Available Encryption algorithms

David Pottage david at electric-spoon.com
Tue May 27 16:30:55 CEST 2008

On Tue, May 27, 2008 10:04 am, Onno van Eijk wrote:

> I am a little confused about the available Encryption algorithms for the
> Neo1973. When I enter the ATcommand "AT%EM=2,7" in libgsmd-tool (in
> atcmd mode) it get the response:
> STR=`AT%EM=2,7'
> RSTR=`%EM: 1,1,0,3,0,1,1,0,0,1,1,0
> 6,0,0,0,0,1,1,1,4,0,0,0,0,1,0,0,0,0'
> According to
> http://wiki.openmoko.org/wiki/GTA01_gsm_modem#Power_Parameters_.282.2C7.29
> this should mean that A5/1 and A5/3 Encryption algorithms should be
> available. But all the information I found on the TI Calypso chipset state
> the ciphering processor implements both A5/1 and A5/2 algorithms.
> Can somebody confirm whether A5/2 of A5/3 is supported by the neo1973?

The A5/* cyphers are used to encrypt voice data between the phone and the
base station. What cyphers you can use depends on what your phone and
network support. (In some countries consumer crypto is forbidden so all
GSM voice calls are in the clear).

I don't actually know, but I would assume that both Neo 1973 and
Freerunner support whatever the GSM module supports. Remember that when
you make a voice call the analogue audio is routed from the mic directly
to the GSM module where it is digitized and sent over the network. The
Freerunner does not get involved.

If there is a difference between what the spec sheet for the GSM modem
supports and what the AT command says is supported, then my guess would be
that the GSM modem is also considering what is permitted by the network &
SIM card. Alternatively there may be a bug in the OpenMoko software that
runs and interprets that AT command.

David Pottage

Error compiling committee.c To many arguments to function.

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