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Lorentz Center

International Center for Workshops in the Sciences

International Center for Workshops in the Sciences

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"Survey: Leakage Resilience and the Bounded Retrieval Model". This survey discusses recent advances in the field of Leakage-Resilient Cryptography. This booming area is concerned with the design of cryptographic primitives resistant to arbitraryside-channel attacks, where an attacker can repeatedly and adaptively learn information about the secret key, subject *only* to the constraint that the *overall amount* of such information is bounded by some parameter L. We start by surveying recent results in the so called Relative Leakage Model, where all the parameters of the system are allowed to depend on L, and the goal is to make L large relative to the length of the secret key. We conclude by showing how to extend the relative leakage results to the Bounded Retrieval Model (aka "Absolute Leakage Model''), where only the secret key length is allowed to be slightly larger than L, but all other system parameters (e.g., public-key, communication, etc.) are independent of the absolute value of L.
On the "only computation leaks information" paradigm The "only computation leaks information paradigm" for designing leakage-resilient cryptographic schemes was first formulated by Micali and Reyzin (TCC 2004). Essentially, it postulates that only these parts of the memory that take part in the computation can leak information. This assumption was later used by Dziembowski and Pietrzak (FOCS 2008) and Pietrzak (Eurocrypt 2009) to construct leakage-resilient stream-ciphers, and by Faust et al (EUROCRYPT 2009) to construct leakage-resilient signature schemes. We will give a short introduction to this area, focusing on the work of Dziembowski and Pietrzak.
“Practical Difficulties of Physical Attacks” In this talk we'll firstly discuss the practical problems we
face when securing embedded cryptosystem implementations against side-channel
analysis. Indeed, even on very simple hardware architecture in which leakages
are well identified, securing a very simple piece of code against first order
SCA can be much more complex than expected. Secondly, we will discuss the
pertinence of high order attacks in practice depending on the characteristics
of the attacker and of the device. We'll show that in some cases, second order
SCA can't unfortunately be used to validate the security of a device during an
evaluation. Finally, we'll present how to quantify the impact of a successful
attack by using the so-called JIL quotation. We'll see that such an attack can be
tolerated as long as high potential attackers are not able to put it into
practice
“Practical aspects of physical security, implementation attacks and countermeasures” In this presentation we review the main side-channel attacks and invasive attacks the embedded security industry has to deal with and which types of countermeasures are relevant and practical. We provide some estimate of acceptable performance and area impact of practical countermeasures and insights into development constraints for embedded security chips. We also introduce a fairly new security primitive called Physically Unclonable Functions which allows to protect against a major category of implementation attacks, namely invasive attacks. We explain the physical security advantages of this approach and analyze how PUFs help to provide essentially much higher security at a low cost. ---
“Recovering cryptographic keys with the cold boot attack” The "cold boot" attack is a side-channel attack that allows an attacker to extract encryption keys from data that is still left in a computer's RAM after the power has been cut. I will discuss the kind of data an attacker can find in practice, some practical and theoretical aspects of finding keys hidden in gigabytes of data, experimental results on errors introduced during the attack, and techniques for efficiently correcting bit errors in encryption keys from both symmetric and public-key encryption systems.
“Private Circuits” "Private circuits" are circuits that can store a secret, perform computations involving the secret, and maintain its secrecy even in the presence of side-channel attacks. This talk will survey work on private circuits (including joint works with Manoj Prabhakaran, Amit Sahai, and David Wagner) and discuss some related open questions. Yuval Ishai, Technion and UCLA ---
“Advanced Topics in
Side-Channel Attacks” Advanced
side-channel attacks typically become relevant in the context of attacks on
devices that implement countermeasures. This talk discusses different ountermeasures and attacks on these countermeasures. The
talk in particular discusses masking countermeasures and attacks like template
attacks, higher-order attacks and mutual information analysis. Based on these
attacks, the challenges of securely implementing cryptographic algorithms in
practice are discussed. ---
“Hamster wheel keys” In this talk we will
present key evolution algorithms allowing to better resist
side channel attacks. All the methods that will be presented are based on the
following idea. We consider functions f, other than trees, such that f^i(x) can be computed from x in less than i successive applications of f, using a computational
shortcut. Typical examples of such functions are f(x)=c
x^e mod p, the concatenation of such functions for
small p values or their ECC equivalents. In the considered scenario, a smart
card contains a secret k_0 updated after each session by the operation k_{i+1}=f(k_i) thereby offering
resistance to an attacker capable of reading some bits of k_i
from a side channel leakage. The terminal uses the shortcut to derive directly
k_{i+1} from k_0. We will present different known
PRNGs featuring this property and evaluate their degree of resistance to
leakage using a number of artithmetic techniques
(LLL, Coppersmith etc) for different parameter combinations. ---
In this tutorial I aim to introduce several core concepts in the area of side-channel analysis. This includes attack strategies, such as simple and differential power analysis, the notion of leakage of a device (and the exploitation of this leakage), as well as countermeasures and their pros and cons. Finally, I will discuss the most popular research directions pursued by theoreticians and practitioners in the area. ---
“Leakage Resilient
Cryptography in Practice” Using the design of
a secure PRG as a motivating example, we discuss several models and
constructions for leakage resilient cryptography, in the light of observations
from the practice of side-channel attacks. This is a joint work with
Francois-Xavier Standaert and Yu Yu
and Jean-Jacques Quisquater and Moti
Yung and Elisabeth Oswald. ---
"On Security
Evaluation Testing" For the security
evaluation of products and systems penetration testing is traditionally of fundamental
importance. Penetration testing is done by evaluation labs, mostly according to
certification schemes. New research findings in practical physical analysis are
thereby continuously taken into account. This talk discusses two
different certification schemes: the Common Criteria and the FIPS 140. Both schemes
are introduced with a focus on vulnerability analysis for
cryptographic modules with high needs for physical security. As examples, we discuss the
penetration testing approach for smartcard ICs in the Common Criteria
scheme and the test requirements for multiple chip cryptographic modules
according to the FIPS 140 scheme. ---
“Public-key Cryptosystems Resilient to Key Leakage” Most of the work in the analysis of cryptographic schemes has traditionally focused on abstract adversarial models that do not capture "side-channel attacks". Such attacks exploit various forms of unintended leakage of sensitive information, which is inherent to almost all physical implementations. Inspired by extremely devastating real-life attacks, in this talk I will describe a recent approach for modeling and combating side-channel attacks. I will focus on a framework for modeling a wide range of attacks that rely on partial leakage of secret keys. In particular, I will present a rather simple and efficient construction of a public-key encryption scheme that is resilient to leakage of almost its whole secret key, as well as a generic method for constructing leakage-resilient encryption schemes that can be based on a variety of number-theoretic assumptions. Based on joint work with Moni Naor. ---
“Hardware security
of silicon chips: progress, pitfalls and challenges for physical attacks” Tamper resistance of
secure silicon devices like microcontrollers and smartcards is an important
subject since the outbreak of attacks in the late nineties. Embedded memory in
microcontrollers, smartcards, FPGAs and ASICs are among the security concerns
as these areas usually store critical parts of algorithms, secret data and
cryptographic keys. It seemed to be relatively easy and straightforward to
attack silicon chips ten years ago. Many of those old and well known tools no
longer work for modern chips. However, this did not mean a relief for hardware
manufacturers and developers as new tools and techniques have emerged posing
even greater threat. One of the greatest shake-ups happened in 2002 with
introduction of optical fault injection attacks. This lead to separation of a
new class of attacks called semi-invasive and which are very efficient and
low-cost. This even forced the revision of certain security evaluation
requirements. Despite to a long time since introduction, optical attacks still
bring many surprises and their danger and effectiveness is sometimes
dangerously underestimated. There are many examples to that including recent
achievements which I will introduce in this talk. I will present an overview of
tools and techniques used in the old days and nowadays. I will discuss
challenges that still exist for modern chips including the ways it could be
overcome. I will discuss hardware security awareness and its lead to
countermeasures. At the end I will give some anecdotal examples how hardware
security can be ruined by careless implementation and management. ---
“Design methods and
tools for side-channel secure circuits” Designing secure
embedded devices is a joint optimization problem of many parameters. The most
important ones are area, e.g. transistor count or memory footprint, performance,
e.g. real-time throughput or average response time, energy or power
consumption, for battery operated devices or for cooling issues and
flexibility, for updates, remote reconfigurations and so on. Security against
passive and active attacks is yet another optimization goal. In this presentation, systematic design
methods and tools will be described to make devices resistant against
side-channel attacks. taking the other design parameters into account. The
quality of the methods and tools depends on the engineering and mathematical
models used during the design phase of the circuit. We will try to link the
engineering models used in the design of circuits with the abstract models
proposed by the computer science theory community for side-channel leakage. ---
“Non-Malleable Codes
and Applications to Tamper-Resilient Security” Joint
work with Stefan Dziembowski and Krzysztof Pietrzak. We introduce the
notion of “non-malleable codes” which relaxes the notion of error correction
and error detection. Informally, a code is non-malleable if the message
contained in a modified codeword is either the original message, or a
completely unrelated value. In contrast to error-correction and error-detection, non malleability
can be achieved for very rich classes of modifications. We construct an efficient code that is
non-malleable with respect to modifications that effect each bit of the
codeword arbitrarily (i.e. leave it untouched, flip it or set it to either 0 or
1), but independently of the value of the other bits of the codeword. Using the
probabilistic method, we also show a very strong and general statement: there
exists a non-malleable code for every “small enough” family F of functions via
which codewords can be modified. Although this
probabilistic method argument does not directly yield efficient constructions,
it gives us efficient non-malleable codes in the random-oracle model for very
general classes of tampering functions-e.g. functions where every bit in the
tampered codeword can depend arbitrarily on any 99% of the bits in the original
codeword. As an application of non-malleable codes, we show that they provide
an elegant algorithmic solution to the task of protecting functionalities implemented
in hardware (e.g. signature cards) against “tampering attacks”. In such
attacks, the secret state of a physical system is tampered, in the hopes that
future interaction with the modified system will reveal some secret
information. This problem, was previously studied in
the work of Gennaro et al. in 2004 under the name
“algorithmic tamper proof security” (ATP). We show that non-malleable codes can
be used to achieve important improvements over the prior work. In particular,
we show that any functionality can be made secure against a large class of
tampering attacks, simply by encoding the secret-state with a non-malleable
code while it is stored in memory. --- [Back] |