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Abstract We present the first information-theoretic steganographic protocol with an asymptotically optimal ratio of key length to message length that operates on arbitrary covertext distributions with constant min-entropy. Our results are also applicable to the computational setting: our stegosystem can be composed over a pseudorandom generator to send longer messages in a computationally secure fashion. In this respect our scheme offers a significant improvement in terms of the number of pseudorandom bits generated by the two parties in comparison to previous results known in the computational setting. Central to our approach for improving the overhead for general distributions is the use of combinatorial constructions that have been found to be useful in other contexts for derandomization: almost t-wise independent function families.
new paradigm called OABS, in which the computational overhead at user side is greatly reduced through outsourcing such intensive computation to an untrusted signing-cloud service provider (S-CSP). Furthermore, we apply this novel paradigm to existing ABS to reduce complexity and present two schemes, i) in the first OABS scheme, the number of exponentiations involving in signing is reduced from $O(d)$ to $O(1)$ (nearly three), where $d$ is the upper bound of threshold value defined in the predicate; ii) our second scheme is built on Herranz et al\'s construction with constant-size signatures. The number of exponentiations in signing is reduced from $O(d^2)$ to $O(d)$ and the communication overhead is $O(1)$. Security analysis demonstrates that both OABS schemes are secure in terms of the unforgeability and attribute-signer privacy definitions specified in the proposed security model. Finally, to allow for high efficiency and flexibility, we discuss extensions of OABS and show how to achieve accountability and outsourced verification as well.
We show that if the RSA cryptosystem is used in such a symmetric application, it is possible to determine the public RSA modulus if the public exponent is known and short, such as 3 or F4=65537, and two or more plaintext/ciphertext (or, if RSA is used for signing, signed value/signature) pairs are known.
(3PAKE) protocol, more than two parties can communicate and
set up common shared secret key using the server. Recently,
Tan et al. proposed an enhanced 3PAKE scheme based on
elliptic curve cryptography (ECC) to minimize the operations and
make compatible for mobile commerce environments. However,
Nose showed the scheme of Tan et al. is susceptible to the
impersonation attack and the man-in-middle attack. However, in
this paper we have shown that Tan et al. protocol is susceptible to
the known session-speciﬁc temporary information attack and the
clock synchronization attack too. Afterwards, we have proposed
the protocol that withstands against the above mentioned attacks.
In addition, our proposed approach is based on the hash function
in place of the encryption/decryption function that was used in
Tan et al. scheme.
Encryption (ABE) for general circuits. Our construction is based on
the existence of multilinear maps. We prove selective security of
our scheme in the standard model under the natural multilinear
generalization of the BDDH assumption. Our scheme achieves both
Key-Policy and Ciphertext-Policy variants of ABE.
that are multiplicative subgroups of the embedding fields. The algebraic tori can be expressed by the affine representation or the trace representation. Although the affine representation allows decompression maps, decompression maps for the trace representation has not been known. In this paper, we propose a trace representation with decompression maps for the characteristics 2 and 3. We first construct efficient decompression maps for trace maps by adding extra information to the trace representation. Our decompressible trace representation with additional information is as efficient as the affine representation is in terms of the costs of compression, decompression and exponentiation, and the size.
of Brickell-Davenport Theorem to the general case. After analyzing that result under a new point of view and identifying its combinatorial nature, we present a characterization of the (not necessarily perfect)
secret sharing schemes that are associated to matroids. Some optimality properties of such schemes are discussed.