Cryptography is the bedrock of secure communication, and understanding its principles is essential for every cybersecurity professional. In this episode, we introduce core cryptographic concepts including confidentiality, integrity, non-repudiation, and authenticity, and how these are enabled through mathematical transformations of data. We focus especially on Public Key Infrastructure (PKI), which provides a scalable framework for managing digital certificates, public and private keys, and certificate authorities (CAs). PKI enables secure web browsing (HTTPS), email encryption, digital signatures, and authenticated device communication, making it one of the most pervasive and important trust models in cybersecurity. We discuss key pair generation, certificate signing requests (CSRs), trust chains, revocation mechanisms, and the role of intermediate and root certificates. When deployed and maintained correctly, PKI allows organizations to establish identity, encrypt sensitive traffic, and verify the legitimacy of applications and systems. Without it, the digital world would be vulnerable to impersonation, interception, and forgery.