X.509
X.509 is an international standard that defines the format for public key certificates, which are used in public key infrastructure (PKI) to verify the identity of entities such as websites, servers, and users. It specifies the structure of certificates, including fields like subject, issuer, public key, validity period, and digital signatures, enabling secure authentication and encryption in networks like the internet. These certificates are foundational for protocols such as TLS/SSL, which secure web communications.
Developers should learn X.509 when working on systems that require secure authentication, encryption, or digital signatures, such as web applications, APIs, IoT devices, or enterprise networks. It is essential for implementing HTTPS, VPNs, email security (S/MIME), and code signing, as it ensures trust and prevents man-in-the-middle attacks by validating identities through certificate authorities (CAs).