Poly1305
Implementation derived from poly1305-donna-16.h See for details: https://github.com/floodyberry/poly1305-donna
KeySize
TagSize
$_instance :
init( $key)
update( $ctx, $m, $bytes)
finish( $ctx, $mac)
instance()
auth( $mac, $m, $bytes, $key)
U8TO16( $p, $pos)
U16TO8( $p, $pos, $v)
blocks( $ctx, $m, $mpos, $bytes)