Distributed Sensor Networks (DSNs) are ad-hoc mobile networks that include sensor nodes with limited computation and communication capabilities. DSNs are dynamic in the sense that they allow addition and deletion of sensor nodes after deployment to grow the network or replace failing and unreliable nodes. DSNs may be deployed in hostile areas where communication is monitored and nodes are subject to capture and surreptitious use by an adversary. Hence DSNs require cryptographic protection of communications, sensor-capture detection, key revocation and sensor disabling. In this paper, we present a key-management scheme designed to satisfy both operational and security requirements of DSNs. The scheme includes selective distribution and revocation of keys to sensor nodes as well as node re-keying without substantial computation and communication capabilities. It relies on probabilistic key sharing among the nodes of a random graph and uses simple protocols for shared-key discovery and path-key establishment, and for key revocation, re-keying, and incremental addition of nodes. The security and network connectivity characteristics supported by the key-management scheme are discussed and simulation experiments presented.

/pdf/a-key-management-scheme-for-distributed-sensor-networks-2arngir92b.pdf

A key-management scheme for distributed sensor networks

This paper describes a new replication algorithm that is able to tolerate Byzantine faults. We believe that Byzantinefault-tolerant algorithms will be increasingly important in the future because malicious attacks and software errors are increasingly common and can cause faulty nodes to exhibit arbitrary behavior. Whereas previous algorithms assumed a synchronous system or were too slow to be used in practice, the algorithm described in this paper is practical: it works in asynchronous environments like the Internet and incorporates several important optimizations that improve the response time of previous algorithms by more than an order of magnitude. We implemented a Byzantine-fault-tolerant NFS service using our algorithm and measured its performance. The results show that our service is only 3% slower than a standard unreplicated NFS.

/pdf/practical-byzantine-fault-tolerance-58gb0de0hd.pdf

Practical Byzantine fault tolerance

Our growing reliance on online services accessible on the Internet demands highly available systems that provide correct service without interruptions. Software bugs, operator mistakes, and malicious attacks are a major cause of service interruptions and they can cause arbitrary behavior, that is, Byzantine faults. This article describes a new replication algorithm, BFT, that can be used to build highly available systems that tolerate Byzantine faults. BFT can be used in practice to implement real services: it performs well, it is safe in asynchronous environments such as the Internet, it incorporates mechanisms to defend against Byzantine-faulty clients, and it recovers replicas proactively. The recovery mechanism allows the algorithm to tolerate any number of faults over the lifetime of the system provided fewer than 1/3 of the replicas become faulty within a small window of vulnerability. BFT has been implemented as a generic program library with a simple interface. We used the library to implement the first Byzantine-fault-tolerant NFS file system, BFS. The BFT library and BFS perform well because the library incorporates several important optimizations, the most important of which is the use of symmetric cryptography to authenticate messages. The performance results show that BFS performs 2p faster to 24p slower than production implementations of the NFS protocol that are not replicated. This supports our claim that the BFT library can be used to build practical systems that tolerate Byzantine faults.

/pdf/practical-byzantine-fault-tolerance-and-proactive-recovery-41bx19pxe1.pdf

Practical byzantine fault tolerance and proactive recovery

In recent years, IP protection of FPGA hardware designs has become a requirement for many IP vendors. In [34], Simpson and Schaumont proposed a fundamentally different approach to IP protection on FPGAs based on the use of Physical Unclonable Functions (PUFs). Their work only assumes the existence of a PUF on the FPGAs without actually proposing a PUF construction. In this paper, we propose new protocols for the IP protection problem on FPGAs and provide the first construction of a PUF intrinsic to current FPGAs based on SRAM memory randomness present on current FPGAs. We analyze SRAM-based PUF statistical properties and investigate the trade offs that can be made when implementing a fuzzy extractor.

/pdf/fpga-intrinsic-pufs-and-their-use-for-ip-protection-4zcbpcd9em.pdf

FPGA Intrinsic PUFs and Their Use for IP Protection

Storage outsourcing is a rising trend which prompts a number of interesting security issues, many of which have been extensively investigated in the past. However, Provable Data Possession (PDP) is a topic that has only recently appeared in the research literature. The main issue is how to frequently, efficiently and securely verify that a storage server is faithfully storing its client's (potentially very large) outsourced data. The storage server is assumed to be untrusted in terms of both security and reliability. (In other words, it might maliciously or accidentally erase hosted data; it might also relegate it to slow or off-line storage.) The problem is exacerbated by the client being a small computing device with limited resources. Prior work has addressed this problem using either public key cryptography or requiring the client to outsource its data in encrypted form.In this paper, we construct a highly efficient and provably secure PDP technique based entirely on symmetric key cryptography, while not requiring any bulk encryption. Also, in contrast with its predecessors, our PDP technique allows outsourcing of dynamic data, i.e, it efficiently supports operations, such as block modification, deletion and append.

http://sprout.ics.uci.edu/pubs/a9-ateniese.pdf

Scalable and efficient provable data possession

We describe a parallelizable block-cipher mode of operation that simultaneously provides privacy and authenticity. OCB encrypts-and-authenticates a nonempty string M e {0,1} using \lceil |M|/n\rceil + 2 block-cipher invocations, where n is the block length of the underlying block cipher. Additional overhead is small. OCB refines a scheme, IAPM, suggested by Charanjit Jutla. Desirable properties of OCB include: the ability to encrypt a bit string of arbitrary length into a ciphertext of minimal length; cheap offset calculations; cheap session setup; a single underlying cryptographic key; no extended-precision addition; a nearly optimal number of block-cipher calls; and no requirement for a random IV. We prove OCB secure, quantifying the adversary's ability to violate the mode's privacy or authenticity in terms of the quality of its block cipher as a pseudorandom permutation (PRP) or as a strong PRP, respectively.

/pdf/ocb-a-block-cipher-mode-of-operation-for-efficient-6z81aboaqg.pdf

OCB: a block-cipher mode of operation for efficient authenticated encryption

We describe a message authentication algorithm, UMAC, which can authenticate messages (in software, on contemporary machines) roughly an order of magnitude faster than current practice (e.g., HMAC-SHA1), and about twice as fast as times previously reported for the universal hash-function family MMH. To achieve such speeds, UMAC uses a new universal hash-function family, NH, and a design which allows effective exploitation of SIMD parallelism. The "cryptographic" work of UMAC is done using standard primitives of the user's choice, such as a block cipher or cryptographic hash function; no new heuristic primitives are developed here. Instead, the security of UMAC is rigorously proven, in the sense of giving exact and quantitatively strong results which demonstrate an inability to forge UMAC-authenticated messages assuming an inability to break the underlying cryptographic primitive. Unlike conventional, inherently serial MACs, UMAC is parallelizable, and will have ever-faster implementation speeds as machines offer up increasing amounts of parallelism. We envision UMAC as a practical algorithm for next-generation message authentication.

/pdf/umac-fast-and-secure-message-authentication-3algbmjwnk.pdf

UMAC: Fast and Secure Message Authentication

We describe a message authentication algorithm, UMAC, which can authenticate messages (in software, on contemporary machines) roughly an order of magnitude faster than current practice (e.g., HMAC-SHA1), and about twice as fast as times previously reported for the universal hash-function family MMH. To achieve such speeds, UMAC uses a new universal hash-function family, NH, and a design which allows effective exploitation of SIMD parallelism The cryptographic work of UMAC is done using standard primitives of the user's choice, such as a block cipher or cryptographic hash function; no new heuristic primitives are developed here. Instead, the security of UMAC is rigorously proven, in the sense of giving exact and quantitatively strong results which demonstrate an inability to forge UMAC-authenticated messages assuming an inability to break the underlying cryptographic primitive. Unlike conventional, inherently serial MACs, UMAC is parallelizable, and will have ever-faster implementation speeds as machines offer up increasing amounts of parallelism. We envision UMAC as a practical algorithm for next-generation message authentication.

UMAC : Fast and secure message authentication

We study software performance of authenticated-encryption modes CCM, GCM, and OCB. Across a variety of platforms, we find OCB to be substantially faster than either alternative. For example, on an Intel i5 ("Clarkdale") processor, good implementations of CCM, GCM, and OCB encrypt at around 4.2 cpb, 3.7 cpb, and 1.5 cpb, while CTR mode requires about 1.3 cpb. Still we find room for algorithmic improvements to OCB, showing how to trim one blockcipher call (most of the time, assuming a counter-based nonce) and reduce latency. Our findings contrast with those of McGrew and Viega (2004), who claimed similar performance for GCM and OCB.

/pdf/the-software-performance-of-authenticated-encryption-modes-2mn0gu3skc.pdf

The software performance of authenticated-encryption modes

We argue that the invertibility of a block cipher can reduce the security of schemes that use it, and a better starting point for scheme design is the non-invertible analog of a block cipher, that is, a pseudorandom function (PRF). Since a block cipher may be viewed as a pseudorandom permutation, we are led to investigate the reverse of the problem studied by Luby and Rackoff, and ask: “how can one transform a PRP into a PRF in as security-preserving a way as possible?” The solution we propose is data- dependent re- keying. As an illustrative special case, let E: {0, 1}n x {0, 1}n → {0, 1}n be the block cipher. Then we can construct the PRF F from the PRP E by setting F(k, x) = E(E(k, x), x). We generalize this to allow for arbitrary block and key lengths, and to improve efficiency. We prove strong quantitative bounds on the value of data-dependent re-keying in the Shannon model of an ideal cipher, and take some initial steps towards an analysis in the standard model.

/pdf/luby-rackoff-backwards-increasing-security-by-making-block-2h9wqn53n1.pdf

Ted Krovetz

Papers

OCB: a block-cipher mode of operation for efficient authenticated encryption

UMAC: Fast and Secure Message Authentication

UMAC : Fast and secure message authentication

The software performance of authenticated-encryption modes

Luby-Rackoff backwards: Increasing security by making block ciphers non-invertible