CTX_get_mac_size(). The length of the &quot;size&quot; parameter should not exceed that of a <b>size_t</b>.</p>

<dl>

<dt id="key-OSSL_MAC_PARAM_KEY-octet-string">&quot;key&quot; (<b>OSSL_MAC_PARAM_KEY</b>) &lt;octet string&gt;</dt>
<dd>

<p>Sets the MAC key. Setting this parameter is identical to passing a <i>key</i> to <a href="../man3/EVP_MAC_init.html">EVP_MAC_init(3)</a>.</p>

</dd>
<dt id="size-OSSL_MAC_PARAM_SIZE-unsigned-integer">&quot;size&quot; (<b>OSSL_MAC_PARAM_SIZE</b>) &lt;unsigned integer&gt