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We concern security of shrinking generator against fault attacks. While this pseudorandom bitstream generator is cryptographically strong and well suited for hardware implementations, especially for cheap artefacts, we show that using it for the devices that are not fault resistant is risky. That is, even if a device concerned is tamper-proof, generating random faults and analyzing the results may reveal secret keys stored inside the device. For the attack we flip a random bit and observe propagation of errors. The attack uses peculiar properties of the shrinking generator and presents a new kind of threats for designs based on combining weaker generators. In particular, it indicates that potentially all designs based on combining LFSR generators might be practically weak due to slow propagation of errors in a single LFSR.

We present two efficient and simple fault attacks on the shrinking generator. In a first case if the attacker can stop control generator for some small number of steps and observe the output, then with high probability he can deduce the full control sequence, and so the other input bitstream. The second method assumes that the attacker can disturb the control sequence (in an unpredictable and random way) and observe many samples of such experiments. Then he can reconstruct a certain sequence that agrees with the input sequence of the generator on a large fraction of bits.

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 re-encryption. 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.

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.

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.

It is believed that masking is an effective countermeasure against power analysis attacks: before a certain operation involving a key is performed in a cryptographic chip, the input to this operation is combined with a random value. This has to prevent leaking information since the input to the operation is random.We show that this belief might be wrong. We present a Hamming weight attack on an addition operation. It works with random inputs to the addition circuit, hence masking even helps in the case when we cannot control the plaintext. It can be applied to any round of the encryption. Even with moderate accuracy of measuring power consumption it determines explicitly subkey bits. The attack combines the classical power analysis (over Hamming weight) with the strategy of the saturation attack performed using a random sample.We conclude that implementing addition in cryptographic devices must be done very carefully as it might leak secret keys used for encryption. In particular, the simple key schedule of certain algorithms (such as IDEA and Twofish) combined with the usage of addition might be a serious danger.