Post-quantum signature algorithms based on the hidden discrete logarithm problem

New options of the hidden discrete logarithm problem are proposed as cryptographic primitive of the post-quantum signature algorithms. Two signature schemes using computations in finite non-commutative algebras with associative multiplication operation are introduced. The main feature of the proposed signature algorithms consists in using locally invertible elements of algebras. Two different types of algebras are used: i) containing global bi-side unit and ii) containing a large set of global right-side units

Stream Deniable-Encryption Algorithms

A method for stream deniable encryption of secret message is proposed, which is computationally indistinguishable from the probabilistic encryption of some fake message. The method uses generation of two key streams with some secure block cipher. One of the key streams is generated depending on the secret key and the other one is generated depending on the fake key. The key streams are mixed with the secret and fake data streams so that the output ciphertext looks like the ciphertext produced by some probabilistic encryption algorithm applied to the fake message, while using the fake key. When the receiver or/and sender of the ciphertext are coerced to open the encryption key and the source message, they open the fake key and the fake message. To disclose their lie the coercer should demonstrate possibility of the alternative decryption of the ciphertext, however this is a computationally hard problem

Some applications of quasigroups in cryptology

In the paper we present based on quasigroups new deniable encryption method, generalisation of Markovski stream cipher, and generalisation of El-Gamal enciphering system

Fast DDP-Based Ciphers: Design and Differential Analysis of Cobra-H64

Use of the controlled operations is considered as a new approach to the design of fast hardware-oriented ciphers. Data-dependent (DD) permutations and DD two-place operations are used in a new ten-round cipher named Cobra-H64 which is fast and cheap when implemented in hardware. The peculiarity of the iterated 64-bit cipher Cobra-H64 is the very fast encryption in the case of frequent change of keys, since no preprocessing is used to perform key scheduling. The whole secret key is directly used in each round. The Cryptosystem Cobra-H64 is characterized by high parallelism of the data transformation. Time delay of one round is 15t+, where t+ is the time delay of the XOR operation. The analysis performed has shown that Cobra-H64 is secure against differential attacks

Variable Bit Permutations: Linear Characteristics and Pure VBP-Based Cipher

This paper describes linear characteristics of the variable bit permutations (VBP) that are used in the form of the data-dependent permutations. This primitive suites well to the design of fast cheap-hardware-oriented ciphers. Because of the existence of one characteristic with bias ? we discuss possibility to design a pure VBP-based block ciphers that are indistinguishable from a random transformation. We present design of the cipher which is based only on VBP, fixed permutations, and XOR operations. Performed analysis has shown that the designed pure VBP-based block cipher is secure against differential and linear attacks confirming the efficiency of the VBP as cryptographic primitive

Fast software-oriented hash function based on data-dependent lookup operations

The paper considers a method of the construction of the iterated hash function on the bases of the data-dependent lookup operations used previously in the design of the fast software suitable ciphers. To transform encryption function into a block one-way function we use the data-dependent initial condition at each transformation cycle of the round function except the first cycle. The variable initial conditions has been also used to strengthen chaining while constructing the iterated hash function. While fixing initial condition the round function can be transformed into a block cipher suitable to perform fast disk encryption. The size of the input data block of the round function and of the block cipher is parameterized defining their suitability for different practical applications