Recommendation ITU-T X.508 | ISO/IEC 9594-12 is intended to fill the gap between Recommendation ITU-T X.509 | ISO/IEC 9594-8 and Recommendation ITU-T X.510 | ISO/IEC 9594-11 by giving a description of selected cryptographic algorithm with references to more detailed specifications. To establish the theory behind the cryptographic algorithm, an informative annex gives in introduction to the supporting mathematics. Also, some considerations on migration to post quantum algorithm are included. Section 3 provides a best practice guideline for establishing and maintaining a PKI with emphasis on specific environment outside the traditional PKI environments, such as guidance for establishing a PKI for networks of Internet of Things (IoT) and smart grid.