5 EVP_MAC, EVP_MAC_fetch, EVP_MAC_up_ref, EVP_MAC_free, EVP_MAC_is_a,
6 EVP_MAC_get0_name, EVP_MAC_names_do_all, EVP_MAC_get0_description,
7 EVP_MAC_get0_provider, EVP_MAC_get_params, EVP_MAC_gettable_params,
8 EVP_MAC_CTX, EVP_MAC_CTX_new, EVP_MAC_CTX_free, EVP_MAC_CTX_dup,
9 EVP_MAC_CTX_get0_mac, EVP_MAC_CTX_get_params, EVP_MAC_CTX_set_params,
10 EVP_MAC_CTX_get_mac_size, EVP_MAC_CTX_get_block_size, EVP_Q_mac,
11 EVP_MAC_init, EVP_MAC_init_SKEY, EVP_MAC_update, EVP_MAC_final, EVP_MAC_finalXOF,
12 EVP_MAC_gettable_ctx_params, EVP_MAC_settable_ctx_params,
13 EVP_MAC_CTX_gettable_params, EVP_MAC_CTX_settable_params,
14 EVP_MAC_do_all_provided - EVP MAC routines
18 #include <openssl/evp.h>
20 typedef struct evp_mac_st EVP_MAC;
21 typedef struct evp_mac_ctx_st EVP_MAC_CTX;
23 EVP_MAC *EVP_MAC_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
24 const char *properties);
25 int EVP_MAC_up_ref(EVP_MAC *mac);
26 void EVP_MAC_free(EVP_MAC *mac);
27 int EVP_MAC_is_a(const EVP_MAC *mac, const char *name);
28 const char *EVP_MAC_get0_name(const EVP_MAC *mac);
29 int EVP_MAC_names_do_all(const EVP_MAC *mac,
30 void (*fn)(const char *name, void *data),
32 const char *EVP_MAC_get0_description(const EVP_MAC *mac);
33 const OSSL_PROVIDER *EVP_MAC_get0_provider(const EVP_MAC *mac);
34 int EVP_MAC_get_params(EVP_MAC *mac, OSSL_PARAM params[]);
36 EVP_MAC_CTX *EVP_MAC_CTX_new(EVP_MAC *mac);
37 void EVP_MAC_CTX_free(EVP_MAC_CTX *ctx);
38 EVP_MAC_CTX *EVP_MAC_CTX_dup(const EVP_MAC_CTX *src);
39 EVP_MAC *EVP_MAC_CTX_get0_mac(EVP_MAC_CTX *ctx);
40 int EVP_MAC_CTX_get_params(EVP_MAC_CTX *ctx, OSSL_PARAM params[]);
41 int EVP_MAC_CTX_set_params(EVP_MAC_CTX *ctx, const OSSL_PARAM params[]);
43 size_t EVP_MAC_CTX_get_mac_size(EVP_MAC_CTX *ctx);
44 size_t EVP_MAC_CTX_get_block_size(EVP_MAC_CTX *ctx);
45 unsigned char *EVP_Q_mac(OSSL_LIB_CTX *libctx, const char *name, const char *propq,
46 const char *subalg, const OSSL_PARAM *params,
47 const void *key, size_t keylen,
48 const unsigned char *data, size_t datalen,
49 unsigned char *out, size_t outsize, size_t *outlen);
50 int EVP_MAC_init(EVP_MAC_CTX *ctx, const unsigned char *key, size_t keylen,
51 const OSSL_PARAM params[]);
52 int EVP_MAC_init_SKEY(EVP_MAC_CTX *ctx, EVP_SKEY *skey, const OSSL_PARAM params[]);
53 int EVP_MAC_update(EVP_MAC_CTX *ctx, const unsigned char *data, size_t datalen);
54 int EVP_MAC_final(EVP_MAC_CTX *ctx,
55 unsigned char *out, size_t *outl, size_t outsize);
56 int EVP_MAC_finalXOF(EVP_MAC_CTX *ctx, unsigned char *out, size_t outsize);
58 const OSSL_PARAM *EVP_MAC_gettable_params(const EVP_MAC *mac);
59 const OSSL_PARAM *EVP_MAC_gettable_ctx_params(const EVP_MAC *mac);
60 const OSSL_PARAM *EVP_MAC_settable_ctx_params(const EVP_MAC *mac);
61 const OSSL_PARAM *EVP_MAC_CTX_gettable_params(EVP_MAC_CTX *ctx);
62 const OSSL_PARAM *EVP_MAC_CTX_settable_params(EVP_MAC_CTX *ctx);
64 void EVP_MAC_do_all_provided(OSSL_LIB_CTX *libctx,
65 void (*fn)(EVP_MAC *mac, void *arg),
70 These types and functions help the application to calculate MACs of
71 different types and with different underlying algorithms if there are
74 MACs are a bit complex insofar that some of them use other algorithms
75 for actual computation. HMAC uses a digest, and CMAC uses a cipher.
76 Therefore, there are sometimes two contexts to keep track of, one for
77 the MAC algorithm itself and one for the underlying computation
78 algorithm if there is one.
80 To make things less ambiguous, this manual talks about a "context" or
81 "MAC context", which is to denote the MAC level context, and about a
82 "underlying context", or "computation context", which is to denote the
83 context for the underlying computation algorithm if there is one.
87 B<EVP_MAC> is a type that holds the implementation of a MAC.
89 B<EVP_MAC_CTX> is a context type that holds internal MAC information
90 as well as a reference to a computation context, for those MACs that
91 rely on an underlying computation algorithm.
93 =head2 Algorithm implementation fetching
95 EVP_MAC_fetch() fetches an implementation of a MAC I<algorithm>, given
96 a library context I<libctx> and a set of I<properties>.
97 See L<crypto(7)/ALGORITHM FETCHING> for further information.
99 See L<OSSL_PROVIDER-default(7)/Message Authentication Code (MAC)> for the list
100 of algorithms supported by the default provider.
102 The returned value must eventually be freed with
105 EVP_MAC_up_ref() increments the reference count of an already fetched
108 EVP_MAC_free() frees a fetched algorithm.
109 NULL is a valid parameter, for which this function is a no-op.
111 =head2 Context manipulation functions
113 EVP_MAC_CTX_new() creates a new context for the MAC type I<mac>.
114 The created context can then be used with most other functions
117 EVP_MAC_CTX_free() frees the contents of the context, including an
118 underlying context if there is one, as well as the context itself.
119 NULL is a valid parameter, for which this function is a no-op.
121 EVP_MAC_CTX_dup() duplicates the I<src> context and returns a newly allocated
124 EVP_MAC_CTX_get0_mac() returns the B<EVP_MAC> associated with the context
127 =head2 Computing functions
129 EVP_Q_mac() computes the message authentication code
130 of I<data> with length I<datalen>
131 using the MAC algorithm I<name> and the key I<key> with length I<keylen>.
132 The MAC algorithm is fetched using any given I<libctx> and property query
133 string I<propq>. It takes parameters I<subalg> and further I<params>,
134 both of which may be NULL if not needed.
135 If I<out> is not NULL, it places the result in the memory pointed at by I<out>,
136 but only if I<outsize> is sufficient (otherwise no computation is made).
137 If I<out> is NULL, it allocates and uses a buffer of suitable length,
138 which will be returned on success and must be freed by the caller.
139 In either case, also on error,
140 it assigns the number of bytes written to I<*outlen> unless I<outlen> is NULL.
142 EVP_MAC_init() sets up the underlying context I<ctx> with information given
143 via the I<key> and I<params> arguments. The MAC I<key> has a length of
144 I<keylen> and the parameters in I<params> are processed before setting
145 the key. If I<key> is NULL, the key must be set via I<params> either
146 as part of this call or separately using EVP_MAC_CTX_set_params().
147 Providing non-NULL I<params> to this function is equivalent to calling
148 EVP_MAC_CTX_set_params() with those I<params> for the same I<ctx> beforehand.
149 Note: There are additional requirements for some MAC algorithms during
150 re-initalization (i.e. calling EVP_MAC_init() on an EVP_MAC after EVP_MAC_final()
151 has been called on the same object). See the NOTES section below.
153 EVP_MAC_init() should be called before EVP_MAC_update() and EVP_MAC_final().
155 EVP_MAC_init_SKEY() is similar to EVP_MAC_init() but it accepts an opaque
156 B<EVP_SKEY> object as a key.
158 EVP_MAC_update() adds I<datalen> bytes from I<data> to the MAC input.
160 EVP_MAC_final() does the final computation and stores the result in
161 the memory pointed at by I<out> of size I<outsize>, and sets the number
162 of bytes written in I<*outl> at.
163 If I<out> is NULL or I<outsize> is too small, then no computation
165 To figure out what the output length will be and allocate space for it
166 dynamically, simply call with I<out> being NULL and I<outl>
167 pointing at a valid location, then allocate space and make a second
168 call with I<out> pointing at the allocated space.
170 EVP_MAC_finalXOF() does the final computation for an XOF based MAC and stores
171 the result in the memory pointed at by I<out> of size I<outsize>.
173 EVP_MAC_get_params() retrieves details about the implementation
175 The set of parameters given with I<params> determine exactly what
176 parameters should be retrieved.
177 Note that a parameter that is unknown in the underlying context is
180 EVP_MAC_CTX_get_params() retrieves chosen parameters, given the
181 context I<ctx> and its underlying context.
182 The set of parameters given with I<params> determine exactly what
183 parameters should be retrieved.
184 Note that a parameter that is unknown in the underlying context is
187 EVP_MAC_CTX_set_params() passes chosen parameters to the underlying
188 context, given a context I<ctx>.
189 The set of parameters given with I<params> determine exactly what
190 parameters are passed down.
191 If I<params> are NULL, the underlying context should do nothing and return 1.
192 Note that a parameter that is unknown in the underlying context is
194 Also, what happens when a needed parameter isn't passed down is
195 defined by the implementation.
197 EVP_MAC_gettable_params() returns an L<OSSL_PARAM(3)> array that describes
198 the retrievable and settable parameters. EVP_MAC_gettable_params()
199 returns parameters that can be used with EVP_MAC_get_params().
201 EVP_MAC_gettable_ctx_params() and EVP_MAC_CTX_gettable_params()
202 return constant L<OSSL_PARAM(3)> arrays that describe the retrievable
203 parameters that can be used with EVP_MAC_CTX_get_params().
204 EVP_MAC_gettable_ctx_params() returns the parameters that can be retrieved
205 from the algorithm, whereas EVP_MAC_CTX_gettable_params() returns
206 the parameters that can be retrieved in the context's current state.
208 EVP_MAC_settable_ctx_params() and EVP_MAC_CTX_settable_params() return
209 constant L<OSSL_PARAM(3)> arrays that describe the settable parameters that
210 can be used with EVP_MAC_CTX_set_params(). EVP_MAC_settable_ctx_params()
211 returns the parameters that can be retrieved from the algorithm,
212 whereas EVP_MAC_CTX_settable_params() returns the parameters that can
213 be retrieved in the context's current state.
215 =head2 Information functions
217 EVP_MAC_CTX_get_mac_size() returns the MAC output size for the given context.
219 EVP_MAC_CTX_get_block_size() returns the MAC block size for the given context.
220 Not all MAC algorithms support this.
222 EVP_MAC_is_a() checks if the given I<mac> is an implementation of an
223 algorithm that's identifiable with I<name>.
225 EVP_MAC_get0_provider() returns the provider that holds the implementation
228 EVP_MAC_do_all_provided() traverses all MAC implemented by all activated
229 providers in the given library context I<libctx>, and for each of the
230 implementations, calls the given function I<fn> with the implementation method
231 and the given I<arg> as argument.
233 EVP_MAC_get0_name() return the name of the given MAC. For fetched MACs
234 with multiple names, only one of them is returned; it's
235 recommended to use EVP_MAC_names_do_all() instead.
237 EVP_MAC_names_do_all() traverses all names for I<mac>, and calls
238 I<fn> with each name and I<data>.
240 EVP_MAC_get0_description() returns a description of the I<mac>, meant
241 for display and human consumption. The description is at the discretion
242 of the mac implementation.
246 Parameters are identified by name as strings, and have an expected
247 data type and maximum size.
248 OpenSSL has a set of macros for parameter names it expects to see in
249 its own MAC implementations.
250 Here, we show all three, the OpenSSL macro for the parameter name, the
251 name in string form, and a type description.
253 The standard parameter names are:
257 =item "key" (B<OSSL_MAC_PARAM_KEY>) <octet string>
259 Its value is the MAC key as an array of bytes.
261 For MACs that use an underlying computation algorithm, the algorithm
262 must be set first, see parameter names "algorithm" below.
264 =item "iv" (B<OSSL_MAC_PARAM_IV>) <octet string>
266 Some MAC implementations (GMAC) require an IV, this parameter sets the IV.
268 =item "custom" (B<OSSL_MAC_PARAM_CUSTOM>) <octet string>
270 Some MAC implementations (KMAC, BLAKE2) accept a Customization String,
271 this parameter sets the Customization String. The default value is the
274 =item "salt" (B<OSSL_MAC_PARAM_SALT>) <octet string>
276 This option is used by BLAKE2 MAC.
278 =item "xof" (B<OSSL_MAC_PARAM_XOF>) <integer>
280 It's a simple flag, the value 0 or 1 are expected.
282 This option is used by KMAC.
284 =item "digest-noinit" (B<OSSL_MAC_PARAM_DIGEST_NOINIT>) <integer>
286 A simple flag to set the MAC digest to not initialise the
287 implementation specific data. The value 0 or 1 is expected.
289 This option is deprecated and will be removed in a future release.
290 The option may be set, but is ignored.
292 =item "digest-oneshot" (B<OSSL_MAC_PARAM_DIGEST_ONESHOT>) <integer>
294 A simple flag to set the MAC digest to be a oneshot operation.
295 The value 0 or 1 is expected.
297 This option is deprecated and will be removed in a future release.
298 The option may be set, but is ignored.
300 =item "properties" (B<OSSL_MAC_PARAM_PROPERTIES>) <UTF8 string>
302 =item "digest" (B<OSSL_MAC_PARAM_DIGEST>) <UTF8 string>
304 =item "cipher" (B<OSSL_MAC_PARAM_CIPHER>) <UTF8 string>
306 For MAC implementations that use an underlying computation cipher or
307 digest, these parameters set what the algorithm should be.
309 The value is always the name of the intended algorithm,
312 Note that not all algorithms may support all digests.
313 HMAC does not support variable output length digests such as SHAKE128
316 =item "size" (B<OSSL_MAC_PARAM_SIZE>) <unsigned integer>
318 For MAC implementations that support it, set the output size that
319 EVP_MAC_final() should produce.
320 The allowed sizes vary between MAC implementations, but must never exceed
321 what can be given with a B<size_t>.
323 =item "tls-data-size" (B<OSSL_MAC_PARAM_TLS_DATA_SIZE>) <unsigned integer>
325 This parameter is only supported by HMAC. If set then special handling is
326 activated for calculating the MAC of a received mac-then-encrypt TLS record
327 where variable length record padding has been used (as in the case of CBC mode
328 ciphersuites). The value represents the total length of the record that is
329 having the MAC calculated including the received MAC and the record padding.
331 When used EVP_MAC_update must be called precisely twice. The first time with
332 the 13 bytes of TLS "header" data, and the second time with the entire record
333 including the MAC itself and any padding. The entire record length must equal
334 the value passed in the "tls-data-size" parameter. The length passed in the
335 B<datalen> parameter to EVP_MAC_update() should be equal to the length of the
336 record after the MAC and any padding has been removed.
340 All these parameters should be used before the calls to any of
341 EVP_MAC_init(), EVP_MAC_update() and EVP_MAC_final() for a full
343 Anything else may give undefined results.
347 The MAC life-cycle is described in L<life_cycle-mac(7)>. In the future,
348 the transitions described there will be enforced. When this is done, it will
349 not be considered a breaking change to the API.
351 The usage of the parameter names "custom", "iv" and "salt" correspond to
352 the names used in the standard where the algorithm was defined.
354 Some MAC algorithms store internal state that cannot be extracted during
355 re-initalization. For example GMAC cannot extract an B<IV> from the
356 underlying CIPHER context, and so calling EVP_MAC_init() on an EVP_MAC object
357 after EVP_MAC_final() has been called cannot reset its cipher state to what it
358 was when the B<IV> was initially generated. For such instances, an
359 B<OSSL_MAC_PARAM_IV> parameter must be passed with each call to EVP_MAC_init().
363 EVP_MAC_fetch() returns a pointer to a newly fetched B<EVP_MAC>, or
364 NULL if allocation failed.
366 EVP_MAC_up_ref() returns 1 on success, 0 on error.
368 EVP_MAC_names_do_all() returns 1 if the callback was called for all names. A
369 return value of 0 means that the callback was not called for any names.
371 EVP_MAC_free() returns nothing at all.
373 EVP_MAC_is_a() returns 1 if the given method can be identified with
374 the given name, otherwise 0.
376 EVP_MAC_get0_name() returns a name of the MAC, or NULL on error.
378 EVP_MAC_get0_provider() returns a pointer to the provider for the MAC, or
381 EVP_MAC_CTX_new() and EVP_MAC_CTX_dup() return a pointer to a newly
382 created EVP_MAC_CTX, or NULL if allocation failed.
384 EVP_MAC_CTX_free() returns nothing at all.
386 EVP_MAC_CTX_get_params() and EVP_MAC_CTX_set_params() return 1 on
389 EVP_Q_mac() returns a pointer to the computed MAC value, or NULL on error.
391 EVP_MAC_init(), EVP_MAC_init_SKEY(), EVP_MAC_update(), EVP_MAC_final(), and
392 EVP_MAC_finalXOF() return 1 on success, 0 on error.
394 EVP_MAC_CTX_get_mac_size() returns the expected output size, or 0 if it isn't
395 set. If it isn't set, a call to EVP_MAC_init() will set it.
397 EVP_MAC_CTX_get_block_size() returns the block size, or 0 if it isn't set.
398 If it isn't set, a call to EVP_MAC_init() will set it.
400 EVP_MAC_do_all_provided() returns nothing at all.
410 #include <openssl/evp.h>
411 #include <openssl/err.h>
412 #include <openssl/params.h>
415 EVP_MAC *mac = EVP_MAC_fetch(NULL, getenv("MY_MAC"), NULL);
416 const char *cipher = getenv("MY_MAC_CIPHER");
417 const char *digest = getenv("MY_MAC_DIGEST");
418 const char *key = getenv("MY_KEY");
419 EVP_MAC_CTX *ctx = NULL;
421 unsigned char buf[4096];
427 OSSL_PARAM params[3];
432 OSSL_PARAM_construct_utf8_string("cipher", (char*)cipher, 0);
435 OSSL_PARAM_construct_utf8_string("digest", (char*)digest, 0);
436 params[params_n] = OSSL_PARAM_construct_end();
440 || (ctx = EVP_MAC_CTX_new(mac)) == NULL
441 || !EVP_MAC_init(ctx, (const unsigned char *)key, strlen(key),
445 while ( (read_l = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
446 if (!EVP_MAC_update(ctx, buf, read_l))
450 if (!EVP_MAC_final(ctx, buf, &final_l, sizeof(buf)))
454 for (i = 0; i < final_l; i++)
455 printf("%02X", buf[i]);
458 EVP_MAC_CTX_free(ctx);
463 EVP_MAC_CTX_free(ctx);
465 fprintf(stderr, "Something went wrong\n");
466 ERR_print_errors_fp(stderr);
470 A run of this program, called with correct environment variables, can
473 $ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc \
474 LD_LIBRARY_PATH=. ./foo < foo.c
475 Result: C5C06683CD9DDEF904D754505C560A4E
477 (in this example, that program was stored in F<foo.c> and compiled to
484 L<EVP_MAC-BLAKE2(7)>,
489 L<EVP_MAC-Siphash(7)>,
490 L<EVP_MAC-Poly1305(7)>,
496 These functions were added in OpenSSL 3.0.
498 The EVP_MAC_init_SKEY() function was added in OpenSSL 3.5.
502 Copyright 2018-2025 The OpenSSL Project Authors. All Rights Reserved.
504 Licensed under the Apache License 2.0 (the "License"). You may not use
505 this file except in compliance with the License. You can obtain a copy
506 in the file LICENSE in the source distribution or at
507 L<https://www.openssl.org/source/license.html>.