Transport Layer Security

Overview #

Transport Layer Security is the degree of resistance to encountering an Unfortunate event at the Transport Layer

Transport Layer Security (TLS) is also, and most often, the Standard protocol for creating secure connection between clients and servers at the Transport Layer

Transport Layer Security is an improved and standardized form of the Secure Socket Layer (SSL).


The primary goal of Transport Layer Security is to provide a secure channel between two communicating peers; the only requirement from the underlying transport is a reliable, in-order, data stream.

Specifically, the secure channel should provide the following properties:

These properties should be true even in the face of an attacker who has complete control of the network, as described in Internet Threat Model (BCP 72).

Transport Layer Security consists of two primary components:

  • A handshake protocol that authenticates the communicating parties, negotiates cryptographic modes and parameters, and establishes shared keying material. The handshake protocol is designed to resist tampering; an Active attacker should not be able to force the peers to negotiate different parameters than they would if the connection were not under attack.
  • A Record Protocol that uses the parameters established by the handshake protocol to protect traffic between the communicating peers. The Record Protocol divides traffic up into a series of records, each of which is independently protected using the traffic keys.
Transport Layer Security is application protocol independent; higher-level protocols can layer on top of TLS transparently. The TLS standard, however, does not specify how protocols add security with TLS; how to initiate TLS handshaking and how to interpret the authentication certificates exchanged are left to the judgment of the designers and implementers of protocols that run on top of TLS.

Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)#

Transport Layer Security (Transport Layer Security) and Datagram Transport Layer Security (DTLS) are widely used to protect data exchanged over application protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the last few years, several serious attacks on TLS have emerged, including attacks on its most commonly used cipher suites and their modes of operation. This document provides recommendations for improving the security of deployed services that use TLS and DTLS. The Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are applicable to the majority of use cases.


SSL-TLS is a protocol with a long history and several versions. First prototypes came from Netscape, when they were developing the first versions of their flagship browser, Netscape Navigator (this browser killed off Mosaic in the early times of the Browser Wars, which are still raging, albeit with new competitors).

SSL Version 1 has never been made public so we do not know how it looked like. SSL version 2 (SSLv2), is described in a draft, had a number of weaknesses, some of them rather serious, so it is deprecated (RFC 6176) and newer SSL-TLS implementations do not support it (while older deactivated by default).

SSLv3 version 3 was an enhanced protocol which still works today and is widely supported. Although still a property of Netscape Communications (or whoever owns that nowadays), the protocol has been published as an "historical RFC" RFC 6101. Meanwhile, the protocol was standardized, with a new name in order to avoid legal issues, the new name is TLS.

Three versions of TLS have been produced to far, each with its dedicated RFC:

They are internally very similar with each other, and with SSLv3, to the point that an implementation can easily support SSLv3 and all three TLS versions with at least 95% of the code being common.

Still internally, all versions are designated by a version number with the major.minor format; SSLv3 is then 3.0, while the TLS versions are, respectively, 3.1, 3.2 and 3.3.

Thus, it is no wonder that TLS 1.0 is sometimes called SSL 3.1 (and it is not incorrect either). SSL 3.0 and TLS 1.0 differ by only some minute details. TLS 1.2 is becoming widely supported, although there is impetus for that, because of possible weaknesses (see below, for the "BEAST attack"). TLS 1.0 are supported nearly "everywhere". TLS 1.3 is still an Internet Draft

TLS Protocol Limitations#

In addition to Exploits against Transport Layer Security, there are also some fundamental TLS Protocol Limitations.

How SSL-TLS Works#

In LDAP TLS is implemented by the usage of the StartTLS or using LDAPS which does NOT imply SSL.

TLS Maturity Model#

More Information#

There might be more information for this subject on one of the following: