Establishing online services can bring significant advantages for users and for the businesses. However, it has many issues related to integrity and confidentiality. Adopting public key cryptography is important to provide high level of confidentiality and authentication services for online transactions, but it needs a trusted way of distributing public keys. Public Key Infrastructure (PKI) is a solution for assuring the authenticity of public keys via qualified digital certificates. The first part of this paper covers the basic concept of PKI and overview of its implementation, and the related issues on digital certificates and X.509 standard. The second part covers the case study of UAE's implementation of the PKI focusing on the Emirate ID's smart card experience. Finally, this paper discusses about the attacks that threaten the PKI.