Abstract. We introduce Ad hoc Anonymous Identification schemes, a new multi-user cryptographic primitive that allows participants from a user population to form ad-hoc groups, and then prove membership anonymously in such groups. Our schemes are based on the notion of accumulator with one-way domain, a natural extension of cryptographic accumulators we introduce in this work. We provide a formal model for Ad hoc Anonymous Identification schemes and design secure such schemes both generically (based on any accumulator with one-way domain) and for a specific efficient implementation of such an accumulator based on the Strong RSA Assumption. A salient feature of our approach is that all the identification protocols take time independent of the size of the ad-hoc group. All our schemes and notions can be generally and efficiently amended so that they allow the recovery of the signer's identity by an authority, if the latter is desired. Using the Fiat-Shamir transform, we also obtain constant-size, signerambiguous group and ring signatures (provably secure in the Random Oracle Model). For ring signatures, this is the first such constant-size scheme, as all the previous proposals had signature size proportional to the size of the ring. For group signatures, we obtain schemes comparable in performance with state-of-the-art schemes, with the additional feature that the role of the group manager during key registration is extremely simple and essentially passive: all it does is accept the public key of the new member (and update the constant-size public key of the group).

We describe a new networking primitive, called a Path Verification Mechanism (PVM). There has been much recent work about how senders and receivers express policies about the paths that their packets take. For instance, a company might want fine-grained control over which providers carry which traffic between its branch offices, or a receiver may want traffic sent to it to travel through an intrusion detection service.While the ability to express policies has been well-studied, the ability to enforce policies has not. The core challenge is: if we assume an adversarial, decentralized, and high-speed environment, then when a packet arrives at a node, how can the node be sure that the packet followed an approved path? Our solution, ICING, incorporates an optimized cryptographic construction that is compact, and requires negligible configuration state and no PKI. We demonstrate ICING's plausibility with a NetFPGA hardware implementation. At 93% more costly than an IP router on the same platform, its cost is significant but affordable. Indeed, our evaluation suggests that ICING can scale to backbone speeds.

We describe a new family of parallelizable bounded distance decoding algorithms for the Barnes-Wall lattices, and analyze their decoding complexity. The algorithms are parameterized by the number p = 4 k ≤ N 2 of available processors, work for Barnes-Wall lattices in arbitrary dimension N = 2 n , correct any error up to squared unique decoding radius d 2 min /4, and run in worst-case time O(N log 2 N/ √ p). Depending on the value of the parameter p, this yields efficient decoding algorithms ranging from a fast sequential algorithm with quasi-linear decoding complexity O(N log 2 N ), to a fully parallel decoding circuit with polylogarithmic depth O(log 2 N ) and polynomially many arithmetic gates.

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