Security certificates are digital documents used to verify the identity of websites, users, or devices in online communications. They are commonly based on the X.509 standard and are issued by trusted Certificate Authorities (CAs). By using cryptographic techniques, security certificates help establish secure, encrypted connections - such as HTTPS - between clients and servers. This process ensures that sensitive data, like passwords or credit card numbers, is transmitted safely and that users are connecting to legitimate, trusted systems. Security certificates play a critical role in preventing cyber threats such as man-in-the-middle attacks, phishing, and data breaches by authenticating identities and enabling secure data exchange across networks.