Algebraic key establishment protocols based on the difficulty of solving equations over algebraic structures are described as a theoretical basis for constructing public-key cryptosystems.

Plutus is a cryptographic storage system that enables secure file sharing without placing much trust on the file servers. In particular, it makes novel use of cryptographic primitives to protect and share files. Plutus features highly scalable key management while allowing individual users to retain direct control over who gets access to their files. We explain the mechanisms in Plutus to reduce the number of cryptographic keys exchanged between users by using filegroups, distinguish file read and write access, handle user revocation efficiently, and allow an untrusted server to authorize file writes. We have built a prototype of Plutus on OpenAFS. Measurements of this prototype show that Plutus achieves strong security with overhead comparable to systems that encrypt all network traffic.

Abstract. The braid groups are infinite non-commutative groups naturally arising from geometric braids. The aim of this article is twofold. One is to show that the braid groups can serve as a good source to enrich cryptography. The feature that makes the braid groups useful to cryptography includes the followings: (i) The word problem is solved via a fast algorithm which computes the canonical form which can be efficiently manipulated by computers. (ii) The group operations can be performed efficiently. (iii) The braid groups have many mathematically hard problems that can be utilized to design cryptographic primitives. The other is to propose and implement a new key agreement scheme and public key cryptosystem based on these primitives in the braid groups. The efficiency of our systems is demonstrated by their speed and information rate. The security of our systems is based on topological, combinatorial and group-theoretical problems that are intractible according to our current mathematical knowledge. The foundation of our systems is quite different from widely used cryptosystems based on number theory, but there are some similarities in design. Key words: public key cryptosystem, braid group, conjugacy problem, key exchange, hard problem, non-commutative group, one-way function, public key infrastructure 1

Wireless networks of miniaturized, low-power sensor/actuator devices are poised to become widely used in commercial and military environments. The communication security problems for these networks are exacerbated by the limited power and energy of the sensor devices. In this paper, we describe the design and implementation of public-key-(PK)-based protocols that allow authentication and key agreement between a sensor network and a third party as well as between two sensor networks. Our work is novel in that PK technology was commonly believed to be too inefficient for use on low-power devices. As part of our solution, we exploit the efficiency of public operations in the RSA cryptosystem and design protocols that place the computationally expensive operations on the parties external to the sensor network, when possible. Our protocols have been implemented on UC Berkeley MICA2 motes using the TinyOS development environment.

Lattices are regular arrangements of points in n-dimensional space, whose study appeared in the 19th century in both number theory and crystallography. Since the appearance of the celebrated LenstraLenstra -Lov'asz lattice basis reduction algorithm twenty years ago, lattices have had surprising applications in cryptology. Until recently, the applications of lattices to cryptology were only negative, as lattices were used to break various cryptographic schemes. Paradoxically, several positive cryptographic applications of lattices have emerged in the past five years: there now exist public-key cryptosystems based on the hardness of lattice problems, and lattices play a crucial role in a few security proofs.

Abstract We introduce a new class of computational problems which we call the "one-more-RSAinversion " problems. Our main result is that two problems in this class, which we call the chosen-target and known-target inversion problems respectively, have polynomially-equivalent computational complexity. We show how this leads to a proof of security for Chaum's RSA-based blind signature scheme in the random oracle model based on the assumed hardness of either of these problems. We define and prove analogous results for "one-more-discrete-logarithm " problems. Since the appearence of the preliminary version of this paper, the new problems we have introduced have found other uses as well.

Abstract. Secure and reliable group communication is an active area of research. Its popularity is caused by the growing importance of group-oriented and collaborative applications. The central research challenge is secure and efficient group key management. While centralized methods are often appropriate for key distribution in large multicast-style groups, many collaborative group settings require distributed key agreement techniques. This work investigates a novel group key agreement approach which blends so-called key trees with Diffie-Hellman key exchange. It yields a secure protocol suite (TGDH) that is both simple and fault-tolerant. Moreover, the efficiency of TGDH appreciably surpasses that of prior art. 1

Lattices are regular arrangements of points in space, whose study appeared in the 19th century in both number theory and crystallography.

Secure communication is critical in military environments where the network infrastructure is vulnerable to various attacks and compromises. A conventional centralized solution breaks down when the security servers are destroyed by the enemies. In this paper we design and evaluate a security framework for multi-layer ad-hoc wireless networks with unmanned aerial vehicles (UAVs). In battlefields, the framework adapts to the contingent damages on the network infrastructure. Depending

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