doc/man7/provider.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 provider - OpenSSL operation implementation providers

 =head1 SYNOPSIS

 =for openssl generic

 #include <openssl/provider.h>

 =head1 DESCRIPTION

 =head2 General

 A I<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 I<operation> is something one wants to do, such as encryption and
 decryption, key derivation, MAC calculation, signing and verification,
 etc.

 An I<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.

 =head2 Provider

 I<NOTE: This section is mostly interesting for provider authors.>

 A I<provider> offers an initialization function, as a set of base
 functions in the form of an B<OSSL_DISPATCH> array, and by extension,
 a set of B<OSSL_ALGORITHM>s (see L<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 C<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);

 I<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 I<in>.

 I<in> is a dispatch array of base functions offered by the OpenSSL
 libraries, and the available functions are further described in
 L<provider-base(7)>.

 I<*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
 L<provider-base(7)>, and they are the central means of communication
 between the OpenSSL libraries and the provider.

 I<*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.

 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 B<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);

 I<provctx> is the provider specific context that was passed back by
 the initialization function.

 I<operation_id> is an operation identity (see L</Operations> below).

 I<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 B<OSSL_ALGORITHM> is the foundation of any OpenSSL
 library API that uses providers for their implementation, most
 commonly in the I<fetching> type of functions
 (see L</Fetching algorithms> below).

 =head2 Operations

 I<NOTE: This section is mostly interesting for provider authors.>

 Operations are referred to with numbers, via macros with names
 starting with C<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:

 =over 4

 =item Digests

 In the OpenSSL libraries, the corresponding method object is
 B<EVP_MD>.
 The number for this operation is B<OSSL_OP_DIGEST>.
 The functions the provider can offer are described in
 L<provider-digest(7)>

 =item Symmetric ciphers

 In the OpenSSL libraries, the corresponding method object is
 B<EVP_CIPHER>.
 The number for this operation is B<OSSL_OP_CIPHER>.
 The functions the provider can offer are described in
 L<provider-cipher(7)>

 =item Message Authentication Code (MAC)

 In the OpenSSL libraries, the corresponding method object is
 B<EVP_MAC>.
 The number for this operation is B<OSSL_OP_MAC>.
 The functions the provider can offer are described in
 L<provider-mac(7)>

 =item Key Derivation Function (KDF)

 In the OpenSSL libraries, the corresponding method object is
 B<EVP_KDF>.
 The number for this operation is B<OSSL_OP_KDF>.
 The functions the provider can offer are described in
 L<provider-kdf(7)>

 =item Key Exchange

 In the OpenSSL libraries, the corresponding method object is
 B<EVP_KEYEXCH>.
 The number for this operation is B<OSSL_OP_KEYEXCH>.
 The functions the provider can offer are described in
 L<provider-keyexch(7)>

 =item Asymmetric Ciphers

 In the OpenSSL libraries, the corresponding method object is
 B<EVP_ASYM_CIPHER>.
 The number for this operation is B<OSSL_OP_ASYM_CIPHER>.
 The functions the provider can offer are described in
 L<provider-asym_cipher(7)>

 =item Serialization

 In the OpenSSL libraries, the corresponding method object is
 B<OSSL_SERIALIZER>.
 The number for this operation is B<OSSL_OP_SERIALIZER>.
 The functions the provider can offer are described in
 L<provider-serializer(7)>

 =back

 =head2 Fetching algorithms

 =head3 Explicit fetch

 I<NOTE: This section is mostly interesting to OpenSSL users.>

 Users of the OpenSSL libraries never query the provider directly for
 its diverse implementations and dispatch tables.
 Instead, the diverse OpenSSL APIs often have fetching functions that
 do the work, and they return an appropriate method object back to the
 user.
 These functions usually have the name C<APINAME_fetch>, where
 C<APINAME> is the name of the API, for example L<EVP_MD_fetch(3)>.

 These fetching functions follow a fairly common pattern, where three
 arguments are passed:

 =over 4

 =item The library context

 See L<OPENSSL_CTX(3)> for a more detailed description.
 This may be NULL to signify the default (global) library context, or a
 context created by the user.
 Only providers loaded in this library context (see
 L<OSSL_PROVIDER_load(3)>) will be considered by the fetching
 function.

 =item An identifier

 This is most commonly an algorithm name (this is the case for all EVP
 methods), but may also be called something else.

 =for comment For example, an OSSL_STORE implementation would use the
 URI scheme as an identifier.

 =item A property query string

 See L<property(7)> for a more detailed description.
 This is used to select more exactly which providers will get to offer
 an implementation.

 =back

 The method object that is fetched can then be used with diverse other
 functions that use them, for example L<EVP_DigestInit_ex(3)>.

 =head3 Implicit fetch

 I<NOTE: This section is mostly interesting to OpenSSL users.>

 OpenSSL has a number of functions that return a method object with no
 associated implementation, such as L<EVP_sha256(3)>,
 L<EVP_blake2b512(3)> or L<EVP_aes_128_cbc(3)>, which are present for
 compatibility with OpenSSL before version 3.0.

 When they are used with functions like L<EVP_DigestInit_ex(3)> or
 L<EVP_CipherInit_ex(3)>, the actual implementation to be used is
 fetched implicitly using default search criteria.

 Implicit fetching can also occur when a NULL algorithm parameter is
 supplied.
 In this case an algorithm implementation is implicitly fetched using
 default search criteria and an algorithm name that is consistent with
 the type of EVP_PKEY being used.

 =head3 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.

 =head1 OPENSSL PROVIDERS

 OpenSSL comes with a set of providers.

 The algorithms available in each of these providers may vary due to build time
 configuration options. The L<openssl-list(1)> command can be used to list the
 currently available algorithms.

 The names of the algorithms shown from L<openssl-list(1)> can be used as an
 algorithm identifier to the appropriate fetching function.

 =head2 Default provider

 The default provider is built in as part of the F<libcrypto> library.
 Should it be needed (if other providers are loaded and offer
 implementations of the same algorithms), the property "provider=default"
 can be used as a search criterion for these implementations. Some
 non-cryptographic algorithms (such as serializers for loading keys and
 parameters from files) are not FIPS algorithm implementations in themselves but
 support algorithms from the FIPS provider and are allowed for use in "FIPS
 mode". The property "fips=yes" can be used to select such algorithms.

 =head2 FIPS provider

 The FIPS provider is a dynamically loadable module, and must therefore
 be loaded explicitly, either in code or through OpenSSL configuration
 (see L<config(5)>).
 Should it be needed (if other providers are loaded and offer
 implementations of the same algorithms), the property "provider=fips" can
 be used as a search criterion for these implementations. All approved algorithm
 implementations in the FIPS provider can also be selected with the property
 "fips=yes". The FIPS provider also contains a number of non-approved algorithm
 implementations and these can be selected with the property "fips=no".

 =head2 Legacy provider

 The legacy provider is a dynamically loadable module, and must therefore
 be loaded explicitly, either in code or through OpenSSL configuration
 (see L<config(5)>).
 Should it be needed (if other providers are loaded and offer
 implementations of the same algorithms), the property "provider=legacy" can be
 used as a search criterion for these implementations.

 =head2 Null provider

 The null provider is built in as part of the F<libcrypto> library. It contains
 no algorithms in it at all. When fetching algorithms the default provider will
 be automatically loaded if no other provider has been explicitly loaded. To
 prevent that from happening you can explicitly load the null provider.

 =head1 EXAMPLES

 =head2 Fetching

 Fetch any available implementation of SHA2-256 in the default context:

  EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", NULL);
  ...
  EVP_MD_meth_free(md);

 Fetch any available implementation of AES-128-CBC in the default context:

  EVP_CIPHER *cipher = EVP_CIPHER_fetch(NULL, "AES-128-CBC", NULL);
  ...
  EVP_CIPHER_meth_free(cipher);

 Fetch an implementation of SHA2-256 from the default provider in the default
 context:

  EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", "provider=default");
  ...
  EVP_MD_meth_free(md);

 Fetch an implementation of SHA2-256 that is not from the default provider in the
 default context:

  EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", "provider!=default");
  ...
  EVP_MD_meth_free(md);

 Fetch an implementation of SHA2-256 from the default provider in the specified
 context:

  EVP_MD *md = EVP_MD_fetch(ctx, "SHA2-256", "provider=default");
  ...
  EVP_MD_meth_free(md);

 Load the legacy provider into the default context and then fetch an
 implementation of WHIRLPOOL from it:

  /* This only needs to be done once - usually at application start up */
  OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy");

  EVP_MD *md = EVP_MD_fetch(NULL, "WHIRLPOOL", "provider=legacy");
  ...
  EVP_MD_meth_free(md);

 Note that in the above example the property string "provider=legacy" is optional
 since, assuming no other providers have been loaded, the only implementation of
 the "whirlpool" algorithm is in the "legacy" provider. Also note that the
 default provider should be explicitly loaded if it is required in addition to
 other providers:

  /* This only needs to be done once - usually at application start up */
  OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy");
  OSSL_PROVIDER *default = OSSL_PROVIDER_load(NULL, "default");

  EVP_MD *md_whirlpool = EVP_MD_fetch(NULL, "whirlpool", NULL);
  EVP_MD *md_sha256 = EVP_MD_fetch(NULL, "SHA2-256", NULL);
  ...
  EVP_MD_meth_free(md_whirlpool);
  EVP_MD_meth_free(md_sha256);


 =head1 SEE ALSO

 L<EVP_DigestInit_ex(3)>, L<EVP_EncryptInit_ex(3)>,
 L<OPENSSL_CTX(3)>,
 L<EVP_set_default_properties(3)>,
 L<EVP_MD_fetch(3)>,
 L<EVP_CIPHER_fetch(3)>,
 L<EVP_KEYMGMT_fetch(3)>,
 L<openssl-core.h(7)>,
 L<provider-base(7)>,
 L<provider-digest(7)>,
 L<provider-cipher(7)>,
 L<provider-keyexch(7)>

 =head1 HISTORY

 The concept of providers and everything surrounding them was
 introduced in OpenSSL 3.0.

 =head1 COPYRIGHT

 Copyright 2019-2020 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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

	provider - OpenSSL operation implementation providers

	=head1 SYNOPSIS

	=for openssl generic

	#include <openssl/provider.h>

	=head1 DESCRIPTION

	=head2 General

	A I<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 I<operation> is something one wants to do, such as encryption and
	decryption, key derivation, MAC calculation, signing and verification,
	etc.

	An I<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.

	=head2 Provider

	I<NOTE: This section is mostly interesting for provider authors.>

	A I<provider> offers an initialization function, as a set of base
	functions in the form of an B<OSSL_DISPATCH> array, and by extension,
	a set of B<OSSL_ALGORITHM>s (see L<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 C<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);

	I<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 I<in>.

	I<in> is a dispatch array of base functions offered by the OpenSSL
	libraries, and the available functions are further described in
	L<provider-base(7)>.

	I<*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
	L<provider-base(7)>, and they are the central means of communication
	between the OpenSSL libraries and the provider.

	I<*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.

	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 B<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);

	I<provctx> is the provider specific context that was passed back by
	the initialization function.

	I<operation_id> is an operation identity (see L</Operations> below).

	I<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 B<OSSL_ALGORITHM> is the foundation of any OpenSSL
	library API that uses providers for their implementation, most
	commonly in the I<fetching> type of functions
	(see L</Fetching algorithms> below).

	=head2 Operations

	I<NOTE: This section is mostly interesting for provider authors.>

	Operations are referred to with numbers, via macros with names
	starting with C<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:

	=over 4

	=item Digests

	In the OpenSSL libraries, the corresponding method object is
	B<EVP_MD>.
	The number for this operation is B<OSSL_OP_DIGEST>.
	The functions the provider can offer are described in
	L<provider-digest(7)>

	=item Symmetric ciphers

	In the OpenSSL libraries, the corresponding method object is
	B<EVP_CIPHER>.
	The number for this operation is B<OSSL_OP_CIPHER>.
	The functions the provider can offer are described in
	L<provider-cipher(7)>

	=item Message Authentication Code (MAC)

	In the OpenSSL libraries, the corresponding method object is
	B<EVP_MAC>.
	The number for this operation is B<OSSL_OP_MAC>.
	The functions the provider can offer are described in
	L<provider-mac(7)>

	=item Key Derivation Function (KDF)

	In the OpenSSL libraries, the corresponding method object is
	B<EVP_KDF>.
	The number for this operation is B<OSSL_OP_KDF>.
	The functions the provider can offer are described in
	L<provider-kdf(7)>

	=item Key Exchange

	In the OpenSSL libraries, the corresponding method object is
	B<EVP_KEYEXCH>.
	The number for this operation is B<OSSL_OP_KEYEXCH>.
	The functions the provider can offer are described in
	L<provider-keyexch(7)>

	=item Asymmetric Ciphers

	In the OpenSSL libraries, the corresponding method object is
	B<EVP_ASYM_CIPHER>.
	The number for this operation is B<OSSL_OP_ASYM_CIPHER>.
	The functions the provider can offer are described in
	L<provider-asym_cipher(7)>

	=item Serialization

	In the OpenSSL libraries, the corresponding method object is
	B<OSSL_SERIALIZER>.
	The number for this operation is B<OSSL_OP_SERIALIZER>.
	The functions the provider can offer are described in
	L<provider-serializer(7)>

	=back

	=head2 Fetching algorithms

	=head3 Explicit fetch

	I<NOTE: This section is mostly interesting to OpenSSL users.>

	Users of the OpenSSL libraries never query the provider directly for
	its diverse implementations and dispatch tables.
	Instead, the diverse OpenSSL APIs often have fetching functions that
	do the work, and they return an appropriate method object back to the
	user.
	These functions usually have the name C<APINAME_fetch>, where
	C<APINAME> is the name of the API, for example L<EVP_MD_fetch(3)>.

	These fetching functions follow a fairly common pattern, where three
	arguments are passed:

	=over 4

	=item The library context

	See L<OPENSSL_CTX(3)> for a more detailed description.
	This may be NULL to signify the default (global) library context, or a
	context created by the user.
	Only providers loaded in this library context (see
	L<OSSL_PROVIDER_load(3)>) will be considered by the fetching
	function.

	=item An identifier

	This is most commonly an algorithm name (this is the case for all EVP
	methods), but may also be called something else.

	=for comment For example, an OSSL_STORE implementation would use the
	URI scheme as an identifier.

	=item A property query string

	See L<property(7)> for a more detailed description.
	This is used to select more exactly which providers will get to offer
	an implementation.

	=back

	The method object that is fetched can then be used with diverse other
	functions that use them, for example L<EVP_DigestInit_ex(3)>.

	=head3 Implicit fetch

	I<NOTE: This section is mostly interesting to OpenSSL users.>

	OpenSSL has a number of functions that return a method object with no
	associated implementation, such as L<EVP_sha256(3)>,
	L<EVP_blake2b512(3)> or L<EVP_aes_128_cbc(3)>, which are present for
	compatibility with OpenSSL before version 3.0.

	When they are used with functions like L<EVP_DigestInit_ex(3)> or
	L<EVP_CipherInit_ex(3)>, the actual implementation to be used is
	fetched implicitly using default search criteria.

	Implicit fetching can also occur when a NULL algorithm parameter is
	supplied.
	In this case an algorithm implementation is implicitly fetched using
	default search criteria and an algorithm name that is consistent with
	the type of EVP_PKEY being used.

	=head3 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.

	=head1 OPENSSL PROVIDERS

	OpenSSL comes with a set of providers.

	The algorithms available in each of these providers may vary due to build time
	configuration options. The L<openssl-list(1)> command can be used to list the
	currently available algorithms.

	The names of the algorithms shown from L<openssl-list(1)> can be used as an
	algorithm identifier to the appropriate fetching function.

	=head2 Default provider

	The default provider is built in as part of the F<libcrypto> library.
	Should it be needed (if other providers are loaded and offer
	implementations of the same algorithms), the property "provider=default"
	can be used as a search criterion for these implementations. Some
	non-cryptographic algorithms (such as serializers for loading keys and
	parameters from files) are not FIPS algorithm implementations in themselves but
	support algorithms from the FIPS provider and are allowed for use in "FIPS
	mode". The property "fips=yes" can be used to select such algorithms.

	=head2 FIPS provider

	The FIPS provider is a dynamically loadable module, and must therefore
	be loaded explicitly, either in code or through OpenSSL configuration
	(see L<config(5)>).
	Should it be needed (if other providers are loaded and offer
	implementations of the same algorithms), the property "provider=fips" can
	be used as a search criterion for these implementations. All approved algorithm
	implementations in the FIPS provider can also be selected with the property
	"fips=yes". The FIPS provider also contains a number of non-approved algorithm
	implementations and these can be selected with the property "fips=no".

	=head2 Legacy provider

	The legacy provider is a dynamically loadable module, and must therefore
	be loaded explicitly, either in code or through OpenSSL configuration
	(see L<config(5)>).
	Should it be needed (if other providers are loaded and offer
	implementations of the same algorithms), the property "provider=legacy" can be
	used as a search criterion for these implementations.

	=head2 Null provider

	The null provider is built in as part of the F<libcrypto> library. It contains
	no algorithms in it at all. When fetching algorithms the default provider will
	be automatically loaded if no other provider has been explicitly loaded. To
	prevent that from happening you can explicitly load the null provider.

	=head1 EXAMPLES

	=head2 Fetching

	Fetch any available implementation of SHA2-256 in the default context:

	EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", NULL);
	...
	EVP_MD_meth_free(md);

	Fetch any available implementation of AES-128-CBC in the default context:

	EVP_CIPHER *cipher = EVP_CIPHER_fetch(NULL, "AES-128-CBC", NULL);
	...
	EVP_CIPHER_meth_free(cipher);

	Fetch an implementation of SHA2-256 from the default provider in the default
	context:

	EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", "provider=default");
	...
	EVP_MD_meth_free(md);

	Fetch an implementation of SHA2-256 that is not from the default provider in the
	default context:

	EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", "provider!=default");
	...
	EVP_MD_meth_free(md);

	Fetch an implementation of SHA2-256 from the default provider in the specified
	context:

	EVP_MD *md = EVP_MD_fetch(ctx, "SHA2-256", "provider=default");
	...
	EVP_MD_meth_free(md);

	Load the legacy provider into the default context and then fetch an
	implementation of WHIRLPOOL from it:

	/* This only needs to be done once - usually at application start up */
	OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy");

	EVP_MD *md = EVP_MD_fetch(NULL, "WHIRLPOOL", "provider=legacy");
	...
	EVP_MD_meth_free(md);

	Note that in the above example the property string "provider=legacy" is optional
	since, assuming no other providers have been loaded, the only implementation of
	the "whirlpool" algorithm is in the "legacy" provider. Also note that the
	default provider should be explicitly loaded if it is required in addition to
	other providers:

	/* This only needs to be done once - usually at application start up */
	OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy");
	OSSL_PROVIDER *default = OSSL_PROVIDER_load(NULL, "default");

	EVP_MD *md_whirlpool = EVP_MD_fetch(NULL, "whirlpool", NULL);
	EVP_MD *md_sha256 = EVP_MD_fetch(NULL, "SHA2-256", NULL);
	...
	EVP_MD_meth_free(md_whirlpool);
	EVP_MD_meth_free(md_sha256);


	=head1 SEE ALSO

	L<EVP_DigestInit_ex(3)>, L<EVP_EncryptInit_ex(3)>,
	L<OPENSSL_CTX(3)>,
	L<EVP_set_default_properties(3)>,
	L<EVP_MD_fetch(3)>,
	L<EVP_CIPHER_fetch(3)>,
	L<EVP_KEYMGMT_fetch(3)>,
	L<openssl-core.h(7)>,
	L<provider-base(7)>,
	L<provider-digest(7)>,
	L<provider-cipher(7)>,
	L<provider-keyexch(7)>

	=head1 HISTORY

	The concept of providers and everything surrounding them was
	introduced in OpenSSL 3.0.

	=head1 COPYRIGHT

	Copyright 2019-2020 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
	L<https://www.openssl.org/source/license.html>.

	=cut