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10 allée Clovis 93160 Noisy-le-Grand France julien@trigofacile.com http://www.trigofacile.com/

Applications Independent Submission NNTP Usenet NetNews TLS STARTTLS This document provides recommendations for improving the security of the Network News Transfer Protocol (NNTP) when using Transport Layer Security (TLS). It modernizes the NNTP usage of TLS to be consistent with TLS best current practices. If approved, this document updates RFC 4642.

The Network News Transfer Protocol (NNTP) has been using Transport Layer Security (TLS) (along with its precursor, Secure Sockets Layer or SSL) since at least year 2000. The use of TLS in NNTP was formalized in , providing at the same time implementation recommendations. In order to address the evolving threat model on the Internet today, this document provides stronger recommendations regarding that use. In particular, this document updates by specifying that NNTP implementations and deployments MUST follow the best current practices documented in the "Recommendations for Secure Use of TLS and DTLS" . This includes stronger recommendations regarding SSL/TLS protocol versions, fallback to lower versions, strict TLS, TLS-level compression, TLS session resumption, cipher suites, public key lengths, forward secrecy, and other aspects of using TLS with NNTP. Notably, this document updates in the following aspects: NNTP implementations and deployments SHOULD disable TLS-level compression (Section 3.3 of ), thus no longer using TLS as a means to provide data compression (contrary to Abstract and Section 2.2.2 of ). NNTP implementations and deployments SHOULD prefer strict TLS configuration (Section 3.2 of ), that is to say they SHOULD use TCP port 563 dedicated to NNTP over TLS, and begin the TLS negotiation immediately upon connection (contrary to a dynamic upgrade from unencrypted to TLS-protected traffic via the use of the STARTTLS command, as Section 1 of was encouraging). For the same reasons as those given in Appendix A of transposed to NNTP, strict TLS is the preferred way of using TLS with NNTP. NNTP implementations and deployments MUST NOT negotiate RC4 cipher suites () contrary to Section 5 of that REQUIRED them to implement the TLS_RSA_WITH_RC4_128_MD5 cipher suite so as to ensure that any two NNTP compliant implementations can be configured to interoperate. This document removes that requirement, so that NNTP client and server implementations follow the recommendations of Section 4.2.1 of instead.

Any term not defined in this document has the same meaning as it does in or the NNTP core specification . 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 .

Please write the first letter of "Elie" and the penultimate letter of "allee" with an acute accent wherever possible -- they are respectively U+00C9 ("É" in XML) and U+00E9 ("é" in XML). Also, the letters "ae" in "Baeuerle" should be written as an a-umlaut (U+00E4, "ä" in XML).

The best current practices documented in the "Recommendations for Secure Use of TLS and DTLS" are included here by reference. Therefore, NNTP implementations and deployments compliant with this document is REQUIRED to also comply with . Instead of repeating those recommendations here, this document mostly provides supplementary information regarding secure implementation and deployment of NNTP technologies.

NNTP supports the use of the COMPRESS command, defined in Section 2.2 of , to compress data between an NNTP client and server. Although this NNTP extension might have slightly stronger security properties than TLS-level compression (since NNTP compression can be activated after authentication has completed, thus reducing the chances that authentication credentials can be leaked via for instance a CRIME attack, as described in Section 2.6 of ), this document neither encourages nor discourages use of NNTP COMPRESS extension.

NNTP implementations of news servers are encouraged to support options to configure the minimal TLS protocol version to accept, and which cipher suites, signature algorithms or named groups (like elliptic curves) to use for incoming connections. Additional options can naturally also be supported. The goal is to enable administrators of news servers to easily and quickly strengthen security, if need be (for instance by rejecting cipher suites considered unsafe with regards to local policy). News clients may also support similar options, either configurable by the user or enforced by the news reader.

already provides recommendations and requirements for certificate validation in the context of checking the client or the server's identity. Wherever possible, it is best to prefer certificate-based authentication (along with SASL ), and ensure that: Clients authenticate servers. Servers authenticate clients. Servers authenticate other peer servers. This document does not mandate certificate-based authentication, although such authentication is strongly preferred. As mentioned in Section 2.2.2 of , the AUTHINFO SASL command (Section 2.4 of ) with the EXTERNAL mechanism (Appendix A of ) MAY be used to authenticate a client once its TLS credentials have been successfully exchanged. Given the pervasiveness of eavesdropping , even an encrypted but unauthenticated connection might be better than an unencrypted connection (this is similar to the "better-than-nothing security" approach for IPsec ). Encrypted but unauthenticated connections include connections negotiated using anonymous Diffie‑Hellman mechanisms or using self-signed certificates, among others. When an NNTP server receives a Netnews article, it MAY add a <diag‑match> (Section 3.1.5 of ), which appears as "!!" in the Path header field of that article, to indicate that it verified the identity of the client or peer server. This document encourages the construction of such Path header fields, as described in Section 3.2.1 of .

It is strongly encouraged that NNTP clients provide ways for end users (and that NNTP servers provide ways for administrators) to complete the following tasks: Determine if a given incoming or outgoing connection is encrypted using a security layer (either using TLS or an SASL mechanism that negotiates a security layer). Determine the version of TLS used for encryption of a given stream. If authenticated encryption is used, determine how the connection was authenticated or verified. Inspect the certificate offered by an NNTP server. Determine the cipher suite used to encrypt a connection. Be warned if the certificate changes for a given server. Be warned if a given server stops advertising the STARTTLS capability label in response to the CAPABILITIES command (of course when a security layer is not already in place) whereas it advertised the STARTTLS capability label during the previous connection. Be warned if a failure response to the STARTTLS command is received from the server whereas the STARTTLS capability label was advertised. Note that the last two tasks cannot occur when strict TLS is used.

Beyond the security considerations already described in and , the author wishes to add the following caveat when not using strict TLS. NNTP servers need ensure that they are not vulnerable to the STARTTLS command injection vulnerability (CERT vulnerability ID #555316). Though this command MUST NOT be pipelined, an attacker could pipeline it. Therefore, NNTP servers MUST discard any NNTP command received between the use of STARTTLS and the end of TLS negotiation.

This document has no actions for IANA.

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The Network News Transfer Protocol (NNTP) has been in use in the Internet for a decade, and remains one of the most popular protocols (by volume) in use today. This document is a replacement for RFC 977, and officially updates the protocol specification. It clarifies some vagueness in RFC 977, includes some new base functionality, and provides a specific mechanism to add standardized extensions to NNTP. [STANDARDS-TRACK] This memo defines an extension to the Network News Transfer Protocol (NNTP) that allows an NNTP client and server to use Transport Layer Security (TLS). The primary goal is to provide encryption for single-link confidentiality purposes, but data integrity, (optional) certificate-based peer entity authentication, and (optional) data compression are also possible. [STANDARDS-TRACK] The Transport Layer Security (TLS) protocol (RFC 2246) includes features to negotiate selection of a lossless data compression method as part of the TLS Handshake Protocol and to then apply the algorithm associated with the selected method as part of the TLS Record Protocol. TLS defines one standard compression method which specifies that data exchanged via the record protocol will not be compressed. This document describes an additional compression method associated with a lossless data compression algorithm for use with TLS, and it describes a method for the specification of additional TLS compression methods. [STANDARDS-TRACK] The Simple Authentication and Security Layer (SASL) is a framework for providing authentication and data security services in connection-oriented protocols via replaceable mechanisms. It provides a structured interface between protocols and mechanisms. The resulting framework allows new protocols to reuse existing mechanisms and allows old protocols to make use of new mechanisms. The framework also provides a protocol for securing subsequent protocol exchanges within a data security layer.This document describes how a SASL mechanism is structured, describes how protocols include support for SASL, and defines the protocol for carrying a data security layer over a connection. In addition, this document defines one SASL mechanism, the EXTERNAL mechanism.This document obsoletes RFC 2222. [STANDARDS-TRACK] This document defines an extension to the Network News Transfer Protocol (NNTP) that allows a client to indicate an authentication mechanism to the server, to perform an authentication protocol exchange, and optionally to negotiate a security layer for subsequent protocol interactions during the remainder of an NNTP session.This document updates and formalizes the AUTHINFO USER/PASS authentication method specified in RFC 2980 and deprecates the AUTHINFO SIMPLE and AUTHINFO GENERIC authentication methods. Additionally, this document defines a profile of the Simple Authentication and Security Layer (SASL) for NNTP. [STANDARDS-TRACK] This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] This document specifies how to use the Internet Key Exchange (IKE) protocols, such as IKEv1 and IKEv2, to setup "unauthenticated" security associations (SAs) for use with the IPsec Encapsulating Security Payload (ESP) and the IPsec Authentication Header (AH). No changes to IKEv2 bits-on-the-wire are required, but Peer Authorization Database (PAD) and Security Policy Database (SPD) extensions are specified. Unauthenticated IPsec is herein referred to by its popular acronym, "BTNS" (Better-Than-Nothing Security). [STANDARDS-TRACK] This document specifies the syntax of Netnews articles in the context of the Internet Message Format (RFC 5322) and Multipurpose Internet Mail Extensions (MIME) (RFC 2045). This document obsoletes RFC 1036, providing an updated specification to reflect current practice and incorporating incremental changes specified in other documents. [STANDARDS-TRACK] This document defines the architecture of Netnews systems and specifies the correct manipulation and interpretation of Netnews articles by software that originates, distributes, stores, and displays them. It also specifies the requirements that must be met by any protocol used to transport and serve Netnews articles. [STANDARDS-TRACK] Pervasive monitoring is a technical attack that should be mitigated in the design of IETF protocols, where possible. This document requires that Transport Layer Security (TLS) clients and servers never negotiate the use of RC4 cipher suites when they establish connections. This applies to all TLS versions. This document updates RFCs 5246, 4346, and 2246. Transport Layer Security (TLS) 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 are applicable to the majority of use cases. This document provides recommendations for the use of Transport Layer Security (TLS) in the Extensible Messaging and Presence Protocol (XMPP). This document updates RFC 6120.

This section lists detailed changes this document applies to . The second sentence in the Abstract of is replaced with the following text: The primary goal is to provide encryption for single-link confidentiality purposes, but data integrity, and (optional) certificate-based peer entity authentication are also possible. The third and fourth paragraphs in Section 1 of are replaced with the following text: TCP port 563 is dedicated to NNTP over TLS, and registered in the IANA Service Name and Transport Protocol Port Number Registry for that usage. NNTP implementations using TCP port 563 begin the TLS negotiation immediately upon connection and then continue with the initial steps of an NNTP session. This use of strict TLS on a separate port is the preferred way of using TLS with NNTP. As some existing implementations negotiate TLS via a dynamic upgrade from unencrypted to TLS-protected traffic during an NNTP session, this specification formalizes the STARTTLS command in use for that purpose. However, as already mentioned above, implementations SHOULD use strict TLS on a separate port. The second sentence of the first paragraph in Section 2.2.2 of is replaced with the following text: The STARTTLS command is usually used to initiate session security, although it can also be used for client and/or server certificate authentication. The third paragraph in Section 5 of is removed. Consequently, NNTP no longer requires to implement any cipher suites, other than those prescribed by TLS and Section 4.2.1 of .

Some governments enforce legislation prohibiting the export of strong cryptographic technologies. Nothing in this document ought to be taken as advice to violate such prohibitions.

This document draws heavily on ideas in by Peter Saint‑Andre and Thijs Alkemade, and a large portion of this text was borrowed from that specification. The author would like to thank the following individuals for contributing their ideas and support for writing this specification: Michael Bäuerle, Richard Kettlewell, and Chris Newman.

Clarify in the introduction of that NNTP implementations compliant with this document are REQUIRED to also comply with . Improve the wording of to mention that configuration is primarily intended for news servers. Also, be more consistent in the options to accept, and include signature algorithms and named groups.

Should the paragraph starting with "Servers MUST be able to understand backwards-compatible TLS Client Hello messages" in Section 2.2.2 of remain as-is or should it be modernized with another wording? (And which one? or is it already done by the reference to ?) Should the paragraphs in Section 5 of dealing with how the client checks the server hostname and the binding between the identity of servers and the public keys presented be modernized? (Obsolete them in favour of RFC 6125 for instance? or maybe is enough as it also points to RFC 6125) Regarding peering between mode-switching news servers, should something specific be added? NNTP has port 119, and NNTP over TLS has port 563. NNSP has port 433 but no dedicated port for TLS. Shouldn't a port for NNSP over TLS be registered? Otherwise, both reading and peering are supposed to use port 563, which may be inconvenient. We could then recommend the use of stunnel with TCP wrappers, or an equivalent mechanism, listening to that new separate port for mode-switching news servers that do not natively support TLS for peering.