small_order example

return self::sk_to_pk($sk);
    }

    /** * @param string $pk * @return string * @throws SodiumException * @throws TypeError */
    public static function pk_to_curve25519($pk)
    {
        if (self::small_order($pk)) {
            throw new SodiumException('Public key is on a small order');
        }
        $A = self::ge_frombytes_negate_vartime(self::substr($pk, 0, 32));
        $p1 = self::ge_mul_l($A);
        if (!self::fe_isnonzero($p1->X)) {
            throw new SodiumException('Unexpected zero result');
        }

        # fe_1(one_minus_y);         # fe_sub(one_minus_y, one_minus_y, A.Y);         # fe_invert(one_minus_y, one_minus_y);

return self::verify_core32($sig, $filePath, $publicKey);
        }

        /* Security checks */
        if (
            (ParagonIE_Sodium_Core_Ed25519::chrToInt($sig[63]) & 240)
                &&
            ParagonIE_Sodium_Core_Ed25519::check_S_lt_L(self::substr($sig, 32, 32))
        ) {
            throw new SodiumException('S < L - Invalid signature');
        }
        if (ParagonIE_Sodium_Core_Ed25519::small_order($sig)) {
            throw new SodiumException('Signature is on too small of an order');
        }
        if ((self::chrToInt($sig[63]) & 224) !== 0) {
            throw new SodiumException('Invalid signature');
        }
        $d = 0;
        for ($i = 0; $i < 32; ++$i) {
            $d |= self::chrToInt($publicKey[$i]);
        }
        if ($d === 0) {
            throw new SodiumException('All zero public key');
        }

return self::sk_to_pk($sk);
    }

    /** * @param string $pk * @return string * @throws SodiumException * @throws TypeError */
    public static function pk_to_curve25519($pk)
    {
        if (self::small_order($pk)) {
            throw new SodiumException('Public key is on a small order');
        }
        $A = self::ge_frombytes_negate_vartime($pk);
        $p1 = self::ge_mul_l($A);
        if (!self::fe_isnonzero($p1->X)) {
            throw new SodiumException('Unexpected zero result');
        }

        # fe_1(one_minus_y);         # fe_sub(one_minus_y, one_minus_y, A.Y);         # fe_invert(one_minus_y, one_minus_y);