On Date: Thu, 25 Apr 1996, Boyd Roberts <boyd @
>check out http://ourworld.compuserve.com/homepages/bruiser/a5.htm
>for the scoop on a5, the crypto-system for gsm. it's not real strong.
This is getting a bit away from firewalls, but since everyone is so
keen on GSM encryption...
`A5' does not refer to a single algorithm. It refers to one of 9
different air interface encryption algorthims (`no encryption' and 8
others). Currently two different algorithms are defined: A5.1 and
A5.1 is strong enough for its export to some countries to be banned
(presumably using something similar to the US ITAR regulations,
although I don't know the details). Those countries (the list
includes China and Vietnam) use the weaker A5.2 instead.
Given that the above URL includes a reference to a Chinese paper, I
strongly suspect that it refers to A5.2, rather than A5.1.
I have not seen algorithms for either A5.1 or A5.2, so I don't know
what their relative cryptographic strengths are. In any case, the
encryption only applies to the radio part - it'll stop someone
listening in with a scanner but has no effect on wire-taps.
Peter Jeremy (VK2PJ) peter .
Alcatel Australia Limited
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