5 provider - OpenSSL operation implementation providers
11 #include <openssl/provider.h>
17 A I<provider>, in OpenSSL terms, is a unit of code that provides one
18 or more implementations for various operations for diverse algorithms
19 that one might want to perform.
21 An I<operation> is something one wants to do, such as encryption and
22 decryption, key derivation, MAC calculation, signing and verification,
25 An I<algorithm> is a named method to perform an operation.
26 Very often, the algorithms revolve around cryptographic operations,
27 but may also revolve around other types of operation, such as managing
28 certain types of objects.
32 I<NOTE: This section is mostly interesting for provider authors.>
34 A I<provider> offers an initialization function, as a set of base
35 functions in the form of an B<OSSL_DISPATCH> array, and by extension,
36 a set of B<OSSL_ALGORITHM>s (see L<openssl-core.h(7)>).
37 It may be a dynamically loadable module, or may be built-in, in
38 OpenSSL libraries or in the application.
39 If it's a dynamically loadable module, the initialization function
40 must be named C<OSSL_provider_init> and must be exported.
41 If it's built-in, the initialization function may have any name.
43 The initialization function must have the following signature:
45 int NAME(const OSSL_PROVIDER *provider,
46 const OSSL_DISPATCH *in, const OSSL_DISPATCH **out,
49 I<provider> is the OpenSSL library object for the provider, and works
50 as a handle for everything the OpenSSL libraries need to know about
52 For the provider itself, it may hold some interesting information,
53 and is also passed to some of the functions given in the dispatch
56 I<in> is a dispatch array of base functions offered by the OpenSSL
57 libraries, and the available functions are further described in
60 I<*out> must be assigned a dispatch array of base functions that the
61 provider offers to the OpenSSL libraries.
62 The functions that may be offered are further described in
63 L<provider-base(7)>, and they are the central means of communication
64 between the OpenSSL libraries and the provider.
66 I<*provctx> should be assigned a provider specific context to allow
67 the provider multiple simultaneous uses.
68 This pointer will be passed to various operation functions offered by
71 One of the functions the provider offers to the OpenSSL libraries is
72 the central mechanism for the OpenSSL libraries to get access to
73 operation implementations for diverse algorithms.
74 Its referred to with the number B<OSSL_FUNC_PROVIDER_QUERY_OPERATION>
75 and has the following signature:
77 const OSSL_ALGORITHM *provider_query_operation(void *provctx,
81 I<provctx> is the provider specific context that was passed back by
82 the initialization function.
84 I<operation_id> is an operation identity (see L</Operations> below).
86 I<no_store> is a flag back to the OpenSSL libraries which, when
87 nonzero, signifies that the OpenSSL libraries will not store a
88 reference to the returned data in their internal store of
91 The returned B<OSSL_ALGORITHM> is the foundation of any OpenSSL
92 library API that uses providers for their implementation, most
93 commonly in the I<fetching> type of functions
94 (see L</Fetching algorithms> below).
98 I<NOTE: This section is mostly interesting for provider authors.>
100 Operations are referred to with numbers, via macros with names
101 starting with C<OSSL_OP_>.
103 With each operation comes a set of defined function types that a
104 provider may or may not offer, depending on its needs.
106 Currently available operations are:
112 In the OpenSSL libraries, the corresponding method object is
114 The number for this operation is B<OSSL_OP_DIGEST>.
115 The functions the provider can offer are described in
116 L<provider-digest(7)>
118 =item Symmetric ciphers
120 In the OpenSSL libraries, the corresponding method object is
122 The number for this operation is B<OSSL_OP_CIPHER>.
123 The functions the provider can offer are described in
124 L<provider-cipher(7)>
126 =item Message Authentication Code (MAC)
128 In the OpenSSL libraries, the corresponding method object is
130 The number for this operation is B<OSSL_OP_MAC>.
131 The functions the provider can offer are described in
134 =item Key Derivation Function (KDF)
136 In the OpenSSL libraries, the corresponding method object is
138 The number for this operation is B<OSSL_OP_KDF>.
139 The functions the provider can offer are described in
144 In the OpenSSL libraries, the corresponding method object is
146 The number for this operation is B<OSSL_OP_KEYEXCH>.
147 The functions the provider can offer are described in
148 L<provider-keyexch(7)>
152 In the OpenSSL libraries, the corresponding method object is
154 The number for this operation is B<OSSL_OP_SERIALIZER>.
155 The functions the provider can offer are described in
156 L<provider-serializer(7)>
160 =head2 Fetching algorithms
162 =head3 Explicit fetch
164 I<NOTE: This section is mostly interesting to OpenSSL users.>
166 Users of the OpenSSL libraries never query the provider directly for
167 its diverse implementations and dispatch tables.
168 Instead, the diverse OpenSSL APIs often have fetching functions that
169 do the work, and they return an appropriate method object back to the
171 These functions usually have the name C<APINAME_fetch>, where
172 C<APINAME> is the name of the API, for example L<EVP_MD_fetch(3)>.
174 These fetching functions follow a fairly common pattern, where three
175 arguments are passed:
179 =item The library context
181 See L<OPENSSL_CTX(3)> for a more detailed description.
182 This may be NULL to signify the default (global) library context, or a
183 context created by the user.
184 Only providers loaded in this library context (see
185 L<OSSL_PROVIDER_load(3)>) will be considered by the fetching
190 This is most commonly an algorithm name (this is the case for all EVP
191 methods), but may also be called something else.
193 =for comment For example, an OSSL_STORE implementation would use the
194 URI scheme as an identifier.
196 =item A property query string
198 See L<property(7)> for a more detailed description.
199 This is used to select more exactly which providers will get to offer
204 The method object that is fetched can then be used with diverse other
205 functions that use them, for example L<EVP_DigestInit_ex(3)>.
207 =head3 Implicit fetch
209 I<NOTE: This section is mostly interesting to OpenSSL users.>
211 OpenSSL has a number of functions that return a method object with no
212 associated implementation, such as L<EVP_sha256(3)>,
213 L<EVP_blake2b512(3)> or L<EVP_aes_128_cbc(3)>, which are present for
214 compatibility with OpenSSL before version 3.0.
216 When they are used with functions like L<EVP_DigestInit_ex(3)> or
217 L<EVP_CipherInit_ex(3)>, the actual implementation to be used is
218 fetched implicitly using default search criteria.
220 Implicit fetching can also occur with functions such as
221 L<EVP_PKEY_derive_init_ex(3)> where a NULL algorithm parameter is
223 In this case an algorithm implementation is implicitly fetched using
224 default search criteria and an algorithm name that is consistent with
225 the type of EVP_PKEY being used.
227 =head3 Algorithm naming
229 Algorithm names are case insensitive. Any particular algorithm can have multiple
230 aliases associated with it. The canonical OpenSSL naming scheme follows this
233 ALGNAME[VERSION?][-SUBNAME[VERSION?]?][-SIZE?][-MODE?]
235 VERSION is only present if there are multiple versions of an algorithm (e.g.
236 MD2, MD4, MD5). It may be omitted if there is only one version.
238 SUBNAME may be present where multiple algorithms are combined together,
241 SIZE is only present if multiple versions of an algorithm exist with different
242 sizes (e.g. AES-128-CBC, AES-256-CBC)
244 MODE is only present where applicable.
246 Other aliases may exist for example where standards bodies or common practice
247 use alternative names or names that OpenSSL has used historically.
249 =head1 OPENSSL PROVIDERS
251 OpenSSL comes with a set of providers.
253 The algorithms available in each of these providers may vary due to build time
254 configuration options. The L<openssl-list(1)> command can be used to list the
255 currently available algorithms.
257 The names of the algorithms shown from L<openssl-list(1)> can be used as an
258 algorithm identifier to the appropriate fetching function.
260 =head2 Default provider
262 The default provider is built in as part of the F<libcrypto> library.
263 Should it be needed (if other providers are loaded and offer
264 implementations of the same algorithms), the property "default=yes"
265 can be used as a search criterion for these implementations.
269 The FIPS provider is a dynamically loadable module, and must therefore
270 be loaded explicitly, either in code or through OpenSSL configuration
272 Should it be needed (if other providers are loaded and offer
273 implementations of the same algorithms), the property "fips=yes" can
274 be used as a search criterion for these implementations.
276 =head2 Legacy provider
278 The legacy provider is a dynamically loadable module, and must therefore
279 be loaded explicitly, either in code or through OpenSSL configuration
281 Should it be needed (if other providers are loaded and offer
282 implementations of the same algorithms), the property "legacy=yes" can be
283 used as a search criterion for these implementations.
289 Fetch any available implementation of SHA2-256 in the default context:
291 EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", NULL);
293 EVP_MD_meth_free(md);
295 Fetch any available implementation of AES-128-CBC in the default context:
297 EVP_CIPHER *cipher = EVP_CIPHER_fetch(NULL, "AES-128-CBC", NULL);
299 EVP_CIPHER_meth_free(cipher);
301 Fetch an implementation of SHA2-256 from the default provider in the default
304 EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", "default=yes");
306 EVP_MD_meth_free(md);
308 Fetch an implementation of SHA2-256 that is not from the default provider in the
311 EVP_MD *md = EVP_MD_fetch(NULL, "SHA2-256", "default=no");
313 EVP_MD_meth_free(md);
315 Fetch an implementation of SHA2-256 from the default provider in the specified
318 EVP_MD *md = EVP_MD_fetch(ctx, "SHA2-256", "default=yes");
320 EVP_MD_meth_free(md);
322 Load the legacy provider into the default context and then fetch an
323 implementation of WHIRLPOOL from it:
325 /* This only needs to be done once - usually at application start up */
326 OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy");
328 EVP_MD *md = EVP_MD_fetch(NULL, "WHIRLPOOL", "legacy=yes");
330 EVP_MD_meth_free(md);
332 Note that in the above example the property string "legacy=yes" is optional
333 since, assuming no other providers have been loaded, the only implementation of
334 the "whirlpool" algorithm is in the "legacy" provider. Also note that the
335 default provider should be explicitly loaded if it is required in addition to
338 /* This only needs to be done once - usually at application start up */
339 OSSL_PROVIDER *legacy = OSSL_PROVIDER_load(NULL, "legacy");
340 OSSL_PROVIDER *default = OSSL_PROVIDER_load(NULL, "default");
342 EVP_MD *md_whirlpool = EVP_MD_fetch(NULL, "whirlpool", NULL);
343 EVP_MD *md_sha256 = EVP_MD_fetch(NULL, "SHA2-256", NULL);
345 EVP_MD_meth_free(md_whirlpool);
346 EVP_MD_meth_free(md_sha256);
351 L<EVP_DigestInit_ex(3)>, L<EVP_EncryptInit_ex(3)>,
352 L<EVP_PKEY_derive_init_ex(3)>,
354 L<EVP_set_default_properties(3)>,
356 L<EVP_CIPHER_fetch(3)>,
357 L<EVP_KEYMGMT_fetch(3)>,
358 L<openssl-core.h(7)>,
360 L<provider-digest(7)>,
361 L<provider-cipher(7)>,
362 L<provider-keyexch(7)>
366 The concept of providers and everything surrounding them was
367 introduced in OpenSSL 3.0.
371 Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
373 Licensed under the Apache License 2.0 (the "License"). You may not use
374 this file except in compliance with the License. You can obtain a copy
375 in the file LICENSE in the source distribution or at
376 L<https://www.openssl.org/source/license.html>.