Internet Engineering Task Force C. Paasch Internet-Draft Apple, Inc. Intended status: Experimental A. Ford Expires: November 28, 2016 Pexip May 27, 2016 TLS Authentication for MPTCP draft-paasch-mptcp-tls-authentication-00 Abstract Multipath TCP (MPTCP), described in [4], is an extension to TCP to provide the ability to simultaneously use multiple paths between peers. draft-paasch-mptcp-application-authentication specifies "application layer authentication" for Multipath TCP, an alternatively negotiated keying mechanism for MPTCP. This allows keying material to be sourced from an application layer protocol in order to secure MP_JOIN handshakes. This document explains how to use the proposed application-layer authentication extension with TLS [6], in order to leverage securely exchanged keys for MPTCP security, whilst simultaneously freeing the MPTCP token to be used as a channel for additional information. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 28, 2016. Paasch & Ford Expires November 28, 2016 [Page 1] Internet-Draft TLS Authentication for MPTCP May 2016 Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Technical Implementation . . . . . . . . . . . . . . . . . . 3 3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Normative References . . . . . . . . . . . . . . . . . . 4 5.2. Informative References . . . . . . . . . . . . . . . . . 4 1. Introduction As described in draft-paasch-mptcp-application-authentication, the use of "application-layer authentication" allows the Key used in MPTCP authentication to be provided by the application layer, thus permitting the use of existing secure communication channels for exchanging keying material. Furthermore, this decouples the key from the token and thus allows the token to be used for conveying additional semantics, such as helping front-end proxies route traffic to appropriate back-end servers. TLS [6] provides a secure authentication channel between end hosts, where keys are not transmitted in the clear. The protocol generates a master secret for a connection, and a method is described in [3] for exporting a key generated from this and other properties which can then be used by the application layer. This document shows how to use this exported key, along with the method in draft-paasch- mptcp-application-authentication, for providing alternative keying mechanisms for MPTCP. Paasch & Ford Expires November 28, 2016 [Page 2] Internet-Draft TLS Authentication for MPTCP May 2016 2. Technical Implementation As described in draft-paasch-mptcp-application-authentication, the initial MP_CAPABLE handshake will exchange an arbitrary token for identifying an MPTCP connection. Whilst it is RECOMMENDED that the token is hard to guess, it can be used to carry any data, such as arbitrary routing information, and the security provided by the application-layer security will mitigate any risks of an attacker guessing tokens. When an MPTCP end host wishes to open a new subflow, it will follow the same exchange as described in [4], however the keying material (Key-A and Key-B) will be derived from the TLS handshake, as described in [3]. The "label" field MUST be "EXPORTER-MPTCP". The length used in the key-derivation, following [3] is 16. Key-A are the 64 most-significant bits, while Key-B are the 64 remaining bits. This requires the key exchange to have completed before subflows can be created. Other than the source of the keys, the exchange remains the same. The MP_CAPABLE and MP_JOIN exchange therefore looks like this: Host A Host B ------------------------ ---------- Address A1 Address A2 Address B1 ---------- ---------- ---------- | | | | | SYN + MP_CAPABLE | |--------------------------------------------->| |<---------------------------------------------| | SYN/ACK + MP_CAPABLE(Token-B) | | | | | ACK + MP_CAPABLE(Token-A, Token-B) | |--------------------------------------------->| | | | | | SYN + MP_JOIN(Token-B, R-A) | | |------------------------------->| | |<-------------------------------| | | SYN/ACK + MP_JOIN(HMAC-B, R-B) | | | | | | ACK + MP_JOIN(HMAC-A) | | |------------------------------->| | |<-------------------------------| | | ACK | HMAC-A = HMAC(Key=(Key-A+Key-B), Msg=(R-A+R-B)) HMAC-B = HMAC(Key=(Key-B+Key-A), Msg=(R-B+R-A)) Figure 1: Example Use of MPTCP Authentication Paasch & Ford Expires November 28, 2016 [Page 3] Internet-Draft TLS Authentication for MPTCP May 2016 3. Security Considerations This draft relies on the security provided by TLS [6] and the key export mechanism of [3] to provide additional security for the MPTCP handshake mechanism. These changes remove lingering risks, originally identified in [7], where an intercept of the initial MPTCP handshake could allow session hijack. 4. IANA Considerations IANA would be requested to add a value to the TLS Exporter Label registry as described in [3]. The label is "EXPORTER-MPTCP". 5. References 5.1. Normative References [1] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] Rescorla, E., "Keying Material Exporters for Transport Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, March 2010, . [4] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C. Paasch, "TCP Extensions for Multipath Operation with Multiple Addresses", draft-ietf-mptcp-rfc6824bis-05 (work in progress), January 2016. [5] National Institute of Science and Technology, "Secure Hash Standard", Federal Information Processing Standard (FIPS) 180-3, October 2008, . 5.2. Informative References [6] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/ RFC5246, August 2008, . [7] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6824, January 2013. Paasch & Ford Expires November 28, 2016 [Page 4] Internet-Draft TLS Authentication for MPTCP May 2016 Authors' Addresses Christoph Paasch Apple, Inc. Cupertino US EMail: cpaasch@apple.com Alan Ford Pexip EMail: alan.ford@gmail.com Paasch & Ford Expires November 28, 2016 [Page 5]