701 research outputs found
Return-Map Cryptanalysis Revisited
As a powerful cryptanalysis tool, the method of return-map attacks can be
used to extract secret messages masked by chaos in secure communication
schemes. Recently, a simple defensive mechanism was presented to enhance the
security of chaotic parameter modulation schemes against return-map attacks.
Two techniques are combined in the proposed defensive mechanism: multistep
parameter modulation and alternative driving of two different transmitter
variables. This paper re-studies the security of this proposed defensive
mechanism against return-map attacks, and points out that the security was much
over-estimated in the original publication for both ciphertext-only attack and
known/chosen-plaintext attacks. It is found that a deterministic relationship
exists between the shape of the return map and the modulated parameter, and
that such a relationship can be used to dramatically enhance return-map attacks
thereby making them quite easy to break the defensive mechanism.Comment: 11 pages, 7 figure
Breaking a Chaotic Cryptographic Scheme Based on Composition Maps
Recently, a chaotic cryptographic scheme based on composition maps was
proposed. This paper studies the security of the scheme and reports the
following findings: 1) the scheme can be broken by a differential attack with
chosen-plaintext, where is the size of
plaintext and is the number of different elements in plain-text; 2) the
scheme is not sensitive to the changes of plaintext; 3) the two composition
maps do not work well as a secure and efficient random number source.Comment: 9 pages, 7 figure
Time Scaling of Chaotic Systems: Application to Secure Communications
The paper deals with time-scaling transformations of dynamical systems. Such
scaling functions operate a change of coordinates on the time axis of the
system trajectories preserving its phase portrait. Exploiting this property, a
chaos encryption technique to transmit a binary signal through an analog
channel is proposed. The scheme is based on a suitable time-scaling function
which plays the role of a private key. The encoded transmitted signal is proved
to resist known decryption attacks offering a secure and reliable
communication.Comment: 15 pages, 7 figure
A Basic Framework for the Cryptanalysis of Digital Chaos-Based Cryptography
Chaotic cryptography is based on the properties of chaos as source of
entropy. Many different schemes have been proposed to take advantage of those
properties and to design new strategies to encrypt information. However, the
right and efficient use of chaos in the context of cryptography requires a
thorough knowledge about the dynamics of the selected chaotic system. Indeed,
if the final encryption system reveals enough information about the underlying
chaotic system it could be possible for a cryptanalyst to get the key, part of
the key or some information somehow equivalent to the key just analyzing those
dynamical properties leaked by the cryptosystem. This paper shows what those
dynamical properties are and how a cryptanalyst can use them to prove the
inadequacy of an encryption system for the secure exchange of information. This
study is performed through the introduction of a series of mathematical tools
which should be the basic framework of cryptanalysis in the context of digital
chaos-based cryptography.Comment: 6 pages, 5 figure
Revisiting Shared Data Protection Against Key Exposure
This paper puts a new light on secure data storage inside distributed
systems. Specifically, it revisits computational secret sharing in a situation
where the encryption key is exposed to an attacker. It comes with several
contributions: First, it defines a security model for encryption schemes, where
we ask for additional resilience against exposure of the encryption key.
Precisely we ask for (1) indistinguishability of plaintexts under full
ciphertext knowledge, (2) indistinguishability for an adversary who learns: the
encryption key, plus all but one share of the ciphertext. (2) relaxes the
"all-or-nothing" property to a more realistic setting, where the ciphertext is
transformed into a number of shares, such that the adversary can't access one
of them. (1) asks that, unless the user's key is disclosed, noone else than the
user can retrieve information about the plaintext. Second, it introduces a new
computationally secure encryption-then-sharing scheme, that protects the data
in the previously defined attacker model. It consists in data encryption
followed by a linear transformation of the ciphertext, then its fragmentation
into shares, along with secret sharing of the randomness used for encryption.
The computational overhead in addition to data encryption is reduced by half
with respect to state of the art. Third, it provides for the first time
cryptographic proofs in this context of key exposure. It emphasizes that the
security of our scheme relies only on a simple cryptanalysis resilience
assumption for blockciphers in public key mode: indistinguishability from
random, of the sequence of diferentials of a random value. Fourth, it provides
an alternative scheme relying on the more theoretical random permutation model.
It consists in encrypting with sponge functions in duplex mode then, as before,
secret-sharing the randomness
Bayesian Modeling for Differential Cryptanalysis of Block Ciphers: a DES instance
Encryption algorithms based on block ciphers are among the most widely adopted solutions for providing information security. Over the years, a variety of methods have been proposed to evaluate the robustness of these algorithms to different types of security attacks. One of the most effective analysis techniques is differential cryptanalysis, whose aim is to study how variations in the input propagate on the output. In this work we address the modeling of differential attacks to block cipher algorithms by defining a Bayesian framework that allows a probabilistic estimation of the secret key. In order to prove the validity of the proposed approach, we present as case study a differential attack to the Data Encryption Standard (DES) which, despite being one of the methods that has been most thoroughly analyzed, is still of great interest to the scientific community since its vulnerabilities may have implications on other ciphers
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