http://laforge.gnumonks.org/weblog/2010/11/12/#20101112-history_of_a52_withdrawal

    Date26 Nov 2010
    CategoryCryptography
    2142
    Posted ByAlex
    Recently, I wanted to investigate when and how A5/2 has been withdrawn from both GSM networks and GSM phones alike. Unfortunately there was no existing article discussing this history online, so I went through dozens of meeting reports and other documents that I could find online to recover what had happened. If you don't know what this is all about: It is about the A5/2 air-interface encryption algorithm that was used in certain GSM networks until about 2005-2007.

    A5/2 was specified as a security by obscurity algorithm behind closed doors in the late 1980ies. It was intentionally made weaker than it's (already weak) brother A5/1. The idea was to sell only equipment with A5/2 to the countries of the eastern block, while the less-weak A5/1 encryption was to be used by the western European countries.

    A5/2 had been reverse engineered and disclosed in the late 1990ies, and has undergone a lot of attention from cryptographers such as Ian Goldberg and David A. Wagner. In a 1999 paper, they already expect that it can be broken in real-time.

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