One document matched: draft-raza-dice-compressed-dtls-00.ps
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5 635 M
(DICE Working Group S. Raza) s
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(Internet-Draft SICS, Stockholm) s
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(Intended Status: Standard Track H. Shafagh) s
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( ETH Zurich) s
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( O. Dupont) s
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( Cisco Systems, Paris) s
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(Expires: September 11, 2014 March 10, 2014) s
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(Compression of Record and Handshake Headers for Constrained Environments) s
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( draft-raza-dice-compressed-dtls-00) s
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(Abstract) s
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( This document describes header compression mechanisms for the) s
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( Datagram Transport Layer Security \(DTLS\) [RFC6347] based on the) s
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( encoding scheme standardized in [RFC6282]. The DTLS Record Header) s
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( \(RH\), Handshake Header \(HH\), and optionally handshake message headers) s
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( are compressed using Next Header Compression \(NHC\) defined in) s
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( [RFC6282]. This document neither invalidates any encoding schemes) s
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( proposed in 6LoWPAN [RFC6282] nor compromises the end-to-end security) s
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( properties provided by DTLS. This document aims to increase the) s
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( applicability of DTLS and, thus, CoAPs [draft-ietf-core-coap-18] in) s
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( constrained environments.) s
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(Status of this Memo) s
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( This Internet-Draft is submitted in full conformance with the) s
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( provisions of BCP 78 and BCP 79.) s
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( Internet-Drafts are working documents of the Internet Engineering) s
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( Task Force \(IETF\). Note that other groups may also distribute) s
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( working documents as Internet-Drafts. The list of current Internet-) s
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( Drafts is at http://datatracker.ietf.org/drafts/current/.) s
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( Internet-Drafts are draft documents valid for a maximum of six months) s
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( and may be updated, replaced, or obsoleted by other documents at any) s
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( time. It is inappropriate to use Internet-Drafts as reference) s
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( material or to cite them other than as "work in progress.") s
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( This Internet-Draft will expire on September 11, 2014.) s
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(Copyright and License Notice) s
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( Copyright \(c\) 2014 IETF Trust and the persons identified as the) s
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( document authors. All rights reserved.) s
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
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( This document is subject to BCP 78 and the IETF Trust's Legal) s
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( Provisions Relating to IETF Documents) s
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( \(http://trustee.ietf.org/license-info\) in effect on the date of) s
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( publication of this document. Please review these documents) s
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( carefully, as they describe your rights and restrictions with respect) s
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( to this document. Code Components extracted from this document must) s
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( include Simplified BSD License text as described in Section 4.e of) s
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( the Trust Legal Provisions and are provided without warranty as) s
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( described in the Simplified BSD License.) s
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(Table of Contents) s
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( 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3) s
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( 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3) s
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( 2. Linking DTLS Header Compression with 6LoWPAN . . . . . . . . . 4) s
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( 3. LOWPAN_NHC for the Record Header . . . . . . . . . . . . . . . 4) s
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( 4. LOWPAN_NHC for the Record Plus Handshake Headers . . . . . . . 6) s
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( 5. LOWPAN_NHC for the Handshake Messages . . . . . . . . . . . . . 7) s
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( 6. Summary of DTLS header sizes with and without Compression . . . 10) s
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( 7. Implementation Considerations . . . . . . . . . . . . . . . . . 10) s
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( 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 11) s
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( 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 11) s
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( 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12) s
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( 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12) s
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( 11.1. Normative References . . . . . . . . . . . . . . . . . . . 12) s
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( 11.2. Informative References . . . . . . . . . . . . . . . . . . 12) s
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( Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12) s
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
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(1 Introduction) s
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( To protect CoAP transmissions, Datagram TLS \(DTLS\) has been proposed) s
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( as the primary security protocol. Analogous to TLS-protected HTTP) s
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( \(HTTPs\), the DTLS-secured CoAP protocol is termed CoAPs. DTLS is a) s
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( chatty protocol and requires numerous message exchanges to establish) s
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( a secure session. While DTLS supports a wide range of cryptographic) s
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( primitives for peer authentication and payload protection, it was) s
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( originally designed for network scenarios where message length was) s
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( not a critical design criterion. Therefore, it is inefficient to use) s
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( the DTLS protocol, as it is, for constrained devices. To cope with) s
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( constrained resources and the size limitations of IEEE 802.15.4-based) s
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( networks, 6LoWPAN header compression mechanisms are defined.) s
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( [RFC6282] defines how IPv6 datagrams can be routed over IEEE 802.15.4) s
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( [IEEE802.15.4]-based networks. [RFC6282] defines header compression) s
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( schemes that can significantly reduce the size of IP, IP extensions,) s
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( and UDP headers. It is particularly beneficial to apply the 6LoWPAN) s
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( header compression mechanisms to compress other protocols having) s
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( well-defined header fields, such as DTLS. This document provides) s
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( header compression for the DTLS Record, Handshake, and handshake) s
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( messages headers with 6LoWPAN header compression mechanisms. This) s
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( enables the routing of heavy-weight IP traffic to resource-) s
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( constrained [IEEE802.15.4]-based wireless network.) s
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( The DTLS header compression defined in this documents does not) s
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( compromise the DTLS ability to provide end-to-end security between) s
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( constrained nodes and hosts on the Internet. The security in) s
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( [IEEE802.15.4]-based IP networks or what is more commonly known) s
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( 6LoWPAN networks is particularly important as we connect the insecure) s
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( Internet with the vulnerable wireless network. The purpose of DTLS) s
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( header compression is twofold. First, achieving energy efficiency by) s
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( reducing the message size, since communication requires more energy) s
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( than computation. Second, avoiding 6LoWPAN fragmentation that is) s
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( applied when the size of a datagram is larger than the link layer) s
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( MTU. Avoiding fragmentation, whenever possible, is also important) s
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( from the security point of view as the 6LoWPAN protocol is vulnerable) s
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( to fragmentation attacks [WiSec13].) s
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( Generic Header Compression \(GHC\) [draft-bormann-6lowpan-ghc-06],) s
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( analogous to NHC, is also defined to allow upper layer \(UDP payload) s
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( and above\) header compression. 6LoWPAN-GHC is a generic compression) s
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( scheme for all headers and header-like structures, and is not) s
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( targeted for the DTLS protocol; also, it is generally a slightly less) s
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( efficient approach. It is an alternative to the approach presented in) s
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( this document and it is worth evaluating the two approaches for the) s
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( DTLS Record and Handshake headers.) s
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(1.1 Terminology) s
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
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( The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",) s
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( "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this) s
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( document are to be interpreted as described in RFC 2119 [RFC2119].) s
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(2. Linking DTLS Header Compression with 6LoWPAN) s
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( [RFC6282] defines the general format of NHC that can be used to) s
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( encode DTLD headers. In order to apply 6LoWPAN header compression) s
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( mechanisms to compress headers in the UDP payload, we either require) s
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( a modification in the current NHC encodings for UDP in the 6LoWPAN) s
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( standard, or need to define a new NHC for UDP with different ID bits.) s
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( The first solution requires modification in the current standard and) s
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( hence is not a favorable solution. The second solution, that is used) s
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( in this document, is an extension to the 6LoWPAN standard; a similar) s
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( approach is adapted to distinguish NHC from GHC [draft-bormann-) s
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( 6lowpan-ghc-06]. The ID bits 11110 in the NHC for UDP, as defined in) s
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( the 6LoWPAN standard, indicate that the UDP payload is not) s
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( compressed. We define the ID bits 11011 in the NHC for UDP to) s
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( indicate that the UDP payload is compressed with 6LoWPAN_NHC. The ID) s
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( bits 11011 are currently unassigned in the 6LoWPAN standard. Figure 1) s
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( shows our proposed NHC for UDP that allows compression of UDP) s
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( payload; in the case of DTLS, the UDP payload contains the NHC) s
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( compressed DTLS headers.) s
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( 0 1 2 3 4 5 6 7) s
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( +---+---+---+---+---+---+---+---+) s
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( | 1 | 1 | 0 | 1 | 1 | C | P |) s
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( +---+---+---+---+---+---+---+---+) s
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( Figure 1: 6LOWPAN_NHC for UDP which allows compression of UDP payload) s
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(3. LOWPAN_NHC for the Record Header) s
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( The Record protocol adds header fields of 13 bytes length to each) s
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( packet that is sent throughout the lifetime of a device that uses) s
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( DTLS. The header compression proposed in this section reduces the) s
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( Record header length to 4 bytes \(plus one byte for the NHC\). In) s
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( contrary to the handshake header and messages, the Record header) s
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( remains un-encrypted in all cases. Thus it can always be compressed) s
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( using the mechanism explained in this section.) s
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( In order to provide header compression for the Record and Handshake) s
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( headers, this document discusses two cases. In the first case, the) s
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( Record header fragment field contains a handshake message; the next) s
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( section defines header compression regarding this case. In the second) s
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( case, the fragment field in the Record header is not a handshake) s
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
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( message, it is mostly application data, or could be a DTLS alert) s
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( message or ChangeCipherSpec. Figure 2 shows 6LoWPAN_NHC encoding for) s
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( the Record header \(LOWPAN_NHC_R\).) s
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( 0 1 2 3 4 5 6 7) s
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( +---+---+---+---+---+---+---+---+) s
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( | 1 | 0 | 0 | 1 | V | EC| SN |) s
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( +---+---+---+---+---+---+---+---+) s
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( Figure 2: Proposed LOWPAN NHC encoding for the DTLS Record header) s
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( The encoded bits have the following functions:) s
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( o The first four bits in the NHC represent the NHC ID we define for) s
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( the Record header. These are set to 1001.) s
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( o Version \(V\): If 0, the version is the DTLS latest version which is) s
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( 1.2, and the field is omitted. If 1, the version field is carried) s
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( inline.) s
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( o Epoch \(EC\): If 0, an 8 bit epoch is used and the left most 8 bits) s
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( are omitted. If 1, all 16 bits of the epoch are carried inline. In) s
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( most cases the actual epoch is either 0 or 1. Therefore, an 8 bit) s
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( epoch is used most of the time, allowing for a higher space.) s
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( o Sequence Number \(SN\): The sequence number consists of 48 bits, of) s
5 349 M
( which some are leading zeros. If SN is set to 00, a 16 bit) s
5 338 M
( sequence number is used and the left most 32 bits are omitted. If) s
5 327 M
( 01, a 24 bit sequence number is used and the left most 24 bits are) s
5 316 M
( omitted. If 10, a 32 bit sequence number is used and the left most) s
5 305 M
( 16 bits are omitted. If 11, all 48 bits of the sequence number are) s
5 294 M
( carried inline. The SN field in the Record header contains a value) s
5 283 M
( 1 for the first packet sent, and it is incremented sequentially) s
5 272 M
( for the subsequent packets. Note that by using 16-bit sequence) s
5 261 M
( number we do not limit the size of sequence number to 2^\(16-1\),) s
5 250 M
( but propose to use 16 bits for the sequence number prior to the) s
5 239 M
( transmission of the 2^16th packet on a DTLS connection. From the) s
5 228 M
( 2^16 to 2^\(24-1\) we propose to use 24-bit sequence numbers. Follow) s
5 217 M
( the same procedure for the 32-bit sequence numbers as well.) s
5 206 M
( However, the sender and the receiver sequence-number-counters must) s
5 195 M
( be reset prior to sending the 2^48th packet.) s
5 162 M
( In the Record header, content_type field is always carried inline.) s
5 151 M
( The length field in the Record header is omitted as we expect only) s
5 140 M
( one DTLS record per UDP packet in constrained environments. While a) s
5 129 M
( source device inside a 6LoWPAN sends one DTLS record per UDP packet,) s
5 118 M
( a typical destination device on the conventional Internet side may) s
5 74 M
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(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
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( send multiple DTLS records in a single UDP packet. However, as the) s
5 624 M
( 6BR performs the compression/decompression of incoming packets, there) s
5 613 M
( is the possibility to enforce one DTLS record per UDP packet before) s
5 602 M
( routing these packets in 6LoWPAN networks. The length field can be) s
5 591 M
( deduced from the lower layers: either from the 6LoWPAN header or the) s
5 580 M
( IEEE 802.15.4 header. Figure 3 shows a sample NHC compressed IP/UDP) s
5 569 M
( packet secured with the Record protocol.) s
5 514 M
( | octet 1 | octet 2 | octet 3 | octet 4 |) s
5 503 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 492 M
( | LOWPAN_IPHC | Hop Limit | Source Address|) s
5 481 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 470 M
( | Source Address| Destination Address | LOWPAN_NHC_UDP|) s
5 459 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 448 M
( |S Port |D Port | Checksum | LOWPAN_NHC_R |) s
5 437 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 426 M
( | Content Type | Epoch | Sequence Number |) s
5 415 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 404 M
( | |) s
5 393 M
( + Initialization Vector \(IV\) [16 bytes for AES] +) s
5 382 M
( | |) s
5 371 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 360 M
( | Application Data Fragment \(Variable Size\) |) s
5 349 M
( + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 338 M
( | | |) s
5 327 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +) s
5 316 M
( | |) s
5 305 M
( + MAC \(Variable Size\) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 294 M
( | | padding |Padding Length |) s
5 283 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 261 M
( Figure 3: A sample NHC compressed IP/UDP packet containing an) s
5 250 M
( application data such as a CoAP message.) s
5 217 M
(4. LOWPAN_NHC for the Record Plus Handshake Headers) s
5 195 M
( In the case where the Record header fragment field contains a) s
5 184 M
( handshake message, we compress both the Record header and the) s
5 173 M
( Handshake header using a single encoding byte and define 6LoWPAN_NHC) s
5 162 M
( for Record+Handshake \(6LoWPAN_NHC_RH\). The Handshake protocol) s
5 151 M
( requires 12 bytes of the handshake header. Using the proposed) s
5 140 M
( 6LoWPAN_NHC_RH the handshake header length is reduced to 3 bytes.) s
5 129 M
( Figure 4 shows 6LoWPAN NHC encoding for the Record+Handshake) s
5 118 M
( headers.) s
5 74 M
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(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
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( 0 1 2 3 4 5 6 7) s
5 624 M
( +---+---+---+---+---+---+---+---+) s
5 613 M
( | 1 | 0 | 0 | 1 | V |EC |SN | F |) s
5 602 M
( +---+---+---+---+---+---+---+---+) s
5 580 M
(Figure 4: LOWPAN_NHC encoding for the DTLS Record plus Handshake headers) s
5 558 M
( The encoded bits have the following functions:) s
5 525 M
( o The first four bits represent the ID field that is used to) s
5 514 M
( distinguish 6LoWPAN_NHC_RH from other encodings, and to comply) s
5 503 M
( with 6LoWPAN_NHC encoding scheme. In case of 6LoWPAN_NHC_RHS we) s
5 492 M
( set the ID bits to 1000.) s
5 470 M
( o The Version \(V\) and Epoch \(EC\) are encoded using the same scheme) s
5 459 M
( presented in Section 3.) s
5 437 M
( o If SN is set to 0, a 16 bit sequence number is used and the left) s
5 426 M
( most 32 bits are omitted. If 1, all 48 bits of the sequence number) s
5 415 M
( are carried inline.) s
5 393 M
( o Fragment \(F\): If 0, the handshake message is not fragmented and the) s
5 382 M
( fields fragment_offset and fragment_length are omitted. This is) s
5 371 M
( the common case, which occurs when a handshake message is not) s
5 360 M
( larger than the maximum record size. If 1, the fields) s
5 349 M
( fragment_offset and fragment_length are carried inline.) s
5 316 M
( In contrary to the scheme defined in Section 3, the content_type) s
5 305 M
( field is always omitted as it is obvious based on the ID bits that) s
5 294 M
( the content type is the Handshake protocol. The message_type and) s
5 283 M
( message_sequence fields of the Handshake header are always carried) s
5 272 M
( inline. The length field in the Handshake headers is always omitted) s
5 261 M
( as it can be deduced from the lower layers: either from the 6LoWPAN) s
5 250 M
( header or the IEEE 802.15.4 header. We have to un-compress layer-wise) s
5 239 M
( from lower to higher layers until the UDP header is uncompressed.) s
5 228 M
( Then the length of the UDP payload is known and the DTLS payload) s
5 217 M
( length can be calculated.) s
5 195 M
( With this combined encoding scheme the 25 bytes of Record plus) s
5 184 M
( Handshake headers are bring down to 6 bytes \(plus one additional byte) s
5 173 M
( for the 6LoWPAN_NHC_RH\). Considering that a handshake process) s
5 162 M
( consists of 10 messages, sending 18 less bytes for each message is a) s
5 151 M
( very significant saving. This contributes to the feasibility of using) s
5 140 M
( the chatty handshake protocol for constrained nodes.) s
5 118 M
(5. LOWPAN_NHC for the Handshake Messages) s
5 74 M
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
5 635 M
( The Handshake protocol consists of 10 messages, all having well-) s
5 624 M
( defined headers. We can compress some of the handshake messages. Two) s
5 613 M
( of the handshake messages with most number of header fields are) s
5 602 M
( ClientHello and ServerHello. Using the 6LoWPAN_NHC for the) s
5 591 M
( ClientHello message \(6LoWPAN_NHC_CH\) defined in this document, we can) s
5 580 M
( omit all ClientHello fields except the random field. The minimum) s
5 569 M
( possible size of a ClientHello message without the random field is 10) s
5 558 M
( bytes: version \(2\), session_id length\(1\), cookie length \(1\),) s
5 547 M
( cipher_suites length \(2\), cipher_suites \(2\), compression_methods) s
5 536 M
( length \(1\), compression_methods \(1\). By appling 6LoWPAN_NHC_CH the) s
5 525 M
( minimum possible size of a ClientHello message without a random field) s
5 514 M
( is 1 byte that is used to encode 6LoWPAN_NHC_CH. This is the common) s
5 503 M
( case when DTLS is used to secure CoAP messages. Figure 5 depicts the) s
5 492 M
( NHC encoding for the ClientHello message.) s
5 470 M
( 0 1 2 3 4 5 6 7) s
5 459 M
( +---+---+---+---+---+---+---+---+) s
5 448 M
( | 1 | 0 | 1 | 0 | SI| C |CS |CM |) s
5 437 M
( +---+---+---+---+---+---+---+---+) s
5 415 M
( Figure 5: LOWPAN_NHC encoding for the DTLS ClientHello Message) s
5 393 M
( The function of each compressed header field is described below:) s
5 360 M
( o The first four bits in the 6LoWPAN_NHC_CH represent the ID field) s
5 349 M
( which are set to 1010.) s
5 327 M
( o Session ID \(SI\) and Cookie \(C\): If 0, the session_id and/or cookie) s
5 316 M
( fields are not available and these fields and 8 bits of the) s
5 305 M
( prefixed length fields are omitted. In the \(D\)TLS protocol,) s
5 294 M
( session_id is empty if no session is available, or if the client) s
5 283 M
( wishes to generate new security parameters. The ClientHello) s
5 272 M
( message uses session_id only if the DTLS client wants to resume) s
5 261 M
( the old session. If SI or C is set to 1, the session_id and/or) s
5 250 M
( cookie fields are carried inline.) s
5 228 M
( o Cipher Suites \(CS\): If 0, the default \(mandatory\) cipher suite for) s
5 217 M
( CoAP that supports automatic key management is used and this field) s
5 206 M
( and the prefixed 16 bits length field are omitted. In the current) s
5 195 M
( CoAP draft, TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 is a mandatory) s
5 184 M
( cipher suite. If CS is set to 1, the cipher_suites field is) s
5 173 M
( carried inline.) s
5 151 M
( o Compression Methods \(CM\): If 0, the default compression method,) s
5 140 M
( i.e., COMPRESSION_NULL is used and this field and the prefixed 8) s
5 129 M
( bits length field are omitted. If CM is set to 1, the) s
5 118 M
( compression_methods field is carried inline.) s
5 74 M
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
5 635 M
( The random field in the ClientHello is always carried inline whereas) s
5 624 M
( the version field is always omitted. The version contains the same) s
5 613 M
( value as in the DTLS Record header. In case of TLS/SSL the version) s
5 602 M
( field was defined to let a TLS client specify an older version to be) s
5 591 M
( compatible with an SSL client, which is rarely used in practice. All) s
5 580 M
( current versions of web browsers use the same TLS version in Record) s
5 569 M
( and ClientHello. DTLS 1.2 \(adapted from TLS 1.2\) mentions that the) s
5 558 M
( client sends its latest supported version in the ClientHello message.) s
5 547 M
( All DTLS versions \(1.0 and 1.2\) have compatible ClientHello messages.) s
5 536 M
( If the server does not support this version, then the ServerHello) s
5 525 M
( message contains its supported version. If the client is not capable) s
5 514 M
( of handling server's version, it terminates the connection with a) s
5 503 M
( protocol version alert.) s
5 481 M
( Figure 6 shows a sample compressed IP/UDP datagram that contains a) s
5 470 M
( ClientHello.) s
5 448 M
( | octet 1 | octet 2 | octet 3 | octet 4 |) s
5 437 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 426 M
( | LOWPAN_IPHC | Hop Limit | Source Address|) s
5 415 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 404 M
( | Source Address| Destination Address | LOWPAN_NHC_UDP|) s
5 393 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 382 M
( |S Port |D Port | Checksum | LOWPAN_NHC_RHS|) s
5 371 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 360 M
( | Epoch | Sequence Number | Message Type |) s
5 349 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 338 M
( | Message Sequence | LOWPAN_NHC_C | |) s
5 327 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +) s
5 316 M
( | |) s
5 305 M
( + Client Random \(32 bytes\) +) s
5 294 M
( | |) s
5 283 M
( +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+) s
5 261 M
( Figure 6: A sample NHC compressed IP/UDP packet containing the) s
5 250 M
( ClientHello message.) s
5 228 M
( This document also proposes 6LoWPAN_NHC for the ServerHello message) s
5 217 M
( \(LOWPAN_NHC_SH\). ServerHello is very similar to ClientHello except) s
5 206 M
( that the length of the cipher_suites and compression_methods fields) s
5 195 M
( are fixed to 16 and 8 bits, respectively. Figure 7 shows the 6LoWPAN-) s
5 184 M
( NHC encoding for the ServerHello message.) s
5 162 M
( 0 1 2 3 4 5 6 7) s
5 151 M
( +---+---+---+---+---+---+---+---+) s
5 140 M
( | 1 | 0 | 1 | 1 | V |SI |CS |CM |) s
5 129 M
( +---+---+---+---+---+---+---+---+) s
5 74 M
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(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
5 635 M
( Figure 7: LOWPAN_NHC encoding for the DTLS ServerHello Message) s
5 613 M
( The function of each compressed header field is described below:) s
5 591 M
( o The first four bits in the 6LoWPAN_NHC_SH represent the ID field) s
5 580 M
( set to 1011.) s
5 558 M
( o Version \(V\): In order to avoid version negotiation in the initial) s
5 547 M
( handshake, the DTLS 1.2 standard suggests that the server) s
5 536 M
( implementation should use DTLS version 1.0. If V is set to 0, the) s
5 525 M
( version is DTLS 1.0 and the version field is omitted. However the) s
5 514 M
( DTLS 1.2 clients must not assume that the server does not support) s
5 503 M
( higher versions or it will eventually negotiate DTLS 1.0 rather than) s
5 492 M
( DTLS 1.2. If V is set to 1, the version field is carried inline.) s
5 470 M
( o Session ID \(SI\), Cipher Suite \(CS\), and Compression Method \(CM\) are) s
5 459 M
( encoded in a similar fashion as discussed above for the ClientHello) s
5 448 M
( message. In order to not compromise security the random field in the) s
5 437 M
( ServerHello, like in the ClientHello message, is always carried) s
5 426 M
( inline.) s
5 404 M
(6. Summary of DTLS header sizes with and without Compression) s
5 371 M
( +---+---+---+---+---+---+---+---+---+---+---+---+---+---+) s
5 360 M
( | | Without | With |) s
5 349 M
( + DTLS Header +Compression [bytes]+Compression [bytes]+) s
5 338 M
( | | | |) s
5 327 M
( +---+---+---+---+---+---+---+---+---+---+---+---+---+---+) s
5 316 M
( | Record | 13 | 4* or 5 |) s
5 305 M
( +---+---+---+---+---+---+---+---+---+---+---+---+---+---+) s
5 294 M
( | Handshake | 12 | 3 |) s
5 283 M
( +---+---+---+---+---+---+---+---+---+---+---+---+---+---+) s
5 272 M
( | ClientHello | 10** | 1 |) s
5 261 M
( +---+---+---+---+---+---+---+---+---+---+---+---+---+---+) s
5 250 M
( | ServerHello | 6** | 1 |) s
5 239 M
( +---+---+---+---+---+---+---+---+---+---+---+---+---+---+) s
5 217 M
( * For Record plus handshake case \(Section 4\) the size is 4.) s
5 206 M
( ** Without the random field) s
5 184 M
( Table 1: With the header compression defined in this document we) s
5 173 M
( can clearly reduce significant communication overhead in resource-) s
5 162 M
( constrained networks.) s
5 140 M
(7. Implementation Considerations) s
5 118 M
( We provide an open source implementation of the proposed compression) s
5 74 M
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(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
5 635 M
( scheme in the Contiki operating system. The implementation is) s
5 624 M
( released under BSD license and can be obtained at the following URI:) s
5 613 M
( http://www.shahidraza.info/resources/CoAP-DTLS.zip. We also evaluate) s
5 602 M
( the compressed DTLS and the details are published in Lithe) s
5 591 M
( [Lithe13].) s
5 558 M
(8. Security Considerations) s
5 536 M
( The compression scheme proposed in this document does not compromise) s
5 525 M
( any of the security provided by the DTLS Record header and the) s
5 514 M
( Handshake header. In particular, the SN field is compressed in an on-) s
5 503 M
( demand fashion, as described in Section 3. In order to overcome) s
5 492 M
( replay attacks, it is recommended that the communication end-points) s
5 481 M
( re-establish a connection using handshake before the sequence number) s
5 470 M
( overflows. However, in constrained environments, different) s
5 459 M
( implementations can decide the overflow size; 2^16, 2^24, 2^32, or) s
5 448 M
( 2^48. This leads to a trade-off between the overhead incurred by) s
5 437 M
( establishing a new secure connection \(i.e. a re-handshake\) and by) s
5 426 M
( sending more bits of sequence number. The random number field,) s
5 415 M
( Initialization Vector \(IV\), and Message Authentication Code \(MAC\) are) s
5 404 M
( also not compressed to take full advantage of DTLS security.) s
5 382 M
(9. IANA Considerations) s
5 360 M
( [RFC6282] creates a new IANA registry for the LOWPAN_NHC header type.) s
5 349 M
( This document requests the assignment of following contents:) s
5 327 M
( 11011XXX: The 6LOWPAN_NHC encoding for the UDP header where the UDP) s
5 316 M
( is compressed with LOWPAN_NHC.) s
5 294 M
( 1000XXXX: The 6LOWPAN_NHC encoding for the Record plus Handshake) s
5 283 M
( headers \(LOWPAN_NHC_RH\).) s
5 261 M
( 1001XXXX: The 6LOWPAN_NHC encoding for the Record header) s
5 250 M
( \(LOWPAN_NHC_R\).) s
5 228 M
( 1010XXXX: The 6LOWPAN_NHC encoding for the DTLS ClientHello message) s
5 217 M
( \(LOWPAN_NHC_CH\)) s
5 195 M
( 1011XXXX: The 6LOWPAN_NHC encoding for the DTLS ServerHello message) s
5 184 M
( \(LOWPAN_NHC_SH\)) s
5 162 M
( The Capital letter X in bit positions represent class-specific bit) s
5 151 M
( assignments as defined in Section 3, 4, and 5.) s
5 74 M
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
5 635 M
(10. Acknowledgements) s
5 613 M
( The work is funded by CALIPSO, Connect All IP-based Smart Objects,) s
5 602 M
( funded by the European Commission under FP7 with contract number FP7-) s
5 591 M
( ICT-2011.1.3-288879.) s
5 569 M
(11. References) s
5 547 M
(11.1. Normative References) s
5 525 M
( [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate) s
5 514 M
( Requirement Levels", BCP 14, RFC 2119, March 1997.) s
5 492 M
( [RFC6282] Hui, J., Ed., and P. Thubert, "Compression Format for IPv6) s
5 481 M
( Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,) s
5 470 M
( September 2011.) s
5 448 M
( [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer) s
5 437 M
( Security Version 1.2", RFC 6347, January 2012.) s
5 415 M
( [RFC4303] J. Hui, P. Thubert, "Compression Format for IPv6 Datagrams) s
5 404 M
( over IEEE 802.15.4-Based Networks", RFC 6282, September) s
5 393 M
( 2011) s
5 382 M
(11.2. Informative References) s
5 360 M
( [WiSec13] R. Hummen, J. Hiller, H. Wirtz, M. Henze, H. Shafagh, and) s
5 349 M
( K. Wehrle, "6LoWPAN fragmentation attacks and mitigation) s
5 338 M
( mechanisms," in Proceedings of the 6th ACM Conference on) s
5 327 M
( Security and Privacy in Wireless and Mobile Networks, Apr.) s
5 316 M
( 2013, Budapest, Hungry.) s
5 294 M
( [Lithe13] S. Raza, H. Shafagh, K. Hewage, R. Hummen, Thiemo Voigt,) s
5 283 M
( "Lithe: Lightweight Secure CoAP for the Internet of) s
5 272 M
( Things". IEEE Sensors Journal, 13\(10\), 3711-3720, October) s
5 261 M
( 2013.) s
5 217 M
(Authors' Addresses) s
5 184 M
( Shahid Raza) s
5 173 M
( SICS Swedish ICT AB \(SICS\)) s
5 162 M
( Isafjordsgatan 22, 16440 Kista) s
5 151 M
( SWEDEN) s
5 129 M
( Phone: +46-\(0\)768831797) s
5 118 M
( EMail: shahid@sics.se) s
5 74 M
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5 668 M
(INTERNET DRAFT Compressed-DTLS-for-6LoWPAN March 10, 2014) s
5 635 M
( Hossein Shafagh) s
5 624 M
( ETH Zurich) s
5 613 M
( Universitatstrasse 6, CH-8092 Zurich) s
5 602 M
( SWITZERLAND) s
5 580 M
( Phone: +41 44 63 26136) s
5 569 M
( EMail: shafagh@ethz.ch) s
5 536 M
( Olivier Dupont) s
5 525 M
( Cisco) s
5 514 M
( Cisco Systems, Paris) s
5 503 M
( FRANCE) s
5 481 M
( Phone: +33 158 043 480) s
5 470 M
( Email: odupont@cisco.com) s
5 74 M
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