Fault Jumping Attacks against Shrinking Generator

In this paper we outline two cryptoanalytic attacks against hardware implementation of the shrinking generator by Coppersmith et al., a classic design in low-cost, simple-design pseudorandom bitstream generator. This is a report on work on progress, since implementation and careful adjusting the attack strategy in order to optimize the atatck is still not completed

Rapid mixing and security of chaum’s visual electronic voting

Abstract. Recently, David Chaum proposed an electronic voting scheme that combines visual cryptography and digital processing. It was designed to meet not only mathematical security standards, but also to be accepted by voters that do not trust electronic devices. In this scheme mix-servers are used to guarantee anonymity of the votes in the counting process. The mix-servers are operated by different parties, so an evidence of their correct operation is necessary. For this purpose the protocol uses randomized partial checking of Jakobsson et al., where some randomly selected connections between the (encoded) inputs and outputs of a mix-server are revealed. This leaks some information about the ballots, even if intuitively this information cannot be used for any efficient attack. We provide a rigorous stochastic analysis of how much information is revealed by randomized partial checking in the Chaum’s protocol. We estimate how many mix-servers are necessary for a fair security level. Namely, we consider probability distribution of the permutations linking the encoded votes with the decoded votes given the information revealed by randomized partial checking. We show that the variation distance between this distribution and the uniform distribution is O � � 1 already for a constant number of mix-servers (n is the number of vot

M.: Provable Unlinkability Against Traffic Analysis Already After O(log(n

Abstract. We consider unlinkability of communication problem: given n users, each sending a message to some destination, encode and route the messages so that an adversary analyzing the traffic in the communication network cannot link the senders with the recipients. A solution should have a small communication overhead, that is, the number of additional messages should be kept low. David Chaum introduced idea of mixes for solving this problem. His approach was developed further by Simon and Rackoff, and implemented later as the onion protocol. Even if the onion protocol is widely regarded as secure and used in practice, formal arguments supporting this claim are rare and far from being complete. On top of that, in certain scenarios very simple tricks suffice to break security without breaking the cryptographic primitives. It turns out that one source of difficulties in analyzing the onion protocol’s security is the adversary model. In a recent work, Berman, Fiat and Ta-Shma develop a new and more realistic model in which only a constant fraction of communication lines can be accessed by an adversary, the number of messages does not need to be high and the preferences of the users are taken into account. For this model they prove that with high probability a good level of unlinkability is obtained after O(log 4 n) steps of the onion protocol where n is the number of messages sent. In this paper we improve these results: we show that the same level of unlinkability (expressed as variation distance between certain probability distributions) is obtained with high probability already after O(log n) steps of the onion protocol. Asymptotically, this is the best result possible, since obviously Ω(log n) steps are necessary. On top of that, our analysis is much simpler. It is based on path coupling technique designed for showing rapid mixing of Markov chains

Onions based on universal re-encryption – anonymous communication immune against repetitive attack

Abstract. Encapsulating messages in onions is one of the major techniques providing anonymous communication in computer networks. To some extent, it provides security against traffic analysis by a passive adversary. However, it can be highly vulnerable to attacks by an active adversary. For instance, the adversary may perform a simple so–called repetitive attack: a malicious server sends the same massage twice, then the adversary traces places where the same message appears twice – revealing the route of the original message. A repetitive attack was examined for mix–networks. However, none of the countermeasures designed is suitable for onion–routing. In this paper we propose an “onion-like ” encoding design based on universal reencryption. The onions constructed in this way can be used in a protocol that achieves the same goals as the classical onions, however, at the same time we achieve immunity against a repetitive attack. Even if an adversary disturbs communication and prevents processing a message somewhere on the onion path, it is easy to identify the malicious server performing the attack and provide an evidence of its illegal behavior

alpha-Amanitin induced apoptosis in primary cultured dog hepatocytes.

Amatoxin poisoning is caused by mushroom species belonging to the genera Amanita, Galerina and Lepiota with the majority of lethal mushroom exposures attributable to Amanita phalloides. High mortality rate in intoxications with these mushrooms is principally a result of the acute liver failure following significant hepatocyte damage due to hepatocellular uptake of amatoxins. A wide variety of amatoxins have been isolated; however, alpha-amanitin (alpha-AMA) appears to be the primary toxin. Studies in vitro and in vivo suggest that alpha-AMA does not only cause hepatocyte necrosis, but also may lead to apoptotic cell death. The objective of this study was to evaluate the complex hepatocyte apoptosis in alpha-AMA cytotoxicity. All experiments were performed on primary cultured canine hepatocytes. The cells were incubated for 12 h with alpha-AMA at a final concentration of 1, 5, 10 and 20 microM. Viability test (MTT assay), apoptosis evaluation (TUNEL reaction, detection of DNA laddering and electron microscopy) were performed at 6 and 12 h of exposure to alpha-AMA. There was a clear correlation between hepatocyte viability, concentration of alpha-AMA and time of exposure to this toxin. The decline in cultured dog hepatocyte viability during the exposure to alpha-AMA is most likely preceded by enhanced cellular apoptosis. Our results demonstrate that apoptosis might contribute to pathogenesis of the severe liver injury in the course of amanitin intoxication, particularly during the early phase of poisoning