1. Introduction

Many protocols specified in the IETF rely on Transport Layer Security (TLS) [TLS1.0][TLS1.1][TLS1.2] for security services. This is a good thing, but some TLS clients and servers also support negotiating the use of Secure Sockets Layer (SSL) version 2.0 [SSL2]; however, this version does not provide a sufficiently high level of security. SSL version 2.0 has known deficiencies. This document describes those deficiencies, and it requires that TLS clients and servers never negotiate the use of SSL version 2.0.

RFC 4346 [TLS1.1], and later RFC 5246 [TLS1.2], explicitly warned implementers that the "ability to send version 2.0 CLIENT-HELLO messages will be phased out with all due haste". This document accomplishes this by updating the backward compatibility sections found in TLS [TLS1.0][TLS1.1][TLS1.2].

1.1. Requirements Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].