Paper 2001/106

Cryptanalysis of the COS (2,128) Stream Ciphers

Steve Babbage

Abstract

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 we cryptanalyse both of these ciphers, using a small amount of known keystream — with negligible effort in the case of Mode II, and with effort well below that required for a single DES key search in the case of Mode I.

Metadata
Available format(s)
PDF PS
Category
Secret-key cryptography
Publication info
Published elsewhere. Unknown where it was published
Keywords
COSstream ciphernonlinear feedback shift registercryptanalysis
Contact author(s)
steve babbage @ vodafone com
History
2001-12-11: received
Short URL
https://ia.cr/2001/106
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2001/106,
      author = {Steve Babbage},
      title = {Cryptanalysis of the {COS} (2,128) Stream Ciphers},
      howpublished = {Cryptology {ePrint} Archive, Paper 2001/106},
      year = {2001},
      url = {https://eprint.iacr.org/2001/106}
}
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