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_name,
   6 EVP_MAC_provider, EVP_MAC_get_params, EVP_MAC_gettable_params,
   7 EVP_MAC_CTX, EVP_MAC_CTX_new, EVP_MAC_CTX_free, EVP_MAC_CTX_dup,
   8 EVP_MAC_CTX_mac, EVP_MAC_CTX_get_params, EVP_MAC_CTX_set_params,
   9 EVP_MAC_size, EVP_MAC_init, EVP_MAC_update, EVP_MAC_final,
  10 EVP_MAC_CTX_gettable_params, EVP_MAC_CTX_settable_params,
  11 EVP_MAC_do_all_ex - EVP MAC routines
  12
  13 =head1 SYNOPSIS
  14
  15  #include <openssl/evp.h>
  16
  17  typedef struct evp_mac_st EVP_MAC;
  18  typedef struct evp_mac_ctx_st EVP_MAC_CTX;
  19
  20  EVP_MAC *EVP_MAC_fetch(OPENSSL_CTX *libctx, const char *algorithm,
  21                         const char *properties);
  22  int EVP_MAC_up_ref(EVP_MAC *mac);
  23  void EVP_MAC_free(EVP_MAC *mac);
  24  const char *EVP_MAC_name(const EVP_MAC *mac);
  25  const OSSL_PROVIDER *EVP_MAC_provider(const EVP_MAC *mac);
  26  int EVP_MAC_get_params(EVP_MAC *mac, OSSL_PARAM params[]);
  27
  28  EVP_MAC_CTX *EVP_MAC_CTX_new(EVP_MAC *mac);
  29  void EVP_MAC_CTX_free(EVP_MAC_CTX *ctx);
  30  EVP_MAC_CTX *EVP_MAC_CTX_dup(const EVP_MAC_CTX *src);
  31  EVP_MAC *EVP_MAC_CTX_mac(EVP_MAC_CTX *ctx);
  32  int EVP_MAC_CTX_get_params(EVP_MAC_CTX *ctx, OSSL_PARAM params[]);
  33  int EVP_MAC_CTX_set_params(EVP_MAC_CTX *ctx, const OSSL_PARAM params[]);
  34
  35  size_t EVP_MAC_size(EVP_MAC_CTX *ctx);
  36  int EVP_MAC_init(EVP_MAC_CTX *ctx);
  37  int EVP_MAC_update(EVP_MAC_CTX *ctx, const unsigned char *data, size_t datalen);
  38  int EVP_MAC_final(EVP_MAC_CTX *ctx,
  39                    unsigned char *out, size_t *outl, size_t outsize);
  40
  41  const OSSL_PARAM *EVP_MAC_gettable_params(const EVP_MAC *mac);
  42  const OSSL_PARAM *EVP_MAC_CTX_gettable_params(const EVP_MAC *mac);
  43  const OSSL_PARAM *EVP_MAC_CTX_settable_params(const EVP_MAC *mac);
  44
  45  void EVP_MAC_do_all_ex(OPENSSL_CTX *libctx,
  46                         void (*fn)(EVP_MAC *mac, void *arg),
  47                         void *arg);
  48
  49 =head1 DESCRIPTION
  50
  51 These types and functions help the application to calculate MACs of
  52 different types and with different underlying algorithms if there are
  53 any.
  54
  55 MACs are a bit complex insofar that some of them use other algorithms
  56 for actual computation.  HMAC uses a digest, and CMAC uses a cipher.
  57 Therefore, there are sometimes two contexts to keep track of, one for
  58 the MAC algorithm itself and one for the underlying computation
  59 algorithm if there is one.
  60
  61 To make things less ambiguous, this manual talks about a "context" or
  62 "MAC context", which is to denote the MAC level context, and about a
  63 "underlying context", or "computation context", which is to denote the
  64 context for the underlying computation algorithm if there is one.
  65
  66 =head2 Types
  67
  68 B<EVP_MAC> is a type that holds the implementation of a MAC.
  69
  70 B<EVP_MAC_CTX> is a context type that holds internal MAC information
  71 as well as a reference to a computation context, for those MACs that
  72 rely on an underlying computation algorithm.
  73
  74 =head2 Algorithm implementation fetching
  75
  76 EVP_MAC_fetch() fetches an implementation of a MAC I<algorithm>, given
  77 a library context I<libctx> and a set of I<properties>.
  78 See L<provider(7)/Fetching algorithms> for further information.
  79
  80 The returned value must eventually be freed with
  81 L<EVP_MAC_free(3)>.
  82
  83 EVP_MAC_up_ref() increments the reference count of an already fetched
  84 MAC.
  85
  86 EVP_MAC_free() frees a fetched algorithm.
  87 NULL is a valid parameter, for which this function is a no-op.
  88
  89 =head2 Context manipulation functions
  90
  91 EVP_MAC_CTX_new() creates a new context for the MAC type I<mac>.
  92 The created context can then be used with most other functions
  93 described here.
  94
  95 EVP_MAC_CTX_free() frees the contents of the context, including an
  96 underlying context if there is one, as well as the context itself.
  97 NULL is a valid parameter, for which this function is a no-op.
  98
  99 EVP_MAC_CTX_dup() duplicates the I<src> context and returns a newly allocated
 100 context.
 101
 102 EVP_MAC_CTX_mac() returns the B<EVP_MAC> associated with the context
 103 I<ctx>.
 104
 105 =head2 Computing functions
 106
 107 EVP_MAC_init() sets up the underlying context with information given
 108 through diverse controls.
 109 This should be called before calling EVP_MAC_update() and
 110 EVP_MAC_final().
 111
 112 EVP_MAC_update() adds I<datalen> bytes from I<data> to the MAC input.
 113
 114 EVP_MAC_final() does the final computation and stores the result in
 115 the memory pointed at by I<out> of size I<outsize>, and sets the number
 116 of bytes written in I<*outl> at.
 117 If I<out> is B<NULL> or I<outsize> is too small, then no computation
 118 is made.
 119 To figure out what the output length will be and allocate space for it
 120 dynamically, simply call with I<out> being B<NULL> and I<outl>
 121 pointing at a valid location, then allocate space and make a second
 122 call with I<out> pointing at the allocated space.
 123
 124 EVP_MAC_get_params() retrieves details about the implementation
 125 I<mac>.
 126 The set of parameters given with I<params> determine exactly what
 127 parameters should be retrieved.
 128 Note that a parameter that is unknown in the underlying context is
 129 simply ignored.
 130
 131 EVP_MAC_CTX_get_params() retrieves chosen parameters, given the
 132 context I<ctx> and its underlying context.
 133 The set of parameters given with I<params> determine exactly what
 134 parameters should be retrieved.
 135 Note that a parameter that is unknown in the underlying context is
 136 simply ignored.
 137
 138 EVP_MAC_CTX_set_params() passes chosen parameters to the underlying
 139 context, given a context I<ctx>.
 140 The set of parameters given with I<params> determine exactly what
 141 parameters are passed down.
 142 Note that a parameter that is unknown in the underlying context is
 143 simply ignored.
 144 Also, what happens when a needed parameter isn't passed down is
 145 defined by the implementation.
 146
 147 EVP_MAC_gettable_params(), EVP_MAC_CTX_gettable_params() and
 148 EVP_MAC_CTX_settable_params() get a constant B<OSSL_PARAM> array that
 149 decribes the retrievable and settable parameters, i.e. parameters that
 150 can be used with EVP_MAC_CTX_get_params(), EVP_MAC_CTX_get_params()
 151 and EVP_MAC_CTX_set_params(), respectively.
 152 See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.
 153
 154 =head2 Information functions
 155
 156 EVP_MAC_size() returns the MAC output size for the given context.
 157
 158 EVP_MAC_name() returns the name of the given MAC implementation.
 159
 160 EVP_MAC_provider() returns the provider that holds the implementation
 161 of the given I<mac>.
 162
 163 EVP_MAC_do_all_ex() traverses all MAC implemented by all activated
 164 providers in the given library context I<libctx>, and for each of the
 165 implementations, calls the given function I<fn> with the implementation method
 166 and the given I<arg> as argument.
 167
 168 =head1 PARAMETER NAMES
 169
 170 The standard parameter names are:
 171
 172 =over 4
 173
 174 =item OSSL_MAC_PARAM_KEY ("key") <octet string>
 175
 176 Its value is the MAC key as an array of bytes.
 177
 178 For MACs that use an underlying computation algorithm, the algorithm
 179 must be set first, see parameter names "algorithm" below.
 180
 181 =item OSSL_MAC_PARAM_IV ("iv") <octet string>
 182
 183 Some MAC implementations require an IV, this parameter sets the IV.
 184
 185 =item OSSL_MAC_PARAM_CUSTOM ("custom") <octet string>
 186
 187 Some MAC implementations (KMAC, BLAKE2) accept a Customization String,
 188 this parameter sets the Customization String. The default value is the
 189 empty string.
 190
 191 =item OSSL_MAC_PARAM_SALT ("salt") <octet string>
 192
 193 This option is used by BLAKE2 MAC.
 194
 195 =item OSSL_MAC_PARAM_XOF ("xof") <int>
 196
 197 It's a simple flag, the value 0 or 1 are expected.
 198
 199 This option is used by KMAC.
 200
 201 =item OSSL_MAC_PARAM_FLAGS ("flags") <int>
 202
 203 These will set the MAC flags to the given numbers.
 204 Some MACs do not support this option.
 205
 206 =item OSSL_MAC_PARAM_ENGINE ("engine") <utf8string>
 207
 208 =item OSSL_MAC_PARAM_MD ("md") <utf8string>
 209
 210 =item OSSL_MAC_PARAM_DIGEST ("digest") <utf8string>
 211
 212 =item OSSL_MAC_PARAM_CIPHER ("cipher") <utf8string>
 213
 214 =item OSSL_MAC_PARAM_ALGORITHM ("algorithm") <utf8string>
 215
 216 For MAC implementations that use an underlying computation algorithm,
 217 these parameters set what the algorithm should be, and the engine that
 218 implements the algorithm if needed.
 219
 220 The value is always the name of the intended engine or algorithm.
 221
 222 Note that not all algorithms may support all digests.
 223 HMAC does not support variable output length digests such as SHAKE128
 224 or SHAKE256.
 225
 226 Also note that OSSL_MAC_PARAM_ALGORITHM can be use generically instead
 227 of OSSL_MAC_PARAM_MD, OSSL_MAC_PARAM_DIGEST or OSSL_MAC_PARAM_CIPHER,
 228 and that OSSL_MAC_PARAM_MD and OSSL_MAC_PARAM_DIGEST are also interchangable.
 229
 230 =item OSSL_MAC_PARAM_SIZE <unsigned int>
 231
 232 For MAC implementations that support it, set the output size that
 233 EVP_MAC_final() should produce.
 234 The allowed sizes vary between MAC implementations.
 235
 236 =back
 237
 238 All these parameters should be used before the calls to any of
 239 EVP_MAC_init(), EVP_MAC_update() and EVP_MAC_final() for a full
 240 computation.
 241 Anything else may give undefined results.
 242
 243 =head1 RETURN VALUES
 244
 245 EVP_MAC_fetch() returns a pointer to a newly fetched EVP_MAC, or
 246 NULL if allocation failed.
 247
 248 EVP_MAC_up_ref() returns 1 on success, 0 on error.
 249
 250 EVP_MAC_free() returns nothing at all.
 251
 252 EVP_MAC_name() returns the name of the MAC, or NULL if NULL was
 253 passed.
 254
 255 EVP_MAC_provider() returns a pointer to the provider for the MAC, or
 256 NULL on error.
 257
 258 EVP_MAC_CTX_new() and EVP_MAC_CTX_dup() return a pointer to a newly
 259 created EVP_MAC_CTX, or NULL if allocation failed.
 260
 261 EVP_MAC_CTX_free() returns nothing at all.
 262
 263 EVP_MAC_CTX_get_params() and EVP_MAC_CTX_set_params() return 1 on
 264 success, 0 on error.
 265
 266 EVP_MAC_init(), EVP_MAC_update(), and EVP_MAC_final() return 1 on success, 0
 267 on error.
 268
 269 EVP_MAC_size() returns the expected output size, or 0 if it isn't
 270 set.
 271 If it isn't set, a call to EVP_MAC_init() should get it set.
 272
 273 EVP_MAC_do_all_ex() returns nothing at all.
 274
 275 =head1 EXAMPLE
 276
 277   #include <stdlib.h>
 278   #include <stdio.h>
 279   #include <string.h>
 280   #include <stdarg.h>
 281   #include <unistd.h>
 282
 283   #include <openssl/evp.h>
 284   #include <openssl/err.h>
 285   #include <openssl/params.h>
 286
 287   int main() {
 288       EVP_MAC *mac = EVP_MAC_fetch(NULL, getenv("MY_MAC"), NULL);
 289       const char *cipher = getenv("MY_MAC_CIPHER");
 290       const char *digest = getenv("MY_MAC_DIGEST");
 291       const char *key = getenv("MY_KEY");
 292       EVP_MAC_CTX *ctx = NULL;
 293
 294       unsigned char buf[4096];
 295       ssize_t read_l;
 296       size_t final_l;
 297
 298       size_t i;
 299
 300       OSSL_PARAM params[4];
 301       size_t params_n = 0;
 302
 303       if (cipher != NULL)
 304           params[params_n++] =
 305               OSSL_PARAM_construct_utf8_string("cipher", cipher,
 306                                                strlen(cipher) + 1, NULL);
 307       if (digest != NULL)
 308           params[params_n++] =
 309               OSSL_PARAM_construct_utf8_string("digest", digest,
 310                                                strlen(digest) + 1, NULL);
 311       params[params_n++] =
 312           OSSL_PARAM_construct_octet_string("key", key, strlen(key), NULL);
 313       params[params_n] = OSSL_PARAM_construct_end();
 314
 315       if (mac == NULL
 316           || key == NULL
 317           || (ctx = EVP_MAC_CTX_new(mac)) == NULL
 318           || EVP_MAC_CTX_set_params(ctx, params) <= 0)
 319           goto err;
 320
 321       if (!EVP_MAC_init(ctx))
 322           goto err;
 323
 324       while ( (read_l = read(STDIN_FILENO, buf, sizeof(buf))) < 0) {
 325           if (!EVP_MAC_update(ctx, buf, read_l))
 326               goto err;
 327       }
 328
 329       if (!EVP_MAC_final(ctx, buf, &final_l))
 330           goto err;
 331
 332       printf("Result: ");
 333       for (i = 0; i < final_l; i++)
 334           printf("%02X", buf[i]);
 335       printf("\n");
 336
 337       EVP_MAC_CTX_free(ctx);
 338       EVP_MAC_free(mac);
 339       exit(0);
 340
 341    err:
 342       EVP_MAC_CTX_free(ctx);
 343       EVP_MAC_free(mac);
 344       fprintf(stderr, "Something went wrong\n");
 345       ERR_print_errors_fp(stderr);
 346       exit (1);
 347   }
 348
 349 A run of this program, called with correct environment variables, can
 350 look like this:
 351
 352   $ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc \
 353     LD_LIBRARY_PATH=. ./foo < foo.c
 354   Result: ECCAAFF041B22A2299EB90A1B53B6D45
 355
 356 (in this example, that program was stored in F<foo.c> and compiled to
 357 F<./foo>)
 358
 359 =head1 SEE ALSO
 360
 361 L<property(7)>
 362 L<OSSL_PARAM(3)>,
 363 L<EVP_MAC_BLAKE2(7)>,
 364 L<EVP_MAC_CMAC(7)>,
 365 L<EVP_MAC_GMAC(7)>,
 366 L<EVP_MAC_HMAC(7)>,
 367 L<EVP_MAC_KMAC(7)>,
 368 L<EVP_MAC_SIPHASH(7)>,
 369 L<EVP_MAC_POLY1305(7)>
 370
 371 =head1 HISTORY
 372
 373 These functions were added in OpenSSL 3.0.
 374
 375 =head1 COPYRIGHT
 376
 377 Copyright 2018-2019 The OpenSSL Project Authors. All Rights Reserved.
 378
 379 Licensed under the Apache License 2.0 (the "License").  You may not use
 380 this file except in compliance with the License.  You can obtain a copy
 381 in the file LICENSE in the source distribution or at
 382 L<https://www.openssl.org/source/license.html>.
 383
 384 =cut