TLS

TLS, or Transport Layer Security, is a cryptographic protocol designed to provide confidentiality, integrity, and authentication for communications over a computer network. It is the successor to the Secure Sockets Layer (SSL) protocol and is widely used to secure application protocols such as HTTPS, SMTP, IMAP, and FTPS. TLS sits between the application layer and the transport layer, typically on top of TCP, and can also be used over UDP in the form of DTLS.

TLS uses a handshake to negotiate cryptographic parameters and, if authentication is required, to verify the identities of the communicating parties using X.509 certificates issued by trusted certificate authorities. The handshake establishes a shared secret (often via ephemeral public-key exchange such as ECDHE) which is then used to derive symmetric encryption keys. All subsequent application data is encrypted with one of a set of symmetric ciphers (for example AES-GCM or ChaCha20-Poly1305) and protected for integrity with an AEAD construction. TLS supports session resumption to avoid full handshakes on repeat connections.

TLS versions include TLS 1.0, TLS 1.1, TLS 1.2, and TLS 1.3. TLS 1.3, published in 2018, simplifies the handshake, removes legacy cryptography, and requires forward secrecy. Many deployments now use TLS 1.2 or TLS 1.3 with modern cipher suites, while older versions and weak ciphers are deprecated. The protocol also underpins DTLS for datagram transports used by some real-time applications.

Security and governance: TLS relies on the public key infrastructure and trusted certificate authorities. Correct configuration, up-to-date software, and strong cipher suites are essential to mitigate vulnerabilities such as downgrade attacks, certificate misissuance, and implementation flaws. Regular auditing and proper certificate lifecycle management help maintain secure communications.