PROVIDER(7SSL) OpenSSL PROVIDER(7SSL)
NAME
provider - OpenSSL operation implementation providers
SYNOPSIS
#include <openssl/provider.h>
DESCRIPTION
General
This page contains information useful to provider authors.
A provider, in OpenSSL terms, is a unit of code that provides one or
more implementations for various operations for diverse algorithms that
one might want to perform.
An operation is something one wants to do, such as encryption and
decryption, key derivation, MAC calculation, signing and verification,
etc.
An algorithm is a named method to perform an operation. Very often,
the algorithms revolve around cryptographic operations, but may also
revolve around other types of operation, such as managing certain types
of objects.
See crypto(7) for further details.
Provider
A provider offers an initialization function, as a set of base
functions in the form of an OSSL_DISPATCH(3) array, and by extension, a
set of OSSL_ALGORITHM(3)s (see openssl-core.h(7)). It may be a
dynamically loadable module, or may be built-in, in OpenSSL libraries
or in the application. If it's a dynamically loadable module, the
initialization function must be named "OSSL_provider_init" and must be
exported. If it's built-in, the initialization function may have any
name.
The initialization function must have the following signature:
int NAME(const OSSL_CORE_HANDLE *handle,
const OSSL_DISPATCH *in, const OSSL_DISPATCH **out,
void **provctx);
handle is the OpenSSL library object for the provider, and works as a
handle for everything the OpenSSL libraries need to know about the
provider. For the provider itself, it is passed to some of the
functions given in the dispatch array in.
in is a dispatch array of base functions offered by the OpenSSL
libraries, and the available functions are further described in
provider-base(7).
*out must be assigned a dispatch array of base functions that the
provider offers to the OpenSSL libraries. The functions that may be
offered are further described in provider-base(7), and they are the
central means of communication between the OpenSSL libraries and the
provider.
*provctx should be assigned a provider specific context to allow the
provider multiple simultaneous uses. This pointer will be passed to
various operation functions offered by the provider.
Note that the provider will not be made available for applications to
use until the initialization function has completed and returned
successfully.
One of the functions the provider offers to the OpenSSL libraries is
the central mechanism for the OpenSSL libraries to get access to
operation implementations for diverse algorithms. Its referred to with
the number OSSL_FUNC_PROVIDER_QUERY_OPERATION and has the following
signature:
const OSSL_ALGORITHM *provider_query_operation(void *provctx,
int operation_id,
const int *no_store);
provctx is the provider specific context that was passed back by the
initialization function.
operation_id is an operation identity (see "Operations" below).
no_store is a flag back to the OpenSSL libraries which, when nonzero,
signifies that the OpenSSL libraries will not store a reference to the
returned data in their internal store of implementations.
The returned OSSL_ALGORITHM(3) is the foundation of any OpenSSL library
API that uses providers for their implementation, most commonly in the
fetching type of functions (see "ALGORITHM FETCHING" in crypto(7)).
Operations
Operations are referred to with numbers, via macros with names starting
with "OSSL_OP_".
With each operation comes a set of defined function types that a
provider may or may not offer, depending on its needs.
Currently available operations are:
Digests
In the OpenSSL libraries, the corresponding method object is
EVP_MD. The number for this operation is OSSL_OP_DIGEST. The
functions the provider can offer are described in
provider-digest(7).
Symmetric ciphers
In the OpenSSL libraries, the corresponding method object is
EVP_CIPHER. The number for this operation is OSSL_OP_CIPHER. The
functions the provider can offer are described in
provider-cipher(7).
Message Authentication Code (MAC)
In the OpenSSL libraries, the corresponding method object is
EVP_MAC. The number for this operation is OSSL_OP_MAC. The
functions the provider can offer are described in provider-mac(7).
Key Derivation Function (KDF)
In the OpenSSL libraries, the corresponding method object is
EVP_KDF. The number for this operation is OSSL_OP_KDF. The
functions the provider can offer are described in provider-kdf(7).
Key Exchange
In the OpenSSL libraries, the corresponding method object is
EVP_KEYEXCH. The number for this operation is OSSL_OP_KEYEXCH.
The functions the provider can offer are described in
provider-keyexch(7).
Asymmetric Ciphers
In the OpenSSL libraries, the corresponding method object is
EVP_ASYM_CIPHER. The number for this operation is
OSSL_OP_ASYM_CIPHER. The functions the provider can offer are
described in provider-asym_cipher(7).
Asymmetric Key Encapsulation
In the OpenSSL libraries, the corresponding method object is
EVP_KEM. The number for this operation is OSSL_OP_KEM. The
functions the provider can offer are described in provider-kem(7).
Encoding
In the OpenSSL libraries, the corresponding method object is
OSSL_ENCODER. The number for this operation is OSSL_OP_ENCODER.
The functions the provider can offer are described in
provider-encoder(7).
Decoding
In the OpenSSL libraries, the corresponding method object is
OSSL_DECODER. The number for this operation is OSSL_OP_DECODER.
The functions the provider can offer are described in
provider-decoder(7).
Random Number Generation
The number for this operation is OSSL_OP_RAND. The functions the
provider can offer for random number generation are described in
provider-rand(7).
Key Management
The number for this operation is OSSL_OP_KEYMGMT. The functions
the provider can offer for key management are described in
provider-keymgmt(7).
Signing and Signature Verification
The number for this operation is OSSL_OP_SIGNATURE. The functions
the provider can offer for digital signatures are described in
provider-signature(7).
Store Management
The number for this operation is OSSL_OP_STORE. The functions the
provider can offer for store management are described in
provider-storemgmt(7).
Algorithm naming
Algorithm names are case insensitive. Any particular algorithm can have
multiple aliases associated with it. The canonical OpenSSL naming
scheme follows this format:
ALGNAME[VERSION?][-SUBNAME[VERSION?]?][-SIZE?][-MODE?]
VERSION is only present if there are multiple versions of an algorithm
(e.g. MD2, MD4, MD5). It may be omitted if there is only one version.
SUBNAME may be present where multiple algorithms are combined together,
e.g. MD5-SHA1.
SIZE is only present if multiple versions of an algorithm exist with
different sizes (e.g. AES-128-CBC, AES-256-CBC)
MODE is only present where applicable.
Other aliases may exist for example where standards bodies or common
practice use alternative names or names that OpenSSL has used
historically.
OPENSSL PROVIDERS
OpenSSL provides a number of its own providers. These are the default,
base, fips, legacy and null providers. See crypto(7) for an overview of
these providers.
SEE ALSO
EVP_DigestInit_ex(3), EVP_EncryptInit_ex(3), OSSL_LIB_CTX(3),
EVP_set_default_properties(3), EVP_MD_fetch(3), EVP_CIPHER_fetch(3),
EVP_KEYMGMT_fetch(3), openssl-core.h(7), provider-base(7),
provider-digest(7), provider-cipher(7), provider-keyexch(7)
HISTORY
The concept of providers and everything surrounding them was introduced
in OpenSSL 3.0.
COPYRIGHT
Copyright 2019-2022 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>.
3.0.13 2025-09-18 PROVIDER(7SSL)
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