SSL/TLS protocol overview

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SSL/TLS protocol overview

Originally developed by Netscape in the mid 1990s, the secure sockets layer (SSL) is a

cryptographic protocol designed to provide communication security over the Internet (see

[3] in References). Version 1.0 never publicly released, while version 2.0 was released in

February of 1995 but “contained a number of security flaws which ultimately led to the

design of SSL version 3.0” (see [4] in References). SSLv3.0 was a complete redesign of the

protocol and is still widely supported (since 1996).

The IETF standards body adopted SSLv3.0 with minor tweaks and published it as TLS

version 1.0 (RFC 2246, 1999). The two versions are very similar, but interoperability is

precluded. TLSv1.2 (RFC 5246, 2008) is the latest and recommended version, which is

superior because it offers flexibility and key features that were unavailable in earlier protocol

versions.

All TLS versions were further refined (RFC 6176, 2011) removing their backward

compatibility with SSL such that TLS sessions will never negotiate the use of SSLv2.0.

As shown in Figure 1, SSL/TLS is typically applied in TCP/IP protocol stacks and provides

security services on top of the transport layer. The protocol is composed of two layers: the

TLS record layer and the TLS handshake layer.

At the lowest level, layered on top of a reliable transport protocol is the TLS record protocol.

The record protocol is used for encapsulation of various higher-level protocols and provides

two basic properties:

•

Confidentiality

•

Integrity

Figure 1. SSL/TLS protocol architecture

The TLS Handshake layer consists of three sub-protocols: Handshake, Change cipher

spec, and Alert.

The Handshake protocol is the most complex part of TLS and provides a number of very

important security functions. It allows the server and client to authenticate each other and to

negotiate an encryption algorithm and cryptographic keys before the application protocol

transmits or receives its first byte of data. The TLS handshake protocol provides connection

security that has three basic properties:

•

Cipher suite negotiation

•

Authentication of the server and, optionally, of the client

•

Session key information exchange

An outline of the sub-protocols is provided in the next section.