The official secret is generally regulated with Art. 26 of the Protection of Classified Information Act. Pursuant to that provision, official secret may be introduced only with a law. Categories of information subject to classification as official secret can only be established by law. On that ground, the heads of administrative structures could approve of specific lists of categories of information subject to classification as official secret that only apply for the respective structure.
The approved lists should be publicly available.
The State Commission on Information Security has issued Mandatory Guidelines for the Classification of Information as Official Secret.