Publication

New Directions in Cryptanalysis of Self-Synchronizing Stream Ciphers

Willi Meier, Shahram Khazaei
2008
Conference Papers

Abstract

In cryptology we commonly face the problem of finding an unknown key K from the output of an easily computable keyed function F(C, K) where the attacker has the power to choose the public variable C. In this work we focus on self-synchronizing stream ciphers. First we show how to model these primitives in the above-mentioned general problem by relating appropriate functions F to the underlying ciphers. Then we apply the recently proposed framework presented at AfricaCrypt'08 by Fischer et. al. for dealing with this kind of problems to the proposed T-function based self-synchronizing stream cipher by Klimov and Shamir at FSE'05 and show how to deduce some non-trivial information about the key. We also open a new window for answering a crucial question raised by Fischer et. al. regarding the problem of finding weak IV bits which is essential for their attack.

Official source

https://infoscience.epfl.ch/entities/publication/ec1c0564-7f35-4677-9af2-b34cd13d0622

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Willi Meier, Shahram Khazaei
2008
Conference Papers

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/ec1c0564-7f35-4677-9af2-b34cd13d0622

About this result

Ontological neighbourhood

Computer engineering

Computer security: Public-key cryptography

Related concepts (20)

Block cipher

In cryptography, a block cipher is a deterministic algorithm that operates on fixed-length groups of bits, called blocks. Block ciphers are the elementary building blocks of many cryptographic protocols. They are ubiquitous in the storage and exchange of data, where such data is secured and authenticated via encryption. A block cipher uses blocks as an unvarying transformation. Even a secure block cipher is suitable for the encryption of only a single block of data at a time, using a fixed key.

Stream cipher

A stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream, to give a digit of the ciphertext stream. Since encryption of each digit is dependent on the current state of the cipher, it is also known as state cipher. In practice, a digit is typically a bit and the combining operation is an exclusive-or (XOR).

Trapdoor function

In theoretical computer science and cryptography, a trapdoor function is a function that is easy to compute in one direction, yet difficult to compute in the opposite direction (finding its inverse) without special information, called the "trapdoor". Trapdoor functions are a special case of one-way functions and are widely used in public-key cryptography. In mathematical terms, if f is a trapdoor function, then there exists some secret information t, such that given f(x) and t, it is easy to compute x.

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