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We revisit meet-in-the-middle attacks on block ciphers and recent developments in meet-in-the-middle preimage attacks on hash functions. Despite the presence of a secret key in the block cipher case, we identify techniques that can also be mounted on block ciphers, thus allowing us to improve the cryptanalysis of the block cipher KTANTAN family. The first(More)
We study the natural problem of secure n-party computation (in the passive, computationally unbounded attack model) of the n-product function f G (x 1 ,. .. , x n) = x 1 · x 2 · · · x n in an arbitrary finite group (G, ·), where the input of party Pi is xi ∈ G for i = 1,. .. , n. For flexibility, we are interested in protocols for f G which require only(More)
Our contribution is twofold: first we describe a very compact hardware implementation of AES-128, which requires only 2400 GE. This is to the best of our knowledge the smallest implementation reported so far. Then we apply the threshold countermeasure by Nikova et al. to the AES S-box and yield an implementation of the AES improving the level of resistance(More)
Multireceiver authentication codes allow one sender to construct an authenticated message for a group of receivers such that each receiver can verify authenticity of the received message. In this paper, we give a formal dee-nition of multireceiver authentication codes, derive information theoretic and combinatorial lower bounds on their performance and give(More)
We consider the problem of increasing the threshold parameter of a secret-sharing scheme after the setup (share distribution) phase, without further communication between the dealer and the shareholders. Previous solutions to this problem require one to start off with a non-standard scheme designed specifically for this purpose, or to have communication(More)
We present efficient Identity-Based Encryption (IBE) and signature schemes under the Symmetric External Diffie-Hellman (SXDH) assumption in bilinear groups; our IBE scheme also achieves anonymity. In both the IBE and the signature schemes, all parameters have constant numbers of group elements, and are shorter than those of previous constructions based on(More)
Standard signature schemes are usually designed only to achieve weak unforgeability – i.e. preventing forgery of signatures on new messages not previously signed. However, most signature schemes are randomised and allow many possible signatures for a single message. In this case, it may be possible to produce a new signature on a previously signed message.(More)