JSSE, or Java Secure Socket Extension, is the Java platform’s built-in framework for SSL/TLS. It provides the APIs and runtime components that Java applications use to create encrypted sockets, validate certificates, negotiate protocol versions and cipher suites, and manage client or server keys and trust material.
JSSE matters because it is often the foundation of HTTPS and other secure Java transports, but security depends on how it is configured and what checks are layered on top. A connection can still be vulnerable if hostname verification is disabled, a weak trust store is used, or a custom TrustManager accepts certificates too broadly. In real attacks, that can let a man-in-the-middle present a certificate that is valid in general but wrong for the intended server. In defenses, JSSE is where teams enforce trusted CAs, TLS policy, mutual authentication, and certificate validation rules so the transport actually proves identity, not just encryption.