]> git.ipfire.org Git - thirdparty/openssl.git/blob - doc/man3/EVP_MAC.pod
sec_mem: add note about the perf implications
[thirdparty/openssl.git] / doc / man3 / EVP_MAC.pod
1 =pod
2
3 =head1 NAME
4
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
15
16 =head1 SYNOPSIS
17
18 #include <openssl/evp.h>
19
20 typedef struct evp_mac_st EVP_MAC;
21 typedef struct evp_mac_ctx_st EVP_MAC_CTX;
22
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),
31 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[]);
35
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[]);
42
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);
57
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);
63
64 void EVP_MAC_do_all_provided(OSSL_LIB_CTX *libctx,
65 void (*fn)(EVP_MAC *mac, void *arg),
66 void *arg);
67
68 =head1 DESCRIPTION
69
70 These types and functions help the application to calculate MACs of
71 different types and with different underlying algorithms if there are
72 any.
73
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.
79
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.
84
85 =head2 Types
86
87 B<EVP_MAC> is a type that holds the implementation of a MAC.
88
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.
92
93 =head2 Algorithm implementation fetching
94
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.
98
99 See L<OSSL_PROVIDER-default(7)/Message Authentication Code (MAC)> for the list
100 of algorithms supported by the default provider.
101
102 The returned value must eventually be freed with
103 L<EVP_MAC_free(3)>.
104
105 EVP_MAC_up_ref() increments the reference count of an already fetched
106 MAC.
107
108 EVP_MAC_free() frees a fetched algorithm.
109 NULL is a valid parameter, for which this function is a no-op.
110
111 =head2 Context manipulation functions
112
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
115 described here.
116
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.
120
121 EVP_MAC_CTX_dup() duplicates the I<src> context and returns a newly allocated
122 context.
123
124 EVP_MAC_CTX_get0_mac() returns the B<EVP_MAC> associated with the context
125 I<ctx>.
126
127 =head2 Computing functions
128
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.
141
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.
152
153 EVP_MAC_init() should be called before EVP_MAC_update() and EVP_MAC_final().
154
155 EVP_MAC_init_SKEY() is similar to EVP_MAC_init() but it accepts an opaque
156 B<EVP_SKEY> object as a key.
157
158 EVP_MAC_update() adds I<datalen> bytes from I<data> to the MAC input.
159
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
164 is made.
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.
169
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>.
172
173 EVP_MAC_get_params() retrieves details about the implementation
174 I<mac>.
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
178 simply ignored.
179
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
185 simply ignored.
186
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
193 simply ignored.
194 Also, what happens when a needed parameter isn't passed down is
195 defined by the implementation.
196
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().
200
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.
207
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.
214
215 =head2 Information functions
216
217 EVP_MAC_CTX_get_mac_size() returns the MAC output size for the given context.
218
219 EVP_MAC_CTX_get_block_size() returns the MAC block size for the given context.
220 Not all MAC algorithms support this.
221
222 EVP_MAC_is_a() checks if the given I<mac> is an implementation of an
223 algorithm that's identifiable with I<name>.
224
225 EVP_MAC_get0_provider() returns the provider that holds the implementation
226 of the given I<mac>.
227
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.
232
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.
236
237 EVP_MAC_names_do_all() traverses all names for I<mac>, and calls
238 I<fn> with each name and I<data>.
239
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.
243
244 =head1 PARAMETERS
245
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.
252
253 The standard parameter names are:
254
255 =over 4
256
257 =item "key" (B<OSSL_MAC_PARAM_KEY>) <octet string>
258
259 Its value is the MAC key as an array of bytes.
260
261 For MACs that use an underlying computation algorithm, the algorithm
262 must be set first, see parameter names "algorithm" below.
263
264 =item "iv" (B<OSSL_MAC_PARAM_IV>) <octet string>
265
266 Some MAC implementations (GMAC) require an IV, this parameter sets the IV.
267
268 =item "custom" (B<OSSL_MAC_PARAM_CUSTOM>) <octet string>
269
270 Some MAC implementations (KMAC, BLAKE2) accept a Customization String,
271 this parameter sets the Customization String. The default value is the
272 empty string.
273
274 =item "salt" (B<OSSL_MAC_PARAM_SALT>) <octet string>
275
276 This option is used by BLAKE2 MAC.
277
278 =item "xof" (B<OSSL_MAC_PARAM_XOF>) <integer>
279
280 It's a simple flag, the value 0 or 1 are expected.
281
282 This option is used by KMAC.
283
284 =item "digest-noinit" (B<OSSL_MAC_PARAM_DIGEST_NOINIT>) <integer>
285
286 A simple flag to set the MAC digest to not initialise the
287 implementation specific data. The value 0 or 1 is expected.
288
289 This option is deprecated and will be removed in a future release.
290 The option may be set, but is ignored.
291
292 =item "digest-oneshot" (B<OSSL_MAC_PARAM_DIGEST_ONESHOT>) <integer>
293
294 A simple flag to set the MAC digest to be a oneshot operation.
295 The value 0 or 1 is expected.
296
297 This option is deprecated and will be removed in a future release.
298 The option may be set, but is ignored.
299
300 =item "properties" (B<OSSL_MAC_PARAM_PROPERTIES>) <UTF8 string>
301
302 =item "digest" (B<OSSL_MAC_PARAM_DIGEST>) <UTF8 string>
303
304 =item "cipher" (B<OSSL_MAC_PARAM_CIPHER>) <UTF8 string>
305
306 For MAC implementations that use an underlying computation cipher or
307 digest, these parameters set what the algorithm should be.
308
309 The value is always the name of the intended algorithm,
310 or the properties.
311
312 Note that not all algorithms may support all digests.
313 HMAC does not support variable output length digests such as SHAKE128
314 or SHAKE256.
315
316 =item "size" (B<OSSL_MAC_PARAM_SIZE>) <unsigned integer>
317
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>.
322
323 =item "tls-data-size" (B<OSSL_MAC_PARAM_TLS_DATA_SIZE>) <unsigned integer>
324
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.
330
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.
337
338 =back
339
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
342 computation.
343 Anything else may give undefined results.
344
345 =head1 NOTES
346
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.
350
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.
353
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().
360
361 =head1 RETURN VALUES
362
363 EVP_MAC_fetch() returns a pointer to a newly fetched B<EVP_MAC>, or
364 NULL if allocation failed.
365
366 EVP_MAC_up_ref() returns 1 on success, 0 on error.
367
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.
370
371 EVP_MAC_free() returns nothing at all.
372
373 EVP_MAC_is_a() returns 1 if the given method can be identified with
374 the given name, otherwise 0.
375
376 EVP_MAC_get0_name() returns a name of the MAC, or NULL on error.
377
378 EVP_MAC_get0_provider() returns a pointer to the provider for the MAC, or
379 NULL on error.
380
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.
383
384 EVP_MAC_CTX_free() returns nothing at all.
385
386 EVP_MAC_CTX_get_params() and EVP_MAC_CTX_set_params() return 1 on
387 success, 0 on error.
388
389 EVP_Q_mac() returns a pointer to the computed MAC value, or NULL on error.
390
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.
393
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.
396
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.
399
400 EVP_MAC_do_all_provided() returns nothing at all.
401
402 =head1 EXAMPLES
403
404 #include <stdlib.h>
405 #include <stdio.h>
406 #include <string.h>
407 #include <stdarg.h>
408 #include <unistd.h>
409
410 #include <openssl/evp.h>
411 #include <openssl/err.h>
412 #include <openssl/params.h>
413
414 int main() {
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;
420
421 unsigned char buf[4096];
422 size_t read_l;
423 size_t final_l;
424
425 size_t i;
426
427 OSSL_PARAM params[3];
428 size_t params_n = 0;
429
430 if (cipher != NULL)
431 params[params_n++] =
432 OSSL_PARAM_construct_utf8_string("cipher", (char*)cipher, 0);
433 if (digest != NULL)
434 params[params_n++] =
435 OSSL_PARAM_construct_utf8_string("digest", (char*)digest, 0);
436 params[params_n] = OSSL_PARAM_construct_end();
437
438 if (mac == NULL
439 || key == NULL
440 || (ctx = EVP_MAC_CTX_new(mac)) == NULL
441 || !EVP_MAC_init(ctx, (const unsigned char *)key, strlen(key),
442 params))
443 goto err;
444
445 while ( (read_l = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
446 if (!EVP_MAC_update(ctx, buf, read_l))
447 goto err;
448 }
449
450 if (!EVP_MAC_final(ctx, buf, &final_l, sizeof(buf)))
451 goto err;
452
453 printf("Result: ");
454 for (i = 0; i < final_l; i++)
455 printf("%02X", buf[i]);
456 printf("\n");
457
458 EVP_MAC_CTX_free(ctx);
459 EVP_MAC_free(mac);
460 exit(0);
461
462 err:
463 EVP_MAC_CTX_free(ctx);
464 EVP_MAC_free(mac);
465 fprintf(stderr, "Something went wrong\n");
466 ERR_print_errors_fp(stderr);
467 exit (1);
468 }
469
470 A run of this program, called with correct environment variables, can
471 look like this:
472
473 $ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc \
474 LD_LIBRARY_PATH=. ./foo < foo.c
475 Result: C5C06683CD9DDEF904D754505C560A4E
476
477 (in this example, that program was stored in F<foo.c> and compiled to
478 F<./foo>)
479
480 =head1 SEE ALSO
481
482 L<property(7)>
483 L<OSSL_PARAM(3)>,
484 L<EVP_MAC-BLAKE2(7)>,
485 L<EVP_MAC-CMAC(7)>,
486 L<EVP_MAC-GMAC(7)>,
487 L<EVP_MAC-HMAC(7)>,
488 L<EVP_MAC-KMAC(7)>,
489 L<EVP_MAC-Siphash(7)>,
490 L<EVP_MAC-Poly1305(7)>,
491 L<provider-mac(7)>,
492 L<life_cycle-mac(7)>
493
494 =head1 HISTORY
495
496 These functions were added in OpenSSL 3.0.
497
498 The EVP_MAC_init_SKEY() function was added in OpenSSL 3.5.
499
500 =head1 COPYRIGHT
501
502 Copyright 2018-2025 The OpenSSL Project Authors. All Rights Reserved.
503
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>.
508
509 =cut