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Transport Layer Security

Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securing HTTPS remains the most publicly visible. The TLS protocol aims primarily to provide security, including privacy (confidentiality), integrity, and authenticity through the use of cryptography, such as the use of certificates, between two or more communicating computer applications. It runs in the presentation layer and is itself composed of two layers: the TLS record and the TLS handshake protocols. The closely related Datagram Transport Layer Security (DTLS) is a communications protocol that provides security to datagram-based applications. In technical writing, references to "(D)TLS" are often seen when it applies to both versions. TLS is a proposed Internet Engineering Task Force (IETF) standard, first defined in 1999, and the current version is TLS 1.3, defined in August 2018. TLS builds on the now-deprecated SSL (Secure Sockets Layer) specifications (1994, 1995, 1996) developed by Netscape Communications for adding the HTTPS protocol to their Navigator web browser. Client-server applications use the TLS protocol to communicate across a network in a way designed to prevent eavesdropping and tampering. Since applications can communicate either with or without TLS (or SSL), it is necessary for the client to request that the server set up a TLS connection. One of the main ways of achieving this is to use a different port number for TLS connections. Port 80 is typically used for unencrypted HTTP traffic while port 443 is the common port used for encrypted HTTPS traffic. Another mechanism is to make a protocol-specific STARTTLS request to the server to switch the connection to TLS – for example, when using the mail and news protocols. Once the client and server have agreed to use TLS, they negotiate a stateful connection by using a handshaking procedure (see ).

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