_size() returns the MAC block size for the given context. Not all MAC algorithms support this.</p>

<p>EVP_MAC_is_a() checks if the given <i>mac</i> is an implementation of an algorithm that&#39;s identifiable with <i>name</i>.</p>

<p>EVP_MAC_get0_provider() returns the provider that holds the implementation of the given <i>mac</i>.</p>

<p>EVP_MAC_do_all_provided() traverses all MAC implemented by all activated providers in the given library context <i>libctx</i>, and for each of the implementations, call