Attacks in Stream Ciphers: A Survey

Nowadays there are different types of attacks in block and stream ciphers. In this work we will present some of the most used attacks on stream ciphers. We will present the newest techniques with an example of usage in a cipher, explain and comment. Previous we will explain the difference between the block ciphers and stream ciphers

D.STVL.9 - Ongoing Research Areas in Symmetric Cryptography

This report gives a brief summary of some of the research trends in symmetric cryptography at the time of writing (2008). The following aspects of symmetric cryptography are investigated in this report: • the status of work with regards to different types of symmetric algorithms, including block ciphers, stream ciphers, hash functions and MAC algorithms (Section 1); • the algebraic attacks on symmetric primitives (Section 2); • the design criteria for symmetric ciphers (Section 3); • the provable properties of symmetric primitives (Section 4); • the major industrial needs in the area of symmetric cryptography (Section 5)

A note on distinguishing attacks

A new distinguishing attack scenario for stream ciphers, allowing a resynchronization collision attack, is presented. The attack can succeed if the part of the state that depends on both the key and the IV is smaller than twice the key size. It is shown that the attack is applicable to block ciphers in OFB mode. For OFB mode, the attack is more powerful than the previously known generic distinguishing attack since it will directly recover a part of the plaintext while having the same asymptotic complexity as the generic distinguishing attack. The attack is also demonstrated on the eSTREAM candidate LEX. LEX is not vulnerable to any of the previously known generic distinguishing attack but is vulnerable to the new attack. It is shown that if approximately 265.7 resynchronizations using LEX are performed for the same key, some plaintext might be recovered