How about security?
One of the main problems with analogue cordless telephones is that everyone
with a FM radio receiver can listen in on the conversation. Simple
digitial cordless telephones make it harder to listen in since the speech
is digitally encoded. However with a little knowledge and some general
available digital components this is easy to decode. Another problem is
unauthorized use of the base system. With analogue cordless telephones
others can easily make call's through your base system without paying for
it. Lost or stolen handsets open up your base system for the
unauthorized user to access and use on your cost. All these issues are
addressed by the DECT standard and solutions provided.
Gaining access
Before a DECT handset can be used on a base system at all a subscription
has to be made. During this subscription process identity information is
exchanged between the base system and the DECT handset. These are stored
on both sides for later use. But this procedure itself must be secure as
well. This is done in two ways. First of all the identities aren't
exchanged in their pure form, but encrypted. Together with a
authentication code provided by the base system and entered in the DECT
handset this encryption is seeded. Since the encryption algorithm itself
is secret it is very hard to intervene in this procedure.
The conversation
Making a conversation means that a link has to be established between the
DECT handset and the base system. As soon as this link is established an
encryption request is exchanged. This request is accompanied by a seed
which is used together with values established during the subscription
procedure. Therefore the encryption parameters are different for every
session. These encryption parameters are then used to encrypt the speech
data send between the DECT handset and base system, thus making it
virtually impossible to listen in on the conversation.
Denying access
Removing the subscription data from a DECT handset effectively blocks the
access by this DECT handset to the base system. If the DECT handset is
stolen or lost this cannot be done on the handset itself. But the
subscription can be marked in the base system as disabled. In case the DECT
handset tries to start a communication session it identifies itself to the
base system. The base system then sends a command to remove the subscription
data for this base system from the DECT handset. Now without a new
subscription it is impossible to even start a communication session with
this base system let alone initiate a call.
Written by my own two hands and an ASCII editor.
Problems? write me
Last updated June 24, 2000
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