5,490 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
AONT-LT: a Data Protection Scheme for Cloud and Cooperative Storage Systems
We propose a variant of the well-known AONT-RS scheme for dispersed storage
systems. The novelty consists in replacing the Reed-Solomon code with rateless
Luby transform codes. The resulting system, named AONT-LT, is able to improve
the performance by dispersing the data over an arbitrarily large number of
storage nodes while ensuring limited complexity. The proposed solution is
particularly suitable in the case of cooperative storage systems. It is shown
that while the AONT-RS scheme requires the adoption of fragmentation for
achieving widespread distribution, thus penalizing the performance, the new
AONT-LT scheme can exploit variable length codes which allow to achieve very
good performance and scalability.Comment: 6 pages, 8 figures, to be presented at the 2014 High Performance
Computing & Simulation Conference (HPCS 2014) - Workshop on Security, Privacy
and Performance in Cloud Computin
All or Nothing at All
We continue a study of unconditionally secure all-or-nothing transforms
(AONT) begun in \cite{St}. An AONT is a bijective mapping that constructs s
outputs from s inputs. We consider the security of t inputs, when s-t outputs
are known. Previous work concerned the case t=1; here we consider the problem
for general t, focussing on the case t=2. We investigate constructions of
binary matrices for which the desired properties hold with the maximum
probability. Upper bounds on these probabilities are obtained via a quadratic
programming approach, while lower bounds can be obtained from combinatorial
constructions based on symmetric BIBDs and cyclotomy. We also report some
results on exhaustive searches and random constructions for small values of s.Comment: 23 page
- …