The COS Stream Ciphers are Extremely Weak

Cryptanalysis of Stream Cipher COS(2, 128) Mode I

Filiol and Fontaine recently proposed a family of stream ciphers named COS. COS is based on nonlinear feedback shift registers and was claimed to be highly secure. Babbage showed that COS (2, 128) Mode II is extremely weak. But Babbage’s attack is very expensive to break the COS (2, 128) Mode I (the complexity is around 2). In this paper, we show that the COS (2, 128) Mode I is very weak. Secre...

COS Ciphers are not "extremely weak"! - The Design Rationale of COS Ciphers

Cryptanalysis of the COS (2, 128) Stream Ciphers

A new family of very fast stream ciphers called COS (for “crossing over system”) has been proposed by Filiol and Fontaine, and seems to have been adopted for at least one commercial standard. COS(2,128) Mode I and COS(2,128) Mode II are particular members of this family for which the authors proposed a cryptanalysis challenge. The ciphers accept secret keys of 256, 192 or 128 bits. In this note...

Stream ciphers and the eSTREAM project

Stream ciphers are an important class of symmetric cryptographic algorithms. The eSTREAM project contributed significantly to the recent increase of activity in this field. In this paper, we present a survey of the eSTREAM project. We also review recent time/memory/data and time/memory/key trade-offs relevant for the generic attacks on stream ciphers.

A New Ultrafast Stream Cipher Design: COS Ciphers

This paper presents a new stream cipher family whose output bits are produced by blocks. We particularly focus on the member of this family producing 128-bit blocks with a 256-bit key. The design is based on a new technique called crossing over which allows to vectorize stream ciphering by using nonlinear shift registers. These algorithms offer a very high cryptographic security and much higher...