B<p1> and B<p2>.
For B<cmd> = B<EVP_PKEY_CTRL_SET_MAC_KEY>, B<p1> is the length of the MAC key,
-and B<p2> is MAC key. This is used by Poly1305, HMAC and CMAC.
+and B<p2> is MAC key. This is used by Poly1305, SipHash, HMAC and CMAC.
Applications will not normally call EVP_PKEY_CTX_ctrl() directly but will
instead call one of the algorithm specific macros below.