4 research outputs found
An Inverse-free Single-Keyed Tweakable Enciphering Scheme
In CRYPTO 2003, Halevi and Rogaway proposed CMC, a tweakable enciphering scheme (TES) based on a blockcipher. It requires two blockcipher keys and it is not inverse-free (i.e., the decryption algorithm uses the inverse (decryption) of the underlying blockcipher). We present here a new inverse-free, single-keyed TES. Our construction is a tweakable strong pseudorandom permutation (tsprp), i.e., it is secure against chosen-plaintext-ciphertext adversaries assuming that the underlying blockcipher is a pseudorandom permutation (prp), i.e., secure against chosen-plaintext adversaries. In comparison, sprp assumption of the blockcipher is required for the sprp security of CMC. Our scheme can be viewed as a mixture of type-1 and type-3 Feistel cipher and so we call it FMix or mixed-type Feistel cipher
OleF: an Inverse-Free Online Cipher. An Online SPRP with an Optimal Inverse-Free Construction
Online ciphers, in spite of being insecure against an sprp adversary, can be desirable at places because of their ease of implementation and speed. Here we propose a single-keyed inverse-free construction that achieves online sprp security with an optimal number of blockcipher calls. We also include a partial block construction, without requiring any extra key
Designing Tweakable Enciphering Schemes Using Public Permutations
A tweakable enciphering scheme (TES) is a length preserving (tweakable) encryption scheme that provides (tweakable) strong pseudorandom permutation security on arbitrarily long messages. TES is traditionally built using block ciphers and the security of the mode depends on the strong pseudorandom permutation security of the underlying block cipher. In this paper, we construct TESs using public random permutations. Public random permutations are being considered as a replacement of block cipher in several cryptographic schemes including AEs, MACs, etc. However, to our knowledge, a systematic study of constructing TES using public random permutations is missing. In this paper, we give a generic construction of a TES which uses a public random permutation, a length expanding public permutation based PRF and a hash function which is both almost xor universal and almost regular. Further, we propose a concrete length expanding public permutation based PRF construction. We also propose a single keyed TES using a public random permutation and an AXU and almost regular hash function
FAST: Disk Encryption and Beyond
This work introduces \sym{FAST} which is a new family of tweakable enciphering schemes. Several instantiations of \sym{FAST} are
described. These are targeted towards two goals, the specific task of disk encryption and a more general scheme suitable for
a wide variety of practical applications. A major contribution of this work is to present detailed and careful software implementations of
all of these instantiations. For disk encryption, the results from the implementations show
that \sym{FAST} compares very favourably to the IEEE disk encryption standards XCB and EME2 as well as the more recent proposal
AEZ.
\sym{FAST} is built using a fixed input length pseudo-random function
and an appropriate hash function. It uses a single-block key, is parallelisable and can be instantiated using only the encryption
function of a block cipher.
The hash function can be instantiated using either the Horner\u27s rule based usual polynomial hashing or hashing based on the more efficient
Bernstein-Rabin-Winograd polynomials. Security of \sym{FAST} has been rigorously analysed using the standard provable security
approach and concrete security bounds have been derived.
Based on our implementation results, we put forward \sym{FAST} as a serious candidate for standardisation and deployment