ParagonIE\Halite\Asymmetric\SignatureSecretKey::__construct PHP Method

    public function __construct(HiddenString $keyMaterial)
    {
        if (CryptoUtil::safeStrlen($keyMaterial->getString()) !== \Sodium\CRYPTO_SIGN_SECRETKEYBYTES) {
            throw new InvalidKey('Signature secret key must be CRYPTO_SIGN_SECRETKEYBYTES bytes long');
        }
        parent::__construct($keyMaterial);
        $this->isSigningKey = true;
    }