secure a WS called via GPRS

Hello,
I need to secure a web service that is used by GPRS devices (so amount of
data is important) running NET CF 2.0. My requirenment is that every client
may be authenticated, and its identity cannot be spoofed. I also like that
data downloaded from server is encrypted, but this is not indispensable. My
webservice may something also loads/unloads about 1 to 10 MB of data.

Is WS 3.0 a right way to have this goal (it seems quite hard to start), or
better I may develop a custom security model with cryptography and
public/private kaeys?

thanks


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