Ali Alhamdan

Slide attacks on the Sfinks stream cipher

Sfinks is a shift register based stream cipher designed for hardware implementation and submitted to the eSTREAM project. In this paper, we analyse the initialisation process of Sfinks. We demonstrate a slid property of the loaded state of the Sfinks cipher, where multiple key-IV pairs may produce phase shifted keystream sequences. The state update functions of both the initialisation process and keystream generation and also the pattern of the padding affect generation of the slid pairs.

Weaknesses in the Initialisation Process of the Common Scrambling Algorithm Stream Cipher

The Common Scrambling Algorithm Stream Cipher (CSA-SC) is a shift register based stream cipher designed to encrypt digital video broadcast. CSA-SC produces a pseudo-random binary sequence that is used to mask the contents of the transmission. In this paper, we analyse the initialisation process of the CSA-SC keystream generator and demonstrate weaknesses which lead to state convergence, slid pairs and shifted keystreams. As a result, the cipher may be vulnerable to distinguishing attacks, time-memory-data trade-off attacks or slide attacks.

Flaws in the Initialisation Process of Stream Ciphers

The initialisation process is a key component in modern stream cipher design. A well-designed initialisation process should not reveal any information about the secret key, or possess properties that may help to facilitate attacks. This paper analyses the initialisation processes of shift register based stream ciphers and identifies four flaws which lead to compression, state convergence, the existence of slid pairs and possible weak Key-IV combinations. These flaws are illustrated using the A5/1 stream cipher as a case study. We also provide some design recommendations for the intialisation process in stream ciphers, to overcome these and other flaws.