5,172 research outputs found
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
Regular subgroups with large intersection
In this paper we study the relationships between the elementary abelian
regular subgroups and the Sylow -subgroups of their normalisers in the
symmetric group , in view of the interest that
they have recently raised for their applications in symmetric cryptography
On the lexicographic representation of numbers
It is proven that, contrarily to the common belief, the notion of zero is not
necessary for having positional representations of numbers. Namely, for any
positive integer , a positional representation with the symbols for is given that retains all the essential properties of the usual
positional representation of base (over symbols for ).
Moreover, in this zero-free representation, a sequence of symbols identifies
the number that corresponds to the order number that the sequence has in the
ordering where shorter sequences precede the longer ones, and among sequences
of the same length the usual lexicographic ordering of dictionaries is
considered. The main properties of this lexicographic representation are proven
and conversion algorithms between lexicographic and classical positional
representations are given. Zero-free positional representations are relevantt
in the perspective of the history of mathematics, as well as, in the
perspective of emergent computation models, and of unconventional
representations of genomes.Comment: 15 page
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