Initialisation flaws in the A5-GMR-1 satphone encryption algorithm

Bhartiya, Vishesh & Simpson, Leonie (2016) Initialisation flaws in the A5-GMR-1 satphone encryption algorithm. In Australasian Computer Science Week Multiconference (ACSC2016), 2-5 February 2016, Canberra, A.C.T.

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Abstract

A5-GMR-1 is a synchronous stream cipher used to provide confidentiality for communications between satellite phones and satellites. The keystream generator may be considered as a finite state machine, with an internal state of 81 bits. The design is based on four linear feedback shift registers, three of which are irregularly clocked. The keystream generator takes a 64-bit secret key and 19-bit frame number as inputs, and produces an output keystream of length between $2^8$ and $2^{10}$ bits.

Analysis of the initialisation process for the keystream generator reveals serious flaws which significantly reduce the number of distinct keystreams that the generator can produce. Multiple (key, frame number) pairs produce the same keystream, and the relationship between the various pairs is easy to determine. Additionally, many of the keystream sequences produced are phase shifted versions of each other, for very small phase shifts. These features increase the effectiveness of generic time-memory tradeoff attacks on the cipher, making such attacks feasible.

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ID Code: 93134
Item Type: Conference Paper
Refereed: Yes
Keywords: Stream ciphers, Satellite phones, Initialisation, Cryptanalysis, Time-memory attacks
DOI: 10.1145/2843043.2843357
ISBN: 9781450340427
Subjects: Australian and New Zealand Standard Research Classification > INFORMATION AND COMPUTING SCIENCES (080000) > DATA FORMAT (080400)
Divisions: Current > Institutes > Institute for Future Environments
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2016 ACM
Deposited On: 22 Feb 2016 23:50
Last Modified: 22 Jun 2017 11:32

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