37           EVP_CIPHER_fetch(3), EVP_MD_fetch(3), etc) to find the desired
38           algorithm.
39
40           Multiple names / identities allow a specific algorithm
41           implementation to be fetched multiple ways.  For example, the RSA
42           algorithm has the following known identities:
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44           •   "RSA"
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46           •   "rsaEncryption"
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48               This is the name of the algorithm's OBJECT IDENTIFIER (OID), as
49               given by the PKCS#1 RFC's ASN.1 module <https://www.rfc-
50               editor.org/rfc/rfc8017#appendix-C>
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52           •   1.2.840.113549.1.1.1
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54               This is the OID itself for "rsaEncryption", in canonical
55               decimal text form.
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57           The resulting algorithm_names string would look like this:
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59            "RSA:rsaEncryption:1.2.840.113549.1.1.1"
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61           The OpenSSL libraries use the first of the algorithm names as the
62           main or canonical name, on a per algorithm implementation basis.
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64           See the notes "On the subject of algorithm names" below for a more
65           in depth discussion on algorithm_names and how that may interact
66           with applications and libraries, including OpenSSL's.
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68       property_definition
69           This string defines a set of properties associated with a
70           particular algorithm implementation, and is used by the appropriate
71           fetching functionality (such as EVP_CIPHER_fetch(3),
72           EVP_MD_fetch(3), etc) for a finer grained lookup of an algorithm
73           implementation, which is useful in case multiple implementations of
74           the same algorithm are available.
75
76           See property(7) for a further description of the contents of this
77           string.
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79       implementation
80           Pointer to an OSSL_DISPATCH(3) array, containing pointers to the
81           functions of a particular algorithm implementation.
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83       algorithm_description
84           A string with a short human-readable description of the algorithm.
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NOTES

87   On the subject of algorithm names
88       Providers may find the need to register ASN.1 OIDs for algorithms using
89       OBJ_create(3) (via the core_obj_create upcall described in
90       provider-base(7), because some application or library -- possibly still
91       the OpenSSL libraries, even -- use NIDs to look up algorithms.
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93       In that scenario, you must make sure that the corresponding
94       OSSL_ALGORITHM's algorithm_names includes both the short and the long
95       name.
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97       Most of the time, registering ASN.1 OIDs like this shouldn't be
98       necessary, and applications and libraries are encouraged to use
99       OBJ_obj2txt(3) to get a text representation of the OID, which may be a
100       long or short name for OIDs that are registered, or the OID itself in
101       canonical decimal text form if not (or if OBJ_obj2txt(3) is called with
102       no_name = 1).
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104       It's recommended to make sure that the corresponding OSSL_ALGORITHM's
105       algorithm_names include known names as well as the OID itself in
106       canonical decimal text form.  That should cover all scenarios.
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SEE ALSO

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

113       OSSL_ALGORITHM was added in OpenSSL 3.0
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116       Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
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118       Licensed under the Apache License 2.0 (the "License").  You may not use
119       this file except in compliance with the License.  You can obtain a copy
120       in the file LICENSE in the source distribution or at
121       <https://www.openssl.org/source/license.html>.
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1253.1.1                             2023-08-31             OSSL_ALGORITHM(3ossl)
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