Source: https://en.wikipedia.org/wiki/Transport_Layer_Security

Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), both of which are frequently referred to as ‘SSL’, are cryptographic protocols designed to provide communications security over a computer network.[1] They use X.509certificates and hence asymmetric cryptography to authenticate the counterpart with whom they are communicating,[2] and to negotiate a symmetric session key. This session key is then used to encrypt data flowing between the parties. This allows for data/message confidentiality, and message authentication codes for message integrity and as a by-product, message authentication.[clarification needed] Several versions of the protocols are in widespread use in applications such as web browsing,email, Internet faxing, instant messaging, and voice-over-IP (VoIP). An important property in this context is forward secrecy, so the short-term session key cannot be derived from the long-term asymmetric secret key.[3]

As a consequence of choosing X.509 certificates, certificate authorities and a public key infrastructure are necessary to verify the relation between a certificate and its owner, as well as to generate, sign, and administer the validity of certificates. While this can be more beneficial than verifying the identities via a web of trust, the 2013 mass surveillance disclosures made it more widely known that certificate authorities are a weak point from a security standpoint, allowing man-in-the-middle attacks (MITM).[4][5]

The Internet Protocol Suite places TLS and SSL as tools into the application layer, while the OSI model characterizes them as being initialized in Layer 5 (session layer) and operating in Layer 6 (presentation layer). The session layer employs a handshake using an asymmetric cipher in order to establish cipher settings and a shared key for a session; the presentation layer encrypts the rest of the communication using a symmetric cipher and the session key. TLS and SSL may be characterized to work on behalf of the underlying transport layer protocol, which carries encrypted data.

TLS is an Internet Engineering Task Force (IETF) standards track protocol, first defined in 1999 and updated in RFC 5246 (August 2008) and RFC 6176 (March 2011). It is based on the earlier SSL specifications (1994, 1995, 1996) developed by Netscape Communications[6] for adding the HTTPS protocol to their Navigator web browser.

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