19.1. When providing services to individuals and legal entities in electronic form, the State shall identify the individuals and legal entities using electronic signatures and identification and login systems with methods and tools determined by the Government. Article 20. Public key infrastructure Print 20.1. Relations connected to public key infrastructure shall be regulated by the said law. Article 21. Central system of exchange of official documents Print 21.1. When sending and receiving official letters electronically other than official e-mail, the data subjects shall connect to and use the shared system of official letter exchange. 21.2. A person or legal entity may connect to and use the shared system for exchanging official letters when sending and receiving official letters electronically with the data subject in a form other than official e-mail. Article 22. Information exchange registration system Print 22.1. Information sent and received by the main system shall be recorded by the information exchange registration system, as well as the time of sending and receiving, the sender and recipient, the unique value indicating the content of the information and other information. Article 23. Notification delivery system Print 23.1. The person responsible for the information shall deliver notices electronically to persons and legal entities using the notice delivery system in the following cases: 23.1.1. closed and restricted information belonging to a person or legal entity was accessed by other persons; 23.1.2. information about the process and decisions of requests and complaints made to the respondent; 23.1.3. a reminder to people and legal entities about the need to receive public services; 23.1.4. regarding payment of taxes and fines; 23.1.5. The date of the referendum and election day. 23.2. The person responsible for the information may inform the person or legal entity about the notification that can be received and the form in which it can be received, except as specified in Article 23.1 of this law. 23.3. An e-mail address for a person with a civil registration number specified in Section 4.1.1 of the Law on Civil Registration and a legal entity with a legal entity's state registration number shall be created in the system for delivering notifications at the request of a person or legal entity. 23.4. Persons and legal entities may use e-mail addresses other than those specified in Article 23.3 of this Law on the basis of registration in the notification delivery system. 23.5. Clause 23.1.1 of this law shall not apply if the closed and restricted information is transmitted to the competent authority within the scope of execution. Article 24. Unified system of public services Print 24.1. The integrated state service system is a means of delivering public information, state and other services to people and legal entities in electronic form. 24.2. The person responsible for the information shall provide the services provided to individuals and legal entities in electronic form using the integrated state service system. 24.3. The government shall approve the model of reference and description to be provided by the data subject through the integrated system of public services. 24.4. An electronic document with a unique number issued by the unified system of state services is as valid as a paper document. Article 25. Payment system