doc/man3/EVP_MAC.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 EVP_MAC, EVP_MAC_fetch, EVP_MAC_up_ref, EVP_MAC_free,
 EVP_MAC_is_a, EVP_MAC_number, EVP_MAC_name, EVP_MAC_names_do_all,
 EVP_MAC_provider, EVP_MAC_get_params, EVP_MAC_gettable_params,
 EVP_MAC_CTX, EVP_MAC_CTX_new, EVP_MAC_CTX_free, EVP_MAC_CTX_dup,
 EVP_MAC_CTX_mac, EVP_MAC_CTX_get_params, EVP_MAC_CTX_set_params,
 EVP_MAC_CTX_get_mac_size, EVP_MAC_init, EVP_MAC_update, EVP_MAC_final,
 EVP_MAC_gettable_ctx_params, EVP_MAC_settable_ctx_params,
 EVP_MAC_do_all_provided - EVP MAC routines

 =head1 SYNOPSIS

  #include <openssl/evp.h>

  typedef struct evp_mac_st EVP_MAC;
  typedef struct evp_mac_ctx_st EVP_MAC_CTX;

  EVP_MAC *EVP_MAC_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
                         const char *properties);
  int EVP_MAC_up_ref(EVP_MAC *mac);
  void EVP_MAC_free(EVP_MAC *mac);
  int EVP_MAC_is_a(const EVP_MAC *mac, const char *name);
  int EVP_MAC_number(const EVP_MAC *mac);
  const char *EVP_MAC_name(const EVP_MAC *mac);
  void EVP_MAC_names_do_all(const EVP_MAC *mac,
                            void (*fn)(const char *name, void *data),
                            void *data);
  const OSSL_PROVIDER *EVP_MAC_provider(const EVP_MAC *mac);
  int EVP_MAC_get_params(EVP_MAC *mac, OSSL_PARAM params[]);

  EVP_MAC_CTX *EVP_MAC_CTX_new(EVP_MAC *mac);
  void EVP_MAC_CTX_free(EVP_MAC_CTX *ctx);
  EVP_MAC_CTX *EVP_MAC_CTX_dup(const EVP_MAC_CTX *src);
  EVP_MAC *EVP_MAC_CTX_mac(EVP_MAC_CTX *ctx);
  int EVP_MAC_CTX_get_params(EVP_MAC_CTX *ctx, OSSL_PARAM params[]);
  int EVP_MAC_CTX_set_params(EVP_MAC_CTX *ctx, const OSSL_PARAM params[]);

  size_t EVP_MAC_CTX_get_mac_size(EVP_MAC_CTX *ctx);
  int EVP_MAC_init(EVP_MAC_CTX *ctx);
  int EVP_MAC_update(EVP_MAC_CTX *ctx, const unsigned char *data, size_t datalen);
  int EVP_MAC_final(EVP_MAC_CTX *ctx,
                    unsigned char *out, size_t *outl, size_t outsize);

  const OSSL_PARAM *EVP_MAC_gettable_params(const EVP_MAC *mac);
  const OSSL_PARAM *EVP_MAC_gettable_ctx_params(const EVP_MAC *mac);
  const OSSL_PARAM *EVP_MAC_settable_ctx_params(const EVP_MAC *mac);

  void EVP_MAC_do_all_provided(OSSL_LIB_CTX *libctx,
                               void (*fn)(EVP_MAC *mac, void *arg),
                               void *arg);

 =head1 DESCRIPTION

 These types and functions help the application to calculate MACs of
 different types and with different underlying algorithms if there are
 any.

 MACs are a bit complex insofar that some of them use other algorithms
 for actual computation.  HMAC uses a digest, and CMAC uses a cipher.
 Therefore, there are sometimes two contexts to keep track of, one for
 the MAC algorithm itself and one for the underlying computation
 algorithm if there is one.

 To make things less ambiguous, this manual talks about a "context" or
 "MAC context", which is to denote the MAC level context, and about a
 "underlying context", or "computation context", which is to denote the
 context for the underlying computation algorithm if there is one.

 =head2 Types

 B<EVP_MAC> is a type that holds the implementation of a MAC.

 B<EVP_MAC_CTX> is a context type that holds internal MAC information
 as well as a reference to a computation context, for those MACs that
 rely on an underlying computation algorithm.

 =head2 Algorithm implementation fetching

 EVP_MAC_fetch() fetches an implementation of a MAC I<algorithm>, given
 a library context I<libctx> and a set of I<properties>.
 See L<provider(7)/Fetching algorithms> for further information.

 See L<OSSL_PROVIDER-default(7)/Message Authentication Code (MAC)> for the list
 of algorithms supported by the default provider.

 The returned value must eventually be freed with
 L<EVP_MAC_free(3)>.

 EVP_MAC_up_ref() increments the reference count of an already fetched
 MAC.

 EVP_MAC_free() frees a fetched algorithm.
 NULL is a valid parameter, for which this function is a no-op.

 =head2 Context manipulation functions

 EVP_MAC_CTX_new() creates a new context for the MAC type I<mac>.
 The created context can then be used with most other functions
 described here.

 EVP_MAC_CTX_free() frees the contents of the context, including an
 underlying context if there is one, as well as the context itself.
 NULL is a valid parameter, for which this function is a no-op.

 EVP_MAC_CTX_dup() duplicates the I<src> context and returns a newly allocated
 context.

 EVP_MAC_CTX_mac() returns the B<EVP_MAC> associated with the context
 I<ctx>.

 =head2 Computing functions

 EVP_MAC_init() sets up the underlying context with information given
 through diverse controls.
 This should be called before calling EVP_MAC_update() and
 EVP_MAC_final().

 EVP_MAC_update() adds I<datalen> bytes from I<data> to the MAC input.

 EVP_MAC_final() does the final computation and stores the result in
 the memory pointed at by I<out> of size I<outsize>, and sets the number
 of bytes written in I<*outl> at.
 If I<out> is NULL or I<outsize> is too small, then no computation
 is made.
 To figure out what the output length will be and allocate space for it
 dynamically, simply call with I<out> being NULL and I<outl>
 pointing at a valid location, then allocate space and make a second
 call with I<out> pointing at the allocated space.

 EVP_MAC_get_params() retrieves details about the implementation
 I<mac>.
 The set of parameters given with I<params> determine exactly what
 parameters should be retrieved.
 Note that a parameter that is unknown in the underlying context is
 simply ignored.

 EVP_MAC_CTX_get_params() retrieves chosen parameters, given the
 context I<ctx> and its underlying context.
 The set of parameters given with I<params> determine exactly what
 parameters should be retrieved.
 Note that a parameter that is unknown in the underlying context is
 simply ignored.

 EVP_MAC_CTX_set_params() passes chosen parameters to the underlying
 context, given a context I<ctx>.
 The set of parameters given with I<params> determine exactly what
 parameters are passed down.
 Note that a parameter that is unknown in the underlying context is
 simply ignored.
 Also, what happens when a needed parameter isn't passed down is
 defined by the implementation.

 EVP_MAC_gettable_params(), EVP_MAC_gettable_ctx_params() and
 EVP_MAC_settable_ctx_params() get a constant B<OSSL_PARAM> array that
 describes the retrievable and settable parameters, i.e. parameters that
 can be used with EVP_MAC_get_params(), EVP_MAC_CTX_get_params()
 and EVP_MAC_CTX_set_params(), respectively.
 See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.

 =head2 Information functions

 EVP_MAC_CTX_get_mac_size() returns the MAC output size for the given context.

 EVP_MAC_is_a() checks if the given I<mac> is an implementation of an
 algorithm that's identifiable with I<name>.

 EVP_MAC_provider() returns the provider that holds the implementation
 of the given I<mac>.

 EVP_MAC_do_all_provided() traverses all MAC implemented by all activated
 providers in the given library context I<libctx>, and for each of the
 implementations, calls the given function I<fn> with the implementation method
 and the given I<arg> as argument.

 EVP_MAC_number() returns the internal dynamic number assigned to
 I<mac>.

 EVP_MAC_name() return the name of the given MAC.  For fetched MACs
 with multiple names, only one of them is returned; it's
 recommended to use EVP_MAC_names_do_all() instead.

 EVP_MAC_names_do_all() traverses all names for I<mac>, and calls
 I<fn> with each name and I<data>.

 =head1 PARAMETERS

 Parameters are identified by name as strings, and have an expected
 data type and maximum size.
 OpenSSL has a set of macros for parameter names it expects to see in
 its own MAC implementations.
 Here, we show all three, the OpenSSL macro for the parameter name, the
 name in string form, and a type description.

 The standard parameter names are:

 =over 4

 =item "key" (B<OSSL_MAC_PARAM_KEY>) <octet string>

 Its value is the MAC key as an array of bytes.

 For MACs that use an underlying computation algorithm, the algorithm
 must be set first, see parameter names "algorithm" below.

 =item "iv" (B<OSSL_MAC_PARAM_IV>) <octet string>

 Some MAC implementations require an IV, this parameter sets the IV.

 =item "custom" (B<OSSL_MAC_PARAM_CUSTOM>) <octet string>

 Some MAC implementations (KMAC, BLAKE2) accept a Customization String,
 this parameter sets the Customization String. The default value is the
 empty string.

 =item "salt" (B<OSSL_MAC_PARAM_SALT>) <octet string>

 This option is used by BLAKE2 MAC.

 =item "xof" (B<OSSL_MAC_PARAM_XOF>) <integer>

 It's a simple flag, the value 0 or 1 are expected.

 This option is used by KMAC.

 =item "flags" (B<OSSL_MAC_PARAM_FLAGS>) <integer>

 These will set the MAC flags to the given numbers.
 Some MACs do not support this option.

 =item "properties" (B<OSSL_MAC_PARAM_PROPERTIES>) <UTF8 string>

 =item "digest" (B<OSSL_MAC_PARAM_DIGEST>) <UTF8 string>

 =item "cipher" (B<OSSL_MAC_PARAM_CIPHER>) <UTF8 string>

 For MAC implementations that use an underlying computation cipher or
 digest, these parameters set what the algorithm should be.

 The value is always the name of the intended algorithm,
 or the properties.

 Note that not all algorithms may support all digests.
 HMAC does not support variable output length digests such as SHAKE128
 or SHAKE256.

 =item "size" (B<OSSL_MAC_PARAM_SIZE>) <unsigned integer>

 For MAC implementations that support it, set the output size that
 EVP_MAC_final() should produce.
 The allowed sizes vary between MAC implementations, but must never exceed
 what can be given with a B<size_t>.

 =item "tls-data-size" (B<OSSL_MAC_PARAM_TLS_DATA_SIZE>) <unsigned integer>

 This parameter is only supported by HMAC. If set then special handling is
 activated for calculating the MAC of a received mac-then-encrypt TLS record
 where variable length record padding has been used (as in the case of CBC mode
 ciphersuites). The value represents the total length of the record that is
 having the MAC calculated including the received MAC and the record padding.

 When used EVP_MAC_update must be called precisely twice. The first time with
 the 13 bytes of TLS "header" data, and the second time with the entire record
 including the MAC itself and any padding. The entire record length must equal
 the value passed in the "tls-data-size" parameter. The length passed in the
 B<datalen> parameter to EVP_MAC_update() should be equal to the length of the
 record after the MAC and any padding has been removed.

 =back

 All these parameters should be used before the calls to any of
 EVP_MAC_init(), EVP_MAC_update() and EVP_MAC_final() for a full
 computation.
 Anything else may give undefined results.

 =head1 RETURN VALUES

 EVP_MAC_fetch() returns a pointer to a newly fetched EVP_MAC, or
 NULL if allocation failed.

 EVP_MAC_up_ref() returns 1 on success, 0 on error.

 EVP_MAC_free() returns nothing at all.

 EVP_MAC_is_a() returns 1 if the given method can be identified with
 the given name, otherwise 0.

 EVP_MAC_name() returns a name of the MAC, or NULL on error.

 EVP_MAC_provider() returns a pointer to the provider for the MAC, or
 NULL on error.

 EVP_MAC_CTX_new() and EVP_MAC_CTX_dup() return a pointer to a newly
 created EVP_MAC_CTX, or NULL if allocation failed.

 EVP_MAC_CTX_free() returns nothing at all.

 EVP_MAC_CTX_get_params() and EVP_MAC_CTX_set_params() return 1 on
 success, 0 on error.

 EVP_MAC_init(), EVP_MAC_update(), and EVP_MAC_final() return 1 on success, 0
 on error.

 EVP_MAC_CTX_get_mac_size() returns the expected output size, or 0 if it isn't set.
 If it isn't set, a call to EVP_MAC_init() should get it set.

 EVP_MAC_do_all_provided() returns nothing at all.

 =head1 EXAMPLES

   #include <stdlib.h>
   #include <stdio.h>
   #include <string.h>
   #include <stdarg.h>
   #include <unistd.h>

   #include <openssl/evp.h>
   #include <openssl/err.h>
   #include <openssl/params.h>

   int main() {
       EVP_MAC *mac = EVP_MAC_fetch(NULL, getenv("MY_MAC"), NULL);
       const char *cipher = getenv("MY_MAC_CIPHER");
       const char *digest = getenv("MY_MAC_DIGEST");
       const char *key = getenv("MY_KEY");
       EVP_MAC_CTX *ctx = NULL;

       unsigned char buf[4096];
       size_t read_l;
       size_t final_l;

       size_t i;

       OSSL_PARAM params[4];
       size_t params_n = 0;

       if (cipher != NULL)
           params[params_n++] =
               OSSL_PARAM_construct_utf8_string("cipher", (char*)cipher, 0);
       if (digest != NULL)
           params[params_n++] =
               OSSL_PARAM_construct_utf8_string("digest", (char*)digest, 0);
       params[params_n++] =
           OSSL_PARAM_construct_octet_string("key", (void*)key, strlen(key));
       params[params_n] = OSSL_PARAM_construct_end();

       if (mac == NULL
           || key == NULL
           || (ctx = EVP_MAC_CTX_new(mac)) == NULL
           || EVP_MAC_CTX_set_params(ctx, params) <= 0)
           goto err;

       if (!EVP_MAC_init(ctx))
           goto err;

       while ( (read_l = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
           if (!EVP_MAC_update(ctx, buf, read_l))
               goto err;
       }

       if (!EVP_MAC_final(ctx, buf, &final_l, sizeof(buf)))
           goto err;

       printf("Result: ");
       for (i = 0; i < final_l; i++)
           printf("%02X", buf[i]);
       printf("\n");

       EVP_MAC_CTX_free(ctx);
       EVP_MAC_free(mac);
       exit(0);

    err:
       EVP_MAC_CTX_free(ctx);
       EVP_MAC_free(mac);
       fprintf(stderr, "Something went wrong\n");
       ERR_print_errors_fp(stderr);
       exit (1);
   }

 A run of this program, called with correct environment variables, can
 look like this:

   $ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc \
     LD_LIBRARY_PATH=. ./foo < foo.c
   Result: C5C06683CD9DDEF904D754505C560A4E

 (in this example, that program was stored in F<foo.c> and compiled to
 F<./foo>)

 =head1 SEE ALSO

 L<property(7)>
 L<OSSL_PARAM(3)>,
 L<EVP_MAC-BLAKE2(7)>,
 L<EVP_MAC-CMAC(7)>,
 L<EVP_MAC-GMAC(7)>,
 L<EVP_MAC-HMAC(7)>,
 L<EVP_MAC-KMAC(7)>,
 L<EVP_MAC-Siphash(7)>,
 L<EVP_MAC-Poly1305(7)>

 =head1 HISTORY

 These functions were added in OpenSSL 3.0.

 =head1 COPYRIGHT

 Copyright 2018-2020 The OpenSSL Project Authors. All Rights Reserved.

 Licensed under the Apache License 2.0 (the "License").  You may not use
 this file except in compliance with the License.  You can obtain a copy
 in the file LICENSE in the source distribution or at
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

	EVP_MAC, EVP_MAC_fetch, EVP_MAC_up_ref, EVP_MAC_free,
	EVP_MAC_is_a, EVP_MAC_number, EVP_MAC_name, EVP_MAC_names_do_all,
	EVP_MAC_provider, EVP_MAC_get_params, EVP_MAC_gettable_params,
	EVP_MAC_CTX, EVP_MAC_CTX_new, EVP_MAC_CTX_free, EVP_MAC_CTX_dup,
	EVP_MAC_CTX_mac, EVP_MAC_CTX_get_params, EVP_MAC_CTX_set_params,
	EVP_MAC_CTX_get_mac_size, EVP_MAC_init, EVP_MAC_update, EVP_MAC_final,
	EVP_MAC_gettable_ctx_params, EVP_MAC_settable_ctx_params,
	EVP_MAC_do_all_provided - EVP MAC routines

	=head1 SYNOPSIS

	#include <openssl/evp.h>

	typedef struct evp_mac_st EVP_MAC;
	typedef struct evp_mac_ctx_st EVP_MAC_CTX;

	EVP_MAC EVP_MAC_fetch(OSSL_LIB_CTX libctx, const char *algorithm,
	const char *properties);
	int EVP_MAC_up_ref(EVP_MAC *mac);
	void EVP_MAC_free(EVP_MAC *mac);
	int EVP_MAC_is_a(const EVP_MAC mac, const char name);
	int EVP_MAC_number(const EVP_MAC *mac);
	const char EVP_MAC_name(const EVP_MAC mac);
	void EVP_MAC_names_do_all(const EVP_MAC *mac,
	void (fn)(const char name, void *data),
	void *data);
	const OSSL_PROVIDER EVP_MAC_provider(const EVP_MAC mac);
	int EVP_MAC_get_params(EVP_MAC *mac, OSSL_PARAM params[]);

	EVP_MAC_CTX EVP_MAC_CTX_new(EVP_MAC mac);
	void EVP_MAC_CTX_free(EVP_MAC_CTX *ctx);
	EVP_MAC_CTX EVP_MAC_CTX_dup(const EVP_MAC_CTX src);
	EVP_MAC EVP_MAC_CTX_mac(EVP_MAC_CTX ctx);
	int EVP_MAC_CTX_get_params(EVP_MAC_CTX *ctx, OSSL_PARAM params[]);
	int EVP_MAC_CTX_set_params(EVP_MAC_CTX *ctx, const OSSL_PARAM params[]);

	size_t EVP_MAC_CTX_get_mac_size(EVP_MAC_CTX *ctx);
	int EVP_MAC_init(EVP_MAC_CTX *ctx);
	int EVP_MAC_update(EVP_MAC_CTX ctx, const unsigned char data, size_t datalen);
	int EVP_MAC_final(EVP_MAC_CTX *ctx,
	unsigned char out, size_t outl, size_t outsize);

	const OSSL_PARAM EVP_MAC_gettable_params(const EVP_MAC mac);
	const OSSL_PARAM EVP_MAC_gettable_ctx_params(const EVP_MAC mac);
	const OSSL_PARAM EVP_MAC_settable_ctx_params(const EVP_MAC mac);

	void EVP_MAC_do_all_provided(OSSL_LIB_CTX *libctx,
	void (fn)(EVP_MAC mac, void *arg),
	void *arg);

	=head1 DESCRIPTION

	These types and functions help the application to calculate MACs of
	different types and with different underlying algorithms if there are
	any.

	MACs are a bit complex insofar that some of them use other algorithms
	for actual computation. HMAC uses a digest, and CMAC uses a cipher.
	Therefore, there are sometimes two contexts to keep track of, one for
	the MAC algorithm itself and one for the underlying computation
	algorithm if there is one.

	To make things less ambiguous, this manual talks about a "context" or
	"MAC context", which is to denote the MAC level context, and about a
	"underlying context", or "computation context", which is to denote the
	context for the underlying computation algorithm if there is one.

	=head2 Types

	B<EVP_MAC> is a type that holds the implementation of a MAC.

	B<EVP_MAC_CTX> is a context type that holds internal MAC information
	as well as a reference to a computation context, for those MACs that
	rely on an underlying computation algorithm.

	=head2 Algorithm implementation fetching

	EVP_MAC_fetch() fetches an implementation of a MAC I<algorithm>, given
	a library context I<libctx> and a set of I<properties>.
	See L<provider(7)/Fetching algorithms> for further information.

	See L<OSSL_PROVIDER-default(7)/Message Authentication Code (MAC)> for the list
	of algorithms supported by the default provider.

	The returned value must eventually be freed with
	L<EVP_MAC_free(3)>.

	EVP_MAC_up_ref() increments the reference count of an already fetched
	MAC.

	EVP_MAC_free() frees a fetched algorithm.
	NULL is a valid parameter, for which this function is a no-op.

	=head2 Context manipulation functions

	EVP_MAC_CTX_new() creates a new context for the MAC type I<mac>.
	The created context can then be used with most other functions
	described here.

	EVP_MAC_CTX_free() frees the contents of the context, including an
	underlying context if there is one, as well as the context itself.
	NULL is a valid parameter, for which this function is a no-op.

	EVP_MAC_CTX_dup() duplicates the I<src> context and returns a newly allocated
	context.

	EVP_MAC_CTX_mac() returns the B<EVP_MAC> associated with the context
	I<ctx>.

	=head2 Computing functions

	EVP_MAC_init() sets up the underlying context with information given
	through diverse controls.
	This should be called before calling EVP_MAC_update() and
	EVP_MAC_final().

	EVP_MAC_update() adds I<datalen> bytes from I<data> to the MAC input.

	EVP_MAC_final() does the final computation and stores the result in
	the memory pointed at by I<out> of size I<outsize>, and sets the number
	of bytes written in I<*outl> at.
	If I<out> is NULL or I<outsize> is too small, then no computation
	is made.
	To figure out what the output length will be and allocate space for it
	dynamically, simply call with I<out> being NULL and I<outl>
	pointing at a valid location, then allocate space and make a second
	call with I<out> pointing at the allocated space.

	EVP_MAC_get_params() retrieves details about the implementation
	I<mac>.
	The set of parameters given with I<params> determine exactly what
	parameters should be retrieved.
	Note that a parameter that is unknown in the underlying context is
	simply ignored.

	EVP_MAC_CTX_get_params() retrieves chosen parameters, given the
	context I<ctx> and its underlying context.
	The set of parameters given with I<params> determine exactly what
	parameters should be retrieved.
	Note that a parameter that is unknown in the underlying context is
	simply ignored.

	EVP_MAC_CTX_set_params() passes chosen parameters to the underlying
	context, given a context I<ctx>.
	The set of parameters given with I<params> determine exactly what
	parameters are passed down.
	Note that a parameter that is unknown in the underlying context is
	simply ignored.
	Also, what happens when a needed parameter isn't passed down is
	defined by the implementation.

	EVP_MAC_gettable_params(), EVP_MAC_gettable_ctx_params() and
	EVP_MAC_settable_ctx_params() get a constant B<OSSL_PARAM> array that
	describes the retrievable and settable parameters, i.e. parameters that
	can be used with EVP_MAC_get_params(), EVP_MAC_CTX_get_params()
	and EVP_MAC_CTX_set_params(), respectively.
	See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.

	=head2 Information functions

	EVP_MAC_CTX_get_mac_size() returns the MAC output size for the given context.

	EVP_MAC_is_a() checks if the given I<mac> is an implementation of an
	algorithm that's identifiable with I<name>.

	EVP_MAC_provider() returns the provider that holds the implementation
	of the given I<mac>.

	EVP_MAC_do_all_provided() traverses all MAC implemented by all activated
	providers in the given library context I<libctx>, and for each of the
	implementations, calls the given function I<fn> with the implementation method
	and the given I<arg> as argument.

	EVP_MAC_number() returns the internal dynamic number assigned to
	I<mac>.

	EVP_MAC_name() return the name of the given MAC. For fetched MACs
	with multiple names, only one of them is returned; it's
	recommended to use EVP_MAC_names_do_all() instead.

	EVP_MAC_names_do_all() traverses all names for I<mac>, and calls
	I<fn> with each name and I<data>.

	=head1 PARAMETERS

	Parameters are identified by name as strings, and have an expected
	data type and maximum size.
	OpenSSL has a set of macros for parameter names it expects to see in
	its own MAC implementations.
	Here, we show all three, the OpenSSL macro for the parameter name, the
	name in string form, and a type description.

	The standard parameter names are:

	=over 4

	=item "key" (B<OSSL_MAC_PARAM_KEY>) <octet string>

	Its value is the MAC key as an array of bytes.

	For MACs that use an underlying computation algorithm, the algorithm
	must be set first, see parameter names "algorithm" below.

	=item "iv" (B<OSSL_MAC_PARAM_IV>) <octet string>

	Some MAC implementations require an IV, this parameter sets the IV.

	=item "custom" (B<OSSL_MAC_PARAM_CUSTOM>) <octet string>

	Some MAC implementations (KMAC, BLAKE2) accept a Customization String,
	this parameter sets the Customization String. The default value is the
	empty string.

	=item "salt" (B<OSSL_MAC_PARAM_SALT>) <octet string>

	This option is used by BLAKE2 MAC.

	=item "xof" (B<OSSL_MAC_PARAM_XOF>) <integer>

	It's a simple flag, the value 0 or 1 are expected.

	This option is used by KMAC.

	=item "flags" (B<OSSL_MAC_PARAM_FLAGS>) <integer>

	These will set the MAC flags to the given numbers.
	Some MACs do not support this option.

	=item "properties" (B<OSSL_MAC_PARAM_PROPERTIES>) <UTF8 string>

	=item "digest" (B<OSSL_MAC_PARAM_DIGEST>) <UTF8 string>

	=item "cipher" (B<OSSL_MAC_PARAM_CIPHER>) <UTF8 string>

	For MAC implementations that use an underlying computation cipher or
	digest, these parameters set what the algorithm should be.

	The value is always the name of the intended algorithm,
	or the properties.

	Note that not all algorithms may support all digests.
	HMAC does not support variable output length digests such as SHAKE128
	or SHAKE256.

	=item "size" (B<OSSL_MAC_PARAM_SIZE>) <unsigned integer>

	For MAC implementations that support it, set the output size that
	EVP_MAC_final() should produce.
	The allowed sizes vary between MAC implementations, but must never exceed
	what can be given with a B<size_t>.

	=item "tls-data-size" (B<OSSL_MAC_PARAM_TLS_DATA_SIZE>) <unsigned integer>

	This parameter is only supported by HMAC. If set then special handling is
	activated for calculating the MAC of a received mac-then-encrypt TLS record
	where variable length record padding has been used (as in the case of CBC mode
	ciphersuites). The value represents the total length of the record that is
	having the MAC calculated including the received MAC and the record padding.

	When used EVP_MAC_update must be called precisely twice. The first time with
	the 13 bytes of TLS "header" data, and the second time with the entire record
	including the MAC itself and any padding. The entire record length must equal
	the value passed in the "tls-data-size" parameter. The length passed in the
	B<datalen> parameter to EVP_MAC_update() should be equal to the length of the
	record after the MAC and any padding has been removed.

	=back

	All these parameters should be used before the calls to any of
	EVP_MAC_init(), EVP_MAC_update() and EVP_MAC_final() for a full
	computation.
	Anything else may give undefined results.

	=head1 RETURN VALUES

	EVP_MAC_fetch() returns a pointer to a newly fetched EVP_MAC, or
	NULL if allocation failed.

	EVP_MAC_up_ref() returns 1 on success, 0 on error.

	EVP_MAC_free() returns nothing at all.

	EVP_MAC_is_a() returns 1 if the given method can be identified with
	the given name, otherwise 0.

	EVP_MAC_name() returns a name of the MAC, or NULL on error.

	EVP_MAC_provider() returns a pointer to the provider for the MAC, or
	NULL on error.

	EVP_MAC_CTX_new() and EVP_MAC_CTX_dup() return a pointer to a newly
	created EVP_MAC_CTX, or NULL if allocation failed.

	EVP_MAC_CTX_free() returns nothing at all.

	EVP_MAC_CTX_get_params() and EVP_MAC_CTX_set_params() return 1 on
	success, 0 on error.

	EVP_MAC_init(), EVP_MAC_update(), and EVP_MAC_final() return 1 on success, 0
	on error.

	EVP_MAC_CTX_get_mac_size() returns the expected output size, or 0 if it isn't set.
	If it isn't set, a call to EVP_MAC_init() should get it set.

	EVP_MAC_do_all_provided() returns nothing at all.

	=head1 EXAMPLES

	#include <stdlib.h>
	#include <stdio.h>
	#include <string.h>
	#include <stdarg.h>
	#include <unistd.h>

	#include <openssl/evp.h>
	#include <openssl/err.h>
	#include <openssl/params.h>

	int main() {
	EVP_MAC *mac = EVP_MAC_fetch(NULL, getenv("MY_MAC"), NULL);
	const char *cipher = getenv("MY_MAC_CIPHER");
	const char *digest = getenv("MY_MAC_DIGEST");
	const char *key = getenv("MY_KEY");
	EVP_MAC_CTX *ctx = NULL;

	unsigned char buf[4096];
	size_t read_l;
	size_t final_l;

	size_t i;

	OSSL_PARAM params[4];
	size_t params_n = 0;

	if (cipher != NULL)
	params[params_n++] =
	OSSL_PARAM_construct_utf8_string("cipher", (char*)cipher, 0);
	if (digest != NULL)
	params[params_n++] =
	OSSL_PARAM_construct_utf8_string("digest", (char*)digest, 0);
	params[params_n++] =
	OSSL_PARAM_construct_octet_string("key", (void*)key, strlen(key));
	params[params_n] = OSSL_PARAM_construct_end();

	if (mac == NULL
	\|\| key == NULL
	\|\| (ctx = EVP_MAC_CTX_new(mac)) == NULL
	\|\| EVP_MAC_CTX_set_params(ctx, params) <= 0)
	goto err;

	if (!EVP_MAC_init(ctx))
	goto err;

	while ( (read_l = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
	if (!EVP_MAC_update(ctx, buf, read_l))
	goto err;
	}

	if (!EVP_MAC_final(ctx, buf, &final_l, sizeof(buf)))
	goto err;

	printf("Result: ");
	for (i = 0; i < final_l; i++)
	printf("%02X", buf[i]);
	printf("\n");

	EVP_MAC_CTX_free(ctx);
	EVP_MAC_free(mac);
	exit(0);

	err:
	EVP_MAC_CTX_free(ctx);
	EVP_MAC_free(mac);
	fprintf(stderr, "Something went wrong\n");
	ERR_print_errors_fp(stderr);
	exit (1);
	}

	A run of this program, called with correct environment variables, can
	look like this:

	$ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc \
	LD_LIBRARY_PATH=. ./foo < foo.c
	Result: C5C06683CD9DDEF904D754505C560A4E

	(in this example, that program was stored in F<foo.c> and compiled to
	F<./foo>)

	=head1 SEE ALSO

	L<property(7)>
	L<OSSL_PARAM(3)>,
	L<EVP_MAC-BLAKE2(7)>,
	L<EVP_MAC-CMAC(7)>,
	L<EVP_MAC-GMAC(7)>,
	L<EVP_MAC-HMAC(7)>,
	L<EVP_MAC-KMAC(7)>,
	L<EVP_MAC-Siphash(7)>,
	L<EVP_MAC-Poly1305(7)>

	=head1 HISTORY

	These functions were added in OpenSSL 3.0.

	=head1 COPYRIGHT

	Copyright 2018-2020 The OpenSSL Project Authors. All Rights Reserved.

	Licensed under the Apache License 2.0 (the "License"). You may not use
	this file except in compliance with the License. You can obtain a copy
	in the file LICENSE in the source distribution or at
	L<https://www.openssl.org/source/license.html>.

	=cut