1,679 research outputs found
The chaining lemma and its application
We present a new information-theoretic result which we call the Chaining Lemma. It considers a so-called âchainâ of random variables, defined by a source distribution X(0)with high min-entropy and a number (say, t in total) of arbitrary functions (T1,âŠ, Tt) which are applied in succession to that source to generate the chain (Formula presented). Intuitively, the Chaining Lemma guarantees that, if the chain is not too long, then either (i) the entire chain is âhighly randomâ, in that every variable has high min-entropy; or (ii) it is possible to find a point j (1 †j †t) in the chain such that, conditioned on the end of the chain i.e. (Formula presented), the preceding part (Formula presented) remains highly random. We think this is an interesting information-theoretic result which is intuitive but nevertheless requires rigorous case-analysis to prove. We believe that the above lemma will find applications in cryptography. We give an example of this, namely we show an application of the lemma to protect essentially any cryptographic scheme against memory tampering attacks. We allow several tampering requests, the tampering functions can be arbitrary, however, they must be chosen from a bounded size set of functions that is fixed a prior
Non-malleable secret sharing against joint tampering attacks
Since thousands of years ago, the goal of cryptography has been to hide messages from prying eyes. In recent times, cryptography two important changes: first, cryptography itself evolved from just being about encryption to a broader class of situations coming from the digital era; second, the way of studying cryptography evolved from creating ``seemingly hard'' cryptographic schemes to constructing schemes which are provably secure.
However, once the mathematical abstraction of cryptographic primitives started to be too hard to break, attackers found another way to defeat security. Side channel attacks have been proved to be very effective in this task, breaking the security of otherwise provably secure schemes. Because of this, recent trends in cryptography aim to capture this situation and construct schemes that are secure even against such powerful attacks.
In this setting, this thesis specializes in the study of secret sharing, an important cryptographic primitive that allows to balance privacy and integrity of data and also has applications to multi-party protocols. Namely, continuing the trend which aims to protect against side channel attacks, this thesis brings some contributions to the state of the art of the so-called leakage-resilient and non-malleable secret sharing schemes, which have stronger guarantees against attackers that are able to learn information from possibly all the shares and even tamper with the shares and see the effects of the tampering.
The main contributions of this thesis are twofold. First, we construct secret sharing schemes that are secure against a very powerful class of attacks which, informally, allows the attacker to jointly leak some information and tamper with the shares in a continuous fashion. Second, we study the capacity of continuously non-malleable secret sharing schemes, that is, the maximum achievable information rate. Roughly speaking, we find some lower bounds to the size that the shares must have in order to achieve some forms of non-malleability
Non-Malleable Codes for Small-Depth Circuits
We construct efficient, unconditional non-malleable codes that are secure
against tampering functions computed by small-depth circuits. For
constant-depth circuits of polynomial size (i.e. tampering
functions), our codes have codeword length for a -bit
message. This is an exponential improvement of the previous best construction
due to Chattopadhyay and Li (STOC 2017), which had codeword length
. Our construction remains efficient for circuit depths as
large as (indeed, our codeword length remains
, and extending our result beyond this would require
separating from .
We obtain our codes via a new efficient non-malleable reduction from
small-depth tampering to split-state tampering. A novel aspect of our work is
the incorporation of techniques from unconditional derandomization into the
framework of non-malleable reductions. In particular, a key ingredient in our
analysis is a recent pseudorandom switching lemma of Trevisan and Xue (CCC
2013), a derandomization of the influential switching lemma from circuit
complexity; the randomness-efficiency of this switching lemma translates into
the rate-efficiency of our codes via our non-malleable reduction.Comment: 26 pages, 4 figure
A Comprehensive Survey on the Implementations, Attacks, and Countermeasures of the Current NIST Lightweight Cryptography Standard
This survey is the first work on the current standard for lightweight
cryptography, standardized in 2023. Lightweight cryptography plays a vital role
in securing resource-constrained embedded systems such as deeply-embedded
systems (implantable and wearable medical devices, smart fabrics, smart homes,
and the like), radio frequency identification (RFID) tags, sensor networks, and
privacy-constrained usage models. National Institute of Standards and
Technology (NIST) initiated a standardization process for lightweight
cryptography and after a relatively-long multi-year effort, eventually, in Feb.
2023, the competition ended with ASCON as the winner. This lightweight
cryptographic standard will be used in deeply-embedded architectures to provide
security through confidentiality and integrity/authentication (the dual of the
legacy AES-GCM block cipher which is the NIST standard for symmetric key
cryptography). ASCON's lightweight design utilizes a 320-bit permutation which
is bit-sliced into five 64-bit register words, providing 128-bit level
security. This work summarizes the different implementations of ASCON on
field-programmable gate array (FPGA) and ASIC hardware platforms on the basis
of area, power, throughput, energy, and efficiency overheads. The presented
work also reviews various differential and side-channel analysis attacks (SCAs)
performed across variants of ASCON cipher suite in terms of algebraic,
cube/cube-like, forgery, fault injection, and power analysis attacks as well as
the countermeasures for these attacks. We also provide our insights and visions
throughout this survey to provide new future directions in different domains.
This survey is the first one in its kind and a step forward towards
scrutinizing the advantages and future directions of the NIST lightweight
cryptography standard introduced in 2023
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