The Taub Faculty of Computer Science Events and Talks

Symmetric ciphers are cryptographic algorithms that use the same cryptographic keys for both encryption and decryption. The key represents a shared secret between users, that is used to maintain a private information link. In our research we focus on cryptanalysis of block ciphers, which are the most widely used realization of symmetric ciphers. Block ciphers are cryptosystems that consist of two algorithms, an encryption algorithm that accepts a symmetric key and a plaintext and outputs a ciphertext, and a decryption algorithm that reveals the plaintext from the ciphertext and the key. Block ciphers are also the basis for many cryptographic protocols. The security of these protocols relies on the security of the underlying block ciphers against attacks. Testing the security of block ciphers is highly important, both for stopping their use if they are found insufficiently secure, and as design criteria how to design new more secure ciphers. Cryptanalysts use many techniques to examine the strength of block ciphers, ranging from differences and linear properties, through representation as polynomials, to more specialized structures, e.g., pairs, statistical characteristics and impossible events. The goal of the cryptanalyst is to design an attack on the block cipher which is faster than exhaustive key search. In our research we combine some of these techniques with additional properties in order to improve the ability to examine the strength of block ciphers, and to design new better ones.