Libert and Vergnaud proposed a unidirectional proxy re-encryption scheme with temporary delegation (IEEE Trans. Inf. Theory, vol. 57, no. 3, pp. 1786–1802, Mar. 2011). They claimed that the scheme is chosen ciphertext secure in the chosen key model. However, their proof has a minor error in the simulation of the re-encryption oracle. The adversary is able to distinguish between the simulated environment and the real attack environment by using responses from the re-encryption oracle. Fortunately, we can amend the proof without any modification of the original scheme.

As wireless sensor networks are often deployed in adverse or hostile environments, key management schemes are required for sensor nodes. The random key predistribution (RKP) scheme is a probabilistic key management scheme where each node is preloaded with a subset of keys that are randomly selected from a pool of keys. If a pair of neighbor nodes have a common key, it can be used to establish a secure link between the nodes. The q-composite RKP scheme requires that a pair of neighbor nodes have at least q common keys for a secure link. In this article, we show that the previous security analysis (i.e., resilience against node capture) of the q-composite RKP scheme is inaccurate and present new formulae for resilience in the RKP scheme and the q-composite RKP scheme.

A distance bounding protocol enables one party to determine a practical upper bound on the distance to another party. It is an effective countermeasure against mafia fraud attacks (a.k.a. relay attacks) which do not alter messages between users but only relay messages. The main idea of distance bounding protocols is to repeat fast bit exchanges. One party sends a challenge bit and another party answers with a response bit and vice versa. By measuring the round-trip time between the challenge and the response, an upper bound on the distance between users can be calculated. If messages are relayed, the round-trip time increases and thus mafia fraud attacks can be detected. We introduce an efficient distance bounding protocol for mutual authentication. It enjoys a reduced false acceptance rate under mafia fraud attacks and does not require an extra confirmation message after the fast bit exchange phase.

Iterative decoding of product codes that uses a soft-in/soft-out decoder based on the Chase algorithm was introduced by R. Pyndiah et al. (see Proc. IEEE GLOBECOM, vol.1/3, p.339-43, 1994). This decoding scheme is quite similar to turbo codes, but makes possible the implementation of the decoder with low complexity while providing acceptable performance. In this paper for the product codes composed of extended Hamming codes, we propose a reduction scheme of test patterns in the Chase algorithm, which can reduce the decoding complexity without performance degradation. Also, we propose a simple, but efficient assignment scheme of artificial extrinsic information to the symbols for which we cannot get reliabilities by the decoding procedure. The simulation results for the proposed schemes are shown and compared with the asymptotic performances that can be calculated by the weight distribution of product codes and the union bound on the BER performances.

The authors conjecture that a proper combination of partial-band tone jamming (PBTJ) and full-band noise jamming (FBNJ) under a given total jamming power constraint may be more effective than PBTJ alone, not only for the case with a low (E/sub s//N/sub J/), but also for the case with high E/sub s//N/sub J/, since the FBNJ can corrupt the jamming state information (JSI). Assuming this combination of PBTJ and FBNJ jamming, they consider three cases of receiver processing-the hard decision (HD) metric without JSI, the HD metric with perfect JSI, and the maximum-likelihood (ML) metric using Viterbi's ratio threshold (VRT) to generate a 1-b symbol decision quality indicator. System performance is evaluated in terms of the Chernoff bound on the probability of symbol error. From extensive numerical analysis the authors conclude that, for the case of the HD metric without JSI, PBTJ-only jamming is the worst form of jamming, as expected, since the receiver does not use JSI at all; for the other cases, a combination of PBTJ and FBNJ is the worst, with the worst ratio of PBTJ power to FBNJ power a function of the values of M and E/sub s//N/sub J/.>

It is shown empirically that the number of good periodically time-varying convolutional codes increases exponentially with the period for any set of parameters. Hence, they can be used to enhance the security of cryptosystems without sacrificing error correction capability. It is shown that some periodically time-varying convolutional codes improve the free distance compared with fixed codes.>

Rate (n-1)/n punctured convolutional codes (n up to 10 and memory length up to 8) are constructed which minimize the required signal-to-noise ratio (SNR) for a bit-error rate (BER) of 10/sup -9/ with and without the restriction of using only four different code generators. Many of these codes improve the free distance and reduce the required SNR more than half a decibel over previously reported codes with the same parameters. This is equivalent to reducing the decoder complexity by one half for the same performance. These codes have many potential applications in systems that require performance improvements with little room for coding overhead.>

For a frequency-hopped noncoherent MFSK communication system without jammer state information (JSI) in a worst case partial band jamming environment, it is well known that the use of a conventional unquantized metric results in very poor performance. In this paper, a "normalized" unquantized energy metric is suggested for such a system. It is shown that with this metric, one can save 2-3 dB in required signal energy over the system with hard decision metric without JSI for the same desired performance. When this very robust metric is compared to the conventional unquantized energy metric with JSI, the loss in required signal energy is shown to be small. Thus, the use of this normalized metric provides performance comparable to systems for which JSI is known. Cutoff rate and bit error rate with dual-kcoding are used for the performance measures.