ParagonIE_Sodium_Core_Poly1305_State::__construct

    public function __construct($key = '')
    {
        if (self::strlen($key) < 32) {
            throw new InvalidArgumentException(
                'Poly1305 requires a 32-byte key'
            );
        }
        /* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
        $this->r = array(
            (int) ((self::load_4(self::substr($key, 0, 4))) & 0x3ffffff),
            (int) ((self::load_4(self::substr($key, 3, 4)) >> 2) & 0x3ffff03),
            (int) ((self::load_4(self::substr($key, 6, 4)) >> 4) & 0x3ffc0ff),
            (int) ((self::load_4(self::substr($key, 9, 4)) >> 6) & 0x3f03fff),
            (int) ((self::load_4(self::substr($key, 12, 4)) >> 8) & 0x00fffff)
        );

        /* h = 0 */
        $this->h = array(0, 0, 0, 0, 0);

        /* save pad for later */
        $this->pad = array(
            self::load_4(self::substr($key, 16, 4)),
            self::load_4(self::substr($key, 20, 4)),
            self::load_4(self::substr($key, 24, 4)),
            self::load_4(self::substr($key, 28, 4)),
        );

        $this->leftover = 0;
        $this->final = false;
    }