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