Transport Layer Security (TLS) Extensions: Extension Definitions
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attachment=26836]
Clarify Server Name Indication with IDNs
When using IDNs, does the server_name extension contain “xn--tmonesimerkki-bfbb.example.net” or “tämäonesimerkki.example.net” in UTF-8? Or are both allowed?
Proposal: find out what IE7 and Firefox do
Mandate certificate_url hash
“If the optional hash is not included with the client certificate URL, the server has no way to verify the name under which the private key in the certificate was used, since the certificate will not appear in the generation of the finished message.”
Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), both commonly referred to as "SSL", are cryptographic protocols that provide communications security over a computer network. Several versions of the protocols find widespread use in applications such as web browsing, e-mail, Internet fax, instant messaging and voice over IP (VoIP). Websites can use TLS to protect all communications between their servers and web browsers.
The security protocol of the transport layer has as main objective the privacy and the integrity of data between two computer applications that communicate. When protected by TLS, connections between a client (for example, a web browser) and a server (for example, wikipedia.org) have one or more of the following properties:
• The connection is private (or secure) because symmetric cryptography is used to encrypt the transmitted data. The keys to this symmetric encryption are generated uniquely for each connection and are based on a negotiated shared secret at the start of the session (see TLS Link Protocol Protocol). The server and the client negotiate the details of the encryption algorithm and the cryptographic keys to be used before the first byte of data is transmitted (see Algorithm below). Negotiation of a shared secret is both secure (negotiated secret is not available to spies and can not be obtained, not even by an attacker standing in the middle of the connection) and reliable (no attacker can modify communications during negotiation without being detected).
• The identity of the partners can be authenticated by public key cryptography. This authentication can be made optional, but is generally required for at least one of the parties (usually the server).
• The connection ensures integrity because each transmitted message includes a message integrity check using a message authentication code to prevent undetected loss or alteration of the data during transmission.
In addition to the above properties, careful configuration of TLS can provide additional privacy-related properties, such as forward secrecy, ensuring that any future disclosure of encryption keys can not be used to decrypt TLS communications recorded in the past.
TLS supports many different methods for exchanging keys, encrypting data, and authenticating message integrity (see Algorithm below). As a result, secure configuration of TLS involves many configurable parameters, and not all options provide all of the privacy-related properties described in the previous list (see Authentication and Key Exchange Table, Encryption Security Table, and Integrity Table of data).
Attempts have been made to subvert aspects of communications security that TLS intends to provide and the protocol has been revised several times to address these security threats (see Security). Web browser developers have also reviewed their products to defend themselves against potential security flaws after they were discovered (see TLS / SSL support history for web browsers).
The TLS protocol comprises two layers: the TLS logging protocol and the TLS link protocol. TLS is a standard Internet Engineering Task Force (IETF) proposal, first defined in 1999 and updated in RFC 5246 (August 2008) and RFC 6176 (March 2011). It is based on previous SSL specifications (1994, 1995, 1996) developed by Netscape Communications to add the HTTPS protocol to your Navigator web browser.