64-bit computing | EPFL Graph Search

In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide. Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size. A computer that uses such a processor is a 64-bit computer. From the software perspective, 64-bit computing means the use of machine code with 64-bit virtual memory addresses. However, not all 64-bit instruction sets support full 64-bit virtual memory addresses; x86-64 and ARMv8, for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all 0's or all 1's, and several 64-bit instruction sets support fewer than 64 bits of physical memory address. The term 64-bit also describes a generation of computers in which 64-bit processors are the norm. 64 bits is a word size that defines certain classes of computer architecture, buses, memory, and CPUs and, by extension, the software that runs on them.

A Mobile World of Security

Christine Neuberg

Security in mobile communications is a topic of increasing relevance in everyday life. We all use mobile devices for everyday communications, maybe even for exchanging confidential information with the work place. This requires security systems that are reliable and stable even though mobility and number of users are increasing. An established solution in today's systems is to use symmetric cryptographic systems by relying on pre-established secrets. There are a few drawbacks. The first problem is that all security information is stored in one central storage place. This implies that users are required to trust this storage place. They need to trust that data is properly handled and well protected. The mechanism of storing pre-established long-term secrets at a central storage also makes it vulnerable to adversaries. As soon as someone gains access to it, he automatically has access to all secret information necessary to capture communications. A second problem is that security mechanisms implemented in today's mobile communication systems were designed for a moderate number of users. Since then, the number of users has grown significantly and continues to do so. It would thus be desirable to have a system that is flexible in terms of the number of users it can handle. The third and maybe the most crucial problem is the fact that today's security systems rely on computational cryptography. This means that the security mechanisms in cellular communication systems were designed with limited computational power of the adversary in mind. However, the computational power of computers is growing and systems might be breakable in the near future. A complementary notion of security is information-theoretic security. Systems built in this spirit are unbreakable even with unlimited computational power. These systems exploit the knowledge of statistical properties of the environment. This means mainly that security systems can be proved to be secure with respect to assumptions on the correlated sources and with respect to the nature of the knowledge the adversary can gain. The main idea of information-theoretic security is that two communication partners have access to correlated random sources. An adversary being potentially present in the system, has only degraded access to the source. The common knowledge can be used in order to generate sequences that are very similar among each other. Because the adversary has access to the random source, he is able to generate his own version of the sequence. It is fundamental that the sequences of the communicationpartners are stronger correlated among each other than with respect to the adversary. This advantage in knowledge can be interpreted as a secret among the communication partners to the adversary. In communicating over an authenticated but public channel, this secret can be extracted from the original sequence by both parties. In order for both keys to be equal, the original sequences need to coincide. This is not necessarily the case, but can be achieved by discussion over the public channel. In the first part of this thesis, we propose a security system that relies on information-theoretic security. We will demonstrate how this system can be implemented in cellular communication systems. The movement of the users is random and we want to use it as a random source. We assume that users are moving along a random itinerary while visiting a random sequence of cells. Users not only visit cells in a random order, they also stay for a random time in each cells. It turns out that it is the sequence of durations that contributes most to the randomness of the sequence. We call the sequence of durations timing. This sequence is known to users and to the infrastructure, but only parts of it are known to potential adversaries. By recording the sequence of cells along with the time of residence, both the user and the infrastructure will be able to acquire very similar sequences. After the collection process, a procedure for key agreement is applied. Due to the underlying process, the key will not be uniformly distributed. As this is a requirement for perfect secret keys, a final part of the protocol is privacy amplification, where the perfectly secret bits will be extracted. This system is lightweight as it is based on readily available information and only a small amount of post-processing is required. In the second part of this thesis, we analyze the performance of the system. For this, we demonstrate how the process of bit collection can be analytically modeled. Our analysis leads to two conclusions. It gives us intuition about how to choose parameters such that the scheme performs optimally. Our scheme can be applied to settings that fulfill certain conditions. Conclusions from analysis allow to specify such conditions. We will show the implication of this conclusion in sketching some alternative applications of our scheme.

EPFL2011

Robust checkers for self-calibrating designs

Frédéric Worm

So far, performance and reliability of circuits have been determined by worst-case characterisation of silicon and of environmental conditions such as noise and temperature. As nanometer technologies exacerbate process variations and reduce noise margins, worst-case design will eventually fail to meet an aggressive combination of objectives in performance, reliability, and power. In order to circumvent these difficulties, researchers have recently proposed a new design paradigm: self-calibrating circuits. The design parameters (e.g., operating points) of a self-calibrating circuit are tuned at run-time by a controller. The latter receives feedback from a checker that monitors correct operation of the circuit. A self-calibrating circuit can thus trade dynamically reliability for power or performance, depending on actual silicon capabilities and noise conditions. This thesis pioneers the use of digital self-calibration techniques to dynamically tune the operating points of an on-chip link based on the detection of run-time transfer errors. In particular, we show that the energy overhead induced by the checker and operating point controller is offset by the operating of the link at sub-critical voltage. Such a system-level study strengthens the interest into self-calibrated links by demonstrating their feasibility. The primary focus of the thesis bears on the development of robust and low overhead checkers for a self-calibrating on-chip data link subject to errors caused by operation at sub-critical voltage. Such errors –we call them timing errors– may be numerous and cause error rates as large as 100%. We abstract timing errors by the failure of bit transitions and propose ad-hoc coding techniques to detect them reliably. We emphasise the originality of the coding requirements by showing that (i) traditional error correcting codes (like CRCs) fail to detect timing errors under over-aggressive operation of the link, and (ii) asynchronous codes such as dual-rail detect all timing errors, but incur a significant bandwidth overhead in the synchronous context of our problem. Next, we introduce a novel code-based checker satisfying such requirements and featuring unique detection capabilities towards both timing and additive errors. Then, we contrast the error detection capabilities of the code-based checker with the one of double sampling flip-flops. We stress the complementarity of the two approaches and show how to optimally combine them into an even more robust checker featuring a very limited wiring and circuitry overhead. Finally, we extend our work to computing elements by giving preliminary research directions on the detection of timing errors resulting from the self-calibration of the operating points of an adder. The main contribution of this work is to propose novel checker architectures based on codes and/or double sampling flip-flops to detect massive timing errors caused by self-calibration of the link operating points. A requirement rendering our work unique is that reliable operation of the checker should be ensured over the whole range of bit error rates from 0 to 100%. Furthermore, we have developed a unified framework bringing fundamental insights into the timing error detection capabilities of various practical encoding schemes.

EPFL2006

Improved Linear Cryptanalysis of Reduced-Round MIBS

Asli Bay, Jialin Huang, Serge Vaudenay

MIBS is a 32-round lightweight block cipher with 64-bit block size and two different key sizes, namely 64-bit and 80-bit keys. Bay et al. provided the first impossible differential, differential and linear cryptanalyses of MIBS. Their best attack was a linear attack on the 18-round MIBS-80. In this paper, we significantly improve their attack by discovering more approximations and mounting Hermelin et al.'s multidimensional linear cryptanalysis. We also use Nguyen et al.'s technique to have less time complexity. We attack on 19 rounds of MIBS-80 with a time complexity of 2^{74.23} 19-round MIBS-80 encryptions by using 2^{57.87} plaintext-ciphertext pairs. To the best of our knowledge, the result proposed in this paper is the best cryptanalytic result for MIBS, so far.

Springer2014