Viable cryptosystem designs must address power analysis attacks, and masking is a commonly proposed technique for defending against these side-channel attacks It is possible to overcome simple masking by using higher-order techniques, but apparently only at some cost in terms of generality, number of required samples from the device being attacked, and computational complexity We make progress towards ascertaining the significance of these costs by exploring a couple of attacks that attempt to efficiently employ second-order techniques to overcome masking In particular, we consider two variants of second-order differential power analysis: Zero-Offset 2DPA and FFT 2DPA

Towards efficient second-order power analysis

A new method for digital true random number generation based on asynchronous logic circuits with feedback is introduced. In particular, a concrete technique using the so-called Galois and Fibonacci ring oscillators is developed and analyzed both theoretically and experimentally. The generated random binary sequences may have a very high speed and a higher and more robust entropy rate in comparison with previous proposals for digital random number generators. A new method for digital postprocessing of random data based on irregularly clocked nonautonomous synchronous logic circuits with feedback is also introduced and a concrete technique using a self-clock-controlled linear feedback shift register is proposed. The postprocessing can provide both randomness extraction and computationally secure speed increase of input random data

New Methods for Digital Generation and Postprocessing of Random Data

A fault attack is a powerful cryptanalytic tool which can be applied to many types of cryptosystems which are not vulnerable to direct attacks. The research literature contains many examples of fault attacks on public key cryptosystems and block ciphers, but surprisingly we could not find any systematic study of the applicability of fault attacks to stream ciphers. Our goal in this paper is to develop general techniques which can be used to attack the standard constructions of stream ciphers based on LFSR’s, as well as more specialized techniques which can be used against specific stream ciphers such as RC4, LILI-128 and SOBER-t32. While most of the schemes can be successfully attacked, we point out several interesting open problems such as an attack on FSM filtered constructions and the analysis of high Hamming weight faults in LFSR’s.

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Fault Analysis of Stream Ciphers

The cloud computing paradigm has become a mainstream solution for the deployment of business processes and applications. In the public cloud vision, infrastructure, platform, and software services are provisioned to tenants (i.e., customers and service providers) on a pay-as-you-go basis. Cloud tenants can use cloud resources at lower prices, and higher performance and flexibility, than traditional on-premises resources, without having to care about infrastructure management. Still, cloud tenants remain concerned with the cloud’s level of service and the nonfunctional properties their applications can count on. In the last few years, the research community has been focusing on the nonfunctional aspects of the cloud paradigm, among which cloud security stands out. Several approaches to security have been described and summarized in general surveys on cloud security techniques. The survey in this article focuses on the interface between cloud security and cloud security assurance. First, we provide an overview of the state of the art on cloud security. Then, we introduce the notion of cloud security assurance and analyze its growing impact on cloud security approaches. Finally, we present some recommendations for the development of next-generation cloud security and assurance solutions.

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From Security to Assurance in the Cloud: A Survey

On cloud security requirements, threats, vulnerabilities and countermeasures: A survey

A concept of random masking of arbitrary logic circuits on the logic gate level is developed and several techniques are proposed. The results are important for protecting hardware implementations of cryptographic algorithms against side-channel attacks.

Universal masking on logic gate level

A novel edit distance between two binary input strings and one binary output string of appropriate lengths which incorporates the stop/go clocking in the alternating step generator is introduced. An efficient recursive algorithm for the edit distance computation is derived. The corresponding correlation attack on the two stop/go clocked shift registers is then proposed. By systematic computer simulations, it is shown that the minimum output segment length required for a successful attack is linear in the total length of the two stop/go clocked shift registers. This is verified by experimental attacks on relatively short shift registers.

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Edit Distance Correlation Attack on the Alternating Step Generator

Edit distance correlation attack on the alternating step generator

The need of a certification process for cloud-based services is emerging as a way to address some of the remaining obstacles facing the effective development and diffusion of the cloud-computing paradigm. In this paper we move the first steps towards a complete approach containing a conceptual framework where the specifications of basic, hybrid and incremental certification models for cloud-based services can be given. Specifically, we focus on the definition of a unifying meta-model to provide representational guidelines for (i) the definition of the security properties to be certified, (ii) the types of evidence underlying them, (iii) the phases of the certificate life cycle, as well as of all mechanisms for generating supporting evidence.

Towards the Certification of Cloud Services

The alternating step generator is a well-known keystream generator consisting of two stop/go clocked LFSRs, LFSR1 and LFSR2, whose clocks are controlled by another LFSR, LFSR3, which is clocked regularly. A probabilistic analysis of this generator is conducted which shows that the posterior probabilites of individual bits of the first derivatives of the regularly clocked LFSR1 and LFSR2 sequences, when conditioned on a given segment of the first derivative of the keystream sequence, can be computed efficiently in a number of probabilistic models of interest. The expected values of these probabilities, for a random keystream sequence, are derived by an approximate theoretical analysis and are also verified by systematic computer experiments. It is pointed out that these posterior probabilities can be enhanced in a resynchronization scenario and thus used for a low-complexity fast correlation attack on the two LFSRs. More generally, it is argued that even without resynchronization these probabilities may be significantly different from one half for fast correlation attacks based on iterative decoding algorithms to be successful, although with incresead complexity. A related method for computing the posterior probabilities of individual bits of the LFSR3 sequence, when conditioned on both the keystream sequence and the LFSR1 and LFSR2 sequences, is also developed. As these posterior probabilities are much more different from one half, they can be used for a low-complexity fast correlation attack on LFSR3, provided that the initial states of LFSR1 and LFSR2 are previously reconstructed.

Renato Menicocci

Papers

Universal masking on logic gate level

Edit Distance Correlation Attack on the Alternating Step Generator

Edit distance correlation attack on the alternating step generator

Towards the Certification of Cloud Services

Correlation Analysis of the Alternating Step Generator