Which of the following is the successor of SSL?

GRE (Generic Routing Encapsulation) is a tunneling protocol used to encapsulate packets between network endpoints and is unrelated to SSL or transport-layer encryption.

IPSec is a network-layer security suite commonly used for VPN tunnels and operates at Layer 3, making it a different technology category rather than a successor to SSL.

RSA is a public-key cryptographic algorithm used as one component within SSL and TLS handshakes for key exchange, but is not a protocol and did not succeed SSL.

TLS was standardized by the IETF as the replacement for Netscape's SSL protocol, with TLS 1.0 derived from SSL 3.0 and subsequent versions (1.1, 1.2, 1.3) adding stronger cipher suites and improved handshake security. All versions of SSL are now deprecated due to known vulnerabilities such as POODLE and DROWN, and TLS 1.2 and 1.3 are the current standards for securing transport-layer communications including HTTPS.