Security evaluation of Rakaposhi stream cipher

Mohammad Ali Orumiehchiha, Josef Pieprzyk, Elham Shakour, Ron Steinfeld

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review

7 Citations (Scopus)


Rakaposhi is a synchronous stream cipher, which uses three main components: a non-linear feedback shift register (NLFSR), a dynamic linear feedback shift register (DLFSR) and a non-linear filtering function (NLF). NLFSR consists of 128 bits and is initialised by the secret key K. DLFSR holds 192 bits and is initialised by an initial vector (IV). NLF takes 8-bit inputs and returns a single output bit. The work identifies weaknesses and properties of the cipher. The main observation is that the initialisation procedure has the so-called sliding property. The property can be used to launch distinguishing and key recovery attacks. The distinguisher needs four observations of the related (K,IV) pairs. The key recovery algorithm allows to discover the secret key K after observing 29 pairs of (K,IV). Based on the proposed related-key attack, the number of related (K,IV) pairs is 2(128+192)/4 pairs. Further the cipher is studied when the registers enter short cycles. When NLFSR is set to all ones, then the cipher degenerates to a linear feedback shift register with a non-linear filter. Consequently, the initial state (and Secret Key and IV) can be recovered with complexity 263.87. If DLFSR is set to all zeros, then NLF reduces to a low non-linearity filter function. As the result, the cipher is insecure allowing the adversary to distinguish it from a random cipher after 217 observations of keystream bits. There is also the key recovery algorithm that allows to find the secret key with complexity 254.

Original languageEnglish
Title of host publicationInformation Security Practice and Experience - 9th International Conference, ISPEC 2013, Proceedings
EditorsRobert H. Deng, Tao Feng
Place of PublicationHeidelberg
PublisherSpringer, Springer Nature
Number of pages11
Volume7863 LNCS
ISBN (Print)9783642380327
Publication statusPublished - 2013
Event9th International Conference on Information Security Practice and Experience, ISPEC 2013 - Lanzhou, China
Duration: 12 May 201314 May 2013

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume7863 LNCS
ISSN (Print)03029743
ISSN (Electronic)16113349


Other9th International Conference on Information Security Practice and Experience, ISPEC 2013


  • rakaposhi stream cipher
  • related key attack
  • weak state
  • cryptanalysis
  • distinguishing attack
  • key recovery attack

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