Security is a major concern when sharing sensitive data through networks (e.g. the Internet). In today's world, data is never enough protected the way it should be. Thus, it is essential to develop structures that give a high level of security. Public Key Infrastructure (PKI) refers to a way used to support the secured exchange of data as well as information on the Internet. PKI relies on public key cryptography, digital signatures, and certificates to guarantee the integrity of data through networks. This paper begins by giving a brief introduction to public key cryptography, analysing and comparing the two public key cryptography algorithms, known as RSA and ECC, commonly used in PKI. The comparison focuses on security and efficiency. Then, we explain digital signatures and certificates, which are needed to understand the PKI. We also provide the PKI basics overview, components and operation, models, and their comparison.