Delay Tolerant Networking Research Group S. Farrell Internet Draft Trinity College Dublin <draft-irtf-dtnrg-ltp-extensions-00.txt> M. Ramadas December 2004 Ohio University Expires June 2005 S. Burleigh NASA/Jet Propulsion Laboratory Licklider Transmission Protocol - Extensions Status of this Memo By submitting this Internet-Draft, we certify that any applicable patent or other IPR claims of which we are aware have been disclosed, or will be disclosed, and any of which we become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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 a "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [B97]. Discussions on this internet-draft are being made in the Delay Tolerant Networking Research Group (DTNRG) mailing list. More information can be found in the DTNRG web-site at http://www.dtnrg.org Abstract In an Interplanetary Internet setting deploying the Bundling protocol being developed by the Delay Tolerant Networking Research Group, Licklider Transmission Protocol (LTP), is intended to serve as a reliable convergence layer over single hop deep-space RF links. LTP Farrell et al. Expires - June 2005 [Page 1]
Internet Draft LTP - Extensions December 2004 does ARQ of data transmissions by soliciting selective-acknowledgment reception reports. It is stateful and has no negotiation or handshakes. LTP is designed to provide retransmission-based reliability over links characterized by extremely long message round-trip times (RTTs) and/or frequent interruptions in connectivity. Since communication across interplanetary space is the most prominent example of this sort of environment, LTP is principally aimed at supporting "long- haul" reliable transmission in interplanetary space, but has applications in other environments as well. This document describes extensions to LTP, and is part of a series of related documents describing LTP. Other documents in this series cover the motivation for LTP and the main protocol specification. We recommend reading all the documents in the series before writing code based on this document. Table of Contents 1. Introduction.................................................. 2 2. Security Extensions........................................... 3 2.1 LTP Authentication ...................................... 3 2.2 Cookie Mechanism......................................... 6 3. Security Considerations ...................................... 7 4. IANA Considerations .......................................... 7 5. Acknowledgments .............................................. 7 6. References ................................................... 8 6.1 Normative References ..................................... 8 6.2 Informative References ................................... 8 7. Author's Addresses ........................................... 8 8. Copyright Statement .......................................... 9 1. Introduction This document describes extensions to the base LTP protocol [LTP]. The background to LTP is described in the "motivation" document [LTPMOTIVE]. Currently the extensions defined all aim to provide additional security for LTP. Implementers should note that the LTP extension mechanism allows for multiple occurrences of any extension tag, in both (or either) the header or trailer. For example, the LTP authentication mechanism defined below requires both header and trailer extensions, which both Farrell et al. Expires - June 2005 [Page 2]
Internet Draft LTP - Extensions December 2004 use the same tag. 2. Security Extensions 2.1 LTP Authentication <<Note : The LTP-Auth security mechanism defined here may in future revisions be moved back to the main protocol specification [LTP] if there is community consensus in having it as a critical feature that ought to be included in all implementations of the protocol.>> The LTP Authentication mechanism provides cryptographic authentication of the segment. Implementations MAY support this extension field. If they do not support this header then they MUST ignore it. <<TODO: Check that ignoring is ok for all cases of response generation.>> The LTP authentication extension field has extension tag value 0x00. LTP authentication requires three new fields, the first two of which are carried as the value of the extensions field of the LTP header, and the third of which is carried in the segment trailer. The fields which are carried in the header extensions field are catenated together to form the SDNV-8 value (with the leftmost octet representing the ciphersuite and the remaining octets the KeyID). The KeyID field is optional, and is determined to be absent if the extension value consists of a single octet. Ciphersuite: an eight bit integer value with values defined below. KeyID: An optional key identifier, the interpretation of which is out of scope for this specification (that is, implementers MUST treat these KeyID fields as raw octets, even if they contained an ASN.1 DER encoding of an X.509 IssuerSerial construct [PKIXPROF], for example). The LTP-auth header extension MUST be present in the first segment from any LTP session which uses LTP authentication, but MAY be omitted from subsequent segments in that session. To guard against additional problems arising from lost segments, implementations SHOULD, where bandwidth allows, include these fields in a number of segments in the LTP session. The field carried as a trailer extension is the AuthVal field. It Farrell et al. Expires - June 2005 [Page 3]
Internet Draft LTP - Extensions December 2004 contains the authentication value, which is either a message authentication code (MAC) or a digital signature. This is itself a structured field whose length and formatting depends on the ciphersuite. We define three ciphersuites in this specification. Our approach here is to "hardcode" all algorithm options in a single ciphersuite value so 256 potential ciphersuites are supported by this version of LTP. Ciphersuite Value ----------- ----- OriginAuth 0 Signature 1 NULL 255 1. OriginAuth Ciphersuite The OriginAuth ciphersuite involves generating a MAC over the LTP segment and appending the resulting AuthVal field to the end of the segment. There is only one MACing algorithm defined for this which is HMAC-SHA1-80 [HMAC]. The AuthVal field in this case contains just the output of the HMAC-SHA1-80 algorithm which is a fixed width field (10 octets). <<Need to check if this is still the best HMAC variant to pick - and whether to truncate and so allow the extra bits for key mgt. later on.>> 2. Signature Ciphersuite The Signature ciphersuite involves generating a digital signature of the LTP segment and appending the resulting AuthVal field to the end of the segment. There is only one signature algorithm currently defined for this which is RSA with SHA1 [RSA]. Since the length of an RSA signature depends on the signing key and is often longer than the maximum value supported by the SDNV data-type, we include (inside the SDNV-8 value) a two octet length field which contains the length of the digital signature in bits. So the AuthVal field in this case is as follows (where the signature value occupies the minimum number of octets, e.g. 128 octets for a 1024 bit signature). <<Should we move to rsa with sha256?>> +--------------+---------/\/\/\----+ |length-in-bits| signature value | |(2 octets) | | +--------------+---------/\/\/\----+ Farrell et al. Expires - June 2005 [Page 4]
Internet Draft LTP - Extensions December 2004 3. NULL Ciphersuite <<It is probably debatable whether it is better to include this or not. A purist crypto position would probably be "just allow a CRC if that's what you want", a more code-centric position might be "I have working HMAC code, why not use that?". So this ciphersuite may well change or disappear as the document progresses.>> The NULL ciphersuite is basically the same as the OriginAuth ciphersuite, but with a hardcoded key. This ciphersuite effectively provides only data integrity without authentication, and thus is subject to active attacks and is the equivalent of providing a CRC. The hardcoded key to be used with this ciphersuite is the following: HMAC_KEY : c37b7e64 92584340 : bed12207 80894115 : 5068f738 <<The above is the test vector from RFC 3537, but who cares anyway?>> In each case the bytes which are input to the cryptographic algorithm consist of the entire LTP segment except the AuthVal. In particular the header extensions field which may contain the ciphersuite number and the KeyID field are part of the input. <<This causes a problem if somehow we get two separate LTP auth headers. Two possible fixes - include the KeyID in the trailer in that case, or else just require the originator to only include the corresponding header when calculating the trailer and then make the recipient search when it happens, which'll be never, or nearly so. I might want two LTP auth headers if I'm not sure about which ciphersuite or public key will work for the LTP peer, which should be rare but can happen (esp the "which public key" part). I think that I favor making the recipient search for now.>> The output bytes of the cryptographic operation are the payload of the AuthVal field. The following shows an example LTP-auth header, starting from and including the extensions field ext tag sndv-8 c-s k-id +----+----+----+----+----+ |0x11|0x00|0x81|0x00|0x24| +----+----+----+----+----+ Farrell et al. Expires - June 2005 [Page 5]
Internet Draft LTP - Extensions December 2004 The Extensions field has the value 0x11 meaning 1 header extension is present (the LTP-auth one, denoted by the MS-nibble value of 1) and one trailer extension (the AuthVal, not shown). The next octet is the extension tag (0x00 for LTP-auth), followed by the SDNV-8 length (encoded as 0x81) containing the one octet ciphersuite (0x00 meaning OriginAuth) and lastly the KeyID which is an SDNV-8, in this case with a short value of 0x24. 2.2 Cookie mechanism <<Note: this mechanism is not yet entirely worked-out and is included at this stage mainly to get feedback as to whether or not it should be included with LTP.>> The use of cookies is a well known way to make denial-of-service attacks harder to mount. We may define an extension field which can contain a cookie value for use in cases where an implementation is liable to such attacks. The cookie is placed in the header in an extension field. The cookie extension field has extension tag value 0x01. The cookie extension requires no trailer field. The cookie value can essentially be viewed as a sufficiently long random number, where the length can be determined by the implementation (longer cookies are harder to guess and therefore better, though using more bandwidth). Note that cookies values can be derived using lots of different schemes so long as they produce random looking and hard to guess values. The first cookie inserted into a segment for this session is called the initial cookie. Cookies do not outlast an LTP session. <<Revisit this?? Could have a TTL too?>> The basic mode of operation is that an LTP engine can include a cookie in a segment at any time. After that time all segments corresponding to that LTP session MUST contain a good cookie value - that is, all segments both to and from the engine MUST contain a good cookie. Clearly, there will be some delay before the cookie is seen in incoming segments - implementations MUST determine an acceptable delay for these cases, and MUST only accept segments without a cookie until that time. The cookie value can be extended at any time by catenating more random bits. This allows both LTP engines to contribute to the randomness of the cookie, where that is useful. It also allows a node Farrell et al. Expires - June 2005 [Page 6]
Internet Draft LTP - Extensions December 2004 which considers the cookie value too short (say due to changing circumstances) to add additional security. In this case, the extended cookie value becomes the "to-be-checked-against" cookie value for all future segments (modulo the communications delay as above). <<Probably extending my own cookie is only useful if cookies can outlast sessions.>> It can happen that both sides emit segments containing an initial cookie before their peer has a chance to see any cookie. In that case two cookie extension fields MUST be included in all segments subsequently (once the traffic has caught up). That is, the sender and recipient cookies are handled independently. In such cases, both cookie values MUST be "good" at all relevant times (i.e. modulo the delay). In this case, the peer's initial cookie MUST arrive before the calculated delay for receipt of segments containing this engine's cookie - there is only a finite window during which a second cookie can be inserted into the session. A "good" cookie is therefore one which starts with the currently stored cookie value, or else a new cookie where none has been seen in that session so far. Once a cookie value is seen and treated as "good" (e.g. an extended value), the previous value is no longer "good". Modulo the communications delay, segments with an incorrect or missing cookie value MUST be silently discarded. 3. Security Considerations <<TBS and will include consideration of cookie sizes as well as combining LTP auth with cookies.>> 4. IANA Considerations At present there are none known. 5. Acknowledgments Many thanks to Tim Ray, Vint Cerf, Bob Durst, Kevin Fall, Adrian Hooke, Keith Scott, Leigh Torgerson, Eric Travis, and Howie Weiss for their thoughts on this protocol and its role in Delay-Tolerant Networking architecture. Part of the research described in this document was carried out at the Jet Propulsion laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This work was performed under DOD Contract DAA-B07- 00-CC201, DARPA AO H912; JPL Task Plan No. 80-5045, DARPA AO H870; Farrell et al. Expires - June 2005 [Page 7]
Internet Draft LTP - Extensions December 2004 and NASA Contract NAS7-1407. Thanks are also due to Shawn Ostermann, Hans Kruse, and Dovel Myers at Ohio University for their suggestions and advice in making various design decisions. Part of this work was carried out at Trinity College Dublin as part of the SeNDT contract funded by Enterprise Ireland's research innovation fund. 6. References 6.1 Normative References [LTP] Ramadas, M., Burleigh, S., and Farrell, S., "Licklider Transmission Protocol - Specification", draft-irtf-dtnrg-ltp-02.txt (Work in Progress), December 2004. [B97] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [HMAC] Krawczyk, H. et al, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997. [RSA] Kaliski, B, Staddon J, "PKCS #1: RSA Cryptography Specifications Version 2.0", RFC 2437, October 1998. 6.2 Informative References [LTPMOTIVE] Burleigh, S., Ramadas, M., and Farrell, S., "Licklider Transmission Protocol - Motivation", draft-irtf-dtnrg-ltp- motivation-00.txt (Work in Progress), December 2004. [PKIXPROF] Housley, R. et al, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002. 7. Author's Addresses Stephen Farrell Distributed Systems Group Computer Science Department Trinity College Dublin Ireland Telephone +353-1-608-3070 Email stephen.farrell@cs.tcd.ie Manikantan Ramadas Farrell et al. Expires - June 2005 [Page 8]
Internet Draft LTP - Extensions December 2004 Internetworking Research Group 301 Stocker Center Ohio University Athens, OH 45701 Telephone +1 (740) 593-1562 Email mramadas@irg.cs.ohiou.edu Scott C. Burleigh Jet Propulsion Laboratory 4800 Oak Grove Drive M/S: 179-206 Pasadena, CA 91109-8099 Telephone +1 (818) 393-3353 FAX +1 (818) 354-1075 Email Scott.Burleigh@jpl.nasa.gov 8. Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights." This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Farrell et al. Expires - June 2005 [Page 9]
