Initialisation flaws in the A5-GMR-1 satphone encryption algorithm
V. Bhartia, Leonie Ruth Simpson · Proceedings of the Australasian Computer Science Week Multiconference · 2016
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 berween 28 and 210 bits.