A5/2 Guide, Meaning , Facts, Information and Description
A5/2 is a stream cipher used to provide voice privacy in the GSM cellular telephone protocol.The cipher is based around a combination of three linear feedback shift registers with irregular clocking and a non-linear combiner.
In 1999, Ian Goldberg and David Wagner cryptanalyzed A5/2 in the same month it was published, and showed that it was extremely weak — so much so that low end equipment can probably break it in real time.