1. The European Parliament and the Council of the European Union, Directive 1999/93/EC on a community framework for electronic signatures, 1999, (Available at: https://eur-lex.europa.eu/legal-content/en/TXT/?uri=CELEX3A31999L0093).
2. The European Parliament and the Council of the European Union, Regulation (EU) No 910/2014 of the European Parliament and of the Council of 23 July 2014 on electronic identification and trust services for electronic transactions in the internal market and repealing Directive 1999/93/EC, 2014, (Available at: http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=uriserv:OJ.L_.2014.257.01.0073.01.ENG).
3. Electronic signatures and security issues: An empirical study;Srivastava;Computer Law & Security Review,2009
4. Towards a standardised preservation service for qualified electronic signatures and qualified electronic seals;Otto,2019
5. The European Commission, Proposal for a regulation of the european parliament and of the council amending Regulation (EU) No 910/2014 as regards establishing a framework for a European Digital Identity, 2021, (Available at: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX3A52021PC0281).