ParagonIE\Halite\KeyFactory::deriveSignatureKeyPair PHP Method

    public static function deriveSignatureKeyPair(HiddenString $password, string $salt, string $level = self::INTERACTIVE) : SignatureKeyPair
    {
        $kdfLimits = self::getSecurityLevels($level);
        // VERSION 2+ (argon2)
        if (Util::safeStrlen($salt) !== \Sodium\CRYPTO_PWHASH_SALTBYTES) {
            throw new CryptoException\InvalidSalt('Expected ' . \Sodium\CRYPTO_PWHASH_SALTBYTES . ' bytes, got ' . Util::safeStrlen($salt));
        }
        // Digital signature keypair
        $seed = \Sodium\crypto_pwhash(\Sodium\CRYPTO_SIGN_SEEDBYTES, $password->getString(), $salt, $kdfLimits[0], $kdfLimits[1]);
        $keyPair = \Sodium\crypto_sign_seed_keypair($seed);
        $secretKey = \Sodium\crypto_sign_secretkey($keyPair);
        // Let's wipe our $kp variable
        \Sodium\memzero($keyPair);
        return new SignatureKeyPair(new SignatureSecretKey(new HiddenString($secretKey)));
    }

 public function testDeriveSigningKey()
 {
     $keypair = KeyFactory::deriveSignatureKeyPair('apple', "
\t\n\v\f\r");
     $sign_secret = $keypair->getSecretKey();
     $sign_public = $keypair->getPublicKey();
     $this->assertTrue($sign_secret instanceof ASecretKey);
     $this->assertTrue($sign_public instanceof APublicKey);
     // Can this be used?
     $message = 'This is a test message';
     $signed = Asymmetric::sign($message, $sign_secret);
     $this->assertTrue(Asymmetric::verify($message, $sign_public, $signed));
     $this->assertEquals($sign_public->getRawKeyMaterial(), ".À>¸t\fÿ³ŽêßþŒé9" . "7}ýî¤mÉKƒëT sOº");
 }