Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Mixing Email with BABEL’96Ceki Gulcu, Gene TsudikIBM Zurich, Switzerlandcs6461, Fall 2008Computer Science, Michigan TechByung ChoiIntroduction●The most critical network building block for anonymity: Mix by Chaum’81●Absolute anonymity: dining cryptographers algorithm and protocol by Chaum’88–Impractical due to the large protocol overhead–Hard to provide secure pairwise channels and a synchronized broadcast channel●Advancement being soughtRelated work●Anonymous Email systems–Penet: Finland 1990s–Cypherpunk: 1990s – now?–Mixmaster: 1990s – now?–Implementations of the concept of Mix by a single individual or a group of contributors●Systematic improvements neededDesired properties (requirements)●Email systems accommodate anonymity●Hard to determine the sender●Recipient can reply the anonymous sender●End-point anonymity preserved, intermediate mixes are not maximally trusted● Infrastructure resistant to active attacks●Sender gets an anonymous confirmation●Low noiseNotationMix, revistedAttacks●Passive–Content correlation: ●uniform length, padding, nonce–Time correlation: ●Regular vs. interval batching●Active–Isolate and Identify–Message replay: ●time stamp, message identifier–Cascading or chaining mixesBABEL ●Forward path–Composition by sender–Processing by mixes–What does a mix know?Forward messageForward messageBABEL●Return path–Creating RPI–Replying by recipient–Reply processing by BABEL–Handling replies at the originator–Two-way anonymous conversation–Security of replies–Inter-mix Detours–Indirect repliesReturn pathRPIReturn path informationReply messageTwo-way anonymitySecurity of repliesInter-mix detoursKeeping message size constantHeeding anonymity●Fixed-path systems●System staunchness, miss & guess factors●Quest for confusion–Probabilistic deferment–Hybrid approachTrickle attackInterval batchingProbabilistic defermentBinomial
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