mirror of https://github.com/openssl/openssl.git
419 lines
14 KiB
Plaintext
419 lines
14 KiB
Plaintext
=pod
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=head1 NAME
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EVP_MAC, EVP_MAC_fetch, EVP_MAC_up_ref, EVP_MAC_free,
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EVP_MAC_is_a, EVP_MAC_number, EVP_MAC_name, EVP_MAC_names_do_all,
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EVP_MAC_provider, EVP_MAC_get_params, EVP_MAC_gettable_params,
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EVP_MAC_CTX, EVP_MAC_CTX_new, EVP_MAC_CTX_free, EVP_MAC_CTX_dup,
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EVP_MAC_CTX_mac, EVP_MAC_CTX_get_params, EVP_MAC_CTX_set_params,
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EVP_MAC_CTX_get_mac_size, EVP_MAC_init, EVP_MAC_update, EVP_MAC_final,
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EVP_MAC_gettable_ctx_params, EVP_MAC_settable_ctx_params,
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EVP_MAC_do_all_provided - EVP MAC routines
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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typedef struct evp_mac_st EVP_MAC;
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typedef struct evp_mac_ctx_st EVP_MAC_CTX;
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EVP_MAC *EVP_MAC_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
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const char *properties);
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int EVP_MAC_up_ref(EVP_MAC *mac);
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void EVP_MAC_free(EVP_MAC *mac);
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int EVP_MAC_is_a(const EVP_MAC *mac, const char *name);
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int EVP_MAC_number(const EVP_MAC *mac);
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const char *EVP_MAC_name(const EVP_MAC *mac);
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void EVP_MAC_names_do_all(const EVP_MAC *mac,
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void (*fn)(const char *name, void *data),
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void *data);
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const OSSL_PROVIDER *EVP_MAC_provider(const EVP_MAC *mac);
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int EVP_MAC_get_params(EVP_MAC *mac, OSSL_PARAM params[]);
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EVP_MAC_CTX *EVP_MAC_CTX_new(EVP_MAC *mac);
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void EVP_MAC_CTX_free(EVP_MAC_CTX *ctx);
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EVP_MAC_CTX *EVP_MAC_CTX_dup(const EVP_MAC_CTX *src);
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EVP_MAC *EVP_MAC_CTX_mac(EVP_MAC_CTX *ctx);
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int EVP_MAC_CTX_get_params(EVP_MAC_CTX *ctx, OSSL_PARAM params[]);
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int EVP_MAC_CTX_set_params(EVP_MAC_CTX *ctx, const OSSL_PARAM params[]);
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size_t EVP_MAC_CTX_get_mac_size(EVP_MAC_CTX *ctx);
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int EVP_MAC_init(EVP_MAC_CTX *ctx);
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int EVP_MAC_update(EVP_MAC_CTX *ctx, const unsigned char *data, size_t datalen);
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int EVP_MAC_final(EVP_MAC_CTX *ctx,
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unsigned char *out, size_t *outl, size_t outsize);
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const OSSL_PARAM *EVP_MAC_gettable_params(const EVP_MAC *mac);
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const OSSL_PARAM *EVP_MAC_gettable_ctx_params(const EVP_MAC *mac);
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const OSSL_PARAM *EVP_MAC_settable_ctx_params(const EVP_MAC *mac);
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void EVP_MAC_do_all_provided(OSSL_LIB_CTX *libctx,
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void (*fn)(EVP_MAC *mac, void *arg),
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void *arg);
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=head1 DESCRIPTION
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These types and functions help the application to calculate MACs of
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different types and with different underlying algorithms if there are
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any.
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MACs are a bit complex insofar that some of them use other algorithms
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for actual computation. HMAC uses a digest, and CMAC uses a cipher.
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Therefore, there are sometimes two contexts to keep track of, one for
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the MAC algorithm itself and one for the underlying computation
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algorithm if there is one.
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To make things less ambiguous, this manual talks about a "context" or
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"MAC context", which is to denote the MAC level context, and about a
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"underlying context", or "computation context", which is to denote the
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context for the underlying computation algorithm if there is one.
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=head2 Types
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B<EVP_MAC> is a type that holds the implementation of a MAC.
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B<EVP_MAC_CTX> is a context type that holds internal MAC information
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as well as a reference to a computation context, for those MACs that
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rely on an underlying computation algorithm.
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=head2 Algorithm implementation fetching
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EVP_MAC_fetch() fetches an implementation of a MAC I<algorithm>, given
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a library context I<libctx> and a set of I<properties>.
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See L<provider(7)/Fetching algorithms> for further information.
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See L<OSSL_PROVIDER-default(7)/Message Authentication Code (MAC)> for the list
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of algorithms supported by the default provider.
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The returned value must eventually be freed with
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L<EVP_MAC_free(3)>.
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EVP_MAC_up_ref() increments the reference count of an already fetched
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MAC.
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EVP_MAC_free() frees a fetched algorithm.
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NULL is a valid parameter, for which this function is a no-op.
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=head2 Context manipulation functions
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EVP_MAC_CTX_new() creates a new context for the MAC type I<mac>.
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The created context can then be used with most other functions
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described here.
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EVP_MAC_CTX_free() frees the contents of the context, including an
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underlying context if there is one, as well as the context itself.
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NULL is a valid parameter, for which this function is a no-op.
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EVP_MAC_CTX_dup() duplicates the I<src> context and returns a newly allocated
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context.
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EVP_MAC_CTX_mac() returns the B<EVP_MAC> associated with the context
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I<ctx>.
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=head2 Computing functions
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EVP_MAC_init() sets up the underlying context with information given
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through diverse controls.
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This should be called before calling EVP_MAC_update() and
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EVP_MAC_final().
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EVP_MAC_update() adds I<datalen> bytes from I<data> to the MAC input.
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EVP_MAC_final() does the final computation and stores the result in
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the memory pointed at by I<out> of size I<outsize>, and sets the number
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of bytes written in I<*outl> at.
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If I<out> is NULL or I<outsize> is too small, then no computation
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is made.
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To figure out what the output length will be and allocate space for it
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dynamically, simply call with I<out> being NULL and I<outl>
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pointing at a valid location, then allocate space and make a second
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call with I<out> pointing at the allocated space.
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EVP_MAC_get_params() retrieves details about the implementation
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I<mac>.
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The set of parameters given with I<params> determine exactly what
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parameters should be retrieved.
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Note that a parameter that is unknown in the underlying context is
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simply ignored.
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EVP_MAC_CTX_get_params() retrieves chosen parameters, given the
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context I<ctx> and its underlying context.
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The set of parameters given with I<params> determine exactly what
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parameters should be retrieved.
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Note that a parameter that is unknown in the underlying context is
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simply ignored.
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EVP_MAC_CTX_set_params() passes chosen parameters to the underlying
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context, given a context I<ctx>.
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The set of parameters given with I<params> determine exactly what
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parameters are passed down.
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Note that a parameter that is unknown in the underlying context is
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simply ignored.
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Also, what happens when a needed parameter isn't passed down is
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defined by the implementation.
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EVP_MAC_gettable_params(), EVP_MAC_gettable_ctx_params() and
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EVP_MAC_settable_ctx_params() get a constant B<OSSL_PARAM> array that
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describes the retrievable and settable parameters, i.e. parameters that
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can be used with EVP_MAC_get_params(), EVP_MAC_CTX_get_params()
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and EVP_MAC_CTX_set_params(), respectively.
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See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.
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=head2 Information functions
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EVP_MAC_CTX_get_mac_size() returns the MAC output size for the given context.
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EVP_MAC_is_a() checks if the given I<mac> is an implementation of an
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algorithm that's identifiable with I<name>.
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EVP_MAC_provider() returns the provider that holds the implementation
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of the given I<mac>.
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EVP_MAC_do_all_provided() traverses all MAC implemented by all activated
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providers in the given library context I<libctx>, and for each of the
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implementations, calls the given function I<fn> with the implementation method
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and the given I<arg> as argument.
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EVP_MAC_number() returns the internal dynamic number assigned to
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I<mac>.
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EVP_MAC_name() return the name of the given MAC. For fetched MACs
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with multiple names, only one of them is returned; it's
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recommended to use EVP_MAC_names_do_all() instead.
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EVP_MAC_names_do_all() traverses all names for I<mac>, and calls
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I<fn> with each name and I<data>.
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=head1 PARAMETERS
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Parameters are identified by name as strings, and have an expected
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data type and maximum size.
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OpenSSL has a set of macros for parameter names it expects to see in
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its own MAC implementations.
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Here, we show all three, the OpenSSL macro for the parameter name, the
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name in string form, and a type description.
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The standard parameter names are:
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=over 4
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=item "key" (B<OSSL_MAC_PARAM_KEY>) <octet string>
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Its value is the MAC key as an array of bytes.
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For MACs that use an underlying computation algorithm, the algorithm
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must be set first, see parameter names "algorithm" below.
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=item "iv" (B<OSSL_MAC_PARAM_IV>) <octet string>
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Some MAC implementations require an IV, this parameter sets the IV.
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=item "custom" (B<OSSL_MAC_PARAM_CUSTOM>) <octet string>
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Some MAC implementations (KMAC, BLAKE2) accept a Customization String,
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this parameter sets the Customization String. The default value is the
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empty string.
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=item "salt" (B<OSSL_MAC_PARAM_SALT>) <octet string>
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This option is used by BLAKE2 MAC.
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=item "xof" (B<OSSL_MAC_PARAM_XOF>) <integer>
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It's a simple flag, the value 0 or 1 are expected.
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This option is used by KMAC.
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=item "flags" (B<OSSL_MAC_PARAM_FLAGS>) <integer>
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These will set the MAC flags to the given numbers.
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Some MACs do not support this option.
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=item "properties" (B<OSSL_MAC_PARAM_PROPERTIES>) <UTF8 string>
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=item "digest" (B<OSSL_MAC_PARAM_DIGEST>) <UTF8 string>
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=item "cipher" (B<OSSL_MAC_PARAM_CIPHER>) <UTF8 string>
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For MAC implementations that use an underlying computation cipher or
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digest, these parameters set what the algorithm should be.
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The value is always the name of the intended algorithm,
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or the properties.
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Note that not all algorithms may support all digests.
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HMAC does not support variable output length digests such as SHAKE128
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or SHAKE256.
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=item "size" (B<OSSL_MAC_PARAM_SIZE>) <unsigned integer>
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For MAC implementations that support it, set the output size that
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EVP_MAC_final() should produce.
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The allowed sizes vary between MAC implementations, but must never exceed
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what can be given with a B<size_t>.
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=item "tls-data-size" (B<OSSL_MAC_PARAM_TLS_DATA_SIZE>) <unsigned integer>
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This parameter is only supported by HMAC. If set then special handling is
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activated for calculating the MAC of a received mac-then-encrypt TLS record
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where variable length record padding has been used (as in the case of CBC mode
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ciphersuites). The value represents the total length of the record that is
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having the MAC calculated including the received MAC and the record padding.
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When used EVP_MAC_update must be called precisely twice. The first time with
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the 13 bytes of TLS "header" data, and the second time with the entire record
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including the MAC itself and any padding. The entire record length must equal
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the value passed in the "tls-data-size" parameter. The length passed in the
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B<datalen> parameter to EVP_MAC_update() should be equal to the length of the
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record after the MAC and any padding has been removed.
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=back
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All these parameters should be used before the calls to any of
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EVP_MAC_init(), EVP_MAC_update() and EVP_MAC_final() for a full
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computation.
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Anything else may give undefined results.
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=head1 RETURN VALUES
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EVP_MAC_fetch() returns a pointer to a newly fetched EVP_MAC, or
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NULL if allocation failed.
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EVP_MAC_up_ref() returns 1 on success, 0 on error.
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EVP_MAC_free() returns nothing at all.
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EVP_MAC_is_a() returns 1 if the given method can be identified with
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the given name, otherwise 0.
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EVP_MAC_name() returns a name of the MAC, or NULL on error.
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EVP_MAC_provider() returns a pointer to the provider for the MAC, or
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NULL on error.
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EVP_MAC_CTX_new() and EVP_MAC_CTX_dup() return a pointer to a newly
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created EVP_MAC_CTX, or NULL if allocation failed.
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EVP_MAC_CTX_free() returns nothing at all.
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EVP_MAC_CTX_get_params() and EVP_MAC_CTX_set_params() return 1 on
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success, 0 on error.
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EVP_MAC_init(), EVP_MAC_update(), and EVP_MAC_final() return 1 on success, 0
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on error.
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EVP_MAC_CTX_get_mac_size() returns the expected output size, or 0 if it isn't set.
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If it isn't set, a call to EVP_MAC_init() should get it set.
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EVP_MAC_do_all_provided() returns nothing at all.
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=head1 EXAMPLES
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#include <stdarg.h>
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#include <unistd.h>
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#include <openssl/evp.h>
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#include <openssl/err.h>
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#include <openssl/params.h>
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int main() {
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EVP_MAC *mac = EVP_MAC_fetch(NULL, getenv("MY_MAC"), NULL);
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const char *cipher = getenv("MY_MAC_CIPHER");
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const char *digest = getenv("MY_MAC_DIGEST");
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const char *key = getenv("MY_KEY");
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EVP_MAC_CTX *ctx = NULL;
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unsigned char buf[4096];
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size_t read_l;
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size_t final_l;
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size_t i;
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OSSL_PARAM params[4];
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size_t params_n = 0;
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if (cipher != NULL)
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params[params_n++] =
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OSSL_PARAM_construct_utf8_string("cipher", (char*)cipher, 0);
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if (digest != NULL)
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params[params_n++] =
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OSSL_PARAM_construct_utf8_string("digest", (char*)digest, 0);
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params[params_n++] =
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OSSL_PARAM_construct_octet_string("key", (void*)key, strlen(key));
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params[params_n] = OSSL_PARAM_construct_end();
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if (mac == NULL
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|| key == NULL
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|| (ctx = EVP_MAC_CTX_new(mac)) == NULL
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|| EVP_MAC_CTX_set_params(ctx, params) <= 0)
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goto err;
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if (!EVP_MAC_init(ctx))
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goto err;
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while ( (read_l = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
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if (!EVP_MAC_update(ctx, buf, read_l))
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goto err;
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}
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if (!EVP_MAC_final(ctx, buf, &final_l, sizeof(buf)))
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goto err;
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printf("Result: ");
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for (i = 0; i < final_l; i++)
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printf("%02X", buf[i]);
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printf("\n");
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EVP_MAC_CTX_free(ctx);
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EVP_MAC_free(mac);
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exit(0);
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err:
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EVP_MAC_CTX_free(ctx);
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EVP_MAC_free(mac);
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fprintf(stderr, "Something went wrong\n");
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ERR_print_errors_fp(stderr);
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exit (1);
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}
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A run of this program, called with correct environment variables, can
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look like this:
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$ MY_MAC=cmac MY_KEY=secret0123456789 MY_MAC_CIPHER=aes-128-cbc \
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LD_LIBRARY_PATH=. ./foo < foo.c
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Result: C5C06683CD9DDEF904D754505C560A4E
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(in this example, that program was stored in F<foo.c> and compiled to
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F<./foo>)
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=head1 SEE ALSO
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L<property(7)>
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L<OSSL_PARAM(3)>,
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L<EVP_MAC-BLAKE2(7)>,
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L<EVP_MAC-CMAC(7)>,
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L<EVP_MAC-GMAC(7)>,
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L<EVP_MAC-HMAC(7)>,
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L<EVP_MAC-KMAC(7)>,
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L<EVP_MAC-Siphash(7)>,
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L<EVP_MAC-Poly1305(7)>
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=head1 HISTORY
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These functions were added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2018-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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