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Innovative Authentication Techniques for Packet Fragments in Intermittent Networks

This paper explores the complexities of authenticating packet fragments in intermittent and oversubscribed network scenarios. It addresses the issue of determining which fragment to send first when a router link becomes available. The study emphasizes the importance of prioritizing valuable traffic while acknowledging the challenges of fragmentation and authentication. Key considerations include the potential for fragmented data to travel via different paths, the implications of lost fragments, and various solutions for creating compact but secure authentication methods. It builds on prior research in fragmentation issues and proposes novel approaches for robust data integrity.

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Innovative Authentication Techniques for Packet Fragments in Intermittent Networks

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  1. Authentication for Fragments Craig Partridge BBN Technologies craig@bbn.com

  2. The Problem Packet (Fragments) An Intermittent Link Comes Up Router Which Fragment Do You Send?

  3. Why An Issue? • New network scenarios with intermittent (potentially) oversubscribed links • A desire to send the most valuable traffic first • Large native unit of authentication • Mobigrams • DTN bundles

  4. Starting Assumptions • “Datagram” may be (re)fragmented at any point in the data and at any time (including during transmission) • Fragments do not all follow the same path

  5. Bytes 1..j Auth Unit P+1 Bytes k..n Auth Unit P “Datagram” may be (re)fragmented at any point in the data and at any time (including during transmission • Nice assumption • Can pre-empt fragments during transmission • Very general • Apparently untenable • Creates unauthenticatable fragments • Creates new style of attack on fragments • Must fragment on boundaries determined by origin (ugh!)

  6. Fragments do not all follow same path • Distributed Romanow-Floyd problem • Fragment lost on path 1 means fragments on path 2 now can only do harm, yet path 2 must treat them as valuable • Shared keys problematic • Every fragmentation point has private key with each origin? • Public key signatures are BIG • Either • Each fragment is self authenticating (see PK is BIG) • Or we distribute aggregated authentication information down all possible paths (can we make it small enough?)

  7. Can We Make Authentication Information Small Enough? • An idea: send function definition, not signature • Implies result of function is known • E.g. fragment #5 has digital hash of 5 • Such functions exist… • But either compact in representation OR strong enough to provide digital signature • NOT both (yet!) • Why this is a HOTNETS paper

  8. While I Take Questions… • This builds on prior work • Kent/Mogul, “Fragmentation Considered Harmful” • Romanow/Floyd, “Dynamics of TCP Traffic over ATM Networks” • Matthis/Heffner/Chandler, “Fragmentation Considered Very Harmful” • Toilet paper authentication ideas in DTN list

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